desalination study report - website

November 2008

Desalination Study Report

WATER SUPPLY PROJECT -

DUBLIN REGION (DRAFT PLAN)

(Previously titled: Greater Dublin

Water Supply - Major Source

Development (Draft Plan))

Water Supply Project – Dublin Region Desalination Study Report

MDW0158RP0080F01 i F01

TABLE OF CONTENTS

EXECUTIVE SUMMARY.....................................................................................................................ES1

INTRODUCTION....................................................................................................................ES1

DEMAND PROJECTIONS .....................................................................................................ES2

NEW WATER SUPPLY OPTIONS ..........................................................................................ES3

SELECTION OF OPTIMUM TECHNOLOGY..........................................................................ES3

PROPOSED DESIGN ............................................................................................................ES3

TREATMENT SITE OPTIONS ...............................................................................................ES4

BRINE DISPERSION MODELLING .......................................................................................ES4

ENERGY REQUIREMENTS ..................................................................................................ES4

ENVIRONMENTAL CONSIDERATIONS...............................................................................ES5

ECONOMIC ASSESSMENT ..................................................................................................ES5

1 INTRODUCTION AND BACKGROUND ......................................................................................... 1

1.1 LONG TERM WATER SUPPLIES FOR THE DUBLIN REGION....................................................... 1

1.2 DUBLIN REGION (WATER SUPPLY AREA)- DEMAND PROJECTIONS....................................... 2

1.3 PREVIOUS STUDIES & MILESTONES.................................................................................... 2

1.4 WATER SUPPLY OPTIONS ................................................................................................... 3

1.4.1 Phased Water Supply Requirements from the New Supply Source................. 4

2 DEMAND PROJECTIONS / PHASED SUPPLY REQUIREMENTS FROM A NEW MAJOR

SOURCE ................................................................................................................................................. 5

2.1 DEMAND PROJECTIONS – PROCESS ....................................................................... 5

2.2 REPORTS REVIEW....................................................................................................... 5

2.3 DEMAND ESTIMATION METHODOLOGY................................................................... 6

2.4 DOMESTIC DEMAND.................................................................................................... 6

2.4.1 Population ......................................................................................................... 6

2.4.2 Per Capita Consumption (PCC)........................................................................ 7

2.5 NON DOMESTIC DEMAND (INDUSTRIAL & COMMERCIAL)....................................................... 7

2.6 CUSTOMER SIDE LEAKAGE LOSSES..................................................................................... 8

2.7 DISTRIBUTION LEAKAGE LOSSES ........................................................................................ 9

2.8 HEADROOM ...................................................................................................................... 9

2.9 AVERAGE/PEAK DEMAND PROJECTIONS – GDA (2007-2011-2031) .................................... 10

2.10 PRODUCTION CAPABILITY OF EXISITING SOURCES ............................................................. 10

2.11 DEMAND/SUPPLY BALANCE .............................................................................................. 12

2.12 NEW SOURCE PRODUCTION REQUIREMENTS ..................................................................... 13


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2.13 WATER CONSERVATION ................................................................................................... 15

2.14 SUMMARY ...................................................................................................................... 16

2.14.1 Demand Drivers.............................................................................................. 16

2.14.2 Supply Sources .............................................................................................. 16

2.14.3 Leakage.......................................................................................................... 17

2.14.4 Water Conservation........................................................................................ 17

2.14.5 Longterm Demand / Supply Considerations. ................................................. 17

3 WATER SUPPLY OPTIONS ......................................................................................................... 18

3.1 INTRODUCTION – UPDATED INFO AVAILABLE ..................................................................... 18

3.1.1 Option A .......................................................................................................... 18

3.1.2 Option B .......................................................................................................... 18

3.1.3 Option C .......................................................................................................... 19

3.1.4 Option D .......................................................................................................... 19

3.1.5 Option E .......................................................................................................... 19

3.1.6 Option F .......................................................................................................... 19

3.1.7 Option G.......................................................................................................... 19

3.1.8 Option H .......................................................................................................... 20

3.1.9 Option I............................................................................................................ 20

3.1.10 Option J .......................................................................................................... 20

3.2 DESALINATION AS A TREATMENT PROCESS....................................................................... 20

3.3 DESALINATION WATER SUPPLY INFRASTRUCTURE ........................................................... 20

3.3.1 Technical Evaluation of Desalinated Water Supply ........................................ 21

3.3.2 Routing and Site Selection.............................................................................. 23

3.3.3 Economic Evaluation of Desalinated Water Supply........................................ 24

3.3.4 Modelling of Brine Dispersion Impacts............................................................ 25

3.3.5 Environmental Assessments........................................................................... 25

4 TECHNOLOGY REVIEW............................................................................................................... 26

4.1 INTRODUCTION – HISTORY OF DESALINATION DEVELOPMENT ............................................. 26

4.2 VEOLIA EXPERIENCE........................................................................................................ 26

4.3 REVIEW OF AVAILABLE TECHNOLOGIES ............................................................................. 27

4.3.1 Introduction ..................................................................................................... 27

4.3.2 Energy Source ................................................................................................ 28

4.3.3 Seawater Intake and Brine Discharge ............................................................ 29

4.3.4 Desalination Economics.................................................................................. 30

4.4 REVIEW OF MAIN DESALINATION PROCESSES.................................................................... 31

4.4.1 Distillation........................................................................................................ 31

4.4.2 Membrane Processes: Reverse Osmosis....................................................... 46


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4.4.3 Conclusion ...................................................................................................... 54

4.5 FUTURE DEVELOPMENT ................................................................................................... 57

4.5.1 Latest Developments in Distillation Processes ............................................... 57

4.5.2 Latest Developments in Reverse Osmosis Processes................................... 57

4.5.3 Hybrid Configurations...................................................................................... 59

4.5.4 Other Desalination Processes ........................................................................ 61

5 SELECTION OF OPTIMUM TECHNOLOGY – IRISH APPLICATION......................................... 68

5.1 METHODOLOGY.............................................................................................................. 68

5.1.1 Technology Selection Scoring System ........................................................... 68

5.1.2 Appropriate Processes for Dublin and Scoring System.................................. 70

5.2 RECOMMENDED TECHNOLOGY......................................................................................... 72

5.3 DISCUSSION OF RESULTS ................................................................................................ 75

5.3.1 Costs ............................................................................................................... 75

5.3.2 Energy consumption ....................................................................................... 75

5.3.3 Environmental impact...................................................................................... 75

5.3.4 Robustness ..................................................................................................... 76

5.3.5 Operation ........................................................................................................ 76

5.3.6 Safety .............................................................................................................. 76

6 PRELIMINARY DESIGN................................................................................................................ 77

6.1 INTRODUCTION ............................................................................................................... 77

6.2 DESIGN CRITERIA ............................................................................................................ 77

6.2.1 General ........................................................................................................... 77

6.2.2 Capacity .......................................................................................................... 77

6.2.3 Raw Water Quality .......................................................................................... 78

6.2.4 Treated Water Quality ..................................................................................... 80

6.3 DESALINATION WATER TREATMENT PLANT PRELIMINARY DESIGN ....................................... 80

6.3.1 General ........................................................................................................... 80

6.3.2 Main Assumptions........................................................................................... 81

6.3.3 Intakes and outfalls ......................................................................................... 82

6.3.4 Pre-treatment .................................................................................................. 83

6.3.5 Reverse Osmosis............................................................................................ 93

6.3.6 Post Treatment.............................................................................................. 102

6.3.7 Sludge Treatment.......................................................................................... 106

6.3.8 Chemicals ..................................................................................................... 112

6.3.9 Automation and Controls .............................................................................. 124


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7 SITE SELECTION........................................................................................................................ 129

7.1 INTRODUCTION ............................................................................................................. 129

7.2 SITES CONSIDERED FOR DESALINATION OPTION.............................................................. 130

7.2.1 South Dublin.................................................................................................. 130

7.2.2 Ringsend ....................................................................................................... 130

7.2.3 Howth Headland............................................................................................ 131

7.2.4 Ardgillan ........................................................................................................ 131

7.2.5 Balbriggan & Gormanstown .......................................................................... 131

7.2.6 Loughshinny South & North .......................................................................... 132

7.3 CORRIDOR SELECTION FOR DESALINATION OPTION ....................................................... 132

7.3.1 Transmission Pipeline Route Selection ........................................................ 132

7.3.2 Route Selection Methodology ....................................................................... 133

8 BRINE DISPERSION MODELLING ............................................................................................ 134

8.1 INTRODUCTION ............................................................................................................. 134

8.2 MODELLING SYSTEM ..................................................................................................... 136

8.2.1 Tidal Model.................................................................................................... 136

8.2.2 Effluent Dispersion Model ............................................................................. 137

8.3 TIDAL MODELLING SIMULATIONS .................................................................................... 138

8.3.1 Irish Seas Model ........................................................................................... 138

8.3.2 The Desalination Discharge Model ............................................................... 139

8.4 DISPERSION MODEL SIMULATIONS ................................................................................. 141

8.4.1 Effluent Inputs ............................................................................................... 141

8.4.2 Dispersion Modelling..................................................................................... 142

8.4.3 Dispersion Characteristics ............................................................................ 142

8.4.4 Dispersion Model Simulations....................................................................... 142

8.5 DISPERSION MODELLING RESULTS................................................................................. 142

8.5.1 Initial Dilution................................................................................................. 142

8.5.2 Medium and Far Field Brine Dispersion........................................................ 144

8.6 DISCUSSION OF DISPERSION RESULTS ........................................................................... 161

8.6.1 Initial Dilution................................................................................................. 161

8.6.2 Medium and Far Field Dispersion ................................................................. 161

8.7 COSTING ...................................................................................................................... 161

8.8 SUMMARY & CONCLUSIONS ........................................................................................... 162

9 ENERGY REQUIREMENTS........................................................................................................ 163

9.1 INTRODUCTION ............................................................................................................. 163

9.2 ENERGY DEMAND OF DESALINATION TECHNOLOGIES ..................................................... 163

9.3 EXISTING ENERGY AND PRIMARY FUEL SOURCES .......................................................... 163


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9.3.1 Natural Gas ................................................................................................... 164

9.3.2 Direct Supply from Local Grid ....................................................................... 164

9.4 POTENTIAL FOR ALTERNATIVE ENERGY SUPPLY OPTIONS .............................................. 164

9.4.1 Wind .............................................................................................................. 164

9.4.2 Wave, Tidal and Hydropower Technologies ................................................. 165

9.4.3 Solar Photovoltaic and Thermal/Steam Turbine Technologies .................... 165

9.4.4 Biomass and Biofuel Technologies............................................................... 165

9.5 SINGLE ENERGY MARKET ............................................................................................... 166

9.6 CARBON FOOTPRINT MODEL .......................................................................................... 167

9.6.1 Energy Consumption..................................................................................... 167

9.6.2 Carbon Footprint Model Development .......................................................... 168

9.6.3 Energy Supply Scenarios.............................................................................. 168

9.6.4 Summary....................................................................................................... 170

9.6.5 Anticipated Supply Scenarios ....................................................................... 171

9.7 RECOMMENDATIONS..................................................................................................... 172

10 ENVIRONMENTAL CONSIDERATIONS................................................................................. 174

10.1 INTRODUCTION........................................................................................................ 174

10.2 ACTIVITIES ARISING FROM THE IMPLEMENTATION OF WATER TREATMENT BY

DESALINATION 174

10.3 ENVIRONMENTAL ASSESSMENTS .................................................................................... 174

10.3.1 Biodiversity, Flora and Fauna....................................................................... 174

10.3.2 Population and Human Health ..................................................................... 175

10.3.3 Water ............................................................................................................ 176

10.3.4 Air and Climate ............................................................................................. 177

10.3.5 Cultural Heritage (including Archaeology and Architecture) ........................ 178

10.3.6 Landscape .................................................................................................... 178

10.3.7 Material Assets (including Landuse) ............................................................ 178

10.3.8 Soil................................................................................................................ 178

10.4 CONCLUSIONS.............................................................................................................. 179

11 ECONOMIC ASSESSMENT .................................................................................................... 180

11.1 CAPITAL COSTS............................................................................................................ 180

11.1.1 Seawater Abstraction Intakes and Brine Discharge Outfalls ....................... 180

11.1.2 Desalination Treatment Plant ....................................................................... 181

11.1.3 Drinking Water Transmission ....................................................................... 182

11.1.4 One-off items................................................................................................ 183

11.2 CAPITAL RENEWALS .................................................................................................. 183

11.3 OPERATING COSTS....................................................................................................... 184


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11.3.1 Maintenance ................................................................................................. 184

11.3.2 Energy .......................................................................................................... 184

11.3.3 Chemicals and Standing Charges................................................................ 185

11.3.4 Opex summary ............................................................................................. 186

11.4 WHOLE LIFE COST .................................................................................................. 187

12 CONCLUSIONS ....................................................................................................................... 188


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LIST OF FIGURES

Figure 1.1 Greater Dublin Area / Dublin Region (Water Supply Area) ............................................... 1

Figure 1.2 Key Milestones in Dublin Region Strategic Water Supply Planning.................................. 2

Figure 1.3 Water Supply Options Summary ....................................................................................... 3

Figure 2.1 New Source Supply Phases ............................................................................................ 14

Figure 2.2 High / Low Demand Growth Scenarios ........................................................................... 16

Figure 3.1 Water Supply Options Summary ..................................................................................... 18

Figure 3.2 Desalination Plant Principal Infrastructure....................................................................... 21

Figure 3.3 RO Plant with Conventional Pre-treatment...................................................................... 23

Figure 4.1 Desalination Concept....................................................................................................... 27

Figure 4.2 Simplified Flow-sheet of Desalination Process............................................................... 28

Figure 4.3 Schematic of multi-effect evaporator desalination process (horizontal tube – parallel feed configuration).................................................................................................................................. 33

Figure 4.4 Schematic of a multi-effect evaporator desalination process with thermal vapour compression. .................................................................................................................................. 34

Figure 4.5 Schematic of a multi-effect evaporator desalination process with mechanical vapour compression. .................................................................................................................................. 35

Figure 4.6 Diagram of MSF plant...................................................................................................... 38

Figure 4.7 View of a typical MSF plant ............................................................................................. 39

Figure 4.8 Schematic of a multi-stage flash desalination process with brine recirculation............... 40

Figure 4.9 Outline of the typical costs for 20 year for an MED plant. ............................................... 45

Figure 4.10 View of a large capacity distillation facility ................................................................... 46

Figure 4.11 Principle of Reverse Osmosis ...................................................................................... 47

Figure 4.12 Schematic of hollow fibre membrane structure............................................................ 48

Figure 4.13 Typical schematic of a reverse osmosis system.......................................................... 49

Figure 4.14 Typical 20 year osmosis is desalination plant cost. ..................................................... 53

Figure 4.15 Treatment chain of Los Angeles water reclamation plant – 17 MLD ........................... 54

Figure 4.16 Interior view of RO plant at Ashkelon, Southern Israel ................................................ 55

Figure 4.17 Exterior view of RO plant at Ashkelon, Southern Israel (320 Mld)............................... 56

Figure 4.18 schematic of a hybrid system....................................................................................... 60

Figure 4.19 Principle of solar distillation.......................................................................................... 61

Figure 4.20 Schematic of forward osmosis (FO) process ............................................................... 63

Figure 4.21 Schematic of Electro-dialysis (ED) process ................................................................. 64

Figure 5.1 Global distribution of installed desalination capacity by technology adapted from 1998 survey (International desalination association) .............................................................................. 76

Figure 6.1 Examples of sea water salinity ........................................................................................ 78

Figure 6.2 Temperature variations of sea water during the year according to the Irish Marine Institute: ......................................................................................................................................... 79

Figure 6.3 View of a Dissolved Air Flotation Unit (DAF) for the solid-liquid separation process ...... 88


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Figure 6.4 Constituent parts of a spiral wound module used in Reverse Osmosis treatment process ......................................................................................................................................... 93

Figure 6.5 View of cartridge filters used to protect membranes from colloidal fouling ..................... 94

Figure 6.6 The water characteristics at the outlet of the RO plant and after post-treatment are as follows ....................................................................................................................................... 103

Figure 6.7 Summation of maximum production of sludge and the corresponding flow and TSS (Total Suspended Matter) concentration ................................................................................................ 108

Figure 8.1 Extent of 45m grid domain showing outfall location ...................................................... 134

Figure 8.2 Extent of Irish Sea Tidal Surge Model ........................................................................... 138

Figure 8.3 Base model and detailed 45m model bathymetries....................................................... 140

Figure 8.4 Typical current speed mid-ebb spring tide..................................................................... 140

Figure 8.5 Typical current speed mid-flood spring tide................................................................... 141

Figure 8.6 Brine plume dimensions per outlet ................................................................................ 143

Figure 8.7 Initial dilution prediction ................................................................................................. 143

Figure 8.8 Typical Suspended Sediment Plume Excursion over Tidal Cycle - Surface 5m layer .. 144

Figure 8.9 Maximum Plume Envelope Suspended Sediment–Surface 5m layer (no settlement).. 145

Figure 8.10 Average Plume Envelope Suspended Sediment – Surface 5m layer (no settlement) .... ................................................................................................................................... 145

Figure 8.11 Maximum Plume Envelope Suspended Sediment – Central 15m layer (no settlement) . ................................................................................................................................... 146

Figure 8.12 Average Plume Envelope Suspended Sediment – Central 15m layer (no settlement) ... ................................................................................................................................... 146

Figure 8.13 Maximum Plume Envelope Suspended Sediment – Seabed 1m layer (no settlement) .. ................................................................................................................................... 147

Figure 8.14 Average Plume Envelope Suspended Sediment – Seabed 1m layer (no settlement) .... ................................................................................................................................... 147

Figure 8.15 Maximum Sediment Deposition ................................................................................. 148

Figure 8.16 Average Sediment Deposition.................................................................................... 148

Figure 8.17 Maximum Plume Envelope Suspended Sediment – Surface 5m layer (settlement) . 149

Figure 8.18 Average Plume Envelope Suspended Sediment – Surface 5m layer (settlement) ... 149

Figure 8.19 Maximum Plume Envelope Suspended Sediment – Central 15m layer (settlement) 150

Figure 8.20 Average Plume Envelope Suspended Sediment – Central 15m layer (settlement) .. 150

Figure 8.21 Maximum Plume Envelope Suspended Sediment – Seabed 1m layer (settlement) . 151

Figure 8.22 Average Plume Envelope Suspended Sediment – Seabed 1m layer (settlement) ... 151

Figure 8.23 Maximum Plume Envelope Iron – Surface 5m layer.................................................. 152

Figure 8.24 Average Plume Envelope Iron – Surface 5m layer .................................................... 152

Figure 8.25 Maximum Plume Envelope Iron – Central 15m layer................................................. 153

Figure 8.26 Average Plume Envelope Iron – Central 15m layer................................................... 153

Figure 8.27 Maximum Plume Envelope Iron – Seabed 1m layer.................................................. 154

Figure 8.28 Average Plume Envelope Iron – Seabed 1m layer .................................................... 154

Figure 8.29 Maximum Plume Envelope Phosphonate – Surface 5m layer................................... 155

Figure 8.30 Average Plume Envelope Phosphonate – Surface 5m layer..................................... 155

Figure 8.31 Maximum Plume Envelope Phosphonate – Central 15m layer ................................. 156


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Figure 8.32 Average Plume Envelope Phosphonate – Central 15m layer.................................... 156

Figure 8.33 Maximum Plume Envelope Phosphonate – Seabed 1m layer................................... 157

Figure 8.34 Average Plume Envelope Phosphonate – Seabed 1m layer..................................... 157

Figure 8.35 Maximum Plume Envelope Salt (above background) – Surface 5m layer ................ 158

Figure 8.36 Average Plume Envelope Salt (above background) – Surface 5m layer................... 158

Figure 8.37 Maximum Plume Envelope Salt (above background) – Central 15m layer ............... 159

Figure 8.38 Average Plume Envelope Salt (above background) – Central 15m layer ................. 159

Figure 8.39 Maximum Plume Envelope Salt (above background) – Seabed 1m layer ................ 160

Figure 8.40 Average Plume Envelope Salt (above background) – Seabed 1m layer................... 160

Figure 9.1 Electricity market regulatory framework ........................................................................ 166

Figure 9.2 Annual Energy Consumptions ....................................................................................... 167

Figure 9.3 Annual Energy Consumptions per m3 delivered............................................................ 168

Figure 9.4 Annual Cost for Different Energy Sources..................................................................... 169

Figure 9.5 Annual CO2 Emissions for All Energy Supply Scenarios............................................... 169

Figure 9.6 Annual Carbon Tax for All Energy Supply Scenarios .................................................... 170

Figure 9.7 Desalination Summary – Total Annual Cost of Energy Supply ..................................... 170

Figure 11.1 Annual Energy Cost for Grid Supply .......................................................................... 185

Figure 11.2 Chemicals Annual Cost.............................................................................................. 185

Figure 11.3 OPEX summary.......................................................................................................... 186


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LIST OF TABLES

Table 1.1 Supply Requirements from New Source ........................................................................... 4

Table 2.1 Greater Dublin Water Supply Area Population 2007-2011-2031 ...................................... 7

Table 2.2 Projected Domestic Demand 2005-2011-2031 ................................................................. 7

Table 2.3 Industrial Demand / Hectare – Wet & Dry Industries......................................................... 8

Table 2.4 GDA Non-Domestic Growth 2007-2011-2031 ................................................................... 8

Table 2.5 Customer Side Leakage Losses: 2007-2011-2031 ........................................................... 9

Table 2.6 Distribution Leakage Losses: 2007-2011-2031 ................................................................. 9

Table 2.7 Average/Peak Demand - GDA (2007-2011-2031)........................................................... 10

Table 2.8 GDA Production Capacity – Existing/Proposed............................................................... 11

Table 2.9 GDA Sustainable Production Capacity – 2007/2011/2015.............................................. 11

Table 2.10 GDA Peak Production Capacity (Ml/d) (Excluding Kildare Wellfields/Barrow) ................ 12

Table 2.11 Demand/Supply Balance (Ml/d) ....................................................................................... 12

Table 2.12 Average Supply Requirements from the New Source ..................................................... 13

Table 2.13 Peak Supply Requirements from New Source ................................................................ 13

Table 2.14 New Source Installed Capacity........................................................................................ 14

Table 3.1 Desalination Infrastructure Details:.................................................................................. 21

Table 3.2 Calculation of average cost of water delivered to the Dublin Region over the assumed 25 year operating period ..................................................................................................................... 24

Table 4.1 Energy consumption of different configuration of MED processes.................................. 36

Table 4.2 Energy consumption of different configuration of MSF processes .................................. 41

Table 4.3 Investment cost for distillation processes ........................................................................ 43

Table 4.4 Comparison of energy consumption of different distillation processes, when energy source is gas: ................................................................................................................................. 44

Table 4.5 Investment cost for membrane processes....................................................................... 52

Table 4.6 Comparison of energy consumption of different membrane processes, when energy source is fuel. ................................................................................................................................. 52

Table 4.7 Comparison of the energy needed by the membrane processes:................................... 66

Table 5.1 Comparison of all desalination processes, including lab-scale and bench-scale processes ....................................................................................................................................... 73

Table 5.2 Detailed comparison of the main desalination processes: distillation, reverse osmosis and hybrid configurations ............................................................................................................... 74

Table 6.1 Critical Raw Water Parameters for Desalination ............................................................. 80

Table 6.2 Summary of the phasing of the Desalination Treatment Plant construction ................... 82

Table 6.3 Limitations on raw water quality which permit direct filtration.......................................... 83

Table 6.4 Sizing and phasing of the DAF tanks .............................................................................. 89

Table 6.5 Sizing of the Dual Media Filtration Units.......................................................................... 91

Table 6.6 Characteristics of the Backwash Equipment ................................................................... 92

Table 6.7 Operation sequence for backwash of filters .................................................................... 92


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Table 6.8 Sizing and phasing of booster pump equipment ............................................................. 95

Table 6.9 Sizing and phasing cartridge filter equipment.................................................................. 95

Table 6.10 Sizing and phasing requirements for 1st pass through membranes ................................ 97

Table 6.11 Sizing and phasing requirements for 2nd pass through membranes ............................... 98

Table 6.12 Sizing and phasing of HP pump for 1st pass.................................................................... 99

Table 6.13 Sizing and phasing of Energy Recovery Device.............................................................. 99

Table 6.14 Sizing and phasing of booster pump 1st pass (downstream of work exchanger) .......... 100

Table 6.15 Sizing and phasing of HP pump for 2nd pass................................................................. 100

Table 6.16 Phasing requirements of flushing pump capacity and pump head................................ 101

Table 6.17 CIP tank details for phases 1 and 2............................................................................... 102

Table 6.18 Details of degassing towers for CO2 stripping phases 1 and 2 ..................................... 104

Table 6.19 Average and maximum concentration of parameters used in calculation of sludge production ................................................................................................................................... 107

Table 6.20 Assessment of sludge flows form each point of the treatment process ........................ 108

Table 6.21 Sizing and phasing details for mixing tank equipment .................................................. 109

Table 6.22 Sizing and phasing details for sludge thickeners........................................................... 110

Table 6.23 Sizing and phasing details for sludge dewatering equipment (centrifuges) .................. 111

Table 6.24 Sizing and phasing details for sulphuric acid dosing equipment ................................... 113

Table 6.25 Sizing and phasing details for ferric chloride dosing equipment ................................... 114

Table 6.26 Sizing and phasing details for polymer dosing equipment ............................................ 116

Table 6.27 Sizing and phasing details for antiscalant dosing equipment........................................ 118

Table 6.28 Sizing and phasing details for sodium bisulphite dosing equipment ............................. 119

Table 6.29 Sizing and phasing details for caustic soda dosing equipment ..................................... 120

Table 6.30 Sizing and phasing details for the lime process equipment .......................................... 122

Table 6.31 Sizing and phasing details for sodium hypochlorite dosing equipment ......................... 123

Table 6.32 Main control instrumentation to be installed at desalination plant ................................. 127

Table 8.1 Brine discharge characteristics without sludge dispersion ............................................ 135

Table 8.2 Brine discharge characteristics with sludge dispersion ................................................. 135

Table 8.3 Dispersion modelling parameters used ......................................................................... 141

Table 9.1 Quantities of fuel and storage requirements for various biomass and biofuel technologies ....................................................................................................................................... 166

Table 10.1 Designated areas close to Loughshinny........................................................................ 175

Table 11.1 Abstraction and Discharge Pipelines CAPEX................................................................ 181

Table 11.2 Abstraction Pumping Station CAPEX – Phase 1 and 2................................................. 181

Table 11.3 Pre-Treatment CAPEX .................................................................................................. 182

Table 11.4 Reverse Osmosis CAPEX ............................................................................................. 182

Table 11.5 Transmission Pipelines Cost ......................................................................................... 182

Table 11.6 Clear Water Pumping Station ........................................................................................ 183

Table 11.7 One-off Items ................................................................................................................. 183

Table 11.8 Asset lifetime and renewal annual provisions................................................................ 183

Table 11.9 Maintenance Annual Costs............................................................................................ 184


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Table 11.10 Power Capacity Charge ............................................................................................. 184

Table 11.11 Staff Cost.................................................................................................................... 186

Table 11.12 Whole Life Costs of the Scheme at 3%, 5% and 7% Discount Rates ....................... 187


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APPENDICES

APPENDIX A Tracking Desalination Costs No. of Pages 1

APPENDIX B Water Quality Analysis No. of Pages 6

APPENDIX C Potential Desalination Sites No. of Pages 1

APPENDIX D Energy Consumption of Desalination Plants No. of Pages 23

APPENDIX E Carbon Footprint Model No. of Pages 2

APPENDIX F Economic Assessment Details No. of Pages 3

APPENDIX G Desalination Plant Layout No. of Pages 1


MDW0158RP0080F01 ES1 F01

EXECUTIVE SUMMARY

INTRODUCTION

Dublin City Council appointed RPS Consulting Engineers in conjunction with Veolia Water to undertake a Feasibility Study of the options available for providing a new major source of potable water for the Dublin Region (Water Supply Area). The forecast growth in population combined with the projected growth in the extent of the water supply area is such that existing sources, including planned enhancements, will be insufficient to meet future demands within the next ten years. A total requirement of 300 Ml/d is the agreed planning figure for 2031 to cater for average demand/supply shortfalls and provide sufficient headroom for peak supplies, security of supply, contingencies and potential impacts of climate change. Desalination was considered as a possible option to meet this future demand. In order to select the most appropriate technology a review of all existing desalination technologies was undertaken to identify the most suitable technology for the Dublin application.

The key issues addressed in this Report are:

• An appraisal of the existing desalination technologies available including operational, lab-scale and bench-scale processes;

• Recommendations for the most appropriate technology with a preliminary design outline having regard to the water quality assessment of the source water;

• Examination of options and recommendations on selection of the most appropriate site for locating the desalination plant;

• Modelling of brine dispersion at the general site location to simulate the dispersion of effluent discharges associated with the desalination process, including coagulants and anti-scalants along with the brine discharge;

• Examination of the anticipated operational energy demand of a desalination facility and the potential sources of energy available to fuel the technology.

• An assessment of the likely significant environmental effects of constructing a desalination facility has been carried out in order to identify key issues;

• Cost estimates for the works including capital costs, capital renewals and operating costs which have been assessed on an annual basis over 25 years (2016-2040);

In summary, a seawater reverse osmosis desalination plant could be constructed in the north Fingal Area to cater for the water demands of future population growth. Construction would be in two phases - an initial two stream plant with provision for a future third stream of equivalent size. The final production of the plant would be 300 Mld. The first phase would have a capacity of 200 Mld, to be built for 2016, with a possibility to produce only 50 Mld at the start of the plant operation. All future treatment works, land requirements and connections would be provided for in the Phase 1 plant, such that the additional streams would be more easily constructed when required.


MDW0158RP0080F01 ES2 F01

The background to this report is outlined in Section 1.

DEMAND PROJECTIONS

Section 2 assesses demand projections and phased supply requirements from a new major source for current and future development. Based on the production capability of the existing sources and projections on which the long term planning of the Dublin Region’s water supplies should be based the final figures used in the design are summarised here.

New Source Installed Capacity

Dublin Region Peak Demand (2031) = 880 Ml/d

Sustainable Production from Existing Sources = 627 Ml/d

New Source Supply Requirement = 253 Ml/d

Allowance for Security of Supply = 50 Ml/d

303 Ml/d

TOTAL = (say 300 Ml/d)

The phasing of the works will provide flexibility in catering for gradually increasing demand growth as shown in the figure below which illustrates supply phases for the new major water source.

450

500

550

600

650

700

750

800

850

900

950

1000

2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033

Year

Ml/d

Average Demand Growth Sustainable Production from Existing SourcePeak Demand New Source PhasedHeadroom Allownces for Peaks/Contengencies

Planned Sustainable Production

Average Demand

Headroom

Phase 1 (200 Ml/d)

Phase 2 (100 Ml/d)

BME Advanced D & B

Roundwood

Leixlip

BME Stage 3

2016

KCC Barrow

Peak Demand

2026


MDW0158RP0080F01 ES3 F01

NEW WATER SUPPLY OPTIONS

There are currently ten options being evaluated as part of the current studies, seven of which have the River Shannon as their principal supply source and the remainder are from groundwater, marine sources and conjunctive uses. Technical descriptions of each of the ten options are outlined in Section 3.

This report concentrates on utilising a marine source, namely the Irish Sea as a major water supply source for the Dublin Region. To provide a treated water supply sourced from the Irish Sea would involve the construction of a major desalination facility on the East Coast and a pipeline to take the desalinated water to a suitable reservoir where it would enter the supply network for the Dublin Region. The Desalination concept was initially developed during a Feasibility Study (2005) undertaken by RPS-Veolia. A number of key issues in relation to desalination were identified by Veolia during the course of the feasibility study and these have been considered in greater detail as part of this study (Preliminary Report). The approach taken in evaluating the Desalination treatment process includes technical, environmental and economic assessments which are further developed in Section 3.

SELECTION OF OPTIMUM TECHNOLOGY

RPS-Veolia have undertaken a thorough appraisal of the existing desalination technologies available including all operational, lab-scale and bench-scale processes. The details of all the considered technologies are fully documented in Section 4 and the selection methodology and recommended option is outlined in Section 5.

Desalination is a separation process which produces two output streams namely the treated product water and a highly concentrated saline discharge. Three key parameters which greatly influence the technology selected are as follows:

• The requirement for thermal or electrical energy input;

• The characteristics of the source in terms of location, quality, availability of space, physical conditions, means of abstraction and impact of brine discharge on the marine environment;

• The capital and operating costs for desalination.

The leading factors considered when evaluating each of the technologies reviewed included cost, energy, environmental impact, robustness, operability and safety. In addition as part of this appraisal a full water quality assessment of the source water was conducted. Reverse Osmosis is the recommended option for a major water supply process for Dublin in terms of energy consumption, scale of adaptability and environmental impact when compared with both distillation and hybrid technologies.

PROPOSED DESIGN

It is proposed that twin 1800mm diameter pipelines are required to abstract seawater efficiently at maximum capacity (715Mld) and twin 1400mm diameter pipelines will enable the discharge of brine in an optimised manner at maximum flow rate (415Mld). The pipelines will be in the order of 3km and 2km in length respectively. Given the characteristics of the raw water, the following process stages shall be used for drinking water production:


MDW0158RP0080F01 ES4 F01

• Chemical pre-treatment: intended to decrease the SDI before membrane filtration;

• Reverse osmosis for desalination;

• Post-treatment with setting at calco-carbonic equilibrium and final chlorination.

Arising out of the water quality assessment of the source waters, two key parameters which greatly influence the desalination plant design in North Dublin are the Silt Density Index (SDI) and the boron concentrations which were recorded during sampling. Analysis results for both SDI and boron were high when compared with typical values. As a consequence for this application the extent of the pre-treatment processes required are considerable.

The seawater intake and treated water tank constructed in Phase 1 would be adequate for 300 Mld plant removing the need for significant engineering works in Phase 2.

Full details of the proposed treatment processes and analysis can be found in Chapter 6.

TREATMENT SITE OPTIONS

Eight potential sites were considered for the desalination plant. The preferred site for the construction of the plant is in North County Dublin between Loughshinny and Skerries. Having examined the general area required for the treatment plant, this site was selected for the following reasons:-

1. There is sufficient space available to construct the new facility (an area of 15ha required);

2. Close proximity to direct supplies of electricity from local grid;

3. No significant impediments found following an initial review of onshore topography, tidal regime and bathymetry of the area and water quality.

BRINE DISPERSION MODELLING

The discharge of brine and pollutants associated with the operation of a desalination plant were modelled and it emerged that dispersion levels were high due to the tidal regime and high current speeds in the vicinity of the proposed discharge site.

The levels of suspended solids, iron and salt were found to be within acceptable levels outside of the immediate vicinity of the discharge site. Sedimentation levels resulting from the sludge dispersal were found to be very low with very limited settlement occurring during slack water, which is subsequently re-suspended and dispersed as current speeds increase as the tidal cycle progresses.

An estimation of the cost of such a scheme was made assuming that ground conditions are favourable and these along with the brine dispersion model outputs are reported in Section 8.

ENERGY REQUIREMENTS

Preliminary examination of the energy and carbon demand has identified that desalination would have a considerable overall energy demand and associated carbon footprint during the operational phase of the project. Desalination is a very energy intensive process and in an Irish context the cost of gas/oil for energy generation is a key issue for consideration. The construction of a dedicated gas or oil fired power station may have considerable impacts. In terms of alternative renewable energy, regulatory


MDW0158RP0080F01 ES5 F01

constraints require electricity produced from any wind energy project, which exceeds 5MW, be dispatched directly to the national grid. This is then subject to Single Energy Market cost drivers. Therefore the most practicable options for powering the desalination facility would be a direct electrical supply from the National Grid.

ENVIRONMENTAL CONSIDERATIONS

The amount of energy that would be required for the desalination treatment process and the resultant emissions of green house gases when compared with conventional treatment methods are expected to have a significant negative impact on the environment.

The proposed preliminary design contains a substantial pre-treatment facility and requires a second pass RO system to be incorporated to treat both the high SDI (silt density index) and boron levels present in the source water. These factors further contribute to the already anticipated high energy requirement for this treatment process.

In terms of the impacts on population and health the vulnerability of the Irish Sea source to acute or chronic pollution events exposes the treatment process to risks in terms of security of supply and poor quality treated water.

ECONOMIC ASSESSMENT

Cost estimates for the recommended works are set out below and detailed in Chapter 11 and Appendix F of this report.

For a desalination plant the capital and operating costs have been based on the construction of pipelines initially for the long-term capacity (300Mld), while the RO treatment and pumping facilities are designed to match demand growth.

Economic evaluation results are summarised below:

Calculation of average cost of water delivered to the GDA over the assumed 25 year operating period

Option H Cost

CAPEX 611 m€

OPEX 336 m€

Whole Life Cost 947 m€

WLC / Delivered Volume (€/m3) 0.64 €/m3


MDW0158RP0080F01 1 F01

1 INTRODUCTION AND BACKGROUND

1.1 LONG TERM WATER SUPPLIES FOR THE DUBLIN REGION

Dublin City Council have been carrying out long term planning studies over the past three years into how best to provide adequate supplies of drinking water for the estimated 2.2 million people expected to be living in the Dublin Region (Water Supply Area) by 2031.

The Dublin Region (Water Supply Area) includes the administrative areas of Dublin City, Dun Laoghaire-Rathdown, Fingal and South Dublin, along with significant parts of County Wicklow, Co Meath and Co Kildare (see Figure 1.1 below).

Figure 1.1 Greater Dublin Area / Dublin Region (Water Supply Area)


MDW0158RP0080F01 2 F01

1.2 DUBLIN REGION (WATER SUPPLY AREA)- DEMAND PROJECTIONS

The average water requirement, in 2007, for the Dublin Region (Water Supply Area) was approx 540 Mld (million litres per day). It is estimated that, as a result of forecast population growth, this figure will rise to approx 800 Mld day by 2031. Peak requirements at 2031 are estimated at 880 Mld.

The Dublin Region (Water Supply Area) is currently supplied with water from the Rivers Liffey, Vartry and Dodder and a number of groundwater sources in Fingal and north Kildare. The environmentally sustainable production of water from existing Dublin Region sources will not be sufficient to meet the increased demand of the larger projected population as it continues to grow. Water supplies from a new source to augment supplies from all the existing water supply sources will be required by approx 2016. Otherwise, water shortages and curtailment of economic growth will be unavoidable.

1.3 PREVIOUS STUDIES & MILESTONES

Figure 1.2 below sets out the milestones in the new source studies from 1996 (Strategic Study) when the need was first identified, up to the present studies (Feasibility Study / Preliminary Report)

Figure 1.2 Key Milestones in Dublin Region Strategic Water Supply Planning

19961996

DEHLG – Greater Dublin Water Supply Strategic Study 1996 -2016

New Source Requirement identified

DEHLG – Greater Dublin Water Supply Strategic Study 1996 -2016

New Source Requirement identified

2007 – 20082007 – 2008

Preliminary Report Studies / Stakeholders Consultations(Includes all alternative water supply options and issues raised during SEA Phase 1 Public Consultation)

Technical Modelling & Environmental Assessments

Preliminary Report Studies / Stakeholders Consultations(Includes all alternative water supply options and issues raised during SEA Phase 1 Public Consultation)

Technical Modelling & Environmental Assessments

20002000

DEHLG – Review of GDWSSS 1996

Major Source Options identified / shortlisted (3 No)

DEHLG – Review of GDWSSS 1996

Major Source Options identified / shortlisted (3 No)

20052005

Feasibility Study of Short-listed OptionsFeasibility Study of Short-listed Options

20062006

Strategic Environmental Assessment (SEA) – Phase 1

Public Consultation / Feedback June – Oct. 2006

Strategic Environmental Assessment (SEA) – Phase 1

Public Consultation / Feedback June – Oct. 2006

2002 – 20042002 – 2004

Water Services Investment Programme – needs assessment

GDA Local Authorities adopt Requirement for New Source

Water Services Investment Programme – needs assessment

GDA Local Authorities adopt Requirement for New Source

The 1996 Department of Environment, Heritage and Local Government (DEHLG) Strategic Study developed a range of demand/supply projections which first identified that the Dublin Region would require a new water supply source within a 20 year period to supplement the sustainable supply production of existing Dublin Region sources.


MDW0158RP0080F01 3 F01

In 2000, a review of the 1996 study re-confirmed its findings and shortlisted a number of water supply source options for further detailed study. These were; Shannon – Lough Ree, Desalination (Irish Sea) and a conjunctive use option involving the Upper Liffey with the River Barrow. Over the 2002 to 2004 period, following public consultation, the need for a new water supply source was adopted by the Local Authorities in the Dublin Region.

In 2005 DCC, through their consultants RPS-Veolia, carried out a Feasibility Study on the water supply source options shortlisted in the 2000 review.

A Strategic Environmental Assessment (SEA) of the Feasibility Study’s findings commenced in 2006.The initial SEA (Phase 1) involved extensive public consultation from June to Oct 2006. During this period (and subsequently) considerable feedback was received from impacted stakeholders and the general public.

On foot of the feedback received, DCC decided to consider a wider range of water supply options during the Preliminary Report studies. An interim SEA Statement and Newsletter were published in July 2007 outlining the status of the work at that stage and setting out the plan for further studies and also plans for a follow up SEA (Phase 2) of the wider water supply options range.

1.4 WATER SUPPLY OPTIONS

The water supply options which are currently being investigated as part of the Preliminary Report studies are outlined schematically in Figure 1.3 below. Desalination is Option H.

Figure 1.3 Water Supply Options Summary

A-Lough Ree

B-Lough Derg

C-Parteen Basin

D-Lough Ree +Lough Derg

E- Lough Ree+ Storage

F- Lough Derg+ Storage Options

G-Impoundment- Lough Ree [Derg]

H-Desalination

I-Fingal / Kildare Groundwater

J-Liffey / Barrow

Lough

Ree

Lough

Derg

River

Shannon

ATHLONE

MULLINGAR Desalination Plant

Wells

Killaloe

A

B

C

H

G

I

J

PORTLAOISESLIEVE BLOOM

MOUNTAINS

TULLAMORE

Water Treatment Plant

Termination

Point

E

F

Parteen

Basin

Ballycoolen

Former Bogs

Ballymore Eustace

Athy

River

Barrow

Impoundment

Poulaphuca Lake

ESB Ardnacrusha

River Shannon

Head

Race

MDW0158SK0036D13

F2

F1

D

E

G


MDW0158RP0080F01 4 F01

1.4.1 Phased Water Supply Requirements from the New Supply Source

Demand projections for the Dublin Region (Section 2) indicate a requirement for water supplies from a new source to supplement supplies from existing sources by approx 2016. Table 1.1 below summarises the projected population growth to 2031 and the water demand increases associated with that growth. The sustainable production of existing Dublin Region sources (630Mld) can meet average demand up to approx 2016. After 2016, supplies from a new source will be increasingly needed to avoid regular water shortages and rationing.

Table 1.1 Supply Requirements from New Source

Average Supply Requirement at 2031 = 800 Ml/d – 630Ml/d = 170Ml/d

Additional Peak Requirement at 2031 (approx. 3 months / annum) = 80Ml/d

Supply Allowance to Midlands Local Authorities = 50Ml/d

Contingency Allowance = 50Ml/d

Supply (new source) Total = 350Ml/d

630

630

1685

2016

540

530

1370

2006

630470Sustainable Production of

existing Sources (MI/d)

800460Average Total Demand

(MI/d)

21801180Population (000’s)

20311996Dublin Region

Water Supply Area

Infrastructure development proposals and associated capital costs in Section 3 reflect a phased approach to provision of gradually increasing quantities of water supplies to match demand growth from 2016 onwards.


MDW0158RP0080F01 5 F01

2 DEMAND PROJECTIONS / PHASED SUPPLY REQUIREMENTS FROM A NEW MAJOR SOURCE

This section contains demand projections for the Greater Dublin (Water Supply) Area for the period 2007-2031.

The Greater Dublin Water Supply Strategic Study (GDWSSS) 1996 contained demand projections for the period 1996 – 2016. Detailed projections for 2000-2021 were prepared during the subsequent review of GDWSSS96 in 2000. These projections were updated during the Feasibility Study in 2004/5 and again as part of the current studies in 2007/8.

Projected water production from existing GDA sources was also investigated during the current studies in order that the phased supply requirements from a new major source could be determined using the most up to date information available.

2.1 DEMAND PROJECTIONS – PROCESS

The process for estimation of future potable water demand for the Greater Dublin Area involved :

• Review of all relevant reports

• Analysis of trends over the 1996 to 2007 period

• Local Authority Consultations

2.2 REPORTS REVIEW

The following key reports and studies were referenced:

• Greater Dublin Water Supply Strategic Study (GDWSSS) '96

• Year 2000 Review of GDWSSS96

• Greater Dublin Strategic Drainage Study (GDSDS) 2004

• Population and Land use Study 2003 (incl. Strategic & Regional Planning Guidelines/National Spatial Strategy / Local Authority Development Plans)

• Monthly "Water Balance" Report to Greater Dublin Water Supply Steering Group

• Yield of the River Liffey (O’Dwyer / Tobin) - Fingal County Council

• Kildare Water Strategy - Nov 2003 (Nicolas O'Dwyer)

• Wicklow / Meath (demand projection studies)

• Water Services Investment Programme - Assessment of Needs 2007 - 2012

• Strategic Storage Study 2006 (Mc Carthy-Hyder)


MDW0158RP0080F01 6 F01

2.3 DEMAND ESTIMATION METHODOLOGY

The 1996 Strategic Supply Study and Year 2000 Review established the methodologies for best practice demand analysis and forecasting which in turn were based on UK Department of Environment recommendations (Sept. 1995). The demand projections in this report are based on this methodology.

The total demand is arrived at by consideration of a number of sub-components and preparing projections for each to arrive at an overall total. The demand sub-components are as follows:

• Domestic Consumption

• Non Domestic Consumption

• Customer Side Leakage

• Distribution Network Leakage

• Headroom (peak/security of supply/contingency/climate change)

Each of these sub-components are developed in Sections 2.4 to 2.8.

2.4 DOMESTIC DEMAND

Domestic demand is a product of population and per capita consumption (PCC).

2.4.1 Population

Population projections for the GDA were undertaken at a high level of detail during the Greater Dublin Strategic Drainage Study and reported on in the Population & Land Use Report of 2003. This 2003 report took cognisance of the Regional and Strategic Planning Guidelines and National Spatial Strategy long-term CSO and ESRI population projections.

The GDA population projections for 2011 and 2031 contained in the 2003 Population & Land Use Report were used as the basis for forecasting the population projections for the Greater Dublin Water Supply Area which includes Dublin City Council, Fingal, South Dublin, Dun Laoghaire-Rathdown and substantial parts of Kildare, Wicklow and Meath

The population projections for the Kildare, Meath and Wicklow sections of the Greater Dublin Water Supply Area include only for population in Kildare, Meath and Wicklow receiving their supplies from Dublin Sources, i.e. Population figures for Kildare are net of those who will receive future supplies from the River Barrow and Groundwater Sources. A similar approach has been adopted for Meath and Wicklow.

GDA population forecasts in the National Spatial Strategy for 2031 range from 2.0m to 2.6m depending on levels of migration, fertility rates, various economic growth scenarios, etc. The Greater Dublin Strategic Drainage Study based its planning for future infrastructure development on a GDA population of 2.5m at 2031. This study has adopted a similar approach.


MDW0158RP0080F01 7 F01

Table 2.1 below outlines the population projections.

Table 2.1 Greater Dublin Water Supply Area Population 2007-2011-2031

2007 2011 2031

Population 1,429,000 1,594,000 2,189,000

2.4.2 Per Capita Consumption (PCC)

Per Capita Consumption has been increasing steadily over the past 10 years reflecting a growth in affluence and lifestyle changes. Demand analysis indicates that current (2007) PCC levels in the GDA range from 148 l/hd/d (litres per head per day) to 150 l/hd/d.

The constant addition of new housing stock within the water supply area, including greater usage of water efficient appliances, should exert some downward influence on average PCC levels over time. On the other hand the impacts of climate change and continuing lifestyle changes may result in PCC increases.

In discussion with Local Authority operations staff, a figure of 145 l/hd/d was agreed as an appropriate figure for planning purposes from 2011 to 2031, particularly when taken in conjunction with a population projection figure towards the top end of the range. Table 2.2 below outlines the projected domestic consumption for the 2007-2011-2031 period.

Table 2.2 Projected Domestic Demand 2005-2011-2031

2007 2011 2031

Population 1,429,000 1,594,000 2,189,000

Per Capita Consumption

148 l/hd/d 145 l/hd/d 145 l/hd/d

Total Domestic Demand

212 Ml/d 231 Ml/d 317 Ml/d

2.5 NON DOMESTIC DEMAND (INDUSTRIAL & COMMERCIAL)

The estimation of future non-domestic demand was based on a "zoning approach". The Greater Dublin Strategic Drainage Study Report 2004 contained details of lands in each Local Authority area which had been identified for non-domestic zoning purposes.

Having established the extent of potential future non-domestic development lands, average demand estimates per hectare were derived from Table 3.5 of Year 2000 Review of GDWSSS96. The average demand/hectare for wet/dry industry is outlined in Table 2.3.


MDW0158RP0080F01 8 F01

Table 2.3 Industrial Demand / Hectare – Wet & Dry Industries

Dry Industry Wet Industry

17 m3/ha/day 31m3/ha/day

A number of assumptions were made as follows:

• Development of Industrial & Commercial zoned land assumed to be 50% wet, 50% dry

• Scientific & Technology land development assumed to be 100% dry

• By 2031 all currently zoned lands will have been fully developed.

Table 2.4 below outlines the projected growth in non-domestic demand over the 2007-2011-2031 period.

Table 2.4 GDA Non-Domestic Growth 2007-2011-2031

2007 2011 2031

Non Domestic Demand

131 Ml/d 154 Ml/d 267 Ml/d

These projections are inclusive of non-domestic demand associated with new residential development and expansion of serviced industry in existing developed areas. They also include all strategic industry provision.

2.6 CUSTOMER SIDE LEAKAGE LOSSES

Customer side leakage losses average approx 65.0 litres per property per day (l/prop/d) for the GDA (2007). In the short term, this level of customer side leakage is forecast to continue.

In the medium term (post 2011) reductions of 1% per annum have been forecast to reflect the impact of greater consumer awareness through water conservation programmes, network rehabilitation and the effect of constant addition of new connections to the network.

Total customer side leakage losses are a product of leakage per property and forecast property numbers.

Forecast property numbers have been determined from population forecasts and projected household occupancy rates on an individual local authority basis.

Customer Side Leakage Losses for the 2007-2011-2031 period are summarised in Table 2.5 below.


MDW0158RP0080F01 9 F01

Table 2.5 Customer Side Leakage Losses: 2007-2011-2031

2007 2011 2031

Leakage/Property/Day 65 litres 65 litres 53 litres

Household Occupancy Rate – GDA Average

2.50 2.50 2.20

No. of GDA Properties

570,840 637,000 995,000

Customer Side Leakage Losses

37 Ml/d 42 Ml/d 53 Ml/d

2.7 DISTRIBUTION LEAKAGE LOSSES

GDA Local Authorities are in broad agreement on the network leakage level reductions which are likely to be achieved over the 2007-2011-2031 period as a result of active leakage control, water conservation measures and network rehabilitation programmes.

Each GDA Local Authority is starting from a different base with higher leakage currently occurring in the older networks in Dublin City, parts of Fingal and Bray, Co. Wicklow.

International best practice for equivalent networks would indicate leakage levels of 20% as being attainable with pro-active leakage detection supported by ongoing targeted network rehabilitation .The 2007 – 2010 network rehabilitation programme costing €118m is currently underway. The 2007 GDA average leakage was approximately 30%. This and future projections are summarized in Table 2.6 below.

Table 2.6 Distribution Leakage Losses: 2007-2011-2031

2007 2011 2031

Leakage % 30% 25% 20%

Previous demand projections in GDWSSS96 and Year 2000 Review had forecast leakage levels reducing to 16% by 2021. Recent experience in the major leakage detection and repair programme over the last five years demonstrates that the 20% target at 2031 is more appropriate due to the established conditions in the network. The 20% figure is also in line with international best practice for networks of this nature.

2.8 HEADROOM

Water supplies from a new Major Source for the GDA will be required to have sufficient capacity to meet the following supply conditions:

• Average demand shortfalls (i.e. average projected demand minus the sustainable production of existing GDA sources)


MDW0158RP0080F01 10 F01

• Peaks (@ 12.5% above average) estimated from historical patterns (average day/peak week)

• Security of supply (allowance of 50 Ml/d) for all other requirements (unexpected demand or loss of production)

• Contingencies (e.g. wet process industries)

• Climate change impacts (Included in peak/security of supply allowances)

• New supply areas

2.9 AVERAGE/PEAK DEMAND PROJECTIONS – GDA (2007-2011-2031)

Based on the projections of the various demand components outlined in 2.4 to 2.8 above, Table 2.7 summarises the GDA average/peak water supply requirements for the 2007-2011-2031 period.

Table 2.7 Average/Peak Demand - GDA (2007-2011-2031)

2007 2011 2031

Average Demand Ml/d 540 590 800

Peak Demand Ml/d 588 643 880

The Feasibility Study (2005) recommended that long term planning of the GDA's water supplies should be based on these projections. Since any new water supply scheme will not be realised before 2015/16 at the earliest, it follows that such a scheme should have a 25 year design life as a minimum. Therefore, even if demand growth is lower than predicted to 2031, the effect will be the delaying of its realisation by a number of years. It follows that while phasing of the scheme might be adjusted for demand growth, the ultimate capacity requirement will be necessary for the GDA in the longterm.

2.10 PRODUCTION CAPABILITY OF EXISITING SOURCES

Tables 2.8 and 2.9 below outline the current and projected sustainable production capabilities of the existing Dublin public water supply sources and also the anticipated production of Kildare Wellfields and the River Barrow.

The projected production represents the upper sustainable production limit of the respective sources. No contribution has been assumed from the development of any new interim GDA sources as no significant volumes are anticipated.


MDW0158RP0080F01 11 F01

Table 2.8 GDA Production Capacity – Existing/Proposed

Water Treatment Plant * Sustainable Output Year

• Ballymore Eustace (BME)

- Stage 3 Development

274 Ml/d

318 Ml/d

2007

2009

• Leixlip

- Stage 5 Expansion

148 Ml/d

215 Ml/d

2007

2010

• Roundwood 75 Ml/d 2007

• Ballyboden 16 Ml/d 2007

• Bog of the Ring 3 Ml/d 2007

• Kildare Groundwater

- Wellfield Phase 1

- Wellfield Phase 2

3 Ml/d

8 Ml/d

2008

2011

• Kildare River Barrow

- Phase 1

- Phase 2

20 Ml/d

41 Ml/d

2011

2015

* Because of Network Restrictions, production from all sources cannot be fed to all distribution areas. This may result in localised shortages in areas of high growth post 2011.

Table 2.9 GDA Sustainable Production Capacity – 2007/2011/2015

Source Units 2007 2008 2009 2010 2011 2015

BME Ml/d 274 274 318 318 318 318

Leixlip Ml/d 148 148 148 215 215 215

Roundwood Ml/d 75 75 75 75 75 75

Ballyboden Ml/d 16 16 16 16 16 16

Bog of the Ring

Ml/d 3 3 3 3 3 3

TOTAL ML/d 516 516 560 627 627 627

Kildare

- Wellfields

- Barrow

Ml/d

Ml/d

-

-

3

-

3

-

3

-

8

20

8

41

Kildare Total Ml/d - 3 3 3 28 49

The demand projections for Kildare County which are included in GDA demand projections reflect Kildare's requirements from the GDA water supply system and are net of demand being met by production from Wellfields/Barrow. Meath & Wicklow demands supplied from GDA sources are treated in a similar manner.


MDW0158RP0080F01 12 F01

By 2010 the existing GDA Water Supply Sources will have reached their upper sustainable limits of production. There is a non-sustainable peak production capability of approximately 35 - 40 Ml/d available to supplement sustainable production for limited periods. This is illustrated in Table 2.10 below.

Table 2.10 GDA Peak Production Capacity (Ml/d) (Excluding Kildare Wellfields/Barrow)

Production 2007 2008 2009 2010

Sustainable 516 516 560 627

Peak 553 553 597 664

Additional supplies will be required from a new Major Source when the projected future average demand exceeds 627 Ml/d. The critical point will be reached when average demand exceeds peak production from existing sources. These capacities are based on existing capacity calculations using historical yield data. They make no allowance for climate change impacts which may be significant in the region in the longterm.

Projected Demands are superimposed on projected supply in Section 2.13 to identify the timing and quantities of additional supply inputs from a new major source.

2.11 DEMAND/SUPPLY BALANCE

Table 2.11 summarises the demand/supply projections for the 2007/2011-2031 period.

Table 2.11 Demand/Supply Balance (Ml/d)

Year

Average Production – Existing Sources

Average GDA Demands

Peak Production – Existing Sources

Peak GDA Demand

2007 516 540 553 588

2008 516 554 553 603

2009 560 566 597 617

2010 627 578 664 630

2011 627 589 664 643

2012 627 580 664 633

2013 627 591 664 646

2014 627 602 664 658

Critical 2015 627 615 664 672

Period 2016 627 627 664 685

2021 627 685 664 750

2026 627 743 664 815

2031 627 800 664 880


MDW0158RP0080F01 13 F01

The critical period, outlined in red above, is reached when sustainable production from existing sources equals average day demand and peak demand begins to exceed peak production capability. This situation occurs in 2015/16. Supplies from a new major source will be required at that stage if current levels of service are to be maintained.

In addition to the above, localised supply shortages, from 2012 to 2016, are possible in certain areas experiencing high demand growth, since restrictions in the network prevent the outputs from the various production facilities being used in all distribution areas.

NB. The average demand projection for 2021 in the Year 2000 Review (high scenario) was 672 Ml/d compared to a forecast of 685 Ml/d currently.

2.12 NEW SOURCE PRODUCTION REQUIREMENTS

A new major source for the GDA will be operated in conjunction with the existing sources to provide overall supplies in the most cost effective and operationally efficient manner.

Assuming a new source comes on stream in 2016, the minimum supply requirement profile to meet average demand shortfalls can be calculated from Table 2.11 above and are outlined in Table 2.12.

Table 2.12 Average Supply Requirements from the New Source

Year Units Sustainable Production -Existing Sources

Average GDA Demands

Supply Requirements – New Source

2016 Ml/d 627 627 0

2021 Ml/d 627 685 58

2026 Ml/d 627 743 116

2031 Ml/d 627 800 173

Similarly, if the new source is required to meet peak GDA demand (or if peak demand in the GDA is being met by the sustainable production of existing sources) then the supply requirements from the new source are as outlined in Table 2.13. This is the recommended operational scenario.

Table 2.13 Peak Supply Requirements from New Source

Year Units Sustainable Production -Existing Sources

Peak GDA Demands

Supply Requirements – New Source

2016 Ml/d 627 685 58

2021 Ml/d 627 750 123

2026 Ml/d 627 815 188

2031 Ml/d 627 880 253


MDW0158RP0080F01 14 F01

In addition to meeting average and peak supply requirements the New Source should also have sufficient reserve capacity to provide security of supply in the event of existing plant breakdown or other contingencies. A minimum allowance of 50 Ml/d is recommended.

On the basis of the above projected average and peak demand requirements to be supplied by the New Major Source in addition to a reserve capacity for security of supply the recommended maximum installed capacity was determined as follows in Table 2.14.

Table 2.14 New Source Installed Capacity

GDA Peak Demand (2031) = 880 Ml/d

Sustainable Production from Existing Sources = 627 Ml/d

New Source Supply Requirement = 253 Ml/d

Allowance for Security of Supply = 50 Ml/d

303 Ml/d

TOTAL = (say 300 Ml/d)

The total installed capacity of 300 Ml/d can be implemented over a number of phases to provide flexibility in catering for gradually increasing demand growth. Figure 2.1 below illustrates a two phased approach - 200 Ml/d in Phase 1 and 100 Ml/d in Phase 2 - approximately 10 years apart. Figure 2.1 also illustrates the average demand, headroom allowances catering for peak (12.5%) and security of supply (50 Ml/d) as well as the sustainable production from existing sources.

Figure 2.1 New Source Supply Phases

450

500

550

600

650

700

750

800

850

900

950

1000

2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033

Year

Ml/d

Average Demand Growth Sustainable Production from Existing SourcePeak Demand New Source PhasedHeadroom Allownces for Peaks/Contengencies


Average Demand

Headroom

Phase 1 (200 Ml/d)

Phase 2 (100 Ml/d)

BME Advanced D & B

Roundwood

Leixlip

BME Stage 3

2016

KCC Barrow

Peak Demand

2026


MDW0158RP0080F01 15 F01

2.13 WATER CONSERVATION

DCC and GDA Local Authorities are currently involved in a wide range of water conservation activities to ensure that current water availability is utilised in the most efficient manner possible. The initiatives being pursued are in keeping with the provisions of the Water Framework Directive and are a necessary prerequisite to the development of any new water supply sources. The water savings which will result from proactive water conservation measures and the degree to which they have been provided for in the projected demand growth are outlined below.

The principal water conservation measures which are envisaged over the planning period and the impact of their implementation on demand projections are as follows:

1) Proactive Leakage Management – Water savings from proactive leakage management are provided for in demand projections. Current leakage of 30% (2008) is projected to reduce to 20% (2031).If leakage %’s remained constant an additional 80Mld would be required at 2031.

2) Network Rehabilitation – Water savings from network rehabilitation are provided for in demand projections. Current leakage of 30% (2008) projected to reduce to 20% (2031) as per 1) above.

3) 100% metering and volumetric charging of all non domestic consumers in the GDA – Will be fully implemented by end 2008.Non domestic demand projections reflect savings (estimated at 10Mld).

4) Metering and volumetric charging of domestic customers – Government decision required for implementation. Implementation on a phased basis (from 2009 onwards) in line with current practice in England & Wales estimated to achieve approx 10Mld – 15Mld savings by 2031. Not included for in demand projections because of uncertainty.

5) Bye-law implementation re water efficient appliances in new developments – Ongoing in GDA Local Authorities. Demand projections reflect savings (estimated at 5-10Mld by 2031)

6) Awareness Campaigns – Ongoing (most recent is Tap Tips Campaign by DCC). Water savings factored into demand projections as per 5) above.

7) Rainwater Harvesting – Local Authority promotion of rainwater harvesting where practical. Savings included in demand projections as per 5) above.

8) Wastewater Re Use – Savings in non domestic sector through greywater reuse are factored into demand projections as per 3) above. Wastewater treatment and reuse for domestic sector is not included in demand projections on account of technology considerations, high costs and issues of public acceptability.

Proactive water conservation will result in valuable water savings over the planning period and may marginally influence the timing of the requirement for supplies from a new source. Water conservation savings on their own however, will be insufficient to prevent the ultimate need for supplies from a new source. See figure 2.2 below.


MDW0158RP0080F01 16 F01

Figure 2.2 High / Low Demand Growth Scenarios

450

500

550

600

650

700

750

800

850

2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033

Year

Ml/d

Average Demand Growth Sustainable Production from Existing Source


Average Demand

New Source Required

Demand Projections

Accelerated

Low

Low

20% 16%

SCENARIO

Water Conservation Pro-Active

Economic Growth Rate Medium to High to Medium

Population Growth Rate Medium to High to Medium

Leakage at 2031

Low

Low Accelerated

2.14 SUMMARY

2.14.1 Demand Drivers

Demand for water is primarily driven by population increases both for personal consumption and industrial / commercial activity associated with population increases. Economic growth rates and water conservation performance are also contributory factors as illustrated in Fig 2.2 above.

CSO and ESRI population projections for the GDA for 2031 range from 2.0m to 2.6m.The 2003 Greater Dublin Strategic Drainage Study selected a 2.5m population figure as an appropriate figure for the planning of new long-term infrastructure. The new source study adopted the same figure and water demand at 2031 is based on this figure.

Short / medium term demand growth projections are reviewed regularly based on the outturn of preceding years.

2.14.2 Supply Sources

Approx 85% of Dublin’s water comes from the Liffey at Poulahuca for Ballymore-Eustace Water Treatment Plant (WTP) and at Leixlip for Leixlip WTP. The remainder comes from the Vartry and Dodder and some groundwater sources in Fingal and North Kildare. All of these resources are being developed to their sustainable supply limits.


MDW0158RP0080F01 17 F01

2.14.3 Leakage

Progress on leakage reduction has resulted in leakage levels in excess of 40% in the late 1990’s being reduced to 30% today (2007) and the intent is to lower this further to a max 20% by 2031 which is in line with best international practice for similar type networks.

Substantial investment is required, even to retain the current leakage levels, since without investment the networks will continue to deteriorate in a do-nothing scenario.

2.14.4 Water Conservation.

Per Capita Consumption (PCC) in the GDA is currently estimated at 148 – 150 l/hd/d (litres per head per day). This is similar to non-metered domestic consumption in England and Wales. Demand projections for 2031 are based on a reduction of PCC to 145 l/hd/d by 2011, which is then maintained constant for the planning period.

Lowering and maintaining PCC levels will be achieved by the installation of water efficient appliances in new properties as a result of bye-law implementation, increased public awareness of the need for water conservation through media campaigns (e.g. tap tips) and the promotion where practical of rain water harvesting and grey water reuse.

Domestic metering and charging is a decision for central government. If implemented, long-term savings are not likely to exceed 10% of domestic consumption based on operational experience to date in England/Wales.

Non domestic metering and charging will be 100% implemented by end 2008 in the GDA

2.14.5 Longterm Demand / Supply Considerations.

GDA demand is expected to reach 800 Ml/d (Megalitres per day) by 2031. The sustainable maximum production capacity of existing GDA sources is 630 Ml/d, which leads to a shortfall of 170 Ml/d by 2031.

An additional allowance of 80 Ml/d is required to meet peak demands at 2031. Peaks occur on average for 2 or 3 months per year. Peaks can arise during hot summers or as a result of winter frost and associated leakage from pipe fractures.

An allowance of 50 Ml/d has been included for supplies to Midland local authorities between the Shannon and Dublin.

An additional allowance of 50 Ml/d has been included for contingency/security of supply considerations in the GDA and Midlands.

This brings the total supply requirement from a new source to 350 Ml/d (170+80+50+50). Assessment of potential sustainable yields from new source options is based on this figure.


MDW0158RP0080F01 18 F01

3 WATER SUPPLY OPTIONS

3.1 INTRODUCTION – UPDATED INFO AVAILABLE

The water supply options which are being investigated are outlined schematically in Fig 3.1 below. Desalination (Option H) is one of 10 options being investigated. The other nine options have been described in order to set the context in which the desalination studies are being undertaken.

Figure 3.1 Water Supply Options Summary

A-Lough Ree

B-Lough Derg

C-Parteen Basin

D-Lough Ree +Lough Derg

E- Lough Ree+ Storage

F- Lough Derg+ Storage Options

G-Impoundment- Lough Ree [Derg]

H-Desalination

I-Fingal / Kildare Groundwater

J-Liffey / Barrow

Lough

Ree

Lough

Derg

River

Shannon

ATHLONE

MULLINGAR Desalination Plant

Wells

Killaloe

A

B

C

H

G

I

J

PORTLAOISESLIEVE BLOOM

MOUNTAINS

TULLAMORE

Water Treatment Plant

Termination

Point

E

F

Parteen

Basin

Ballycoolen

Former Bogs

Ballymore Eustace

Athy

River

Barrow

Impoundment

Poulaphuca Lake

ESB Ardnacrusha

River Shannon

Head

Race

MDW0158SK0036D13

F2

F1D

E

G

3.1.1 Option A

Option A involves water abstraction from Lough Ree, water treatment and pumping facilities near Lough Ree and pipelines approx 104km in length to convey treated water to the Dublin Region. This option also has the capability of supplying treated water to Midlands Local Authorities along the pipeline route.

3.1.2 Option B

Option B involves water abstraction from Lough Derg, water treatment and pumping facilities near Lough Derg and pipelines approx 122km in length to convey treated water to the Dublin Region.This


MDW0158RP0080F01 19 F01

option also has the capability of supplying treated water to Midlands Local Authorities along the pipeline route.

3.1.3 Option C

Option C involves water abstraction from Parteen Basin (near Parteen weir), water treatment and pumping facilities near Parteen Basin and pipelines approx 158km in length to convey treated water to the Dublin Region. This option also has the capability of supplying treated water to Midlands Local Authorities along the pipeline route.

3.1.4 Option D

Option D involves water abstraction initially (Phase 1) from Lough Ree, water treatment and pumping facilities near Lough Ree and pipelines approx 104km in length to convey treated water to the Dublin Region. A second phase (approx 10 years later) involves abstraction from Lough Derg, treatment near Lough Derg and pumping of treated water via pipelines 73km in length to a booster station located approx midway between Lough Ree and Dublin. This option also has the capability of supplying treated water to Midlands Local Authorities along the pipeline routes from Lough Ree to the Dublin Region and from Lough Derg to the booster station location.

3.1.5 Option E

Option E involves raw water abstraction from Lough Ree, pumping of raw water to a “cutaway bog” site near Rochfortbridge (owned by Bord na Mona),raw water storage facilities at the site ,water treatment and pumping facilities at the site and pipelines to convey treated water to the Dublin Region. Overall raw water and treated water pipelines are approx 104km in length. Storage facilites will accommodate up to 4 months average supply requirements. This option has the capability of supplying treated water to Midlands Local Authorities from Rochfortbridge.

3.1.6 Option F

Option F involves abstraction from Lough Derg in combination with bog storage. Two bogs have been identified as suitable for storage, one near Rochforbridge, Option F1, and the other near Portarlington, Option F2. F1 involves raw water abstraction from Lough Derg, pumping of raw water to a “cutaway bog” site near Rochfortbridge (owned by Bord na Mona) raw water storage facilities at the site, water treatment and pumping facilities at the site and pipelines to convey treated water to the Dublin Region. Overall raw water and treated water pipelines are approx 127km in length. Storage facilities will accommodate up to 2 months average supply requirements. This option has the capability of supplying treated water to Midlands Local Authorities from Rochfortbridge. F2 involves raw water abstraction from Lough Derg, pumping of raw water to a “cutaway bog” site near Portarlington (owned by Bord na Mona) raw water storage facilities at the site, water treatment and pumping facilities at the site and pipelines to convey treated water to the Dublin Region. Overall raw water and treated water pipelines are approx 122km in length. Storage facilities will accommodate up to 2 months average supply requirements. This option has the capability of supplying treated water to Midlands Local Authorities from Portarlington.

3.1.7 Option G

Option G involves abstraction of raw water from Lough Ree during higher flow months, pumping of raw water to a treatment plant near Dublin, pumping of excess raw water to an impoundment in the Dublin/Wicklow mountains for usage during dry periods and delivery of treated water to a designated termination point near Dublin. Total pipeline lengths are approx 113km in length. This option has no capability for supplying treated water to locations en route between the Shannon and Dublin.(This option could also be supplied from Lough Derg )


MDW0158RP0080F01 20 F01

3.1.8 Option H

Option H involves abstraction of sea water from the Irish Sea in north Fingal, desalination of sea water through a Reverse Osmosis (RO) desalination plant, pumping of treated water to Ballycoolen reservoirs via 25 km pipelines and discharge of brine (from the treatment process) back into the Irish Sea.

3.1.9 Option I

Option I involves abstraction of water from groundwater sources, within 80km of Dublin, and piping of groundwater to suitable locations for treatment and introduction into public water supply systems.

3.1.10 Option J

Option J involves the “conjunctive use” of the River Barrow with the Upper Liffey. Approx 50% of the Dublin Region’s water supply comes from Poulaphuca Lake on the Upper Liffey via Ballymore Eustace Water Treatment Plant. A continuous abstraction quantity of 318Ml/d from Poulaphuca for treatment in Ballymore Eustace has been licensed as the maximum sustainable abstraction level from the Liffey for this plant.

The Liffey-Barrow “conjunctive use” option envisages abstractions of water from the Barrow when sustainable quantities may be available (Winter / Spring) and combining these abstractions with variable abstractions from Poulaphuca with a view to increasing the overall supply to Ballymore Eustace Water Treatment Plant over and above what is sustainably available from Poulaphuca on its own.

3.2 DESALINATION AS A TREATMENT PROCESS

This report focuses solely on Option H which involves the evaluation of Desalination of Irish Sea water as a treatment process for the provision of a 300 Mld drinking water supply for the Dublin Region.

3.3 DESALINATION WATER SUPPLY INFRASTRUCTURE

To provide a treated water supply sourced from the Irish Sea would involve the construction of a major desalination facility on the East Coast and a pipeline to take the desalinated water to a suitable reservoir where it would enter the supply network for the Dublin Region. Figure 3.2 and Table 3.1 below illustrate the principal infrastructure components required – Desalination


MDW0158RP0080F01 21 F01

Figure 3.2 Desalination Plant Principal Infrastructure

24 km

Desalination Plant:Phase 2 capacity:

300 Mld

Desalination Plant:Phase 2 capacity:

300 Mld

Ballycoolen ReservoirBallycoolen Reservoir

2 x 1100mm Ø Pressure M

ains

Design capacity: 300 Mld


ains (3km)



ains (2km)


Sea Water Pumping Station:Ph 2 : 715 Mld

Sea Water Pumping Station:Ph 2 : 715 Mld

Reverse Osmosis Treatment Plant:Ph 2 : 300 Mld

Reverse Osmosis Treatment Plant:Ph 2 : 300 Mld

Potable Water Pumping Station:Ph 2 : 300 Mld

Potable Water Pumping Station:Ph 2 : 300 Mld

Table 3.1 Desalination Infrastructure Details:

Sea Water

Intake 3 km: • 2 No x 1800mm diameter

Outlet 2 km: • 2 No x 1400mm diameter Pipelines

Treated Water 24km:

• 2 No x 1100mm diameter

Sea Water Pumping Station 1 No

Reverse Osmosis Treatment Plant 1 No

Treated Water Pumping Station 1 No

Termination at Ballycoolen Reservoir 1 No

The Desalination concept was initially developed during the Feasibility Study (2005) undertaken by RPS-Veolia. The design and costings were based on a state of the art Desalination Plant in Ashkelon, Israel where Veolia played a leading role in the design, construction and commissioning phases. A number of key issues in relation to desalination in an Irish context were identified by Veolia during the course of the feasibility study.

3.3.1 Technical Evaluation of Desalinated Water Supply

The technical evaluation of a desalinated water supply involved the following approach:

1) Assessment of sustainable availability of water


MDW0158RP0080F01 22 F01

2) Identification and development of infrastructure requirements to meet phased demand growth including:

• Water intake and Raw Water Pumping facilities

• Sea water intake Pipelines

• Desalination Water Treatment Plant

• Treated Water Pipelines and Pumping facilities

• Storage facilities

• Integration and connection of new water supplies into Dublin Region water distribution network

• Routing and Site Selection

For desalination abstraction from the Irish Sea is technically feasible. The optimum abstraction point would be located 3 to 4 km from shore to avoid tidal effects and enhance water intake quality in terms of dissolved solids. Disposal and dispersal of brine would also occur 2 to 3 km from shore to ensure long term environmental sustainability.

A number of technically suitable locations were examined along Dublin's east coast for locating a desalination plant. North Fingal was identified as the optimum location because of water quality considerations, suitability for construction of intake / outfall infrastructure, energy availability and the relative ease of bringing treated water supplies from this location into the water distribution system within the Dublin Region.

A number of potential desalination processes were considered as follows:

1) Thermal Evaporation Effect

2) Reverse Osmosis

3) Electrodialysis Reversal

4) Solar Stills

Sections 4.0 and 5.0 present a detailed technological review of each of the potential processes considered and also discusses the selection criteria and methodology for deciding on the most appropriate technology for the Dublin project. Reverse Osmosis (RO) was selected as being the most appropriate desalination technology for an Irish application principally on account of technical efficiency, cost effectiveness and environmental impacts (relative to MED & MSF).

The key indicative infrastructure components of a desalination plant are as follows:

• Intake facilities

• Pre-treatment: disinfection, filtration

• Reverse Osmosis Process


MDW0158RP0080F01 23 F01

• Post Treatment (mineralization)

• Reject Stream (Brine)

• Ancillary facilities - chemical dosing, energy recuperation devices.

Figure 3.3 below illustrates the principal features of a reverse osmosis (RO) desalination plant.

Figure 3.3 RO Plant with Conventional Pre-treatment

Sea

Raw Water

Inlet & Pumping

1st Stage FiltrationAntraciteFilter Surface 1400 m²

2nd Stage FiltrationAntracite + SandFilter Surface 800 m²

High Pressure

Pumps

RO Plant

SoakChlorination

(Sludge = 10,000 m³/d) Energy Recovery DeviceBrine

210,000 m³/d

200,000 m³/d

AcidInjection

69b

67b 100,000 m³/d

100,000 m³/d

CO2

To

DistributionTreated Water TankMineralisation &Neutralisation Disinfection

Ca(OH)2

Cl2

Air

Degasifer

RO With Conventional Pretreatment

Sea

Raw Water

Inlet & Pumping

1st Stage FiltrationAntraciteFilter Surface 1400 m²

2nd Stage FiltrationAntracite + SandFilter Surface 800 m²

High Pressure

Pumps

RO Plant

SoakChlorination

(Sludge = 10,000 m³/d) Energy Recovery DeviceBrine

210,000 m³/d

200,000 m³/d

AcidInjection

69b

67b 100,000 m³/d

100,000 m³/d

CO2

To

DistributionTreated Water TankMineralisation &Neutralisation Disinfection

Ca(OH)2

Cl2

Air

Degasifer

RO With Conventional Pretreatment

3.3.2 Routing and Site Selection

The pipeline route selection process for a desalination plant involved identification of the shortest length route corridors (2km width) between the off-take and termination points, which have least environmental impact and are the most economic route corridors for future construction and operation of a pipeline (or pipelines) consistent with the constraints of the overall design philosophy particularly with respect to elevation profile, operating pressures and optimisation of overall operational requirements.

Major constraints considered :

• Suitable location for abstraction and raw water pumping station.

• Suitable sites for location of Desalination Treatment Works

• Suitable delivery point (Dublin)

• Avoidance of Major Natural Constraints – Mountains / Lakes / Forests / Bogs / Mineral Extraction Areas / Rock

• Avoidance or minimisation of impacts on:

− National Heritage Areas (NHA) − Special Protection Areas (SPA) − Special Areas of Conservation (SAC) − Known Archaeological Sites


MDW0158RP0080F01 24 F01

• Avoidance of:

− Existing Developments − Planned Developments − Motorways, High Voltage Electricity Pylons & Gas Transmission Pipelines

• Compliance with topography / elevation considerations consistent with the overall design philosophy of minimising pumping energy and optimisation of operational criteria.

3.3.3 Economic Evaluation of Desalinated Water Supply

The economic evaluation of a desalinated water supply involved the following approach:

1) Establishing the Net Present Value (NPV) of Capital Costs including infrastructure renewal over an assumed 25 year operating period using a range of discount values

2) Matching infrastructure development to demand growth on a phased basis where practical

3) Establishing the NPV of Operating Costs over an assumed operating period of 25 years using a range of discount values

4) Establishment of residual value after 25 years of operation

5) Calculation of water delivered over a 25 year lifetime

For a desalination plant the capital and operating costs have been based on the construction of pipelines initially for the long-term capacity (300Mld), while the RO treatment and pumping facilities are designed to match demand growth.

Economic evaluation results are summarised in Table 3.2 below

Table 3.2 Calculation of average cost of water delivered to the Dublin Region over the assumed 25 year operating period

Option H Cost

CAPEX 611 m€

OPEX 336 m€

Whole Life Cost 947 m€

WLC / Delivered Volume (€/m3) 0.64 €/m3


MDW0158RP0080F01 25 F01

3.3.4 Modelling of Brine Dispersion Impacts

Modelling of the brine dispersion was undertaken to assess the impact of the discharges from the facility on the receiving water. This exercise included the following:

• Simulation of the dispersion of the effluent discharges associated with the desalination process including coagulant, anti-scalant and brine

• Initial, medium and far dispersion models for brine discharge

• Impact of effluent discharges without sludge dispersion

• Impact of effluent discharges with sludge dispersion

• Estimate of costs

3.3.5 Environmental Assessments

The principal potential environmental impacts identified are as follows :-

• High Energy Use - CO2 production / greenhouse effects

• Ecology of local estuarine / inshore habitats

• Sea angling impacts

• Sea bed disruption - construction methodologies

• Navigation Impacts - during construction / subsequent operation

• Disposal of Brine (effluent) from the Desalination Plant

• Transmission Pipeline - NHA's, SPA's, SAC's, Archaeology etc.

In addition to the above potential impacts, water supplies from the Desalination Source may be perceived by the general public as being aesthetically undesirable for drinking purposes on account of the Irish Sea being used for effluent disposal and potentially containing radioactive material, even though these issues are catered for within the treatment process.

Further details on environmental aspects are included in Section 10.


MDW0158RP0080F01 26 F01

4 TECHNOLOGY REVIEW

4.1 INTRODUCTION – HISTORY OF DESALINATION DEVELOPMENT

The history of desalination processes began primarily with thermal distillation processes. This technology was employed in the first major desalination plants of the 1970’s which were required for rapidly developing cities in the Middle East region. The key factors influencing this technology development were the abundance of low cost energy, a total lack of freshwater resources and the fact that the cost of water was not a limiting factor. Many large scale independent water and power projects were constructed as a result for areas such as Taweelah, Dubai, Jubbail (SA) and Doha.

Following the initial market for large scale distillation projects a second market emerged generating small to medium sized plants catering mainly for tourist zones in tropical and Mediterranean islands during the1980’s for example in the West Indies and Scilly Islands. This period saw the emergence of small capacity Multiple-Effect Distillation and Reverse Osmosis plants.

In contrast to the plants constructed in the Gulf area, there were both high costs and energy consumption associated with these smaller plants. However the technology benefited from the operating experience achieved with these smaller scale units that had been operated during the 1980’s and previous decades. By the 1990’s the use of desalination for municipal water supplies had become more commonplace. Its growing success as a water supply source is mainly as a result of improvements in technology, some decreases in cost and increased pressure on more conventional sources of freshwater.

The greatest commercial growth in desalination has been seen in reverse osmosis (RO) technology which now accounts for approximately 60% of desalination plants worldwide. Improvements in membranes have increased the use of RO which in turn has led to greater efficiencies and reduced energy consumption. By contrast the distillation process is a high energy consumer which means that thermal plants are now less favoured due to higher capital and operating costs.

4.2 VEOLIA EXPERIENCE

Studies on desalination involve investigating the latest technologies and energy efficiencies in order that the merits of this option be fully evaluated for valid comparison to the alternative options. Desalination was primarily identified by Veolia Water, one of the consultants retained by Dublin City Council to assist in identifying solutions for the future water needs of the Dublin Region. Veolia’s expertise has been fundamental in reviewing the available desalination technologies and selecting the appropriate technology for the Dublin application.

Paris-based Veolia Environment (VE) is a major desalination plant builder and membrane supplier, as well as a water utility operator, getting about 34% of its revenue from water-related businesses. SIDEM, a subsidiary of Veolia Water, is one of the world leaders in thermal seawater desalination. Present in Saudi Arabia since the 1970s, the company now boasts 73 desalination facilities in the region. Its most recent contracts include Marafiq, Saudi Arabia (800,000 m3/day), Al Hidd, Bahrain (270,000 m3/day), Al Khobar, Saudi Arabia (267,000 m3/day), and Al Taweelah A1, UAE (240,000 m3/day).

Veolia Water (and its Israeli partners) have designed and built the world's largest desalination plant using reverse osmosis technology in Ashkelon, Israel. With a daily production capacity of 320,000 cubic meters of drinking water (analogous to the volume required for the Dublin option), the Ashkelon


MDW0158RP0080F01 27 F01

desalination plant is comprised of two parallel treatment units each of which has an annual production capacity of 54 million cubic meters.

4.3 REVIEW OF AVAILABLE TECHNOLOGIES

4.3.1 Introduction Desalination is a separation process used to reduce the dissolved salt content of saline water to a usable level. All desalination processes involve three liquid streams: the saline feedwater (brackish water or seawater), low-salinity product water, and a highly concentrated saline stream (waste brine or reject water).

The saline feed water is drawn from oceanic or underground sources. It is separated by the desalination process into the two output streams: the low-salinity product water and highly concentrated saline streams. The use of desalination overcomes the predicament faced by many coastal communities, having access to a practically inexhaustible supply of saline water but having no means of utilising the supply.

Although some substances dissolved in water, such as calcium carbonate, can be removed by chemical treatment, other common constituents, like sodium chloride, require more technically sophisticated methods, collectively known as desalination. In the past, the difficulty and expense of removing various dissolved salts from water made saline waters an impractical source of potable water. However, starting in the 1950s, desalination began to appear to be economically practical for ordinary use, under certain circumstances.

Figure 4.1 Desalination Concept

A by-product of desalination is brine. Brine is a concentrated salt solution (with more than 35 000 mg/L dissolved solids) that must be disposed of, generally by discharge into deep saline aquifers or surface waters with a smaller salt content.


MDW0158RP0080F01 28 F01

Figure 4.2 Simplified Flow-sheet of Desalination Process

A post-treatment chain is added at the end of a desalination plant in order to remineralise the water. Following post-treatment the water quality produced by desalination plants can practically have the same organoleptic features (taste, colour, odour) as the water produced from surface water (rivers, lakes).

4.3.2 Energy Source

A major characteristic of the desalination process is the requirement for thermal or electrical energy input. The form of energy available, the associated cost and the environmental constraints related to the energy source will play a major role in desalination process selection. The different forms of energy are presented below:

Electrical energy

Some desalination processes use electrical power exclusively which can be supplied from the grid or from sources such as wind farms.

Thermal energy

Most distillation process and solar distillation use thermal energy. This energy may originate from many different sources including:

• Steam • Industrial waste heat (higher temperature gases, heated industrial coolant streams,

heated brines, cooling water streams, gas turbine, solid waste incinerators)


MDW0158RP0080F01 29 F01

Solar energy

Solar energy collectors can provide heat or electrical energy, but are suitable only for small desalination plant.

Geothermal brines

Deep artesian bores can provide warm water (say 80°C) and can be a source for a thermal desalination.

The energy requirements for desalination plants depend on the salinity and the temperature of the feed water, the quality of the water to be produced and the desalination technology used.

For large desalination facilities to be located in the Dublin area the energy sources available would be electrical energy from the grid and thermal energy (from steam or industrial waste heat).

Depending on the availability of electrical energy from the grid a variety of desalination processes may be considered including membrane options or hybrid options (use of more than one desalination technologies) If sufficient energy is not available from the existing grid consideration may have to be given to the construction of a new power plant or other alternative sources (e.g. renewables).

4.3.3 Seawater Intake and Brine Discharge 4.3.3.1 Seawater Intake

The factors that affect the selection process include:

Location: the location of the source / intake dictates the viability of a desalination project from a number of aspects. It is important that no discharges are located near the proposed seawater intake and that water quality is not affected by any specific activities resulting in impacts on the water quality stability.

Quality of the feed water: this will dictate the desalination process to adopted. Feed water quality requiring extensive pre-treatment will influence the economic viability of the project. In addition the membranes have limitations on the range of salts concentration which can be treated.

Space available for the intake: depending on the process, the quantity of seawater needed to produce a given fresh flow can vary considerably (requiring higher volumes for distillation processes, particularly for MED), which directly impacts on the size of the intake required.

Physical local conditions: high cliffs can make the implementation of the intake much more difficult and expensive.

Means of abstraction and supply: the quantity of feed water needed to produce a given amount of fresh water depends on the chosen process. Distillation for example, requires a feed water flow rate between 2 to 10 times the fresh water production rate, thereby necessitating a comparatively large structure to abstract the water.

Pre-treatment design is crucial to the successful operation of desalination system. Pre-treatment equipment for large seawater desalination installations normally consists of trash-racks, band-screens and filtration units. For RO, the filtration required is a media type. Distillation plants require scale and bio-fouling prevention.


MDW0158RP0080F01 30 F01

4.3.3.2 Brine Discharge The waste stream produced from the desalination process is referred to as brine discharge. The brine contains the removed salts and in some cases chemicals that may have been added during the process (nature and quantity depending on the process). The discharge volume varies depending on the selected process but there will almost always be a significant quantity of highly saline water. The disposal of the wastewater in an environmentally appropriate manner is an important part of the feasibility and operation of a desalination facility. The environmental impacts are due several factors:

• Salt concentration

• Temperature above the receiving water

• Higher turbidity level

• Lower oxygen levels

• Chemicals and salts from pre-treatment process

• Carbon dioxide release

Generally, the brine can be discharged directly to the sea. Brine is denser than sea water and falls to the sea bed, depending on the outfall location. The discharge location must be selected to ensure an optimal mixing of the brine in the sea.

Mixing with sewage treatment discharge may also be preferable. There are other possibilities to prevent adverse environmental consequences. But the means of properly disposing of the concentrate flow should be one of the principle items investigated early in any study of the feasibility of a desalination facility.

4.3.4 Desalination Economics

In recent years the capital and operating costs for desalination have tended to decrease. As desalinating costs have been decreasing there has been a tendency for the cost of obtaining and treating water from traditional sources to increase due to more stringent water quality standards being applied resulting in increased treatment levels.

The cost of producing 1m3 of desalinated water varies considerably and is dependant on the following key factors:

• The sea water quality (which impacts on the pre-treatment requirements and on the desalination process design)

• Capacity and type of the plant

• Plant location - physical conditions of the area where the plant and the intake are to be located

• State of the market for the selected desalination processes: for example the price of membranes fluctuates and depends on the volume of demands


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• Labour

• Energy cost

• Financing

• The cost of the different desalination process will be detailed in the next part of this document.

• Environmental mitigation issue

4.4 REVIEW OF MAIN DESALINATION PROCESSES 4.4.1 Distillation

Distillation is the oldest and most commonly used method of desalination. The world's first land-based desalination plant, a multiple-effect distillation (MED) process plant that had a capacity of 60 m3/day, was installed on Curaçao, Netherlands Antilles in 1928. Further commercial development of land-based seawater distillation units took place in the late 1950s, and initially relied on the technology developed for industrial evaporators. Since then the modernisation of their design has allowed them to achieve improved reliability.

The principle of the distillation process is as follows:

The distillation process mimics the natural water cycle. Saline water is vaporised and as salt does not enter the vapour phase the resultant condensate forms almost pure water The various distillation processes used to produce potable water all generally operate on the principle of reducing the vapour pressure of water within the process unit to permit boiling to occur at lower temperatures, thereby removing the requirement to use additional heat. To significantly reduce the amount of energy required for vaporisation the distillation process uses multiple boiling in successive vessels each operating at a lower temperature and pressure. These vessels are referred to as “stages” or “effects” depending on the desalination technique used.

There are two kinds of distillation process, based on the simple effect distillation principle:

• Multiple-effect distillation (MED)

• Multiple-stage flash distillation (MSF)

The distillation process requires a considerable amount of energy. Depending on the energy costs in a country, distillation may be cost efficient or prove uneconomical. It is commonly used for desalination in the Middle Eastern countries for example where oil is readily available as an energy source.

However distillation can also be considered an interesting process for cold seawater (for example in Ireland), because the process becomes more cost-effective with increasing numbers of effects or stages.

The simplest arrangement for a distillation unit is the single effect evaporator as outlined in the following section.


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4.4.1.1 Simple-Effect Distillation A horizontal tube is installed in a thermal insulated chamber and is fed by a heated fluid. Cold seawater is sprayed over the tubes and the internal heated fluid causes it to boil. A seawater cooled condenser is placed in the same chamber and the vapour produced is condensated on the condenser. Distillate flowing down the condenser is collected in a tray and extracted by a pump. The volume of seawater taken in (which is greater than the product volume required) is introduced at the upper part of the chamber in order to form a fluid film flowing down the heated bundle. Concentrated seawater, the brine, is then collected under this bundle and extracted by a pump. An ejector keeps the required vacuum level in the chamber.

The energy consumed by this process is the sum of:

• The energy needed to heat the seawater

• The latent heat of evaporation of seawater

The latent heat of evaporation of water is rather important, resulting in high energy costs for simple distillation. Therefore simple distillation does not permit the production of large quantities of water at low cost. In order to reduce the specific heat consumption, the heat introduced in the life cycle must be used several times: this is the principle of multi-effect distillation.

4.4.1.2 Multiple-Effect Distillation The multiple-effect distillation systems use more than one boiling chamber ("effect") in the distillation process to improve the energy consumption.

MED is the oldest large-scale industrial distillation process used for seawater desalination. It presents the following advantages:

• Reliable design

• Technological maturity

• High distillate quality

• Good operating record

• High unit capacities

Today 3.5 % of the world’s desalted water is produced by MED units. However MED has lost ground to the MSF (Multi-stage flash distillation) process owing to advances in component and material design that have rendered the latter more popular.

The heat transfer characteristics between the liquid-vapour phase can be improved using plates or horizontal tubes. The saline water is sprayed onto the evaporator surface in a thin film to promote rapid boiling and evaporation The steam used to heat the surfaces in the first effect is heated from a turbine or boiler.

As shown in the Figure 4.3, the first ‘effect’ exchanger tubes are heated by steam and the saline water is sprayed onto these where only a proportion evaporates. After passing through a demister, the vapour is introduced to the heating tubes of the second ‘effect’ onto which the remaining saline water


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from the first effect is sprayed. A proportion of this vapour condenses into product water and in doing so, gives up its latent heat of vaporisation.

This heat is then used to evaporate a proportion of the second ‘effect’ saline feed. This process is repeated over several ‘effects’. Vapour from the final effect is condensed in the heat rejection stage, where the residual energy is transferred to the first effect feed water. As a result of evaporation in each effect the remaining saline feed becomes more concentrated and is discharged as brine.

The ambient pressure in each effect in the MED process is maintained by a vacuum pump.

Another important factor in this process is scale control. Some substances such as carbonates and sulphates found in seawater begin to leave solution at temperatures approaching 115oC forming a hard scale that coats tubes and surfaces. A significant feature of this process is that the top brine temperature of the first effect can be limited to values below 70°C, thereby reducing the potential for scale formation.

Figure 4.3 Schematic of multi-effect evaporator desalination process (horizontal tube – parallel feed configuration)

As thermal efficiency of the process depends upon the number of effects the determination of the number of effects required is an important design criterion has the following constraints:

• Maximum top brine temperature - limited by scaling phenomenon

• The temperature of the last effect must remain slightly higher than the seawater temperature

• Optimisation between the investment cost and the running cost to produce the lowest price desalted water.

When the number of effect increases, the energy consumption decreases. Namely the energy consumed by a multiple effect is the sum of:

• Energy needed to heat the seawater entering the first effect


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• The latent heat of evaporation of seawater divided by the number of effects

MED plants are based on 2 designs: the horizontal tube multiple effect (HTME) system and the vertical tube falling film evaporator (VTE) system. The main differences are in the arrangement of the evaporation tubes, the side of the tube on which evaporation takes place, and the materials used in the evaporation tubes. Evaporation occurs on the surface of horizontally arranged tubes in the HTME process and inside vertically arranged tubes in the VTE plants. Low-cost materials are used in the construction of HTME plants. Thin film HTME technology is presently considered the most promising for the production of fresh water. The process has all the main features of MED process described above. The evaporator is the centre piece of the process. This is typically supplied by steam boilers in dual-purpose plants cogenerating electricity and steam.

Then steam and seawater can either flow in the same direction (called parallel feed configuration as shown in Figure 4.3 or in the opposite direction.

The parallel feed multiple effects technology is widely used in industrial-scale used desalination.

When the heat for evaporation comes from compression of the vapour phase either mechanically or thermally using steam ejectors, rather than from a direct exchange of heat from steam produced in a boiler, performances can be improved significantly

Therefore there are three types of MED available:

1/ MED without vapour compression

2/ MED with thermal vapour compression (VC):

Thermal vapour compression distillers can either be single purpose units, with package boilers or can be combined with power generation in dual purpose plants, taking steam from heat recovery boilers or extraction from steam turbines. The steam requirements generally are higher than those required for MSF distillers to enable the thermal vapour compressor to work effectively.

Figure 4.4 Schematic of a multi-effect evaporator desalination process with thermal vapour compression.


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3/ MED with mechanical vapour compression (MVC):

The principle of this technology is similar to thermal vapour compression. In this case the compressor is a rotating mechanical unit, usually driven by an electric motor. The capacity of MVC units is largely determined by the size of the compressor available.

Figure 4.5 Schematic of a multi-effect evaporator desalination process with mechanical vapour compression.

MED with vapour compression is generally used in small and medium scale units (20 to 2000m3/d for thermal compression and up to 5000m3/d for mechanical compression).These technologies are currently limited in size because of technical difficulties in building large scale compressors. They appear to be particularly suitable for tourist resorts and industrial plants where fresh water is not readily available.

Therefore only MED without vapour compression could be developed for a high capacity plant such as that being considered for Dublin (300MLD).

Typical performances using MED technology produce water with a salinity of between 10 to 25 mg /L. Additional treatment would be required to further reduce the corrosivity of the water before entering the transmission and distribution system thereby increasing its potability.

4.4.1.2.1 Key Requirements

The key requirements concerning this process are presented below:

Quantity of water required: The seawater flow (input) needed is 8 to 10 times that of the fresh water flow (product output). Therefore a large intake area is required for the distillation process.

Quality of water required: there is no limitation on the salt concentration of the feed water for MED.

Footprint required: 1 ha for every 100 MLD


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Pre-treatment: MED does not require significant pre-treatment, classical filtration and chlorination are sufficient to avoid the development of marine/micro organisms.

Energy consumption: Table 4.1 below compares the energy needed to produce 1 m3 of fresh water and is divided into two parts:

• thermal energy (which can be steam or waste industrial heat) and

• electrical energy (which can be supplied from the grid).

Table 4.1 Energy consumption of different configuration of MED processes

4.4.1.2.2 Operation and Maintenance

The operation and maintenance aspect can vary considerably depending on the process selected. The selected process may require a greater degree of technical expertise to operate, the use of atypical materials/chemicals or have particular safety conditions and hazards.

Operation:

MED is easy to operate, with built-in fail-safe controls. A limited number of instruments enable full control of the plant. If the feed water flow is interrupted, the low-water shutdown will stop the system operation until an sufficient volume of feed water becomes available. Electrical surge protection is part of the standard equipment provided.

High flexibility is a key feature in the operation of the system: the production from a MED unit can vary from 15 to 100 % of the nominal flow without any difficulties: this is a significant advantage of this process.

The process is easy to monitor, consisting of see-through panel for instantaneous checking of the system. Sight glasses and indicator lamps are incorporated for visual inspection of the operating system

MED Distillation process

Thermal energy needed for 1 m

3

of fresh water

(M Joules)

Electrical energy needed for 1 m

3 of

fresh water

(kWh)

Total energy needed for 1 m

3 of

fresh water

(kWh)

MED 7 effects 376 2 106

MED 10 effects 209 3 61

MED with vapour compression 0 16 16


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To monitor and maintain satisfactory water quality a Water Purity Monitor is included which is designed to divert all distilled water produced below a preset purity setpoint. This ensures that water for drinking, bottling or other applications (i.e. Water Store) is always at an acceptable purity level.

Maintenance:

Maintenance of the system generally includes the following:

• Removal of scale and marine growths which forms a hard scale which coats any tubes or surfaces present using high pressure "hydrolaser" sprayers.

• Inspection of all pumps and motors, replacing bearings and bushings, and renewal of the protective coatings on exposed parts (e.g. pumps which would have been primed and painted prior to installation).

• Compared to other desalination process, distillation processes require little maintenance, mostly consisting of the maintenance of the mechanical equipment and coatings.

4.4.1.2.3 Environmental Impact

For distillation process, the wastewater would be characterised by a slight increase in salinity and an elevated temperature. It is expected that the acceptable salinity and temperature increases would be identified in the Environmental requirements and limits for the site selected. In addition, there may be small quantities of added chemicals used in the process (such as antiscale (polyphosphate) and antifoam and biocides such as chlorine) which may be present at very low concentrations in the discharge but which would not pose a threat to environment.

Chlorine concentrations would be limited to levels that would be allowed by other discharge consents and these concentrations would be determined on the basis of little or no environmental impact in the vicinity of the discharge.

4.4.1.2.4 Commercial Maturity

All early thermal desalination plants were of the Multiple Effect Distillation (MED) type where sea water is heated by steam circulated in submerged tubes.

The latest MED plant to be installed is in Bahreïn with a capacity of 273 MLD (10 x MED units producing 27, 3 MLD per unit).

The most recent improvements in MED technology deal with the scaling aspect: greater control has allowed an increase in the maximum temperature of seawater used. The high thermal efficiency of the MED process and its capability to operate at low steam pressures have attracted renewed interest in this process recently.

However MED has lost ground to the multiple-stage flash distillation process (see section 4.1.3) owing to recent advances in component and material design which rendered the latter more popular.


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4.4.1.3 Multiple-Stage Flash Distillation MSF plants are relatively simple to construct and operate. They have no moving parts, other than conventional pumps, and incorporate only a small amount of connection tubing. Product water, or distillate, is of a high level of purity (like MED): it is often sterile and requires little post-treatment.

A lifespan of up to 40 years is now being predicted for large scale plants. 4.4.1.3.1 Description In the MSF process the seawater is heated in a vessel called the brine heater. This is generally done by condensing steam on a bank of tubes that carry the seawater which passes through the vessel. The heated seawater passes through a series of condensation chambers called stages where the ambient pressure is lower causing the water to boil immediately. The sudden introduction of the heated water into the chamber causes it to boil rapidly, flashing into steam. The distilled water is cascaded from one stage to the next. A percentage of this water is converted to steam since boiling will continue only until the water cools (furnishing the heat of vaporisation) to the boiling point. Energy introduced at the brine heater is rejected at the low temperature end.

The pressure gradient between each chamber allows the flow of seawater through each successive stage without pumping.

Most MSF plants operate in a dual-purpose or cogeneration mode, incorporating both power generation and water desalination. Waste or extracted heat produced in electricity generation units can be used to preheat feed water resulting in high thermal efficiencies and improved process economics. Current cogeneration plant designs allow for flexible operation during peak load periods for power or water.

Figure 4.6 Diagram of MSF plant


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Figure 4.7 View of a typical MSF plant

MSF configurations applied on an industrial scale include once-through (MSF-OT) arrangements and brine recirculation (MSF-BR) systems. The use of the former is presently limited: most MSF plants rely on MSF-BR (brine recirculation) a method which is particularly suited to regions with large daily and seasonal temperature fluctuations. This simple configuration improves the thermal efficiency of the process because the recycled steam contains higher energy than the feed seawater. Generally, brine recirculation results in a higher conversion ratio, uses smaller amounts of chemical additives and allows for better control of feed seawater temperature.

The advantages of the MSF-OT system over the MSF-BR system include cost savings and reduced risks. There are also a number of drawbacks. The introduction of cheaper and more effective corrosion-resistant materials and improved additives has played an important role in placing MSF-BR in a favourable position. Moreover, the use of the MSF-OT system is currently limited to small desalination plants, as the seawater flow required is much higher than with the MSF-BR: to produce 1 m3 of fresh water, 7 to 10 m3 of seawater are necessary with MSF-OT, whereas 2 to 3 m3 are required in direct MSF-BR.

The MSF with brine recirculation is the most implemented process, despite needing large recycling pump as the recycle flow rate is very high (between 7 and 12 times the production flow).


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Figure 4.8 Schematic of a multi-stage flash desalination process with brine recirculation

The design specifications of a typical MSF plant generally address 3 essential aspects:

• Distillate production to fresh water flow required

• Top brine temperature (TBT)

• Thermal efficiency of the desalination plant

The top brine temperature (TBT) typically ranges from 90°C to 120°C. The actual temperature depends on the type of antiscale strategy being used. The most significant problems encountered with distillation are scaling and corrosion of materials, which increase as the brine temperature increases. Different measures can be applied to reduce or prevent corrosion and control scale. If scale inhibition is based on the use of organic polymers and sponge ball circulation for tube cleaning, a top brine temperature limit of approximately 110 °C is imposed. When acid dosing is used for scale control, the top temperature may be increased to 120 °C.

4.4.1.3.2 Requirements

The key requirements concerning this process are presented below:

Quantity of water required: for every m3 of fresh water to be produced by MSF (with recirculation) 2 to 3 m3 of seawater are required.

Quality of water required: no limitation on salt concentration of sea water

Footprint required: 0.5 ha for each 50 MLD

Pre-treatment: distillation processes require minimal pre-treatment usually consisting of classical filtration and chlorination to avoid the development of marine organisms.


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Energy consumption: Table 4.2 shows the energy required to produce 1 m3 of fresh water is in divided in two parts: the thermal energy (which can be steam or waste industrial heat) and the electrical energy (which can be supplied from the grid).

Table 4.2 Energy consumption of different configuration of MSF processes

4.4.1.3.3 Operation & Maintenance

The operation and maintenance aspect can vary considerably depending on the process selected. The selected process may require a greater degree of technical expertise to operate, the use of atypical materials/chemicals or have particular safety conditions and hazards.

Operation:

MED is easy to operate, with built-in fail-safe controls. If the feed water flow is interrupted, the low-water shutdown will stop the system operation until a sufficient volume of feed water becomes available. Electrical surge protection is part of the standard equipment provided.

If the unit is operated using water containing less than 1.0 mg/L of hardness and chlorine a self-cleaning system is implemented. A dual alternating tank water softener and commercial activated carbon prefilter will be required.

The process is easy to monitor, consisting of see-through panel for instantaneous checking of the system. Sight glasses and indicator lamps are incorporated for visual inspection of the operating system.

To monitor and maintain satisfactory water quality a Water Purity Monitor is included which is designed to divert all distilled water produced below a preset purity setpoint. This ensures that water for drinking, bottling or other applications (i.e. Water Store) is always at an acceptable purity level.

Maintenance and preventive maintenance work:

Maintenance (including preventative maintenance) of the system consists of the following:

• Repair of damage occurring in any of the stages.

Distillation process

Thermal energy needed for 1 m

3 of

fresh water

(MJoules)


3 of

fresh water

(kWh)

Total energy needed for 1 m

3 of

fresh water

(kWh)

MSF In/Out ratio = 8 293 4 85

MSF In/Out ratio = 10 230 5 69


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• Removal of scale and marine growths in the tubes in all stages using high pressure "hydrolaser" sprayers.

• Removal of the vacuum system ejectors for cleaning, inspection, and replacement as necessary; most parts have a lifetime of 3 to 4 years.

• Inspection of all pumps and motors, replacement of bearings and bushings, and renewal of protective coatings on exposed parts (e.g. pumps which would have been primed and painted prior to installation).

• Compared to other desalination process, distillation processes require little maintenance, mostly consisting of the maintenance of the mechanical equipment and coatings.

Safety/ hazards: One of the main hazards associated with MSF is the risk of seawater flowing into fresh water (e.g from leaks or drilling of tubes). Online detectors provide protection allowing the location of any leakage and stopping the operation of the unit concerned. Redundancy is planned during the design step to anticipate this type of hazard.

4.4.1.3.4 Environmental Impact

For distillation process, the wastewater would be characterised by a slight increase in salinity and an elevated temperature. It is expected that the acceptable salinity and temperature increases would be identified in the Environmental requirements and limits for the site selected. In addition, there may be small quantities of added chemicals used in the process (such as antiscale (polyphosphate) and antifoam and biocides such as chlorine) which may be present at very low concentrations in the discharge but which would not pose a threat to environment. Chlorine concentrations would be limited to levels that would be allowed by other discharge consents and these concentrations would be determined on the basis of little or no environmental impact in the vicinity of the discharge.

4.4.1.3.5 Commercial Maturity

The Multi-stage flash plants was first introduced in 1928 but they were not built commercially until around 1960 when the first units were installed in Kuwait, soon followed by plants in Qatar, the Caribbean and Malta. Subsequently the MSF plant capacities began to increase. By 1970 large units were installed in Abu Dhabi each rated at 9000 m3/d and shortly afterwards the first 22 500 m3/d unit entered service in Kuwait. There are now a significant number of plants with a unit size of 44 MLD in service in Middle East and a few with unit capacities of 78 MLD (2003 – Shuweiat)).

The basic technology of modern large MSF plants is similar to the early units but there have been major developments in scale control techniques, heat transfer and the use of corrosion resistant materials which has made the increase in unit capacity possible.

Nowadays, several projects are underway in Libya. The technical and economical feasibility is examined for plants of different capacities: between 100 and 500 MLD. The technology to be selected is still to be decided but they are likely to be MSF or MED-based.


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4.4.1.4 Costs The performance parameters of the distillation processes are the following:

Thermal performance ratio: This is defined as the flow rate of fresh water produced relative to the heating steam. This parameter gives a measure of the specific process energy consumption.

Specific electrical power consumption: is defined as the ratio of energy consumption, expressed in KWh, to product volume. The energy is consumed by pumping units, instrumentation and control device.

Specific flow rate of cooling water: is the ratio of the flow rate of cooling water to the flow rate of desalinated water output. It constitutes another measure of process efficiency. A high value of this parameter implies higher energy consumption usually ranging from 3 to 10.

Specific heat transfer area: is defined as the total heat transfer area per unit product flow rate. This value depends on the top brine temperature. Operation at high top brine temperatures (90-110 °C) gives little heat transfer area (MSF processes). Lower top brine temperature (60-70 °C) used in single or multiple effects induce larger heat transfer areas.

In a broader sense, the first three parameters largely determine the process efficiency and therefore the running costs, while the fourth parameter plays a major role in specifying the capital costs involved.

Moreover, the economics of a distillation plant is largely dependant on the materials chosen for construction. Structural strength and corrosion resistance are 2 of the main selection criteria. Ultimately, materials used should be suitable for the operating conditions that exist; the materials will be exposed to a specific range of operating temperatures and will come into contact with steam, aerated/de-aerated seawater, concentrated brine and a number of chemicals including the acids and polyphosphate additives used to reduce scaling. Materials used are uncommon and tend to be expensive impacting significantly on the capital costs. The costs of each distillation technology are detailed in Table 4.3.

Table 4.3 Investment cost for distillation processes

Process $US for 1 m3/d

MSF 1200 – 2500

MED without vapour compression 1000 – 2000

MED with vapour compression 1000 - 1600

To compare the energy consumed by the different distillation processes, the thermal and electrical energy needed have been converted into the gas quantity needed to supply these installations. The main natural energy source available in the region of Dublin is gas. In the case of distillation processes, two types of power plant can be used: the single and double purpose unit.


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A single purpose unit is composed of:

• A steam boiler with the desalination unit using the low pressure steam

• A double purpose unit is composed of:

- A high-pressure steam boiler feeding a turbine

- A turbo-generator producing electricity and low pressure steam with the desalination unit using the low-pressure steam.

Single purpose plants have a lower overall thermal efficiency than dual purpose units. That is why the gas quantity required for double purpose units is lower.

Table 4.4 shows an assessment of the amount of gas needed for each distillation process using single or double purpose units assuming that the steam boiler efficiency is 85% and the electricity generator efficiency is 40%.

Table 4.4 Comparison of energy consumption of different distillation processes, when energy source is gas:

Distillation process

Thermal energy

needed for 1 m3 of fresh water

(MJoules)


3 of

fresh water (kWh)

Total energy needed for 1 m3 of fresh

water (kWh)

Gas quantity needed in Kg / m3

of fresh water

Single

purpose unit Double

purpose unit

MSF ratio=8 293 4 85 9.6 4.5

MSF ratio=10 230 5 69 8.1 4.1

MED 7 effects 376 2 106 10.9 4.9

MED 10 effects 209 3 61 6.5 3.3

MED with vapour compression

0

16

16 4.2 4.9

The tables show that MED without vapour compression is the least expensive option. The mean cost of producing water by largescale MED is 0.46 – 0.83 €/m

3.


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Figure 4.9 Outline of the typical costs for 20 year for an MED plant.

Typical 20 year MED desalination plant cost

Staff

15%

Chemical

3%

Energy

30%

Equipment

44%

Maintenance

8%

Staff

Chemical

Maintenance

Energy

Equipment

4.4.1.5 Summary The following summarises the advantages and disadvantages of the thermal processes which have been reviewed in this section.

In general the advantages of distillation are as follows:

• Performance and costs do not depend on feed water salinity

• The distillation process does not need sophisticated pre-treatment

• Distillation offers easy operation and maintenance when compared with other desalination technologies

• In most cases distillation does not require the addition of chemicals or water softening agents to pretreat the feedwater

• Distillation has minimal environmental impacts, although brine disposal must be considered in the plant design

• The technology produces high-quality water in some cases having less than 10 mg/l of total dissolved solids.

• Distillation can be combined with other processes such as using heat energy from an electric-power generation plant

• In the case of Dublin, this process may prove to be energy-efficient as many effects or stages can be used to produce the required volume of product water. As the ambient seawater


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temperature is low, the temperature difference between sea water and top brine temperature required is high.

In general the disadvantages of distillation are as follows:

• Compared to other desalination processes, distillation buildings have a higher visual impact (high stacks, pipe racks etc.), which can be a significant drawback for the Dublin region which is densely inhabited.

Figure 4.10 View of a large capacity distillation facility

• Some distillation processes are energy-intensive, particularly the larger-capacity plants.

• The distillation process, particularly MSF distillation, is very costly in terms of capital costs

• The technology requires the use of chemical products, such as acids, that require special handling by O&M staff

In summary distillation processes constitute a somewhat mature group of technologies, with a number of technological variants often emerging from a given technology family. However it is an expensive technology which presents some drawbacks in the case of Dublin. These disadvantages mostly concern the environmental impact of the technology: poor integration with the landscape and a risk of noise pollution.

There is another family of desalination processes which offers a more cost-effective solution for the production of freshwater: these are the membrane technologies which are presented in the next section.

4.4.2 Membrane Processes: Reverse Osmosis

Membranes are used in two commercially important desalting process namely electrodialysis (ED) and reverse/forward osmosis (RO). Each process uses the ability of membranes to differentiate and selectively separate salts and water.


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The various electrodialysis technologies are more suitable for brackish water applications or for small capacity plants.

In comparison to distillation and electrodialysis, Reverse Osmosis is a relatively new and reliable membrane technology with successful commercialisation since the early 1970’s. A description of reverse osmosis is presented below:

4.4.2.1 Description When two solutions with different concentrations of a solute are mixed, the total amount of solutes in the two solutions will be equally distributed in the total amount of solvent from the two solutions. This is achieved by diffusion, in which solutes will move from areas of high concentration to areas of lower concentrations until the concentration throughout the resulting mixtures are the same, a state called equilibrium. Instead of mixing the two solutions together, they can be put in two compartments where they are separated from each other by a semi permeable membrane. The semi permeable membrane does not allow the solutes to move from one compartment to the other, but allows the solvent to move. Since equilibrium cannot be achieved by the movement of solutes from the compartment with high solute concentration to the one with low solute concentration, it is instead achieved by the movement of the solvent from areas of low solute concentration to areas of high solute concentration. When the solvent moves away from low concentration areas, it causes these areas to become more concentrated. On the other side, when the solvent moves into areas of high concentration, solute concentration will decrease. This process is termed osmosis. The tendency for solvent to flow through the membrane can be expressed as "osmotic pressure", since it is analogous to flow caused by a pressure differential.

In reverse osmosis pressure is applied to the compartment with high solute concentration. There are two forces influencing the movement of water namely the pressure caused by the difference in solute concentration between the two compartments (the osmotic pressure) and the externally applied pressure. In the same way as in conventional osmosis, the solute cannot move from areas of high pressure to areas of low pressure because the membrane is not permeable to it. Only the solvent can pass through the membrane. When the effect of the externally applied pressure is greater than that of the concentration difference net solvent movement will be from areas of high solute concentration to low solute concentration, and reverse osmosis occurs.

Figure 4.11 Principle of Reverse Osmosis


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In the RO process, water from a pressurized saline solution is separated from the dissolved salts by flowing through a water-permeable membrane. The permeate (the liquid flowing through the membrane) is encouraged to flow through the membrane by the pressure differential created between the pressurized feed water and the product water (higher than the osmotic pressure) which is at near-atmospheric pressure. The remaining feed water continues through the pressurized side of the reactor as brine. No heating or phase change takes place. The major energy requirement is for the initial pressurization of the feed water.

In practice, the feed water is pumped into a closed container, against the membrane, to pressurize it. As the product water passes through the membrane, the remaining feed water and brine solution becomes more and more concentrated. To reduce the concentration of dissolved salts remaining, a portion of this concentrated feed water-brine solution is withdrawn from the container. Without this discharge, the concentration of dissolved salts in the feed water would continue to increase, requiring ever-increasing energy inputs to overcome the naturally increased osmotic pressure.

A reverse osmosis system consists of four major components/processes: (1) pre-treatment (2) pressurisation (high pressure pump) (3) membrane separation and (4) post-treatment stabilization (5) energy recovery device.

(1) Pre-treatment: The incoming feed water is pre-treated to be compatible with the membranes by removing suspended solids, adjusting the pH, and adding a threshold inhibitor to control scaling caused by seawater constituents such as calcium sulphate. The pre-treatment needed is important to protect the membranes and is generally more sophisticated than in distillations plants.

(2) Pressurization: The high-pressure pump raises the pressure of the pre-treated feed water to an operating pressure appropriate for the membrane and the salinity of the feed water (in practice this pressure is higher than the osmotic pressure which is around 60 bar for a sea water salinity of 35g/L).

(3) Separation: The permeable membranes inhibit the passage of dissolved salts while permitting the desalinated product water to pass through. Applying feed water to the membrane assembly results in a freshwater product stream and a concentrated brine reject stream. Because no membrane is perfect in its rejection of dissolved salts, a small percentage of salt passes through the membrane and remains in the product water. Important features of a membrane are its selectivity (salt retention rate of salt) and its permeability. Reverse osmosis membranes come in a variety of configurations. Two of the most popular are spiral wound and hollow fine fibre membranes. They are generally made of cellulose acetate, aromatic polyamides or nowadays thin film polymer composites. Both types are used for brackish water and seawater desalination, although the specific membrane and the construction of the pressure vessel vary according to the different operating pressures used for the two types of feed water.

Figure 4.12 Schematic of hollow fibre membrane structure

(4) Post-treatment: The product water from the membrane assembly usually requires pH


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(4) Post-treatment: The product from the membrane assembly usually requires pH adjustment and degasification before being transferred to the distribution system for use as drinking water. The product passes through an aeration column in which the pH is elevated from a value of approximately 5 to a value close to 7. In many cases, this water is discharged to a storage cistern for later use.

4.4.2.2 Energy recovery device The brine flows out of the membrane assembly at a very high pressure. So this water contains considerable energy which can be recovered. There are three technologies available which allow recovery of this energy namely turbo-pumps, pelton turbines and work-exchanger pumps. The efficiency of these pumps is approximately 90%.

Figure 4.13 Typical schematic of a reverse osmosis system

The RO process is defined according to certain variables:

• Osmotic and operating pressure

• Salt rejection

• Permeate recovery

Criteria for RO plant design include the following:

• A high membrane surface to volume ratio

• Adequate structural support


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• Low pressure drop on the concentrate side of the membrane to maintain the driving force for permeation

• Turbulence on the concentrate side to minimize fouling

• Ease of back-flushing and membrane replacement in case of fouling

Because of the close relationship between feed water composition and membrane performance, feed water analysis must be conducted to determine the pre-treatment chain and the membrane specification, including chemical stability over the operational pH range and temperature values. Membrane manufacturers provide system specifications in relation to feed water quality for variables such as salinity, temperature and organic loading. The membranes need to be regularly replaced. The useful life of commercial membranes ranges from 3 to 5 years. On average annual membrane replacement rates range between 5 and 15 %, depending on the feed water quality, pre-treatment condition and stability of operation.

The product water in the RO process is a function of the seawater salinity level, the number of RO membrane stages (several RO passes can be connected in series) and other design parameters. Most RO membranes allow less than 1% salt passage in a single stage, resulting in TDS level of 300 to 400 mg/L in product water.

4.4.2.3 Requirements The key requirements for reverse osmosis are presented below: Seawater quantity: this is characterised by the recovery rate of reverse osmosis which is between 40% and 80% of feed water depending on the seawater quality and the pre-treatment installed. Seawater quality: salt concentration up to 50 g/L Pre-treatment: this depends on the raw water quality (TSS, TOC, algae, pH), but generally it comprises a “choc” chlorination (using a fast acting chlorine to limit the bio-fouling of membranes), coagulation, flocculation, decantation and filtration, cartridge filters, de-chlorination. Footprint: usually between 1 -.3 ha for each 100 Mld (depending on the sea water quality and the pre-treatment design) Energy consumption: RO system only requires electrical energy to operate typically in the range 4kWh/m3. However at various optimised works through the use of energy recovery devices energy consumption can be reduced to 3.5 – 3.8kWh/m3 of fresh water to be produced. 4.4.2.4 Operation and Maintenance Operating experience with reverse osmosis technology has improved over the past 15 years with fewer plants having long-term operational problems. Assuming that a properly designed and constructed unit is installed, the major operational elements associated with the use of RO technology will be the day-to-day monitoring of the system and a systematic program of preventive maintenance. Preventive maintenance includes instrument calibration, pump adjustment, chemical feed inspection and adjustment, leak detection and repair, and structural repair of the system on a planned basis. The main operational concern related to the use of reverse osmosis units is fouling and membrane sensitivity. Fouling is caused when membrane pores are clogged by salts or obstructed by suspended particulates. It limits the amount of water that can be treated before cleaning is required. Membrane fouling can be corrected by cleaning (about every 4 months), and by replacement of the cartridge filter elements (about every 8 weeks). Operation, maintenance, and monitoring of RO plants require trained engineering staff.


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4.4.2.5 Environmental Impact

The waste water arising from the RO process may be variable depending on the extent of pre-treatment necessary to condition the water before it is allowed to contact the membranes. As a minimum, the pre-treatment system would comprise of media filters possibly supplemented by coagulation and flocculation using chemicals such as coagulants and polymers. In the case of the media filter alone, the wastewater arises from backwashing them at regular intervals, thereby removing the suspended matter originally removed from the seawater by the filters. Where coagulation and flocculation is carried out, the backwash from the filters would contain the flocculated chemicals and it would be normal practice to pass this to a sludge treatment process to remove the solids prior to disposal of the wastewater stream. The recovered sludge would require separate disposal to land under controlled conditions.

The reject stream from the RO plant would be characterised by high salinity and possibly a reduction in oxygen content although the latter issue would be addressed in the design of the system to ensure re-oxygenation before entering the main watercourse.

The membranes require chemical cleaning at intervals, the intervals being dictated by the effectiveness of the pre-treatment system. A variety of chemicals is used depending on the nature of the membrane foulants and could include detergents, acid or alkali. Waste from cleaning system should be diverted to a treatment plant (or join the sludge treatment process) for neutralisation prior to disposal. The design of the wastewater system would need to be tailored to the specific requirements at the sites; where possible it has been common practice for wastewater to be discharged into the cooling water flow of an associated power station.

4.4.2.6 Commercial Maturity

The majority of the desalination plant constructed around the world are mostly distillation or reverse osmosis. Around the 1980’s Reverse Osmosis was mostly used for brackish water but today it has become a major competitor of distillation particularly for high capacity plants and salty seawater. The desalination plant at Ashkelon (Southern Israel) is currently the largest operating reverse osmosis plant producing 320 Mld.

Over the past 10 years significant improvements have been made for the RO process. Steady and continuous improvements in the efficiency of membranes, energy recovery, energy reduction, membrane life, control of operations and operational experience have all contributed to lowering the costs associated with this technology. Currently a number of RO plants are being constructed to produce various volumes of product water:

• Algeria - 500 MLD

• Australia - 5 RO planned projects: 55 Mld; 123 Mld; 125 Mld; 125 Mld

• India – 100 ldD

• Israel – 100 Mld

• Barcelona - 200 Mld – in operation in 2009.


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4.4.2.7 Costs

The costs (investment, operation and maintenance) and energy consumption of reverse osmosis are presented in the next tables (4.5, 4.6) and in Figure 4.14. The cost of 1 m3 of water produced by the most economical process is also presented and explained (different origins of this cost and distribution).

Table 4.5 Investment cost for membrane processes

Process Type $US for 1 m3/d

Reverse osmosis 200-500

To compare the energy consumed by the various membrane processes, the thermal and electrical energy needed have been converted in Table 6 into the Gas quantity required to feed these installations.

Table 4.6 Comparison of energy consumption of different membrane processes, when energy source is fuel.

Membrane process

Energy needed for 1 m3 of

fresh water

kWh

Gas quantity needed

In Nm3/m

3 of fresh water

Reverse osmosis on sea water and without energy recovery

12 2.8

Reverse osmosis on sea water and with energy recovery (isobaric

pressure)

2.5 0.9

Reverse osmosis on brackish water

3 0.7

The table above illustrates that the energy efficiency of the reverse osmosis process is dependant upon the salt concentration in the feed water and the presence/absence of an energy recovery device.

The mean cost of produced water by large scale reverse osmosis is 0.3 – 0.91 €/m3. Figure outlines

the typical costs for 20 year for an RO plant.


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Figure 4.14 Typical 20 year osmosis is desalination plant cost.

Typical 20 year reverse osmosis desalination plant cost

Staff / other

19%

Chemical

2%

Energy

19%

Equipment

45%Membrane

replacement

15%

Staff / other

Chemical

Membrane

replacementEnergy

Equipment

4.4.2.8 Other Uses of Reverse Osmosis

Wastewater Recycling

Reverse Osmosis is being used increasingly for the treatment of municipal and industrial wastewaters due to the growing demand for high quality water in large urban areas. As the osmostic pressure of waste water is much lower than sea water (with a salinity of approx 30-40 g/L NaCl). The growing success of membranes in this application is related to improved process designs and improved membrane products. Factors which play a key role in the use of RO membranes include ultra or microfiltration (UF or MF) pretreatment, low fouling membranes, flux rate, recovery and control of fouling and scaling. In particular, high flux rates can be used when UF or MF pretreatment is used. These technologies remove most of the suspended particles that would normally cause heavy fouling of lead elements. Typically, fluxes in the range of 17-21 lmh lead to cleaning frequencies in the range of 3-4 months. By combining the use of membrane pretreatment and chloramination of the feed water through chlorine addition, two of the primary sources of RO membrane fouling can be controlled. The use of chloramine has become a proven means to control biofouling in a membrane for wastewater applications as it is a weaker oxidant allowing greater tolerance of the membranes to exposure.

A number of plants in Singapore which have already been constructed have collected long-term operational data: in Bedok (10 Mld plant) and Kranji (40 Mld plant). From the information gathered it has been demonstrated that the RO membranes operate reliably on wastewater. These large plants began operation in autumn 2002 and have demonstrated an effective means of reclaiming high quality water from difficult source waters, such as municipal wastewaters. Most water produced is not used for direct potable use.

This recovery from wastewater increases the possibilities concerning the type of water resources which can be utilised and allows consideration of waste water recycling as an alternative to surface water treatment or seawater desalination.

Wastewater recycling may be suitable to conserve water and to avoid extracting too much water from the environment by pumping. Using this process the environmental impacts are considerably reduced as it minimizes waste water release into the environment and requires less pumping of surface water.

Many water reclamation plants have been built worldwide using reverse osmosis, mainly in United States and Australia.


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Figure 4.15 Treatment chain of Los Angeles water reclamation plant – 17 MLD

Costs considerations:

Costs for both construction and operation of RO membrane processes depend on many site-specific factors. A recent estimate of capital costs for a 20 Mld wastewater reuse treatment facility utilizing RO membrane technology at King County, Washington was about 0.5 – 0.6 € for 1m3/day.

At present despite the good water quality produced by RO the general public remains slow to embrace the concept of using reclaimed water directly as potable water.

Groundwater Recharge

In the meantime, one of the most common applications for high-pressure membrane technology is for groundwater recharge to replenish an aquifer or to prevent salt-water intrusion.

This process is referred to as indirect potable reuse. Some plants in United States have been producing high-quality recycled water treated by advanced technologies for seawater intrusion barrier injection, with the majority of the injected water entering the groundwater and eventually becoming part of the water supply—hence the term “indirect potable reuse.”

As advanced treatment technologies become more cost-effective and as public acceptance increases, recycled water may be used to augment surface water supplies.

Presently the public may not be prepared to consume reclaimed water, and recycling of wastewater for drinking water production is not permitted in many European countries. However other options for RO reclaimed water are available – it can be supplied through a separate distribution system for a wide range of applications including agricultural and landscape irrigation (as in St. Petersburg), wildlife habitat enhancement (as in Orlando Wetlands Park), a recreational impoundment and groundwater recharge (as in Gainesville) and a surface water augmentation.

4.4.3 Conclusion

RO technology is currently the main competitor to the distillation processes in the field of desalination given its compactness and the relative ease with which it may be packaged and managed, as well as its compatibility with a number of energy sources and its superior environmental profile.


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Reverse osmosis presents several advantages and drawbacks:

Advantages

• The processing system is simple; the only complicating factor is finding or producing a clean supply of feed water to minimize the need for frequent cleaning of the membrane.

• Installation costs are lower by comparison with thermal equivalents

• Systems may be assembled from pre-packaged modules and are compact

• This process is compatible with many energy sources.

• RO technologies can be used to remove both organic and inorganic contaminants.

• RO has low environmental impact apart from carbon dioxide release.

• RO has low visual impact - It can be easily integrated into the surrounding country side

Figure 4.16 Interior view of RO plant at Ashkelon, Southern Israel


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Figure 4.17 Exterior view of RO plant at Ashkelon, Southern Israel (320 Mld)

Disadvantages

• The membranes are sensitive

• RO process is not adapted to high variability of salt concentration in seawater

• The feed water usually needs to be pre-treated to remove particulates (in order to prolong membrane life).

• Operation of a RO plant is more difficult compared with other desalination processes and requires a high quality standard of materials and equipment. Using RO technology with multi-stage flash (MSF) is a more reliable alternative:

• Power requirements are much higher in the case of RO plants because of their high pressure operation

• Though RO plants have lower initial investment and fixed costs than thermal equivalents, they have higher maintenance costs


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4.5 FUTURE DEVELOPMENT 4.5.1 Latest Developments in Distillation Processes

For both MSF and MED thermal distillation systems there are many areas in need of attention such as research & development, engineering, including the high levels of investment needed for plant construction and commissioning, total energy requirements and material corrosion. Research on new low-cost construction materials is in progress. Aluminium for heat exchangers and carbon steel material are presently used while high-grade stainless steel and titanium are proposed for future usage. In addition, polymeric materials are being considered for the tube bundles, a promising possibility given the very low pressure difference between the inside and outside of the tubes.

There is some marginal evolution concerning these topics, but recent research projects have also focused on combining distillation with reverse osmosis to constitute optimum hybrid configuration and on membrane distillation (see in the section 0).

With regard to vapour compression distillation systems, larger units are not considered a viable option in the near future.

4.5.2 Latest Developments in Reverse Osmosis Processes

Prospects for RO development are more promising. However this process also has certain areas requiring attention particularly feed water pre-treatment and membrane fouling. Several improvements to pre-treatment systems are currently being developed. There have been significant improvements in the membrane materials available and utilised during the past few years and further significant advances are expected. The main objectives of the current research in this area are longer membrane lifetimes, lower energy consumption, greater cost-effectiveness and, consequently, wider dissemination of RO technology. With regard to energy consumption in particular, some savings are expected, but no major breakthroughs are foreseen.

These matters are further developed in the next section.

4.5.2.1 Minimisation in Membrane Fouling

Fouling of membranes is one of the main operational and maintenance difficulties of reverse osmosis plants. Chemicals are used to regularly clean membranes, but pre-treatment of seawater is also very important before entering the membrane units. Pre-treatment reduces the silt density index of the feed water. This index is used to determine the fouling potential of particulate and fine colloidal materials that may be present in the feed water. Improper pre-treatment can result in premature aging of RO membranes or fouling, leading to a total plant shutdown.

To control membrane fouling two principal options are available:

Optimisation of pre-treatment: encompassing two new pre-treatment processes namely:

• Macromolecular adsorption

• Micro filtration

Optimisation of anti-scalant:: minimizing the fouling of membranes will have an impact on:

• Chemical costs


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• Lifetime of membrane: reducing the membrane replacements cost

4.5.2.2 Enhancement of Membranes and Modules

Membranes

The selection of the most suitable membrane for a particular application depends on the feed water quality and the product water requirements. Recently membranes have been enhanced to handle the incoming feed water characteristics.

The design of a novel polyamide TFC membrane for seawater desalination with reduced fouling ability is being researched in terms of the effect of surface charge, hydrophobicity/philicity and surface roughness of the TFC membrane.

The development of an antifouling membrane may involve the following:

• Preparation of a TFC polyamide reverse osmosis membranes for seawater desalination based on the conventional interfacial polymerisation of two monomers namely diamine and polyfunctional acid chloride (PAC) on a porous support membrane.

• Changing the surface charge density, hydrophobicity/hydrophilicity and surface roughness of the membrane by adding an organic solvent, surfactant or an electrolyte into the aqueous diamine solution.

• Alter the characteristics of the membrane surface by processes such as streaming potential measurement, contact angle measurement, atomic force microscope (AFM), X-ray photoelectron microscope (XPS) and scanning electron microscope (SEM).

• Conducting reverse osmosis trials with an aqueous 3.5 % sodium chloride solution including potential foulants. The purpose of the trial is to measure the rate of flux reduction across the membrane. Once established the rate of flux reduction is correlated with the surface properties of the membrane by regression analysis to allow optimisation of the characterisitics of the membrane to develop a membrane more resistant to anti-fouling.

Modules

Similarly, enhancements in module design are also being developed. The methodology includes computational fluid dynamics analyse which are undertaken to enhance the performance of the modules by modifying the fluid flow behaviour. On the basis of the results of the theoretical and experimental studies, the advantages and disadvantages of currently employed configurations are assessed and potential modifications or new designs are proposed. Regarding the latter, the mechanical characteristics of the modules need to be considered in order to prevent extensive fatigue and deterioration during operation as well as membrane embossing. The results of current theoretical studies will assist in this direction providing the capability to calculate stresses and forces on solid surfaces in addition to impacting the recovery rate and on the fouling of the membranes.

4.5.2.3 Energy Recovery Devices and High Pressure Pumps

The feasibility of using energy recovery devices for desalination will depend on the quantity of energy in the concentrate available for recovery. In the case of RO it is common now to use energy recovery


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devices connected to the concentrate stream as it leaves the pressure vessel at about 1 to 4 bar (15 to 60 psi) less than the applied pressure from the high-pressure pump. These energy recovery devices are mechanical and generally consist of work or pressure exchangers, turbines, or pumps that can convert the pressure difference to rotating or other types of energy that can be used to reduce the energy needs in the overall process. These can have a significant impact on the economics of operating large plants. They increase in value as the cost of energy increases. Now, energy usage in the range of 3 kWh/m3 (11.4 kWh/1000 gal) for seawater RO (with energy recovery) plants has been reported (Buros, O.K. 2000 2nd Ed.).

Energy recovery in the main membrane desalination processes is based on the conversion of pressure into shaft work and then back to fluid pressure a process which is less efficient than using fluid pressure directly. The se energy recovery devices include turbines, pelton wheels and reverse running pumps. Work exchanger pumps which are generally attached to membranes arrays require the inclusion of high-pressure pump and booster pump in the system. A work exchanger reduces the pumping pressure and electric power consumption by a ratio equal to that of system recovery.

The use of energy recovery equipment becomes more cost-effective in larger scale systems. It is important to select suitable energy recovery equipment which has efficiency relatively constant in the range of the anticipated flow rates.

4.5.2.4 Automation and Operational Optimisation

Much work has been done to determine the level of plant automation and control optimization required in desalination plants to minimise the cost of water produced.

Information has been gathered from reviewing the literature from operating plants in addition to obtaining expert opinions from automation system manufacturers etc. to determine how automation has been and can be best applied in desalination plants (with emphasis on Reverse Osmosis) to meet the project objectives. These reviews also establish which parameters in the Reverse Osmosis desalination processes need to be measured and the conditions under which they need to be measured. A cost-benefit analysis of automation applications, including performance optimizing controls, will determine a well-justified recommendation and definition of automation needed for the Reverse Osmosis process.

4.5.3 Hybrid Configurations

Hybrid system can be used to reduce the overall costs of desalting. Such hybrid systems are not applicable to most desalination installation, but could prove to be an economic benefit in some cases. A hybrid system is a treatment configuration made up of two or more desalination processes. An example is using both distillation and RO processes to desalt seawater at one facility (Buro, O.K. 2000 2nd Ed.).


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Figure 4.18 schematic of a hybrid system

The advantages of a hybrid system can be numerous. Take for example the RO/distillation hybrid:

• The RO system can be fed with a seawater pre-heated to 40°C by a distillation unit which would allow an increase in production of approx 3% fresh water for every 1°C

• The common intake is significantly reduced in size

• The fresh water obtained by distillation (around 25 mg/L) can be mixed with the water produced by reverse osmosis (around 400 mg/L) to obtain an improved water quality which would be more compliant with drinking water regulations and for industrial uses (some industries require very low salt concentration e.g electronics industry)

• In addition the low salinity of the product water obtained with distillation can remove the need for a second stream of RO.

A plant constructed at Fujairah (United Arab Emirates) produces 454 MLD distilled water from 5 MSF units which is mixed with 170.5 MLD of permeate from 17 RO streams is currently the largest hybrid plant in operation.

Another example of a hybrid system could be the use of steam in a dual-purpose plant (electricity and water). The steam is used in a distillation plant to desalt seawater. Alongside the distillation plant could be a seawater RO plant that would be run only in off-peak power period. This would help to stabilize the load on the generator and therefore use lower cost electricity. The RO plant could be designed to produce water with a higher level of total dissolved solids and, thus, also lower production cost. Thermal and membrane processes can be linked in more complex manners to increase both efficiency and improve operations (Buros, O.K. 2000 2nd Ed.).

Fresh water

RO gas

Steam turbine

Sea water

Brine

Frech water Degaso


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4.5.4 Other Desalination Processes Other desalination processes have been developed and tested but subsequently abandoned As they proved to be economically and technically unfeasible for large scale plants. A brief summary of these technologies is presented below for evaluation in terms of the Dublin scenario

4.5.4.1 Other Thermal Techniques Solar distillation In brief, solar distillation uses the sun’s energy to evaporate water from a shallow basin; water vapour is condensed on a cool surface and the condensate is collected as a fresh water product usually along a sloping glass roof (see Figure 4.19).

Figure 4.19 Principle of solar distillation

This process is typically used only for very small capacity installations and would prove inefficient and expensive on a larger particularly in countries where light intensity is very low as in Ireland.

Variations of solar still designs have been made in an effort to increase efficiency, but they all share the following difficulties, which restrict the use of this technique for large-scale production:

• Large solar collection area requirements

• High capital cost

• Vulnerability to weather-related damage

A general rule of thumb for solar stills is that a solar collection area of about one square meter is needed to produce 4 L of water per day.

Thus, for a 4,000-m3/d facility, a minimum land area of 100 hectares would be needed (250 acres/mgd). This operation would take up a tremendous area and could thus create difficulties if located near a city where land is scarce and expensive. The stills themselves are expensive to construct, and although the thermal energy may be free, additional energy is needed to pump the water to and from the facility (Buros, O.K. 2000 2nd Ed.).


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Membrane distillation

Membrane distillation was introduced commercially on a small scale during the 1980s, but it has had demonstrated no commercial success. However recent developments (see below) have warranted consideration of membrane distillation as an option.

In membrane distillation, salt water is warmed to enhance vapour production, and the vapour is exposed to a membrane that can pass water vapour but not liquid water.

Memstill is a newly developed membrane-based distillation concept. The technology uses hydrophobic membranes to separate warm sea water from pure distillate, and combines both a high transport of water vapour and a high transfer of evaporation heat into one membrane module. Because the Memstill module houses a continuum of evaporation stages in a countercurrent flow process, a good recovery of evaporation heat is possible. The process promises to decrease desalination costs to well below 0.50 €/m³, using low grade waste steam or heat as driving force.

Memstill technology presents important advantages in comparison with desalination techniques like MSF, MED and RO, for example:

• Low consumption of heat and electricity

• Very high salt separation factor

• Limited corrosion and fouling

• Small footprint

• No additives

However, this process is at present being tested at both bench and pilot scales. Eight years of development has produced a module concept which is leak-free, resistant to hot sea water and foulants, has a salt reduction factor more than 10,000mg/L, and holds sufficient mass and heat transfer to yield an economical flux performance in scaled-up modules of 300 m2 of membrane area.

The first pilot plant has now operating for a year in Singapore and is still showing good separation quality at moderate (but expected) flux performance. A second pilot has operated for 4 months in Benelux with positive results and will now be further improved for a third pilot test in the Netherlands.

Due to the current status of Memstill development an industrial unit may not be available for many years.

Freezing

This technology is based on the principle that water excludes salt when it crystallises in ice and is independent of the salt concentration of the raw water. The procedure consists of cooling saline water to a temperature where ice crystals form under controlled condition and then in collecting the ice. The ice is then melted and yielding fresh water.

Theoretically, freezing has some advantages over distillation, which was the predominant reason why the freezing process was developed. These advantages include a lower theoretical energy requirement for a single stage operation, a reduced potential for corrosion and fewer scaling or


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precipitation problems. The disadvantages are that it involves handling ice and water mixtures that are mechanically complex to move and process.

There are several different processes that use freezing to desalt seawater, and a number of plants have been built over the past 50 years. However the process has not been a commercial success in the production of fresh water for municipal purposes. At this stage, freeze-desalting technology probably has better application in the treatment of industrial wastes than in the production of municipal drinking water.

Because this process requires complex mechanical equipment, in particular to remove ice from seawater it is no longer employed industrially.

4.5.4.2 Other Membrane Processes

Forward Osmosis (FO)

In Forward Osmosis (FO), like in reverse osmosis, water transports across a semi-permeable membrane that is impermeable to salt. However, instead of using hydraulic pressure to create the driving force for water transport trough the membrane, FO process utilizes a “draw” solution having a significantly higher osmotic pressure than the saline feed water. This “draw” solution flows along the permeate side of the membrane, and water naturally transports across the membrane by osmosis. Osmotic driving force in FO can be significantly greater than in RO, potentially leading to higher water flux rates and recoveries.

The significant issue with this new process is to find the most appropriate “draw” solution.

Figure 4.20 Schematic of forward osmosis (FO) process

Many various draw solution and membranes have been tested but many of the bench-scale studies have proved inconclusive. The process is not currently employed as a viable solution on industrial scales.


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Electrodialysis (ED)

Electrodialysis (ED) was commercially introduced in the early 1960s, about 10 years before RO. The development of electrodialysis provided a cost-effective way to desalt brackish water and attracted considerable interest in this area.

Electrodialysis depends on the following general principles: most salts dissolved in water are composed of positively (cationic) or negatively (anionic) charged ions. These ions are attracted to electrodes with an opposite electric charge. Membranes can be constructed to permit selective passage of either anions or cations.

The dissolved ionic constituents in a saline solution such as sodium (+), calcium (++), and carbonate (--) are dispersed in water, effectively neutralizing their individual charges. When electrodes connected to an outside source of direct current like a battery are placed in a container of saline water, electrical current is carried through the solution, with the ions tending to migrate to the electrode with the opposite charge.

For these phenomena to desalinate water, membranes that will allow either cations or anions (but not both) to pass are placed between a pair of electrodes. These membranes are arranged alternately with an anion-selective membrane followed by a cation-selective membrane. A spacer sheet that permits water to flow along the face of the membrane is placed between each pair of membranes.

One spacer provides a channel that carries feed (and product) water, while the next carries brine. As the electrodes are charged and saline feed water flows along the product water spacer at right angles to the electrodes, the anions in the water are attracted and diverted towards the positive electrode. This dilutes the salt content of the water in the product water channel. The anions pass through the anion-selective membrane, but cannot pass any farther than the cation-selective membrane, which blocks its path and traps the anion in the brine. Similarly, cations under the influence of the negative electrode move in the opposite direction through the cation-selective membrane to the concentrate channel on the other side. Here, the cations are trapped because the next membrane is anion-selective and prevents further movement towards the electrode.

Figure 4.21 Schematic of Electro-dialysis (ED) process


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By this arrangement, concentrated and diluted solutions are created in the spaces between the alternating membranes. These spaces, bounded by two membranes (one anionic and the other cationic) are called cells. The cell pair consists of two cells, one from which the ions migrated (the dilute cell for the product water) and the other in which the ions concentrate (the concentrate cell for the brine stream).

The basic electrodialysis unit consists of several hundred cell pairs bound together with electrodes on the outside and is referred to as a membrane stack. Feed water passes simultaneously in parallel paths through all of the cells to provide a continuous flow of desalted water and brine to emerge from the stack. Depending on the design of the system, chemicals may be added to the streams in the stack to reduce the potential for scaling.

An electrodialysis unit is made up of the following basic components: pretreatment train; membrane stack; low-pressure circulating pump; power supply for direct current ; post-treatment.

The raw feed water must be pre-treated to prevent materials that could harm the membranes or clog the narrow channels in the cells from entering the membrane stack. The feed water is circulated through the stack with a low-pressure pump with enough power to overcome the resistance of the water as it passes through the narrow passages. A rectifier is generally used to transform alternating current to the direct current supplied to the electrodes on the outside of the membrane stacks (Buros, O.K. 2000 2nd Ed).

Electrodialysis has not succeeded to further develop in the desalination market as it tends to be more suitable for the treatment of feed water with low salt concentration (e.g. brackish water).

Reverse osmosis has been the main rival to ED because electrodialysis has only been adapted to low salinity of seawater: between 1 and 2.5 mg/L NaCl. This technology is not applicable to the Dublin region as the seawater salinity is much higher.

Reversal electrodialysis (EDR)

Pre-treatment requirements for ED systems may be minimized through the implementation of electrodialysis reversal (EDR), which operates on the same basic principle as the standard ED process. The main difference between the ED and EDR techniques is that the electrode polarity in the latter is reversed three to four times per hour and the flow streams are simultaneously switched using automatic valves. The net result is that the product and brine cells periodically exchange functions, with salts being transferred in opposite directions across the membranes in consecutive cycles. This reversal aids breaking up and flushing out scale, slime and other deposit in the cells, eliminating the need for additives (generally acids and complexing agents). The membrane stacks still require some cleaning, though much less frequently than would otherwise be necessary.

EDR is a variation of ED. Reversal of electrode polarity increases the useful life of the cell’s electrode and helps clean the membranes. The only difference between the two processes concerns the maintenance and the chemicals costs which translates to minor cost savings compared to ED. Moreover, as EDR is currently only adapted to the treatment of brackish water this technology is not applicable in the case of Dublin.

High efficiency electrodialysis(HEED)

Like traditional electrodialysis, HEED is an electro-membrane process in which the ions are transported through a membrane from one compartment to another under the influence of an electrical potential. In effect, ions are driven from a region of low concentration to one of high concentration.


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The main differences between ED and HEED are as follows:

• HEED requires less membrane area

• HEED is more energy efficient

• Improved gasket designs have resulted in higher separation efficiencies

HEED is available in capacities ranging from 2,000 to 5,000 m3/d with maximum feedwater salinity of 20 g/L and product water purity of 2 mg/L total dissolved solids (TDS).

Hybrid processes consisting of HEED, RO, and/or distillation also offer solutions to an increasingly important issue. For some applications, combined HEED and RO hybrid systems would result in more efficient operation since electrodialysis efficiency decreases with decreasing dilute (product) concentration. The only energy required is electrical energy; approx 24 kWh are needed to produce 1m3 fresh water from sea water which is significantly higher than other desalination technologies available.

Conclusion for Electrodialysis Options

RO is the most widely used membrane technology at the present time. However as presented in this section various other membrane processes have been researched and developed in recent years. These processes however are typically used for desalination of brackish water (e.g. ED and EDR), are only available at laboratory/pilot scales (e.g. forward osmosis) or are considerably more expensive than RO in terms of energy consumption.

Table 4.7 Comparison of the energy needed by the membrane processes:

Membrane process Energy needed for 1 m

3 of

fresh water (kWh/ m

3)

Gas quantity needed

(kg/m3 of fresh water)

Reverse osmosis on sea water and without energy recovery

12 3.2

Reverse osmosis on sea water and with energy recovery

4 1.0

Reverse osmosis on brackish water 3 0.8

Electrodialysis on sea water 30 7.9

Electrodialysis on brackish water 3 0.8

Reversal Electrodialysis on sea water 30 7.9

High Efficiency Electrodialysis on sea water

24 6.3


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4.5.4.3 Thermal Osmosis Process

The thermal osmosis process consists of a special counter-current heat exchanger. It comprises of 2 membranes, the first which is permeable to vapour and impermeable to salts and the second which is impermeable to vapour and permeable to salts. No industrial application of this technology is presently known.

4.5.4.4 Ion Exchange Process

Ion exchange resins can also be used for desalination. These are insoluble synthetic organic compounds that have the ability to exchange some of their ions with those of mineral salts dissolved in the solution (feed water).

Two types of resins can be distinguished:

• Anionic resins that replace the anions of the treated liquid with OH – anions

• Cationic resins with which cations are replaced by H+ or Na+ ions.

The resins have to be regenerated regularly with chemical reagents. Moreover, the resins have to be replaced periodically and as a result the incurred costs are increased when compared to other technologies for the desalination of seawater.

The critical factor in terms of the performance of ion exchange resins is that they can produce very pure water only if salt content of the raw water does not exceed 1g/L. Therefore since this process is effective only for a very low salt content in the feed water this process is not worth considering for the Dublin region.

4.5.4.5 Capacitive Deionisation

In brief this process involves saline water flowing between two porous carbon electrodes. Anions are attracted to the anode and the cations to the cathode. When the electrodes gradually become saturated regeneration is required.

This technology has been tested only at laboratory scale in the United States and no industrial developments have followed the laboratory tests.


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5 SELECTION OF OPTIMUM TECHNOLOGY – IRISH APPLICATION

5.1 METHODOLOGY

5.1.1 Technology Selection Scoring System

All desalination technologies developed to date have been presented in the previous section, including operational, lab-scale and bench-scale processes. The initial aim of this technology review process was to determine the most beneficial desalination technology for the Dublin Water Supply project.

To compare each of the technologies listed in this document, a screening matrix has been devised for technology selection using a scoring system which has been developed for comparison of each process based on the following criteria:

• Maturity of the technology

• Scale adaptability (300 Mld)

• Scale adaptability - 50 Mld

• Development prospects

• State of the market

Each process will be scored from 0 to 100 with regard to relevance in relation to the criteria listed as outlined below:

• Between 0 and 35: low score

• Between 35 and 65: medium score

• Between 65 and 100: high score

Maturity of the technology: Each process has been scored on this criterion based on the number of existing plants using this technology and the number of desalination projects worldwide which intend to implement it.

Therefore a process will get:

• A high score if many plants using this process are operated worldwide, if these plants have been implemented many years ago without any major operational problems since this date and if many projects are planned for future desalination plants using this technology.

• A medium score if some plants using this process are operated worldwide or only recent implementation of the plant exists worldwide, if some little operation problems have been observed on these plants and if some projects are planed for future desalination units using this technology


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• A low score if few plants using this process are operated worldwide (recent implementation or implemented but no longer operated), or if no industrial reference exist for this process (only lab-scale prototype) and if few or no projects are planned using this technology.

Scale adaptability (300 Mld): This criterion has been assessed for each process according to the number of existing plants worldwide using the technology at present with a capacity of approx 200 – 300 Mld and also considering the possibility of scaling-up when no high capacity examples exist. .


• A high score if many of the plants using this process are operated at a capacity of 300 Mld

• A medium score if few plants are operated at a capacity of 300 Mld or if scaling-up possibilities exist for the process.

• A low score if no industrial reference exists for this process (only lab-scale prototype) and no scaling-up perspectives are expected for it.

Scale adaptability (50 Mld): This criterion has been assessed for each process according to the number of existing plants worldwide using the technology at present with a capacity of approx 50 MLD with the possibility of scaling-up when no relevant example exist.


• A high score if many plants using this process are operated at a capacity of 50 Mld

• A medium score if few plants are operated at a capacity of 50 Mld or if scaling-up possibilities exist for this process.

• A low score if no industrial reference exists for this process (only lab-scale prototype) and no scaling-up perspectives are expected for it.

Development prospects: This criterion has been assessed for each process according to the publication of research papers, and the number of process elements being addressed by these papers.


• A high score if many papers exist on recent enhancements of the process and if these enhancements can lead to significant cost-saving, increasing the reliability of the process and simplicity of operation.

• A medium score if papers (recent or old) exist on enhancements of the process but these enhancements do not mean significant cost-saving, increasing the reliability of the process and simplicity of operation.

• A low score if no paper can be found on possible enhancement of the process.

State of the market: This point has been assessed for each process according to the number of suppliers offering this technology.


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• A high score if many suppliers offer this technology for high capacity facilities (> 50 Mld)

• A medium score if some suppliers offer this technology for medium and high capacity facilities (>50 Mld)

• A low score if few suppliers offer this technology.

5.1.2 Appropriate Processes for Dublin and Scoring System

Using the above criteria and scoring system Table 5.1 shows the most appropriate processes for the Dublin project which in summary are:

• Distillation: MED and MSF

• Reverse osmosis (RO)

• Hybrid configurations: RO and distillation

In order to compare these selected processes in further detail, a second selection and scoring system has been established based on the following additional criteria:

• Cost

• Energy Consumption

• Environmental Impact

• Development prospects

• Robustness

• Operation

• Safety

Costs: This criterion has been assessed for each process according to the CAPEX, OPEX, the cost of the system to produce 1 m3 of fresh water and the stability of these costs (which can depend on water quality, energy source availability in the country, and local physical conditions)


• A high score if CAPEX, OPEX, cost of the system to produce 1 m3 of fresh water are low and the cost are very stable (not too dependent on water quality, energy source available in the country, local physical conditions)


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• A medium score if some of the costs (CAPEX, OPEX, ratios) are high but stable (not too dependent on water quality, energy source available in the country, local physical conditions)

• A low score if costs are high and very variable (greatly dependent on water quality

Energy: This criterion has been assessed for each process according to the amount of energy needed to produce 1 m3 of fresh water and the variability of possible energy sources to feed this process.


• A high score if it consumes little energy: less than 4 kWh/ m3 of fresh water

• A medium score if the energy consumption is more than 4 kWh and less than 10 KWh/ m3 of fresh water

• A low score if it needs a lot of energy: more than 10 KWh/ m3 of fresh water

Environmental impact: This criterion has been assessed for each process according to the environmental footprint of the entire system in terms of its integration into the landscape, noise emissions, brine disposal issue and its carbon dioxide emissions.


• A high score if the footprint of the whole system is small, its integration into the landscape is not problematic, low noise emissions and presents little threat to the environment (little impact of the brine disposal and low carbon dioxide release).

• A medium score if footprint of the whole system is higher, it is more difficult to integrate into the surrounding landscape, higher noise emissions and it releases a significant quantities of CO2

• A low score if footprint of the whole system is high, very difficult to integrate into the surrounding landscape, its noisy and presents a considerable impact on the environment (due to the brine disposal and the carbon dioxide release)

Development prospects This criterion has been assessed for each process according to the publication of research papers, and the number of process elements addressed by these papers.


• A high score if many papers exist on recent enhancements of the process and if these enhancements can lead to significant cost-saving, increase of the reliability of the process and improve ease of operations.

• A medium score if papers (recent or old) exist on enhancements of the process but these enhancements do not mean significant cost-saving, increase of the reliability of the process and improve ease of operations.

• A low score if few papers or old papers only exist on possible enhancements of the process.


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Robustness: This criterion has been assessed for each process according to the average lifetime of the existing plants which use this technology, to the working order of these plants (normal, operation incidents, fresh water feeding setback, sensitivity to raw water pollution).


• A high score if plants using this process have been operated for a long time without significant operation problems (lifetime around 30 years)

• A medium score if plants using this process have been operated for a few years (around 10 years) and if some plants have met with little operation problems (like sensitivity to raw water pollution, medium level of maintenance)

• A low score if plants using this process have a short lifetime and if many operational problems are experienced, sensitivity to pollution (leading to stopping of the plant operation for example), considerable maintenance needed to replace the elements of the system.

Operation: This criterion has been assessed for each process according the easiness of operation, the flexibility in the treated flow and the possibility to easily start up / shut down the process if required.


• A high score if it is easy to operate, flexible with regard to the flow to be treated and allow no problems with start up/shut down if required.

• A medium score if the operation of this process needs specific know how and specialised training of staff

• A low score if it is very difficult to operate and not flexible at all (concerning the flow to be treated and the possibility to stop then start the plant when required)

Safety: This criterion has been assessed for each process according hazards posed to the staff working at the plant and to people living in the surrounding area.


• A high score if it poses little or no hazards

• A medium score if it poses some hazards to the staff working on the plant and to people living in the surrounding area

• A low score if it poses many hazards to the staff and to people living in the surrounding area.

5.2 RECOMMENDED TECHNOLOGY

Using the above criteria and scoring system Tables 5.1 and 5.2 show the most appropriate process for the Dublin project namely Reverse Osmosis.


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Table 5.1 Comparison of all desalination processes, including lab-scale and bench-scale processes

Distillation Reverse

Osmosis

Hybrid

Configuration

RO + distillation

Other hybrid

configuration

Forward

osmosis

Electro-

dialysis

Reversal

electrodialysis

High

efficiency

electrodialysis

Solar

distillation Freezing

Thermal

osmosis

process

Ion

exchange

process

Capacitive

deionisation

Maturity 100 80 40 20 20 30 20 5 5 5 5 5 5

scale adaptability (300 Mld)

90 100 50 50 20 5 5 5 2 2 2 2 2

scale adaptability - 50 Mld

90 100 60 50 20 5 5 5 2 2 2 2 2

Development prospects

50 90 90 60 30 20 20 20 5 5 5 5 5

State of the

market

70 100 80 30 10 50 30 5 5 10 5 5 5

Total 400 470 320 210 100 110 80 40 19 24 19 19 19


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Table 5.2 Detailed comparison of the main desalination processes: distillation, reverse osmosis and hybrid configurations

Distillation Hybrid configuration

MSF MED

Reverse osmosis

RO + Distillation

cost 60 50 90 70

energy 60 50 50 60

environmental impact 70 70 90 80

development prospects 40 40 100 90

robustness 80 70 60 60

operation 80 30 90 20

safety 80 80 90 80

TOTAL 470 390 560 460


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5.3 DISCUSSION OF RESULTS The following section discusses the leading factors considered when evaluating each of the technologies reviewed in order to select the most appropriate application for the Dublin Region i.e. Reverse Osmosis (RO):

5.3.1 Costs

The capital costs of MSF and MED are generally higher than RO due to the high cost of uncommon / rare materials which may be required for the construction of certain plant elements. Though RO plants have lower initial investment and fixed costs, they can have higher maintenance costs.

Power requirements are much higher in the case of RO plants because of their high pressure operation which may entail higher operational costs. The overall energy consumption however is much higher for distillation processes (especially for MED) when compared to RO plants.

At high capacities the seawater intake volume required in MSF plants is higher and efficiency is therefore lower. MSF and MED plants also require a greater land area, which can increase the cost due to high land prices.

As shown in Appendix A – Tracking Desalination Costs, RO presents a considerable cost variability (investment and operation) depending on the feed water salinity and quality whereas the distillation process design does not really depend on these factors.

5.3.2 Energy consumption

The scoring system for this particular criterion relates more to the quantity of energy consumed and availability of energy sources for each process type rather than focusing on the cost of the required energy.

Distillation processes can be an attractive option where low-cost thermal energy is readily available. In the case of Dublin, gas would be available to produce steam however the technology may not be attractive considering the high energy consumption rates for distillation processes. Waste heat could also perhaps be used (depending on industrial waste heat available).

RO requires electrical energy only. If the electrical energy cannot be taken from the grid a new power plant would be required increasing as a result the investment costs of this option. If electrical energy is available from the grid RO could be awarded a higher score than is currently presented in the table 5.2 thereby making it more suitable as an option for the Dublin region.

Hybrid configurations present more flexibility concerning the energy source required.

5.3.3 Environmental impact

In terms of impact on the marine environment brine disposal does not constitute an environmental problem for any of the technologies reviewed (refer section 8).


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In terms of landscape integration and noise emissions the distillation processes tend to emit higher noise and do not easily integrate into the landscape. RO is a more compact system than distillation and requires a smaller footprint with lower noise levels.

5.3.4 Robustness

High life times have been reported for distillation systems (up to 40 years) – as RO is a relatively newer technology the full extent of plant life times has not been fully experienced.

5.3.5 Operation

The main processes implemented worldwide are MSF and RO.

RO is the main process proposed for the majority of new installations in the near future

Figure 5.1 Global distribution of installed desalination capacity by technology adapted from 1998 survey (International desalination association)

5.3.6 Safety

Safety does not constitute a real problem for any of the technologies reviewed. The only significant hazard is steam and heat tubes in the distillation process which potentially affects only the staff working on the plant.


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6 PRELIMINARY DESIGN

6.1 INTRODUCTION

A desalination plant would involve the construction of a major Reverse Osmosis desalination facility on the East Coast and a pipeline to take the desalinated water to a suitable reservoir where it would enter the supply network for the Dublin Region. Site selection methodology is available in Section 7.

The total installed capacity of 300 Ml/d can be implemented over a number of phases to provide flexibility in catering for gradually increasing demand growth. A two phased approach to achieve the ultimate demand would see a 200Ml/d plant constructed in Phase 1 (to be operational by 2016) and a further 100 Ml/d in Phase 2 (operational by 2026) - approximately 10 years apart.

The seawater intake and treated water tank constructed in Phase 1 would be adequate for 300 Mld plant removing the need for significant engineering works in Phase 2. Drawings of the desalination plant preliminary design are shown in Appendix G.

6.2 DESIGN CRITERIA 6.2.1 General

This preliminary design of the proposed plant is based on the following principles.

• It is assumed that the quality of the raw water (the sea water) will not change significantly in the next decades and that, results from 2 sampling exercises in August and October obtained data which are representative for the usual water quality of the Irish Sea (see Appendix B – Water Quality Analysis). It is proposed that a sustainable solution will be defined for the final storage of the dewatered sludge. The option of disposal at sea will be considered as no adverse impacts on the marine environment resulted from the discharge dispersion modelling exercise undertaken (see section 8.6.2).

• Provision will be taken in the design of the plant in order to allow safe and easy access to the facility to the public for visits/tours e.g. from schools.

• The plant is designed on the basis of 24 hours a day operation.

• The plant shall be fully automated and have the highest level of safety, reliability and flexibility.

6.2.2 Capacity

The final production of the plant will be 300 Mld. It will be built in two phases: the first phase will have a capacity of 200 Mld, to be built for 2016, with a possibility to produce only 50 Mld at the start of the plant operation, and a second phase of 100 Mld to be added later. The total first phase will be composed of two parallel stream of 100 Mld each.


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6.2.3 Raw Water Quality

2 sets of sea water samples were organised in August and October 2007, giving water quality results representative for the summer and autumn months. The first Round sampling investigated sea water quality at several points:

• Different distances from the shore: 500 m (point A), 1 km (point B) and 3 km (point C) – see Appendix B.

• Different depths: surface, middle, bottom.

The preliminary design presented in this report is based on these water quality sampling results.

The Irish Sea water quality was compared to sea water from other regions where desalinated water is produced. The salinity was found to be quite significant and comparable to that of the Mediterranean Sea. The following table shows the variations in salinity between seawater samples tested in various locations worldwide:

Figure 6.1 Examples of sea water salinity

39 40

713

70

20

36

3640

0

10

20

30

40

50

60

70

80

90

100

mediterranean sea

red sea

baltic sea

caspian sea

dead sea

arabian-persan Gulf

black sea

Iirish sea - Lougshinny

salinity g/L

Seasonal variations of temperature and salinity have been assessed using the survey performed by the “Irish marine institute” and are illustrated in Figure 6.2.


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Figure 6.2 Temperature variations of sea water during the year according to the Irish Marine Institute:

min

max

0

5

10

15

20

1

Température

An important parameter to consider in case of reverse osmosis desalination is the Silt Density Index (SDI), which is representative for the fouling potential of the sea water.

This analysis consisted of filtering 500 ml of sea water through a membrane (5 µm) twice:

• The first time through a new membrane.

• The second time after x minutes (5, 10 or 15 depending on the sea water quality) of sea filtration through the same membrane.

The lengths of time needed to filter the water during both filtering trials are then compared and the difference is expressed in % per minute.

Natural water contains organic and inorganic particles likely to clog the reverse osmosis membranes. The SDI 5 minutes measured in the Irish Sea is 20 (according to data obtained from several regions SDI often varies between 5-30 and occasionally 40). Turbidity, faecal coliforms, organic matter, and algae analysis helped understanding the origin of this quite significant SDI:

• Turbidity suggests that the water is quite charged with particles for a sea water (turbidity is usually less than 1 NTU)

• Organic matter results show usual values (often present at a concentration less than 1 mg/L organic matter quite good settles in sea water)

• Faecal coliforms and algae are numerous and may be responsible for the significant clogging potential of the Irish Sea water.

During the raw water sampling exercises chlorophyll A was found in high quantities; this suggests that algal cells may be numerous in the sea off north Fingal.

No significant pollution risk is estimated to occur in the future since no dangerous discharge is present in the sea at north Fingal.


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6.2.4 Treated Water Quality

At the outlet of the plant, the treated water quality shall be compliant with the EC (Drinking Water) Regulations, 2000 S.I. 439 of 2000.

Table 6.1 shows the critical parameters of the desalination.

Table 6.1 Critical Raw Water Parameters for Desalination

TDS <250 mg/L

Sulphate <250 mg/L

Chloride <250 mg/L

Boron <1 mg/L

The final water alkalinity has been set at 100 mgCaCO3 /L.

6.3 DESALINATION WATER TREATMENT PLANT PRELIMINARY DESIGN

6.3.1 General

Given the characteristics of the raw water, the following process stages shall be used for drinking water production:

• Chemical pre-treatment: intended to decrease the SDI before membrane filtration;

• Reverse osmosis for desalination;

• Post-treatment with setting at calco-carbonic equilibrium and final chlorination. The purpose of setting at the calco-carbonic equilibrium is to reduce scaling and hence protect against corrosion.

A raw water balancing tank will not be provided; a safety buffer capacity will be given by the treated water reservoir. Moreover, the implementation of a raw water balancing tank on such a large scale plant would generate significant constraints on the hydraulic section and lay out which are not justified by the advantages of such a tank.


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Therefore, the recommended treatment stream will be composed of the following stages:

• Shock chlorination

• Coagulation with ferric chloride

• Acidification with sulphuric acid

• Flocculation with anionic polymer

• Dissolved air floatation

• Dual media filtration (anthracite and sand)

• Reverse osmosis desalination with de-chlorination and antiscalant injection

• Setting to calco-carbonic equilibrium and mineralization

• Final disinfection with sodium hypochlorite solution

6.3.2 Main Assumptions

6.3.2.1 Design Flows

The required flow of produced water is 300,000 m3/d (year 2031).

The estimation of the raw water flow to be treated is based on the required treated flow, the conversion rate of the reverse osmosis step and on an estimation of the sludge production volumes.

The water losses in the pre-treatment are around 3.5% of the pre-treated water production, which corresponds to the water losses observed on a well operated surface water treatment plant.

The sludge production estimation is based on the following data:

• Removal of suspended solids:

� 85 % of the suspended solids are removed during the floatation step

� 15 % of the suspended solids are removed during the filtration step

• Concentration of the sludge

� Floatation sludge concentration: 10-15 g/L

� Backwash water concentration: 0.5 to 0.75 g/L

The water losses in the RO plant are around 43.5 % of the final output:

• 55 % in the 1st RO pass: conversion rate is set at 45 %

• 3.33 % in the 2nd RO pass: conversion rate of 2nd pass is set at 90 % and one third of the 1st pass permeate will be treated by the 2nd pass.


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Thus 476,430 m3/d should be abstracted from the sea to convey 200,000 m3/d of treated water to Dublin for phase 1 and 714,640 m3/d for phase 2.

The sludge production estimation is detailed in section 6.3.7.1 of this report.

Below it is proposed that the works are divided into 2 phases: one phase to produce 200,000 m3/d of treated water and a second one for an additional 100,000 m3/d. Thus three streams can be constructed, two streams sized to produce 100,000 m3/d of treated water (238 215 m3/d of raw water with 58% water loss in the pre-treatment and RO steps).

If required, with the exception of the intake structure, treated water tank and outlet pipe, the product water treatment systems can be installed on a stream by stream (modular) basis providing 100,000 m3/d with each additional module. The arrangement of high pressure pumps, energy recovery devices and membrane banks can be designed to allow operational independence and flexibility.

Table 6.2 Summary of the phasing of the Desalination Treatment Plant construction

PHASE 1 PHASE 2

Target year (start operation) 2016 2026

Start construction 2013 2025

Additional production capacity 200,000 m3/d 100,000 m3/d

Design raw water flow 476 430 m3/d 714 430 m3/d

Number of treatment streams 2 1

Flow of one treatment stream 238 215 m3/d 238 215 m3/d

6.3.3 Intakes and outfalls

Twin 1800mm diameter pipelines are needed to abstract seawater efficiently at maximum capacity (715Mld). The required pipeline length is 3km in order to provide a sufficient water depth – 20m – for the intake structures. A minimum elevation above seabed is needed for water quality purpose as well as a minimum depth below water level for navigation safety. Similarly, twin 1400mm diameter pipelines will enable the discharge of brine in an optimised manner at maximum flow rate (415Mld). In this case the pipeline length will only be 2km since brine dispersion modelling demonstrated that this would provide suitable dilution patterns for avoidance of sensitive coastal areas (see modelling results Section 8) The engineering works involved in the construction of these pipelines are complex and expensive. The construction methodology will be:

• tunnelling from the desalination plant

• sand dredging between tunnel exit and pipeline extremities (seawater intakes / brine outfalls)


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Hydraulic calculations indicate that pipelines will have to remain at least 7m below the spring low tide level in order to provide a suitable hydraulic profile for head losses. Therefore, from the desalination plant sump the pipelines will be tunnelled to a point at least 7m below the minimum sea level. The anticipated length of such a tunnel is about 800m. Land intake pit must be lower than spring low tide level plus 7m. With the site elevation of 13mOD that means a sump depth of approx 20m. Excavation assessed for the intake would be 20 m deep and 18mX10m for the area of the sump. The intakes and outfalls will be laid through a single tunnel from the plant site. From the tunnel’s exit, pipelines will be dredged into sand with a minimum cover of 1.6m. Abstraction and discharge pipelines will be dredged in separate trenches from the tunnel in Easterly and South-Easterly directions for the outfalls and intakes, respectively.

6.3.4 Pre-treatment The aim of the pre-treatment is to reduce the SDI of the water to a value less than 3.0, in order to control the life span of the membrane and the operation costs of the reverse osmosis step. Moreover, most of the membranes found on the market are under guarantee for a SDI less than 3.0 or 3.5.

Good performance of the pre-treatment stage is essential in a RO desalination plant to ensure the correct operation of the desalination stage. The RO pre-treatment performance is driven by four main parameters: Total Suspended Solids (TSS), Turbidity, SDI, oil and grease content.

Several pre-treatment technologies have been proven to be high-performance (from pilot tests on different types of water to full scale operational experience) in reducing SDI, depending on the initial value and the general content of the water:

• Direct dual media filtration (one or two stages of filtration)

• Clarification followed by dual media filtration (one or two stages) for high TSS and algae contents.

• Direct micro/ultra filtration

• Clarification followed by micro/ultra filtration for high TSS contents.

The direct dual media filtration is much cheaper in terms of investment and simpler to operate; but is possible only when the quality of the raw water is very good: low SDI; low turbidity and low algae content. Table 6.3 shows the raw water quality limitations for direct dual media filtration.

Table 6.3 Limitations on raw water quality which permit direct filtration

Turbidity (NTU)

Colour (Pt/Co)

Algae (nb/ml)

SS (mg/L)

SDI

Raw water quality limit < 25 < 40 < 2000 <100 <15

Quality objective of filtered water

<0.2 <5 Absence Absence <3


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The algae content and the SDI of Irish water may exceed these limits, according to raw water samplings performed, and direct media filtration will not be sufficient to reduce SDI to the required value upstream membranes. Water quality tests carried out in August and October 2007 recorded SDI’s ranging from 16.8 to 30.0 (average 20) which exceeds limitation figures according to data in table 6.3. Moreover, algae events can lead to high operation costs (increase of filters backwash) and operation difficulties. As the source water is therefore deemed to have a high fouling potential in relation to the membranes a clarification step will be necessary.

For the same reason, direct micro/ultra filtration is not advised on this raw water quality (algae content can result in operation difficulties because of high clogging potential). A clarification step would also be necessary making this pre-treatment option quite expensive compared to the others.

In the case of north Fingal, the raw water has high levels of particles and algae which requires clarification followed by dual media filtration for SDI control and satisfactory operation of the plant.

Contrary to conventional sedimentation, dissolved air floatation (DAF) has shown very good performances on sea water with high algal content. In addition, it allows compact installation. Hence, this technology will be selected as the clarification process.

Open gravity filters will be implemented for the dual media filtration step, as pressure filters are limited in size.

Hence: TSS and turbidity will be removed by coagulation/flocculation/floatation (expected efficiency is 85 % with raw water TSS content) and the residual will be treated by dual media filtration. Algae will be removed by the DAF (expected efficiency is 99%). SDI (indicative for the fouling potential of the water) is the most important parameter, pilot plant trials have shown that coagulation/ flocculation / floatation / Dual Media Filtration were satisfactory with substantial high raw water SDI values (20 to 40 % per minute).

The coagulation step is an important step of the pre-treatment, especially the type of chemical used. Three types of chemical are widely used as coagulant: aluminium sulphate, poly-aluminium-chloride (PAC) and iron salts (ferric chloride and ferrous sulphate).

Aluminium based coagulant are not advised in case of reverse osmosis downstream coagulation. This type of chemical can damage membranes and lead to irreversible fouling. Iron salts are preferable in case of reverse osmosis desalination.

The use of ferric salt presents also the advantage of producing sludge less harmful for the environment than the aluminium salt. Iron is a very common element in the nature, without any health hazard or environmental effect. For this reason ferric chloride will be used for coagulation.

6.3.4.1 Shock Chlorination

Chlorine is injected upstream the seawater pumps in order to control sea shell growth and sea flora. Shock chlorination is performed at the intake.

The chlorine is injected as a sodium hypochlorite solution. The sodium hypochlorite is delivered on site in liquid form. The design criteria of the shock chlorination step are as follows:

• Chlorine dose: 7 mg/l (as Cl pure)

• Frequency: 2 h / day


MDW0158RP0080F01 85 F01

6.3.4.2 pH Adjustment

The pH is adjusted in order to improve the coagulation. The optimum coagulation pH range with ferric chloride is around 7.

Depending on the sea water pH, addition of coagulant alone can be sufficient to drop the coagulation pH in the proper pH range. However, at certain times it is necessary to use acid.

Sulphuric acid (a 96 % solution) is injected in an in line static mixer to reach the pH set value.

Based on the sea water analysis, the dosing rate varies between 20 mg/L and 30 mg/L of 96 % sulphuric acid liquid.

6.3.4.3 Coagulation – Flocculation

The chemical shall be injected directly in the sea water pipe or in the coagulation tank. A pH-meter is installed in the coagulation tank to measure the pH of the water thus the operator is able to adjust it according to the results of the Jar test.

At that level of the treatment chain, a flash mixing is required to quickly scatter the coagulant in the bulk of water. This mixing can be achieve in line with a static mixer, or in a specific tank; this latter solution being more efficient.

The design criteria of the flash mixing step are as follows:

• contact time : 1 minute

• coagulant : FeCl3 (ferric chloride)

• dosing rate : from 20 mg/L to 35 mg/L,

• type of mixer : vertical mixer, with blades specially designed for coagulation

• Velocity gradient : 300 s-1 (G =(W/(µV))0,5)

� G is the velocity gradient

� W is the dissipated energy in the fluid

� µ is the dynamic viscosity

V is the volume of the fluid, that is, the volume of the tank. Provision must be taken in the design of the coagulation tank to avoid bulk rotation of the water, and insure that all the mixing energy is dissipated under low scale turbulences. This criterion is achieved by square shaped tank.

Dimensions of the coagulation units of one treatment stream of phase 1:

• Number of coagulation tanks 5


MDW0158RP0080F01 86 F01

• Contact time 1 minute

• Total volume 165.5 m3

• Sizing of one tank

� Unit volume: 33,1 m3

� Length: 3 m

� Width: 3 m

� Water depth: 3,7 m

� Dissipated power: 1 950 W

� Velocity gradient: 309 s-1

After coagulation, which creates the seeds of the aggregates, the aim of “flocculation” is to increase the probability of contact between the particles. Anionic polymers may be injected in the flocculation tank in order to increase the size and the density of the “floc” which will consequently settle faster and better. Slow mixing will help this physical reaction to succeed.

The design criteria are as follows:

• contact time : 10 to 15 minutes

• flocculant : anionic polymers

• type of mixer : propeller agitator

• Velocity gradient: 30 s-1

• The flocs are fragile; it is very important to avoid any turbulent area between the flocculation tank and the settlers, which would break them and reduce the efficiency of the gravity settling.

Sizing of the flocculation units of one treatment stream:

• Number of flocculation tanks: 10

• Contact time: 10 minutes

• Total volume: 1654,5 m3


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• Dimension of one tank


� Length: 6 m

� Width: 6 m

� Water depth: 4,5 m

� Type of mixer: propeller agitator

� Dissipated power: 580 W

� Velocity gradient: 41 s-1

The bottom of the flocculation tank shall have a 7 % slope for easier sludge evacuation.

6.3.4.4 Floatation

Dissolved Air Floatation (DAF) is a solid-liquid separation process that transfers solids to the liquid surface through attachment of fine air bubbles to solid particles. The phenomenon of DAF consists of three processes:

• Bubble generation;

• Attachment of solids to the bubbles,

• Solids separation.

Indirect floatation will be implemented after coagulation-flocculation. It means that a part of floated water will be recycled and air will be dissolved in this water prior to be suddenly depressurized, and blended with the inlet water.


MDW0158RP0080F01 88 F01

Figure 6.3 View of a Dissolved Air Flotation Unit (DAF) for the solid-liquid separation process

The floatation step will then consists of the following items:

• Mixing tank: mixing of water containing the dissolved air and raw water to be treated

• Floatation tank: separation tank

• Recirculation pumps: for recirculation of 10 % of floated water

• Pressurisation vessel: one for each floatation tank

• Diffuser

• Pipelines for recirculation and air injection

Ten (10) parallel flotation systems will be implemented for each treatment stream.

Sizing of the mixing tanks:

• Number of the mixing tanks: 10

• Contact time: 1.3 minutes


MDW0158RP0080F01 89 F01


� Unit volume: 37.8 m3

� Length: 6 m

� Width: 1.4 m

� Water depth: 4.5 m

Sizing of the floatation tanks:

• Number of mixing tanks: 10

• Contact time: 10 minutes


� Unit volume: 162 m3

� Length: 6 m

� Width: 6 m

� Water depth: 4.5 m

Table 6.4 Sizing and phasing of the DAF tanks

Units Value phase 1 Value phase 2

Total feed water flow rate m3/h 19,851 9925.1

Mirror speed m/h 27 27

Number of flotation system per stream

U 10 10

Recirculation pumps

Number

Unit capacity

Pressure

U

m3/h

bar

22 (2 on stand-by)

107

6

11 (1 on stand-by)

107

6


MDW0158RP0080F01 90 F01

Pressurisation vessels

Number

Unit capacity

Diameter

Height

Unit flow

U

m3

m

m

m3/h

20

1.5

0.95

1.6

107

10

1.5

0.95

1.6

107

Diffusers

Number

Unit flow rate

U

m3/h

1200

1.77

600

1.77

The final floated water will then be collected in a first channel (each floatation tank having its own channel) and the total floated water of one stream will be collected in a second channel leading to filters.

6.3.4.5 Dual Media Filtration

Filtration is performed in open gravity dual media (pumice and sand) filters supplied with a constant flow of floated water and constant water level above the filter: it is an upstream control system with a downstream compensation.

Such a filtration control is provided by a valve fitted with an electro-pneumatic activator with pressure sensor on the upstream water level.

A butterfly valve opens and closes depending on the water levels upstream and downstream. Relative level sensors (pressure sensor type) modulate the opening and the closing of the valve: the downstream sensor is only active when the upstream water level is between the upper and the lower thresholds.

The total head loss between the inlet of the filter and its outlet is always equal to 2.4 m WC.

It is the sum of the head loss in the filter and the head loss of the water level monitoring valve.


MDW0158RP0080F01 91 F01

Table 6.5 Sizing of the Dual Media Filtration Units

The settled water is collected in a channel and flows into the filters through penstocks.

Backwash of the filters:

The backwash is performed with air and water. The characteristics of backwash equipments are given in table 6.6 below.

Item Value – phase 1 (2 streams)

Number of filters (n) per stream

10 (operating 24hours a day)

Type of filters Vertical gravity dual media filters

Length of the filter 16 m

Width of the filter 5.8 m

Filtration rate 11.9 m/h when 9 filters are operated – 10.7 m/h when 10

filters operate

Total filtration area 927.7 m2

Unit filtration area 92.8 m2

Filtration media Sand and Pumice

Media height Sand : 600 mm

Pumice : 600 mm

Grain size distribution Sand : effective size : 0.55 – 0.65 mm

Pumice : effective size : 1.2 – 2 mm

Gravel height (gravel layer under the sand layer)

100 mm

Nozzles Around 40 nozzles / m2


MDW0158RP0080F01 92 F01

Table 6.6 Characteristics of the Backwash Equipment

AIR BACKWASH

Number of compressors per stream of 100 MLD

2 compressors (1 in operation + 1 in stand by)

Unit Flow 4640 m3/h (50 m3/h/m2 of filter area)

Manometric delivery head 0,5 bar

Air pipe diameter 400 mm

WATER BACKWASH

Number of pumps per stream of 100 MLD

3 pumps (2 in operation + 1 in stand by)

Unit flow 1624 m3/h each (35 m3/h/m2 of filter area with 2

pumps)

Manometric delivery head 10 m

Water pipes diameter 600 mm

A daily air and water cleaning of the filters will be carried out and the filters will be equipped with a “slow start” device.

Backwash of the filters will be operated as follows as shown in the following table.

Table 6.7 Operation sequence for backwash of filters

Sequence Type Flow (m/h) Duration (minute)

1) Air Air 50 1

2) Air + Water

Air

Water

50

10

10

3) Water Water 35 10

Note: 6 m3 of water per m

2 of filter is required (557 m

3 for one filter backwash)


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The filtered water will be stored in a tank built under the filters. The volume of the tank is designed for a storage capacity of 3 filter back wash (for each filter): 16,710 m3. 6.3.5 Reverse Osmosis The membrane to be used in the RO treatment process shall have high water permeability and a high degree of semi-permeability, that is, the rate of water transport shall be higher than the rate of transport of dissolved ions. The material shall be resistant to a wide range of pH and temperature and have good mechanical integrity (to stand up the high operating pressures).

The membrane performances shall also be stable over the time concerning the permeability, the salt and boron rejection. Permeability is an important parameter because it highly impacts the energy consumption of the whole process. Lots of advances have been made on commercial membrane concerning this parameter, leading to important energy saving. Optimum value has been reached by the suppliers now. However, changes in stability of permeability and other performances can be noticed between the membranes proposed on the market. Despite good performances of some membranes at the beginning of their life, it can decrease significantly over the time, leading to higher energy consumption at the end of the membrane life.

Two major materials are used for reverse osmosis: cellulose acetate and polyamide. Cellulose acetate is not used for potable water application, because the operating pH range of this type of membrane which is quite narrow (6-8) and leads to cleaning difficulties. That is why the desalination market is dominated by the composite polyamide membranes.

The membrane can be set into different configurations: plate and frame, hollow fibre and spiral wounded configuration. Plate and frame have been abandoned in favour of higher packing density spiral wound and hollow fibre configuration. Hollow fibre required good feed water quality (low TDS content) and is often used for the treatment of brackish water.

As the seawater at Loughshinny is highly charged with TDS composite polyamide membranes in a spiral wound configuration shall be required for the Dublin desalination plant.

Figure 6.4 Constituent parts of a spiral wound module used in Reverse Osmosis treatment process

The construction of a spiral wound module consists of winding several flat sheets around a perforated product tube. The sheets consist of the membrane, the permeate spacer and the feed channel spacer.

The permeate spacer is placed between two membrane sheets and drains permeate to the perforated product tube. The feed channel spacer is place between the membranes and the permeate spacer


MDW0158RP0080F01 94 F01

sheet and is used to enhance mixing of the feed solution. Typical industrial modules are 203 mm in diameter and 1,016 mm long. The modules are placed in pressure vessel, one pressure vessel containing 8 membrane modules in series.

6.3.5.1 Cartridge filters

The pre-treated water shall be filtered through cartridge filters as “last security” before RO, to protect membrane from colloidal fouling. Each filter contains a number of polypropylene wound cartridges, with a nominal cut-off of 5 µm.

Figure 6.5 View of cartridge filters used to protect membranes from colloidal fouling

The cartridge filters are located in the RO building. A hoist and monorail will enable the removal of the cartridge basket (which holds the cartridges) from the vessels for replacement.

Booster pumps will transfer the floated water to the cartridge filters. Antiscalant and sodium bisulphite will be injected in the pipe upstream pumps. This chemical treatment is aimed at:

• controlling scaling agents

• removing the chlorine residual for membrane protection


MDW0158RP0080F01 95 F01

Booster pumps features

Table 6.8 Sizing and phasing of booster pump equipment


Total filtered water flow rate m3/h 18 341 9171

Number of pumps u 8+2 on stand-by 4+1 on stand-by

Type Centrifugal – 1 stage Centrifugal – 1 stage

Unit flow rate m3/h 2357 2357

HP discharge pressure bar 3 to 10 3 to 10

High pressure pump operation variable speed

Hydraulic efficiency 87%

Then the cartridge can be isolated by valves located upstream and downstream.

Table 6.9 Sizing and phasing cartridge filter equipment


Total floated water flow rate m3/h 18,342 9,171

Number of filter trains u 20 (18 on duty, 2 on

stand-by) 10 (9 on duty, 1 on

stand-by)

Nominal feed flow / filter train m3/h 1019 1019

Cartridge filter type Polypropylene Polypropylene

Cartridge filter cut-off µm 5 5

Number of cartridge per train u 230 230

Pressure drop bar 1.5 1.5

6.3.5.2 RO Characteristics

The RO plant will have to be composed of 2 passes in order to meet the European Standard for Boron (concentration in treated water shall be less than 1mg/l).

Removal of Boron requires 2 steps: Boron and TDS cannot be removed by the RO in the same chemical conditions: TDS rejection is optimised at low pH (around 7) whereas boron rejection is maximum at pH around 9-10 depending on the type of membrane.


MDW0158RP0080F01 96 F01

The RO system will be composed of 14 trains (1 train on stand-by per stream) for phase 1 and 7 trains (1 train on stand-by) for phase 2. A train is composed of a skid mounted on a steel frame rack and is arranged with headers for feed water, brine and permeate.

The RO plant will consist of:

• A first pass: one stage of pressure vessels in parallel with an average conversion rate of 45%. 6 trains are needed to produce the required permeate flow, and one train will be installed as stand by for each stream of 100 MLD (to keep the nominal capacity of the plant during membrane cleaning).

• A second pass: three stages of pressure vessels in parallel with an average conversion rate of 90%. 3 trains are necessary to meet the boron standard and one train will be implemented as stand-by for each stream

The number of trains results from an optimisation between investment costs and operational flexibility of the RO system (considering among other factors membrane replacement, cleaning etc). Each stream shall be easily operated to produce half of its capacity (i.e 50,000 m3/d).

The energy contained in the brine of the first RO pass will be recovered by a work exchanger. This type of energy recovery device is the most efficient today, with efficiency up to 96%.

The pressurization system and the energy recovery device will be composed of

• High pressure pumps: nominal flow equal to permeate flow (45% of the inlet flow)

• Work exchanger: a flow equal to the brine flow of the first pass will directly go through work exchangers then through booster pumps to be set at the required pressure.

The RO system is designed using calculation software supplied by membrane manufacturers to simulate the performances of a chosen configuration. Both major membrane suppliers Dow and Hydranautics supply this kind of software. Both were used to test several configurations. The following tables present an optimum configuration with membranes currently available on the market.

The calculations have been made considering the average age of membranes. This average is a function of the chosen replacement rate (each membrane is replaced every 5 to 7 years). Ageing of the membrane is introduced in the simulation data on the membrane calculation software.

The membrane module will be spiral wound polyamide membrane element type, designed not only for tolerance against high operating pressure but also for the best combination of salt and boron rejection capacity.


MDW0158RP0080F01 97 F01

1st pass

Table 6.10 Sizing and phasing requirements for 1st pass through membranes


Total filtered water flow rate m3/h 18,858.6 9,429.3

Number of trains u 14 (1 train on stand-by per stream)

7 (1 train en stand-by per stream)

Number of RO pressures vessels per train

u 160 160

Number of RO membranes per train

u 1536 (8 per pressure vessel)

1536 (8 per pressure vessel)

Type of membrane Low energy Surface water membrane (like SWC5 from hydranautics)

Low energy Surface water membrane (like SWC5 from hydranautics)

Nominal permeate flow per train

m3/h 606 to 707 606 to 707

Feed pressure Min/max at average membrane age (3 years)

bar 54.5-70 54.5-70

Expected permeate backpressure

bar 1 1

Flux l/m2/h 14.6 14.6

Permeate recovery % 45 45

Maximum permeate TDS mg/l 260 260

Permeate boron (min-max) mg/l 0.6-1 0.6-1

2nd pass: One third of the 1st pass permeate flow will be sent to a flushing tank and then further treated by the second pass. The other part of the permeate will be directly routed to the post treatment blending tank. The fraction of flow transferred from the 1st pass to the 2nd pass has been set to meet the boron standard in a worst case scenario (highest temperature), and to allow operating flexibility. The configuration of each treatment stream then permits the operation of each stream at the nominal capacity (i.e. 100 MLD) or half of the nominal capacity (i.e. 50 MLD).

A 1st pass permeate tank will collect the water before transfer to the 2nd pass and will also be used for membrane flushing (in case of stopping of a RO train). The volume of this tank will be equal to 400 m3 (feed of 1 train of 2nd pass for half an hour).

The pH of the second pass shall be set around 10 for Boron removal. Caustic soda will be injected at the suction head of the HP pumps for 2nd pass to reach this pH. Antiscalant will also be necessary for this pass.


MDW0158RP0080F01 98 F01

The 2nd pass will be composed of 3 stages as shown in the following table.

Table 6.11 Sizing and phasing requirements for 2nd pass through membranes


Total feed water flow for 2nd pass

m3/h 2828.8 1414.4

By pass % 66.66 66.66

Number of trains u 6 (1 train on stand-by

per stream) 3 (1 train on stand-

by)

Number of RO pressure vessels per train

u 70 70

Number of RO membranes per train

u 616 (8 per pressure

vessel) 616 (8 per pressure

vessel)

Type of membrane

Low energy brackish water membrane (like

ESPA2+ from hydranautics)

Low energy brackish water membrane (like ESPA2+ from hydranautics)

Feed pressure Min/max at average membrane age (3 years)

bar 13-18 13-18

Expected permeate backpressure

bar 1 1

Flux l/m2/h 23-34 (depending on

the stage) 23-34 (depending on

the stage)

Permeate recovery % 90 90

The feed required pressure for each pass will be reached thanks to high pressure pumps and work exchangers.

6.3.5.3 Pressurisation System and Energy Recovery Devices

Six (6) HP pumps will be provided for phase 1 (1 for 3 trains and 1 on stand-by per stream). They are fixed speed dry mounted horizontal pumps. The equivalent of the permeate flow will be pumped. The remainder will be routed to the energy recovery devices and then the booster pumps. Total feed flow for the 1st RO pass will be set at the required feed pressure (between 64 and 70 bars).


MDW0158RP0080F01 99 F01

HP pumps 1st pass

Table 6.12 Sizing and phasing of HP pump for 1st pass


Total feed flow m3/h 8,488 4,244

Number of High pressure pump

u 4+2 2+1

type Centrifugal – 4 stages Centrifugal – 4 stages

Unit flow rate m3/h 2,122 2,122

HP discharge pressure bar 60 60

High pressure pump operation Fixed speed

Hydraulic efficiency 88%

The expected pressure drop in membrane vessels is around 1 bar, the pressure of the brine will be high and will therefore be recovered. The most efficient devices currently available are work exchangers capable of achieving up to 96% hydraulic efficiency.

Energy recovery devices:

Table 6.13 Sizing and phasing of Energy Recovery Device


Total brine flow m3/h 10,372 5,186

Number of devices u 42 21

Type Work exchanger Work exchanger

Unit capacity m3/h 250 250

Efficiency % 96 96

Outlet pressure bar 52.3 to 67.2 52.3 to 67.2

A set of 3 work exchangers by RO train will be implemented.


MDW0158RP0080F01 100 F01

The energy recovery devices shall be assisted by booster pump to reach the required pressure for the 1st RO pass.

Booster pump 1st pass (downstream work exchanger)

Table 6.14 Sizing and phasing of booster pump 1st pass (downstream of work exchanger)


Total filtered water flow rate m3/h 10,372 5,186

Number of booster pump u 6 (2 on stand-by per

stream) 3 (1 on stand-by

Type centrifugal centrifugal

Unit flow rate m3/h 1,300 1,300

HP discharge pressure bar 2.8 2.8

High pressure pump operation Fixed speed

Hydraulic efficiency % 86

The first pass intermediate tank will collect 33% of the 1st pass permeate flow prior to be pumped by the HP pumps of the 2nd RO pass and then be routed to the RO trains (for Boron removal). This tank will also be used for membrane flushing (see section 6.3.5.4).

HP pumps 2nd pass:

Table 6.15 Sizing and phasing of HP pump for 2nd pass


Total filtered water flow rate m3/h 2,830 1,415

Number of High pressure pump u 6 (2 on stand-by) 3 (1 on stand-by)

Type centrifugal centrifugal

Unit flow rate m3/h 708 708

HP discharge pressure bar 12-18 12-18

High pressure pump operation Variable Speed Drive

Hydraulic efficiency 86


MDW0158RP0080F01 101 F01

6.3.5.4 Cleaning and Flushing System

Each time a RO train shuts down, it will be necessary to flush the seawater out of the membranes with low TDS water (permeate of 1st pass will be used). A flushing system will be provided for this purpose: pumps will be connected to the 1st pass intermediate permeate tank to feed the RO train when necessary.

Table 6.16 Phasing requirements of flushing pump capacity and pump head


Flushing pump capacity m3/h 780 780

Flushing pump head bar 4 4

During normal operation the membranes can accumulate minerals over time as well as organic or biological matter and colloidal particles on their surface. This causes a loss of efficiency manifesting as an increase of feed pressure or a decrease of permeate flow or an increase of salt passage (decline of permeate quality). Thus it is necessary to undertake cleaning of the membrane periodically (average of 3-4 times a year) to return to the basic functioning parameters.

The cleaning system includes pumps, permanent pipelines and valves and consists of:

• One CIP (Cleaning In Place) tank with heater and mixer. It is used for the mixing of chemicals for membrane cleaning and receipt of the return flows during the membrane cleaning.

• A 5 µm cartridge filter system to remove any solid contaminants or scale, which is removed from the vessels.

• 1 cleaning pump (+ 1 on stand-by) to recirculate the cleaning chemicals through the reverse osmosis membranes the cleaning cartridge filters

• Cleaning network and cleaning recirculation loop.

• The chemicals used for the cleaning are

• Citric acid – 30 minutes - 20 g/L

• Caustic soda – 30 minutes - 1g/L


MDW0158RP0080F01 102 F01

Table 6.17 CIP tank details for phases 1 and 2


CIP tank

Number

Capacity

u

m3

2

140

1

-

Cleaning flow per pressure vessel m3/h 10 10

Cleaning flow per train m3/h 1600 1600

Number of cleaning pump u 2 (1 duty + 1 stand-by) 2 (1 duty + 1 stand-by)

Unit capacity of cleaning pump m3/h 1600 1600

After any cleaning cycle, the membranes are flushed and the CIP chemicals are sent to the dirty backwash tank of dual media filters, to be neutralised by dilution prior to be routed to the sludge treatment plant.

Each skid will also have its individual storage tank at adequate elevation to provide gravity feed to membranes. During normal operation, the tank will be filled by permeate of the 1st pass and will be covered to prevent contamination.

6.3.6 Post Treatment The water filtered through reverse osmosis membranes will then need post-treatment: this entails setting at calco-carbonic equilibrium and disinfection to insure a stable, good water quality in the network.

Setting to calco-carbonic equilibrium

The water treated by reverse osmosis contains a high concentration of carbon dioxide with low mineralization. It requires post treatment (demineralisation) to meet the potable water quality standards in Ireland.

CO2 degassing followed by a neutralisation step are necessary,

Aeration can be performed using 3 technologies:

• Degassing tower

• Cascade: using several overflows. The number of overflows depends on the CO2

concentration.

• Bubbling: air injection. High air flow rate are necessary for good performances.

A degassing tower is the more efficient process for aeration and does not need a separate installation for air injection. Due to high CO2 concentrations anticipated in the permeate following reverse osmosis, degassing tower will be used for the post-treatment on this desalination plant.


MDW0158RP0080F01 103 F01

For final neutralisation after degassing, the following methods can be used:

• Addition of lime

• Filtration through calcite

• Addition of sodium carbonate

The action of Calcite filters is quite slow and its use requires large filters, which shall be implemented downstream of the chlorine contact tank and upstream of the final treated water tank to insure a good efficiency of chlorination (requiring low pH). This leads to larger tanks and more complicated construction. Lime is more suitable than sodium carbonate for water having low alkalinity (which will be the case at the outlet of this reverse osmosis plant), because it requires smaller dosage for the same results. That is why lime addition is proposed for this plant.

Figure 6.6 The water characteristics at the outlet of the RO plant and after post-treatment are as follows

Calco carbonic equilibriumeffect of post treatment

Messieurs HALLOPEAU DUBIN RAVARINI

U

Water after RO treatmentTAC = 4.5pH = 5.30pHs=10.3

After CO2 degassingTAC = 4.5pH = 6.30pHs=10.3

FINAL WATERAfter lime

neutralisationTAC = 11.2 pH = 8.42pHs=8,4

5

5,5

6

6,5

7

7,5

8

8,5

9

9,5

10

0,1 1 10 100

TAC [°F]

pH

outlet RO plant initial CO2

Saturation CaCO3 (4.00 °C) water after treatment

treatment final CO2

aeration

lime injection


MDW0158RP0080F01 104 F01

For CO2 stripping, the tower used will be as follows:

Table 6.18 Details of degassing towers for CO2 stripping phases 1 and 2


Number of towers U 12 6

Unit volume of each tower

Diameter

height

m3/h

m

m

58

3.5

6

58

3.5

6

Lime water will be prepared from solid lime in a saturator and injected in the final treated water tank.

A final disinfection will also be performed in the final storage tank. Disinfection is necessary to maintain disinfection residual in the network and control the water quality until its distribution to the consumer.

The chlorine dose shall be controlled by the measure of residual chlorine downstream stream of the contact tank. This residual free chlorine concentration shall not be less than 0.5 mg/L. Baffles will enable optimise the hydrodynamic of the reservoir and maximise the disinfection efficiency and chlorine dosage. Baffled rectangular tanks are the most effective disinfection tank. A weir will be installed at the end of the tank in order to insure a constant height in the tank and thereby control the contact time with chlorine.

Sizing of the post treatment blending tank (1 for each process stream):

• Contact time: 30 min:

• Chlorine dose: 2 mg/l (residual chlorine = 1 mg/l)

• Sizing of each tank


� Length: 30 m

� Width: 17 m

� Water depth: 4 m

Sizing of the final storage tank (3 compartments)

• Residence time: 1h30

• Unit volume: 6252 m3


MDW0158RP0080F01 105 F01

• Length: 53 m

• Width: 90 m

• Water depth: 4 m

• Overflow level (from the bottom): +4.1 m

Disinfection

Although the RO stage will totally remove the microorganism still present in the water, a final disinfection stage is necessary in order to insure the bacteriological quality of the water until the final consumer.

UV or ozone disinfection does not provide any residual downstream of the reactors, and therefore no persistent effect.

Chlorine is the most suitable chemical disinfection for the Dublin water production plant, because it provides a good persistent effect and shows very good disinfection performances.

Chlorination can be performed with:

• Pure chlorine: gaseous chlorine

• Chlorine dioxide

• Hypochlorite solution (sodium hypochlorite, calcium hypochlorite).

I. Commercial solution

II. On-site generation of the solution

Chlorine dioxide often leads to by-product formation in large quantities and generators of chlorine dioxide have a quite low efficiency and reliability.

Gaseous chlorine allows high disinfection efficiency, good persistence effect in the network and requires a smaller footprint when compared to sodium Hypochlorite disinfection. But due to the hazards related to its use, this technology is Moreno longer utilised in Ireland.

Therefore the use of Hypochlorite solution shall be selected. On-site generation of this solution is a complicated process. It requires a specific facility for the generation of hypochlorite solution from salt. Commercial Hypochlorite sodium will be used to simplify the overall operation of the plant.

Remark: the electrolysis of the brine resulting from the desalination, in order to produced sodium hypochlorite is not possible, as it generates bromates, and results in bromate concentrations in the treated water higher then the standards.


MDW0158RP0080F01 106 F01

6.3.7 Sludge Treatment

The sludge produced by the plant will not be chemically harmful to the environment. It is intended to treat the sludge produced by a sludge treatment process on site with ultimate disposal to a landfill site. It is not intended to dispose of the sludge directly to the sea. However, no particular landfill facility has been nominated to accept the treated sludge at this stage. If adequate facilities cannot be found then disposal directly to the sea will be considered. In Section 8.0 as part of the brine dispersion modelling exercise the impact of discharging the waste solids on the marine environment has been assessed.

The treatment of the sludge produced by the clarification step will be implemented; it will comprise the following elements:

• Equalizing tank: to receive the different rejections to treat (air floatation, filters cleaning)

• Sludge thickener: settling of the liquid sludge is performed in a tank and sludge is extracted at a higher concentration.

• Sludge dewatering: in order to reduce the sludge volume, another process is used to reach a minimal sludge dryness of 18%.

The excepted dryness of the sludge after dewatering is 18 % of dry solid, depending on the selected process.

Sludge from the DAF and backwash water from the filters will be processed as follows:

• Mixing tank, collecting the DAF sludge and filter backwash water

• Thickening

• Dewatering

Each process will be designed for the highest volume of produced sludge.

6.3.7.1 Sludge Production and Flow

It is calculated following this general equation.

W/V = SS rw + 0.07*Co + K*Rp + Rs + 1.92*Fe + 2.96*Mn + Ca

W sludge weight (g of dry solids / d)

V Daily volume of raw water treated (m3/d)

SS rw Suspended Solids concentration in raw water

Co Raw water colour (gPtCo/m3)


MDW0158RP0080F01 107 F01

Rp Main reagent dose (g/m3) with a precipitation coefficient (K)

Rs supplementary reagent dose (anionic polymer, PAC)

Fe iron concentration in raw water (g Fe / m3)

Mn manganese concentration in raw water (g Mn / m3)

Ca weight of precipitated calcium carbonate if decarbonation occurs

The table below summarizes the calculation hypotheses:

Table 6.19 Average and maximum concentration of parameters used in calculation of sludge production

Nature of the parameter Abbreviations Average

Concentration Maximal

Concentration

Suspended Solids in raw water SS rw 5 mg / L 15 mg / L

Raw water colour Co 50 g PtCo / m3 80 g PtCo / m3

Ferric chloride (FeCl3)

= coagulant Rp 20 mg / L 35 mg / L

Other chemicals (Polymer dose) Rs 0,1 mg/L 0,1 mg/L

Coefficient K 0.39 /g Fe(OH)3 0.39/g Fe(OH)3

Moreover, no treatment is used to remove iron and manganese, so the corresponding terms mentioned in the last equation are not taken into account.

Thus the daily amount of sludge produced can be estimated at:

• Average of 16.4 g of dry solid per cubic meter of sea water, corresponding to 7.8 TDS/d phase 1 and 11.7 TDS/day in phase 1&2

• Maximum of 34.35 g/m3 (2.1 times more) for one stream of 100 Mld, corresponding to 16.4 TDS/d phase 1 and 24.5 TDS/d phase 1&2

The sludge flow can be estimated at each point of the treatment stream. The following table sums up the design hypothesis used to assess these flows.


MDW0158RP0080F01 108 F01

Table 6.20 Assessment of sludge flows form each point of the treatment process

Parameter Unit Concentration

Proportion of the sludge coming from DAF % 85

Proportion of the sludge coming from filters % 15

Concentration of liquid sludge coming from DAF kg/m3 10

Concentration of liquid sludge coming from filters kg/m3 0.18

The maximum sludge flow coming from the DAF will be 695.5 m3/d for each treatment stream. And the maximum backwash water from the filters will be 6,819 m3/d.

The maximum production of sludge and the corresponding flow and TSS (Total Suspended Matter) concentration are summed up in the figure 6.7. Values are given for one stream of phase 1 and represent design values.

Figure 6.7 Summation of maximum production of sludge and the corresponding flow and TSS (Total Suspended Matter) concentration

DAF Filters

Backwash Water

Sludge

thickeners

Mixing Tank

V = 100 m3

DAF Sludge

6,96 T SS/d

695,5 m3/d

10 g/L

1,23 T SS/d

6 819 m3/d

0,18 g/L

8 045 T

SS/d

268,2 m3/d

Centrifuge

Storage tank

10,8 T SS/d

60 m3/d

180 g/L


MDW0158RP0080F01 109 F01

6.3.7.2 Mixing tank

It is not recommended to feed the sludge thickeners with flow variations. The role of the mixing tank is therefore to absorb the peak flows and to smooth the feed flow of the thickeners.

This tank will be mixed via submersible mixers to avoid sedimentation and homogenize the flow.

Raw sludge is removed by submersible pumps to feed the thickeners.

Table 6.21 Sizing and phasing details for mixing tank equipment

Mixing tank Unit Phase 1 Phase 2

Number of units U 2 (1 per stream) 1

Maximum sludge flow entering one mixing tank

m3/d 7 514.5 7 514.5

Mixing tank unit volume m3 100 100

Mixing tank dimensions:

Length

Width

Water level

m

m

m

8

3

4.2

8

3

4.2

Number of pumps U 2 (1 per stream) +

1 (stand by) 1

Capacity of pumps m3/h 313 313

6.3.7.3 Sludge thickeners

A static thickener allows reaching a concentration of sludge of 30 g/L. The design has been carried out considering the maximal sludge flow produced by one treatment stream.

The extraction of the sludge will be automatic.


MDW0158RP0080F01 110 F01

Table 6.22 Sizing and phasing details for sludge thickeners

Thickeners Unit Phase 1 Phase 2

Number of units U 2 (1 per train) 1

Nominal flow m3/d 7,514.5 m3/d for each

stream 7,514.5 m3/d

Nominal pass loading kg DS/d 8183 per stream 8183 per stream

Maximum mass loading kg TSS/m²/d 50 50

Height m 4 4

Diameter m 20 20

Hazen speed (maxi 1 m/h)

m/h 1 1

The concentration of the thickened sludge will be approximately 30 g/l corresponding to a maximum flow of 268.2 m3/d per stream.

Thickened sludge will then go through a dewatering process after the addition of polymer.

Each dewatering unit will be fed by one pump (total of 3 pumps on duty + 2 on stand by). The unit flow of the pumps will be 22.2 m3/h.

Supernatant (maximum 7246.3 m3/d per stream) water will be rejected to the dirty water tank. The TSS concentration in the supernatant will be less than 30 mg/L.

The slope and the space available on the selected site will allow routing of the supernatant water by gravity to the dirty water tank.

6.3.7.4 Sludge dewatering

One centrifuge for each stream will be installed and one on stand-by.

Polymer shall be added in order to improve the dewatering efficiency of centrifuges.


MDW0158RP0080F01 111 F01

Table 6.23 Sizing and phasing details for sludge dewatering equipment (centrifuges)

Centrifugation Unit Phase 1 Phase 2

Number of units u 3 (2+1) 1

Sludge concentration entering the unit g/l 30 30

Amount of sludge to be dewatered by each unit:

Average production

Maximum production

kg SS/day

kg SS/day

3,802.9

8,045.4

3,802.9

8,045.4

Nominal capacity of one unit kg/h 665 665

Time of running:

Average sludge production

Maximum sludge production

Hours/days

Days/week

Hours/days

Days/week

8

5

17

5

8

5

17

5

Concentration of dewatered sludge g/L 180 180

Max volume of produced sludge m3/week 600 300

Max weekly quantity of dewatered sludge T/week 108 54

A screw conveyor will be installed in order to transport the dewatered sludge into a sludge storage tank.

Each stream will be fitted with one storage tank, and dewatered sludge will be stored in this tank before its final disposal.

The capacity of the tank corresponds to the volume to be stored during 2 days (during one week-end at the maximum sludge production), which equates to 120 m3.

6.3.7.5 Dirty water tank

A tank will be used to collect the waste water produced on the plant:

• Thickeners supernatant,


MDW0158RP0080F01 112 F01

• Centrate from the centrifuges, and

• Waste water from membrane cleaning.

The brine will be routed directly to the sea.

The daily volume of the sludge thickeners supernatant will be 7,247 m3 for each stream (total volume of 21,741 m3/day).

The daily volume of centrate from the centrifuges will be 316 m3 (total volume of 948 m3).

The maximum daily volume of waste water from membrane cleaning will be 2400 m3 but only 6 to 8 cleaning cycles a month are expected to be necessary.

Then the dirty wash water tank will have the following size:

Volume: 3820 m3

Length: 40 m

Width: 24 m

Height of water: 4 m

The pH of the water will be measured in the outlet of the tank; then, depending on the pH, the water will be neutralised by injection of sulphuric acid or caustic soda before transfer to the discharge shaft. Membrane cleaning consists in a chemical cleaning using acid and soda, which may lead to a significant change of pH in the dirty water tank. The water disposed in the sea will then be charged with particles removed by the chemical cleaning which are all kind of particles initially present in the sea water, plus a little concentration of phosphates due to injection of antiscaling (around 300 µg/L).

6.3.8 Chemicals

6.3.8.1 Sulfuric Acid (H2SO4)

It is highly recommended to control the pH in order to improve the coagulation of organic matter. The optimum coagulation pH range for coagulation with ferric chloride is 6-7.

Moreover conducting coagulation in the pH window allows an optimisation of the dosage.

Depending on the raw water pH, addition of coagulant alone can be sufficient to drop the coagulation pH into the correct window. However, the sea water quality needs a pH adjustment to reach this window.

Sulphuric acid will be dosed directly into the coagulation tank. The dosage will depend on the sea water pH, the total alkalinity and the ferric chloride dose; it will be required to reach a pH of 7.


MDW0158RP0080F01 113 F01

Table 6.24 Sizing and phasing details for sulphuric acid dosing equipment

Units Value for phase 1 Value for phase 2

Chemical H2SO4 H2SO4

Role Adjustment of sea water pH Adjustment of sea water pH

Dosing location Static mixer upstream the coagulant tanks

Static mixer upstream the coagulant tanks

Delivery Liquid @96% H2SO4 W/W

Specific gravity 1.83

Liquid @96% H2SO4 W/W


Mean dosing rate

Max dosing rate

20 mg/L

30 mg/L

20mg/L

30 mg/L

Average Chemical flow for ONE stream

As 96% liquid for one coagulation tank

l/h 20.8 20.8

Max chemical flow for ONE stream

As liquid 96% for one coagulation tank

During high raw water pH

l/h 31.2 31.2

Number of dosing pump

Capacity

Type

Variable Speed Drive

u

l/h

10(on duty) + 3(stand by)

Between 20 and 32

Volumetric, diaphragm

YES

5(on duty) + 1(stand by)

Between 20 and 32


YES

Number of storage tank u 2 (1 by stream) 1

Storage capacity

At average dosage

At maximal dosage

m3

days

days

100

20

13.3

50

20

13.3


MDW0158RP0080F01 114 F01

Dosing plant:

The storage tank must be made of ordinary or stainless steel. It will be ventilated and protected against heat and sun.

The acid building will house:

A shower: in case of accidental leakage and contact with the skin

An eye-rinser in case of contact with eyes

Specific breathing device to protect people from inhalation of the product in case of accident

Caustic soda installed on the plant for another use will also be used to neutralise the product in case of leakage or spilling.

All the dosing pumps will be fitted with Variable Speed Drive.

6.3.8.2 Ferric Chloride FeCl3 (coagulant)

Ferric chloride (FeCl3) will be used as coagulant. It will be injected into the pipe upstream the static mixers. The dosage will be determined in accordance with the sea water quality and adjusted by daily laboratory tests (jar tests)

Ferric chloride is not sold pure (FeCl3-6H2O) and only 41% of the commercial product is ferric chloride. Its physical and chemical characteristics are detailed in the table below:

Table 6.25 Sizing and phasing details for ferric chloride dosing equipment

Units Value for phase 1 Value for phase 2

Chemical FeCl3-6H2O FeCl3-6H2O

Role Coagulation of sea water Coagulation of sea water

Optimal pH range pH Unit 6-7 6-7

Dosing location in line upstream the static

mixers in line upstream the static

mixers

Delivery Liquid @41% FeCl3 W/W


Liquid @41% FeCl3 W/W


Mean dosing rate mg/l 20 20

Max dosing rate mg/l 35 35


MDW0158RP0080F01 115 F01

Average chemical flow for ONE tank

As 41% liquid for one coagulation tank

l/h 68.7 68.7

Max chemical flow for ONE tank

As liquid 41% for one coagulation tank

l/h 120.2 120.2

Number of dosing pumps (for one stream)

u 5 (on duty) + 1 (stand by) 5 (on duty) + 2 (stand by)

Capacity l/h Between 68 and 121 Between 68 and 121

Type Volumetric, diaphragm Volumetric, diaphragm

Variable Speed Drive YES YES

TOTAL Number of storage tank

Unit capacity

u

m3

4 (2 by file)

60 m3

2

60

Storage capacity

At average dosage

At maximal dosage

m3

240

14.5

8.3

120

14.5

8.3

The storage tank must be made of ordinary or stainless steel. It will be ventilated and protected against heat and sun.

Dosing plant: each pump will be connected to one dosing point by a specific pipe. The pumps will be fitted with pulse dampeners and safety valves.

The ferric chloride storage room will house:

• A shower: in case of accidental leakage and contact with the skin

• An eye-rinser in case of contact with eyes

• ARI to protect people from inhalation of the product in case of accident


MDW0158RP0080F01 116 F01

A retention area will be installed adjacent to the plant. In the event of an incident (leak or accident during the discharge of the chemical from the truck to the tank), the chemicals shall not be delivered in the environment.

6.3.8.3 Polymer

Anionic polymer should be injected in the flocculation tank to favour contact between particles. (Sulfonate polystyrene could be used: AN910 from FLOEGER for example).

The dosing rates will be set between 0.05 and 0.1 mg/L. Polymer will above all be used during cold temperatures. Excess doses of polymer may result in a poor floatation and rapid clogging of the filters.

The concentration of the polymer solution will be set at 2 g/L. It is prepared in a packaged skid unit, comprising a dosing hopper and three successive stirred tanks for the proper maturation of the solution. The maturation time will be 1 hour. The polymer solution is prepared with non chlorinated filtrated water.

Polymer will also be used for the sludge treatment. Another stream will be installed to feed the sludge treatment plant.

Table 6.26 Sizing and phasing details for polymer dosing equipment

Units Value – phase 1 Value – phase 2

Chemical Sulfonate polystryren

AN 910 PWG

Sulfonate polystryren

AN 910 PWG

Role Flocculation of sea water Flocculation of sea water

Dosing location Flocculation chamber Flocculation chamber

Delivery Powder Powder

Dosing form solution@2g/L of active

product solution@2g/L of active

product

MAIN TREATMENT CHAIN

Dose rate as active product mg/l 0.05 to 0.1 0.05 to 0.1

Min solution flow @ 2g/L for one tank

l/h 24.8 24.8

Max solution flow @ 2g/L for one tank

l/h 49.6 49.6


Capacity

Type


u

l/h

20+5 (stand-by)

Between 24 and 50

Progressive Cavity Pump

YES

10+3(stand-by)

Between 24 and 50


YES


MDW0158RP0080F01 117 F01

SLUDGE DEWATERING

Dose rate as active product kg/t MS 6 6

Solution flow @ 3g/L for one work

l/h 1,331 1,331


Capacity

Type


u

l/h

2+1 (stand-by)

1,331


YES

1

1,331


YES

PREPARATION

Preparation type Fully automatic preparation unit (polypac type) with 3 compartments

Fully automatic preparation unit (polypac type) with 3 compartments

Number of preparation units for process

Unit capacity

u

l/h

4 (2 by line)

500

2

500

Number of preparation units for sludge treatment

Unit capacity

u

l/h

4 (2 by line)

1 330

2

1 330

Average consumption of product (for process and sludge treatment)

kg / week

168 168

Maximum consumption of product (for process and sludge treatment)

kg / week

356 356

Capacity of the commercial product bag

kg 112 112

Number of stored bags u 10 5

Storage capacity

At average dosage

At maximal dosage

days

days

23

11

23

11

Dosing plant:

The polymer solution will be injected by Progressive Cavity Pump dosing pumps. At the outlet of the pump, the solution will be diluted with non chlorinated water, in order to decrease its viscosity. The dosing pipes will be fitted with flushing points.


MDW0158RP0080F01 118 F01

Each pump will be connected to one dosing point by a specific pipe.


6.3.8.4 Antiscalant

The addition of antiscalant into the RO feed stream is typical for RO treatment system in order to control precipitation of soluble salts such as calcium carbonate (CaCO3), calcium sulphate (CaSO4), barium sulphate (BaSO4), strontium sulphate (SrCO4), calcium fluoride (CaF2) and Silica. Anstisaclant will be injected at the following points:

• Inlet of the 1st RO pass : upstream cartridge filters

• Inlet of 2nd RO pass: at the suction head of the HP pumps for the 2nd pass.

Antiscalant consists of synthetic polymer chain macromolecules that attach to the scaling crystals and prevent then from developing. It complies with environmental and potable water standards.

The use of antiscalant is anticipated and shall be used if and when required depending on the operational considerations of the plant.

Table 6.27 Sizing and phasing details for antiscalant dosing equipment


Chemical Proprietary antiscalant Proprietary antiscalant

Role Control of scaling Control of scaling

Dosing location

At the suction head of booster pumps (upstream cartridge filters) and of the HP pumps for 2nd RO pass.

At the suction head of booster pumps (upstream cartridge filters) and of the HP pumps for 2nd RO pass.

Delivery Liquid@100% W/W


Liquid@100% W/W


1st RO pass

Mean dosing rate

Max dosing rate

Average Chemical flow

Max chemical flow

Number of dosing pumps

Capacity

Type

mg/l

mg/l

l/h

l/h

u

l/h

1.5

2

34

45

2 (1 on stand-by)

34 to 45



1.5

2

34

45

2 (1 on stand-by)

34 to 45




MDW0158RP0080F01 119 F01

2nd RO pass

Mean dosing rate

Max dosing rate


Max chemical flow


Capacity

Type

mg/l

mg/l

l/h

l/h

u

l/h

2

3

3.5

5

4+1on stand-by

3.5 to 5



2

3

3.5

5

4+1on stand-by

3.5 to 5



Number of storage tank

Capacity

Autonomy

u

m3

days

2

80

20

2

80

20

6.3.8.5 Sodium Bisulphite

Due to shock chlorination performed at the inlet of the plant, water post-DAF treatment may contain a chlorine residual. RO membranes are not compatible with such chemicals as they are strong oxidizing agents. Sodium bisulphite shall then be injected upstream RO system during shock chlorination, for dechlorination.

Table 6.28 Sizing and phasing details for sodium bisulphite dosing equipment


Chemical NaHSO3 NaHSO3

Role Chlorine residual elimination Chlorine residual elimination

Dosing location Upstream cartridge filters. Upstream cartridge filters.

Delivery Liquid@30% W/W


Liquid@30% W/W


Mean dosing rate

Max dosing rate

mg/l

mg/l

4.5

9

4.5

9


Max chemical flow

l/h

l/h

100

210

100

210


MDW0158RP0080F01 120 F01


Capacity

Type

u

l/h

2 +2 (on stand-by)

100 to 210



1 +1 (on stand-by)

100 to 210




Capacity

Autonomy

u

m3

days

2

100

20

1

100

20

Dosing plant:

The containers will be made of plastic and will not be located close to acid storage (hazards concerning sulphur dioxide)


6.3.8.6 Caustic Soda

Caustic soda is added to increase the pH at the inlet of the 2nd RO pass and optimise the boron removal by the membrane. Membrane rejections are quite small at usual pH (around 7) and are optimum at pH 9-10. Caustic soda will be injected at the suction head of the RO pumps for 2nd pass. One dosing pump will be installed per HP pump.

Table 6.29 Sizing and phasing details for caustic soda dosing equipment


Chemical NaOH NaOH

Role Optimisation of boron

removal Optimisation of boron

removal

Dosing location At the suction head of HP pumps for 2nd RO pass.

At the suction head of HP pumps for 2nd RO pass.

Delivery Liquid@50% NaOH W/W


Liquid@50% NaOH W/W


Mean dosing rate

Max dosing rate

mg/l

mg/l

15

20

15

20


As 50% liquid for 1 RO train

l/h 14 14


MDW0158RP0080F01 121 F01

Max chemical flow

As 50% liquid for 1 RO train

l/h 19 19


Capacity

Type


u

l/h

4 (on duty) + 2 (stand by)

Between 14 and 19


YES

2 (on duty) + 1 (stand by)

Between 14 and 19


YES


Capacity

Autonomy

u

m3

days

2

20

15

3

20

15

The containers must be made of ordinary or stainless steel with an internal ebonite or epoxy covering.

The dosing plant will contain:

• A shower: in case of accidental leakage and contact with the skin

• An eye-rinser in case of contact with eyes

• Water will be used to neutralise the product in case of leakage before to wash the floor and drain off the waste water in the network.


6.3.8.7 Lime

A lime water system will be developed as a part of the post treatment process. It will be injected after CO2 degassing for neutralisation.

To avoid an increase of turbidity in the potable water, lime is injected as lime water rather than lime slurry. The lime water will be prepared by means of a saturator.

The lime preparation system includes 4 lines, each capable of 33% duty, containing the following major item of plant:

• Lime storage silo

• Lime mixing tanks

• Lime pumps

• Saturators and circulation pumps


MDW0158RP0080F01 122 F01

• Lime water tank

• Lime water dosing pump

A lamella saturator will be used, which is better for operation (classical saturators have proven to be labour intensive in their operation). A lamella saturator consists of:

• A mixing tank to dilute and dissolve the lime slurry in the water

• A lamella tank to allow the separation of the un-dissolved lime impurities from the lime water, with a maximum up flow velocity of 8 m/h

• A sludge collecting and recycling system (scrappers). The excess sludge will be routed to the dirty water tank were it will be diluted before discharge to the sea.

Pumps will transfer the lime slurry to the mixing tank of the saturator where it will be mixed with water and the recycled lime sludge prior to entering the settling tanks. The mixing is carried out by rapid mixers.

Lime process requirement

Table 6.30 Sizing and phasing details for the lime process equipment


Chemical Ca(OH)2 Ca(OH)2

Role Demineralisation of RO

permeates Demineralisation of RO

permeates

Mean dosing rate mg/l 40 to 50 40 to 50

Concentration % 95 95

Bulk density of lime kg/ m3 500 500

Quantity (max) kg/h 440 660

Tonnage (max) T/year 160 240

Lime silo

Number

Capacity

Autonomy

u

m3

days

2

100

12

3

100

12


MDW0158RP0080F01 123 F01

Saturators


Number of saturator 2 3

Unit surface 20 20

Diameter of saturator m 5 5

Up flow velocity m/h 8 8

Concentration of the lime water

g/l 1.4 1.4

Lime water flow

Average

Max

m3/h

m3/h

125

160

125

160

Mixing tank

Number

Volume

Residence time

u

m3

min

(number of saturator)

50

10

(number of saturator)

50

10

6.3.8.8 Sodium Hypochlorite (chlorine solution)

Shock chlorination and final treated water disinfection will be performed with sodium hypochlorite.

Shock chlorination will be performed each day during two hours at a treatment rate of 7 mg/L and final chlorination continuously at a treatment rate of 2 mg/L.

Table 6.31 Sizing and phasing details for sodium hypochlorite dosing equipment


Chemical Sodium Hypochlorite

12%

Sodium Hypochlorite

12%

Chock chlorination

Dosing location On line (upstream sea water

pumps) On line (upstream sea water

pumps)

Dose rate as active product mg/l 7 7

Frequency h/day 2 2


MDW0158RP0080F01 124 F01

Pumps

Number

Capacity

Type


u

l/h

2+1(stand-by)

400-500

Centrifugal

No

1+1 (stand-by)

400-500

Centrifugal

No

Final chlorination

Dosing location In the chlorine contact tank In the chlorine contact tank

Dose rate as active product mg/l 0.5 – 2.0 0.5 – 2.0

Frequency Continuous Continuous

Pumps

Number

Capacity

Type


u

l/h

2+1(stand-by)

10 - 25

Volumetric diaphragm pump

No

1+1 (stand-by)

10 -25

Volumetric diaphragm pump

No

Storage

Chlorine solution storage

Number

Storage volume

Concentration of chlorine

U

m3

g/l

2

2 x 80 m3

160

1

80 m3

160

Safety system: each room will be fitted with gas chlorine detectors and hydrogen detectors. In case of high hydrogen concentration in the air an alarm will be triggered and the ventilation system will start.

6.3.9 Automation and Controls

This section describes the plant process automation and the supervisory, control and data acquisition (SCADA) system.

6.3.9.1 General Principles

For safety and cost reasons, modern water treatment plants are generally fully automated. Thus, for the desalination plant, the level of automation will be defined by the following principles:

• The operation of the plant will not need to be manned 24 h per day; routine operation procedure (filters and membrane washing, settler desludging,) and all chemical dosing will be automatic.


MDW0158RP0080F01 125 F01

• In automatic mode, the plant will be run at fixed raw water flow, and start and stop according to level switches in the treated water reservoir.

• The change of nominal production will be set manually.

• The selection of the duty / stand by facilities will be manual.

• The main safety interlocks will trigger a remote alarm (via the INTERNET, or mobile phone); the plant will stop automatically in the case of a major trip or alarm; it will require operator intervention and resetting before starting again.

6.3.9.2 Description of the Main Automation Loops and Procedures

Chemical dosing:

• The frequency of the dosing pumps motor for each ferric chloride pump and polymer pump will be controlled by the raw water flow, according to a rate set by the operator, and corresponding to the expected dosing rate.

• The frequency of the sulphuric acid pumps motors will be controlled by the measure of pH in the coagulation tanks.

• The frequency of the sodium bisulphite pump motors will be controlled by the measure of chlorine in the floated water (post DAF).

• The frequency of caustic soda pumps motors will be controlled by the pH of the 1st pass permeate water.

• The flow of lime water will be controlled by the pH and pHs at the outlet of the degassing towers

• The frequency of the sodium hypochlorite pumps motors will be controlled by the residual free chlorine measure, at the outlet of the contact tank.

Filter control:

The upstream level on each filter will be controlled by a level gauge and an automatic control valve. The set point of the level will be chosen by the operators from the central control unit. Local control panels will not be required.

Filter backwashing: the backwashing sequence (opening and closing of the valves, start and stop of the pumps and blowers) will be preset. The backwashing of each filter will be triggered by temporization of high loss of pressure through the filter.


MDW0158RP0080F01 126 F01

Desludging of the settlers:

The desludging of each settler will be controlled by temporisation. The desludging sequence (opening and closing of the valves, duration of each phase) will be preset by the operator.

Main components of the whole automation system:

The plant automation system comprises:

• Data acquisition and treatment units (local control panel containing programmable logic controllers - PLC) for locally controlling plant processes. The main PLC (raw water station, coagulation, filtration, chemical station and chlorine plant) shall have redundant control panel units, human/machine interface (HMI) and power supply module. Process instrument are fed from this local control panels

• An interconnection with the various PLC and communication with the SCADA work station.

Plant supervision will be implemented.

The plant supervision and the control system (SCADA) will comprise:

• A work station for monitoring, controlling and supervising plant operation

• 2 data servers running in redundant configuration

• One data archive for data storage and retrieval

• PCs connected to the supervision work in order to access data and control manually some elements.

In addition each centrifuge will be controlled by a dedicated PLC.

The plant equipment can be operated from each of the three levels described above:

• Automatic control mode: operations are controlled at the local level independently and autonomously the dedicated section of the plant not requiring any input from the plant supervisory System. The supervisory level only stores performances data of this section.

• Manual control mode: Selected discrete sections of the plant will be operated manually in a local control or remote control mode (commands are entered locally or in the supervisory system).

Each pump will be controlled by motor starters or regulators (automatic) and the opening/closing of valves will be controlled manually.

The automatic control mode will rely on instruments located at many places of the plant. The next table 6.32 resumes the main instruments control to be placed on the plant.


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Table 6.32 Main control instrumentation to be installed at desalination plant

Instrument Type Location

Raw water intake

HP pumps

Work exchangers

Between contact tank and treated water pumping

Between sludge equalizing tank and thickeners (on each train)

Flow meters Electromagnetic

Downstream chlorine booster pumps

Upstream filters

Downstream filters

HP pumps

Booster pumps

Pressure sensors

Pressure exchangers

Coagulation tank

Floatation tank and floated water channels

Upstream level in each filter

Backwash water tank

Chlorine contact tank

Treated water tank

Level detectors Ultrasonic

Chemical storage tank (for each chemical)

Sludge blanket level detector

Ultrasonic In each thickener

Raw water

Downstream dual media filtration Temperature Analyser

Downstream final storage tank

Raw water

In each coagulation tank

Downstream dual media filtration

CIP flushing system

Inlet of 1st RO pass

Inlet of 2nd RO pass

Downstream degassing tower

pH Analyser

In chlorine contact tank


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Raw water

Downstream settlers

Downstream each filter Turbidity Analyser


Raw water

Downstream settlers

Downstream filters TOC Analyser


Inlet / Outlet of the 1st RO pass Conductivity Analyser

Inlet / Outlet of the 2nd RO pass

Redox potential Analyser Downstream cartridge filters

Raw water

Downstream cartridge filters SDI Analyser

Downstream dual media filtration

Downstream cartridge filters Free chlorine Analyser

Downstream chlorine tank and final storage tank

Other parameters will be manually controlled, by water sampling and analysis by the staff. Then any regulated parameters can be controlled downstream the final storage tank.


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7 SITE SELECTION

7.1 INTRODUCTION

The general site location for the desalination plant was selected following the evaluation of each proposed site locations in relation to a number of selection criteria:

• Land availability – Suitable sites for location of Desalination Treatment Works including an area of 10-15 hectares required at a coastal location with adequate access to the site.

• Water Quality requirements – a consistent water supply with little or no fluctuations in sediment and/or salinity capable of supplying 300Mld treated water. Suitable SDI also required.

• Suitable location for abstraction and raw water pumping station. The intake would necessitate the construction of a submerged sea intake 3km in length of RC buried pipeline 1800mm diameter. A land intake structure is required at a level lower than spring low tide level. Bathymetry to be assessed as the intake point to be at a depth of 20m.

• Suitable location for outfall pipework to take into consideration the requirement to disperse the effluent discharges associated with the desalination process, including coagulants, antiscalants and brine. The outfall discharge point to be located in a water depth of 15m at the site.

• Energy availability - Assuming the operation at the plant will be on an uninterrupted 24hr per day basis then the normal operating electrical demand would be in the region of 47.5 MW

• Feasibility of connection to the electrical supply grid: the estimated installed power capacity is 76.6MW – this is including treated water pumping and stand-by equipments

• Feasibility of connection to the water supply grid

• Compliance with topography / elevation considerations consistent with the overall design philosophy of minimising pumping energy and optimisation of operational criteria.

• Agriculture – number of landowners affected

• Residential properties and the approximate distance to nearest populated area

• Environmental considerations

• Avoidance of Major Natural Constraints – Mountains / Lakes / Forests / Bogs / Mineral Extraction Areas / Rock

• Avoidance or minimisation of impacts on:

− National Heritage Areas (NHA)

− Special Protection Areas (SPA)

− Special Areas of Conservation (SAC)

− Known Archaeological Sites

− Cultural Heritage Sites


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• Avoidance of:

− Existing Developments

− Planned Developments

− Motorways, High Voltage Electricity Pylons & Gas Transmission Pipelines

7.2 SITES CONSIDERED FOR DESALINATION OPTION

8 sites were considered for the location of a Desalination Plant:

1. South Dublin

2. Ringsend

3. Howth Headland

4. Ardgillan

5. Balbriggan

6. Gormanstown

7. Loughshinny South

8. Loughshinny North

See Appendix C for a map of the eight potential sites for desalination plant considered.

7.2.1 South Dublin

The South Dublin site being considered lies between Dalkey and the town of Bray. This area was deemed unsuitable due the following factors:

The availability of land in the area north of Bray is extremely limited. Water quality analyses of the Irish Sea were conducted and the results indicated that an extensive pre-treatment facility would be required at the desalination plant in order to treat both high levels of Boron (3-4mg/l B recorded, recommended concentration for RO membranes 1 mg/l B) and a high Silt Density Index (see Appendix B). The footprint of the required facility would therefore be in the region of 15 hectares.

In addition treated water from a desalination plant constructed at this location would require pumping to a storage reservoir accessible to the Dublin Region network. A transmission pipeline from the desalination plant to a termination point (yet to be constructed) would have to be routed over the Wicklow Mountains which would be technically complex, costly and would result in an unfavourable elevation profile.

7.2.2 Ringsend

A key requirement for the location of a desalination plant is the availability of a consistent water supply to avoid excessive replacement of the membranes and subsequently the production of poor quality potable water. The intake should be located in an area where the water supply is not subject to fluctuations in salinity and sediment. Due to the tidal nature of the waters in Dublin Bay a consistent water supply is by no means guaranteed. The intake should also be located in an area where there is little chance of pollution from land-based industries and ocean-going vessels. Considering the


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proximity of Ringsend to the busy shipping lanes accessing Dublin port the significant marine engineering involved in the construction of intake and discharge pipework from a facility in this area would be technically complex and costly. As with other sites, this site would also prove extremely complex from the viewpoint of integrating supplies into the existing network.

7.2.3 Howth Headland

The availability of land in the area of Howth headland is extremely limited. Because a site of 15 hectares would be required to facilitate the proposed treatment plant, this location does not compare favourably with the north Fingal site.

7.2.4 Ardgillan

The proposed site for Ardgillan is located between the towns of Balbriggan and Skerries north of the existing beach. Ardgillan was deemed an unsuitable location in terms of cultural heritage as any potential facility would be visible from Ardgillan Castle which is a site of historical significance situated on an area of elevated coastline.

7.2.5 Balbriggan & Gormanstown

The proposed site at Balbriggan lies on the headland immediately north of Balbriggan town and immediately south of a prehistoric complex (DU002-001) identified by the Record of Monuments and places, consisting of five passage tombs and a fulacht fiadh situated on Bremore Head.

The proposed site at Gormanstown is located directly north of the Delvin River and lies north of the same prehistoric complex (DU002-001). The National Monuments Section and the Underwater Archaeological Unit of the Department of Environment, Heritage and Local Government have been conducting additional archaeological surveys to assess the complex, with a view to increasing its protection level.

The complex is of considerable importance as the possible precursor to the Boyne Valley passage grave cemetery. The Delvin river enters the sea c.500m to the north of the tombs and beyond the mouth of the river is the passage tomb cemetery of Knocknagin in County Meath. The Bremore and Knocknagin cemeteries stand either side of this narrow route inland to the passage tomb at Fourknocks and the monuments on the Hill of Tara, Co.Meath. The area continued to be the focus of human activity and settlement in later periods. Bremore Head is the site of the 16th century Newhavan Harbour and the Cardy Rock Wrecks, while the ruins of a medieval tower house (DU002-00201) and St Molaga’s church (DU002-00202) and graveyard (DU002-00203) are located in the general vicinity of the proposed site.

As with rivers, the coastal landscape has always been a focus for human activity, with the sea providing a source of food and raw materials as well as a means of travel and communication and a place to build communities. In addition to the important burial sites at Bremore and Knocknagin / Gormanston, various archaeological investigations in Gormanston townland on the north side of the river have yielded further evidence of prehistoric activity. The remains of a prehistoric log boat were discovered off Gormanston Beach in 2002 during monitoring of the Irish Sub-Sea Interconnector Pipeline. This is the first such vessel to be identified and recovered from an active marine context in Ireland. A prehistoric pit burial is identified by the Record of Monuments and Places further north on Gormanston Beach (ME028-018). Monitoring for the AGI and Pipeline to the West for Bórd Gáis Éireann in Gormanston townland revealed a Bronze Age habitation site and a hearth site with struck flints.

In terms of archaeological heritage this area is considered to be highly unsuitable as the proposed location of an abstraction and desalination plant. Given the significance and proximity of the


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archaeological complex on Bremore Head, it is recommended that this location be removed as a desalination plant alternative.

In terms of water quality the location of the selected site at Gormanstown, directly north of the Delvin River is furthermore considered an unsuitable location due to its proximity to the beach and therefore the movement of sediment.

7.2.6 Loughshinny South & North

Two sites at Loughshinny (South & North) were identified as being suitable potential locations for the desalination plant (see Appendix C).

South Loughshinny

The potential site at South Loughshinny is in close proximity to Drumanagh headland which is an area associated with archaeological significance.

The site is also in close proximity to the UK gas interconnectors. Pressure reducing regulator skids are present North of Balbriggan and at Loughshinny with a major above Ground Installation present in Ballough to the South-west of this location. South Loughshinny was therefore deemed less suitable as there may be possible construction difficulties as a result of the gas infrastructure present.

North Loughshinny

This general area has a number of suitable sites for locating a desalination plant. Access is reasonably good and construction of intakes and outfalls are technically feasible. Energy is available either in the form of natural gas or a direct supply of electricity from the local grid to the facility could be made available. The proximity of Huntstown Power Station in Meath, currently under expansion, could provide alternative solutions.

7.3 CORRIDOR SELECTION FOR DESALINATION OPTION

A GIS based desktop study was carried out to delineate the proposed transmission route from desalination plant location at site C to termination point at Ballycoolin reservoir. In-house GIS datasets were used for constraint identification and all route options were mapped at 1:50,000 scale using the Ordnance Survey Ireland Discovery Series raster map.

7.3.1 Transmission Pipeline Route Selection

Transmission pipeline corridor was determined mainly by environmental and archaeological constraints and hydraulic requirement. The following is a list of constraints and considerations used in this study:

• Natural Heritage Area (NHAs)

• Special Protection Areas (SPAs)

• Special Areas of Conservation (SACs)

• Archaeological Sites. These were archaeological site locations enclosed by a buffer of 250m


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• Areas classified as Lakes, Forests, Bogs, Mineral Extraction Areas and Populated Areas. These were extracted from “Corine” Land Cover classification, with the minimum land unit of 25Ha.

• Areas designated for future development based on Fingal County Council Development plans, 2005 -2011

• Hydraulic profile - optimum vertical profile with a smooth vertical gradient minimising “depressions/elevations”. A 50m Digital Terrain Model (DTM) was used to create long sections and to refine vertical profile.

7.3.2 Route Selection Methodology

For the route process initiation and orientation purposes a straight line was selected and digitised between the proposed desalination plant and termination point. The length of this line was 24.0km. This route was neither environmentally nor technically feasible, as it passed through the identified constraints and resulted in an unfavourable vertical profile.

A refinement to the straight line involved:

• Avoiding the town of Swords by following its western perimeter

• Avoiding the village of Loughshinny, especially along the L1320 and L5405

• Reducing the maximum elevation from 45mOD to 40mOD at 200m chainage from the desalination plant which is maximum height allowed at such short distance from the desalination plant.

The above changes resulted in a 24.3km route representing the shortest distance between the proposed desalination plant location and termination point whilst avoiding the above constraints. The transmission pipeline will consist of twin 1100mm diameter pipelines laid in Phase 1.

An alternative route was also considered following the existing M1/M50 roads. This option was 29.6km in length. However this option was subsequently rejected due to:

• Potential conflict with existing utilities along the M1/M50

• Lack of space to accommodate Wayleaves

• Potential conflict with Fingal County Development plans

• Engineering issues – crossing at major junctions, traffic disruption during construction phase

• Increased length (this option is 5 km longer that Greenfiled options)


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8 BRINE DISPERSION MODELLING

8.1 INTRODUCTION As part of The Water Supply Project – Dublin Region RPS Consulting Engineers were commissioned to undertake the modelling of brine dispersion for Desalination Plant Study The modelling was undertaken using numerical modelling techniques to simulate the dispersion of effluent discharges associated with the desalination process, including coagulants and antiscalants along with the brine discharge. The outfall discharge point was located in a water depth of 15m at the site shown in Figure 8.1 below.

Figure 8.1 Extent of 45km grid domain showing outfall location

As the desalination process is to take place by the method of reverse osmosis the characteristics of the brine discharges are given in Table 8.1and Table 8.2 for the discharge without and with sludge dispersion respectively. For the purposes of the dispersion study the worst case scenario was modelled using the greatest pollutant concentrations at the highest discharge levels. An estimate of the cost was also made for the scheme.


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Table 8.1 Brine discharge characteristics without sludge dispersion

Volumetric Flow Rates Phase 1 Phase 2

Production capacity (Mld) 200 300

Intake : raw water flow (m3/d) 476,430 714,640

Outfall : reject stream flow (m3/d) 276,430 414,640

Salt/Pollutant Concentrations in Brine Discharge Lower Upper

SS mg/L <1 <1

Coagulant - Iron (FeCl3) mg/L 0 0

Antiscalant - Phosphonate (P205) µg/L 200 300

Salt concentration in Brine g/L 62 69

Table 8.2 Brine discharge characteristics with sludge dispersion

Volumetric Flow Rates Phase 1 Phase 2

Production capacity MLD 200 300

Intake : raw water flow m3/d 476,430 714,640

Outfall : reject stream flow m3/d 276,430 414,640

Salt/Pollutant Concentrations in Brine Discharge Lower Upper

SS mg/L 27 56

Coagulant - Iron (FeCl3) mg/L 33 57

Antiscalant - Phosphonate (P205) µg/L 200 300

Salt concentration in Brine g/L 62 69


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8.2 MODELLING SYSTEM

8.2.1 Tidal Model

The tidal flow simulations which formed the basis for the effluent dispersion simulations were undertaken using the MIKE21 HD and NHD flow model. The HD Module (MIKE21 HD) is the principal module in the MIKE21 package. It provides the hydrodynamic basis for the computations performed in the modules for Effluent Dispersion and Environmental Hydraulics.

The HD Module is a 2-dimensional, depth averaged hydrodynamic model which simulates the water level variations and flows in response to a variety of forcing functions in lakes, estuaries and coastal areas. The water levels and flows are resolved on a rectangular grid covering the area of interest when provided with the bathymetry, bed resistance coefficient, wind field, hydrodynamic boundary conditions, etc.

The system solves the full time-dependent non-linear equations of continuity and conservation of momentum. The solution is obtained using an implicit ADI finite difference scheme of second-order accuracy.

The effects and facilities include:

• Convective and cross momentum;

• Bottom shear stress;

• Wind shear stress at the surface;

• Barometric pressure gradients;

• Coriolis forces;

• Momentum dispersion (e.g. through the Smagorinsky formulation);

• Wave-induced currents;

• Sources and sinks (mass and momentum);

• Evaporation;

• Flooding and drying.

Facilities for focussing on specific areas within the computational domain through the use of transfer boundary data are included within MIKE21 HD.

The NHD Module is an extension to the standard HD Module, which has the capability to simulate consecutively finer nested grids which are dynamically linked together. The use of nested grids allows computationally efficient modelling to take place with the dynamic linking ensuring that there is the correct transfer of momentum across the patch boundaries and allows a larger region to be modelled using fewer cells.


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8.2.2 Effluent Dispersion Model

The modelling of brine dispersion was undertaken with a two stage process

1 Initial dilution simulations

2 Medium and far field dispersion simulations

The initial dilution studies examine the dispersion of the outfall outlet jets in the immediate area of the outfall diffuser. These simulations have been undertaken using the US EPA Visual Plumes programme which examines the flow of the outlet jets under the influence of density, temperature and velocity. The program ignores the eddy mixing within the water column and is therefore conservative.

The outfall was assumed to have 10 ports of 0.4m diameter at 10m centres and designed to jet the brine up into the water column. The brine will be denser than the surrounding seawater. Thus there will be a tendency for the brine plume to initially sink. However the eddying in the water column will mix the brine and seawater as the tidal currents flow across the outfall area.

The second stage in the dispersion modelling was to examine the dispersion in the medium and far field following initial dilution. This was carried out using the MIKE 321 NPA model. Both modelling approaches are described in more detail in the following sections.

8.2.2.1 Initial Dilution Model

The initial dilution of the brine at the proposed outfall was modelled using the US EPA “Plumes” software. The UM3 routine in the software was used for this study.

UM3 is an acronym for the three-dimensional Updated Merge (UM) model. UM3 simulates single and multi-port submerged discharges. UM3 is a Lagrangian model that assumes that the plume is in steady state. However, ambient and discharge conditions can change as long as they do so over time scales which are long compared to the time in which a discharged element reaches the end of the initial dilution phase.

To make UM three-dimensional, the model includes an entrainment term corresponding to the third-dimension: a cross-current term. As a result, single-port plumes are simulated as truly three-dimensional entities. Merged plumes are simulated by distributing the cross-current entrainment over all plumes. Dilution from diffusers oriented parallel to the current is estimated by limiting the effective spacing to correspond to a cross-diffuser flow angle of 20 degrees.

8.2.2.2 Medium and Far Dispersion Model for Brine Discharge

For the effluent dispersion simulations RPS Consulting Engineers used the MIKE321 PA model which describes the transport and fate of solutes or suspended matter and uses data from the hydrodynamic model to provide information on the general movement of the water body.

Within MIKE 321 PA the pollutant is considered as particles being advected with the surrounding water body and dispersed as a result of random processes in a 2-Dimensional or 3-Dimensional regime using the Lagrangian approach. Hence, the resolution of the plume is not restricted by the grid size of the current field.

The model can be used to determine the fate of suspended or dissolved matter that is discharged or accidentally spilled in lakes, estuaries, coastal areas or the open sea. The model simulates the effects


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of wind driven currents, including a mechanism for dealing with the overturning currents at the shoreline. The loss of active material from the water column through either settling or decay can also be included within the model simulations

Although the model uses data from 2-Dimensional depth averaged hydrodynamic flow models; the MIKE321 PA model can apply a logarithmic vertical velocity profile to provide a more accurate assessment of the displacement of particles located at different depths in the water column. This facility was employed in the dispersion simulations to provide a more realistic representation of the situation at full scale. The effluent dispersal was simulated over a period of one month, to include both spring and neap tidal conditions, using the logarithmic vertical velocity profile for the worst case discharge parameters.

8.3 TIDAL MODELLING SIMULATIONS

8.3.1 Irish Seas Model

The tidal flow in the vicinity of the proposed outfall was simulated via a series of sub-models driven by RPS Consulting Engineers’ Irish Sea Surge model, which was used to derive boundary data. The Irish Sea model itself stretches from the Northwestern end of France including the English Channel to Dover to 16° West into the Atlantic, including the Porcupine Bank and Rockall. In the south it reaches from the Northern part of the Bay of Biscay to just south of the Faroes Banks in the North. Overall the model covers the Northern Atlantic Ocean up to a distance of 600km from the Irish Coast as illustrated in Figure 8.2.

Figure 8.2 Extent of Irish Sea Tidal Surge Model


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The model was constructed using flexible mesh technology allowing the size of the computational cells to vary depending on user requirements. Along the Atlantic boundary the model features a mesh size of 13.125’ (24km). The Irish Atlantic coast has been discretised using cells of on average 3km size. In the Irish Sea, which is the area of greatest interest to this study, the maximum cell size is limited to 3.5 km decreasing to 200m along most of the Irish coastline.

The bathymetry was generated using a number of different sources. Large parts of the bathymetry information were obtained from digital charts supplied by C-MAP of Norway. Surveys of several banks and coastal areas have also been included covering in parts or all of

● Wexford and approaches ● Dublin Bay

● Blackwater bank ● Malahide

● Arklow bank ● Rogerstown

● Codling bank ● Greystones

● Carlingford Lough

Both survey data commissioned by RPS Consulting Engineers and the digital charts were quality checked by RPS engineers and compared with Admiralty data and known benchmarks. The datum of the bathymetry data was reduced to mean sea level using over 350 reference levels. A custom made routine interpolated mean sea level corrections for the relevant area and adjusted the bathymetry accordingly.

The simulation of the astronomic tides in the model area is mainly driven by the oscillation of water levels along the open boundaries. The Irish Sea tidal surge model has 6 open boundaries, 5 in the Atlantic and one in the English Channel. The time series of tidal elevation along these boundaries were generated using a global tidal model designed by a team at the Danish National Survey and Cadastre Department (KMS). The KMS global tidal model is based on the prediction of tidal elevations using 8 semidiurnal and diurnal tidal constants (as opposed to UKHO which uses 4-6 constants). These constants were derived through the simulation of the effect of astronomic forces due to the sun and moon on the water surfaces. The model output was further refined with the use of satellite derived altimetry data.

The Irish Seas model which was used to drive the desalination discharge model was verified using tidal diamond data, published on Admiralty Charts, at a number of locations across the domain.

8.3.2 The Desalination Discharge Model

The extent of the base model for the desalination discharge study included the Irish Sea and Saint George’s Channel, as illustrated in Figure 8.3, with a resolution of 405m. The boundary conditions at the northern and southern sides of the model were defined using the Irish Sea surge model. The bathymetry for the base and subsequent models was taken from the same sources as the Irish Sea surge model, as detailed in Section 3.1. A series of sub-models were developed from the base model in order to focus and refine the modelling area. The desalination modelling was undertaken on a 45m grid shown in Figure 8.3 by the black outline.


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Figure 8.3 Base model and detailed 45m model bathymetries

The model was used to simulate tidal flow patterns for a period of one month, to include both neap and spring tides. Typical tide patterns are presented in Figure 8.4 for the mid-ebb tide and Figure 8.5 for the mid-flood tide both during a spring tide.

Figure 8.4 Typical current speed mid-ebb spring tide


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Figure 8.5 Typical current speed mid-flood spring tide

8.4 DISPERSION MODEL SIMULATIONS

8.4.1 Effluent Inputs

The model was run for a period of one month with a constant discharge to ensure the full range of tidal conditions were experienced. Spring tides will give the largest extent of any plume while a neap tide produces a reduced plume area but it will be of a higher concentration.

The modelling took place for the ‘worst case’ scenario. The discharge of brine with sludge dispersion took place at the highest (Phase 2) discharge level. The upper limits of the salt and pollutant concentrations were used. Table 8.3 below details volumetric flow rates and concentrations used during the brine dispersion modelling.

Table 8.3 Dispersion modelling parameters used

Parameter Magnitude

Outfall Discharge (m3/d) 414,640

Suspended Sediment mg/l 56

Coagulant – Iron mg/l 57

Antiscalant – Phosphonate µg/l 300

Salt concentration g/l

(above background g/l)

69

(34)


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8.4.2 Dispersion Modelling

The hydrodynamics of the area were simulated using a two-dimensional model which produced a depth averaged velocity field at a resolution on 45m. However, the medium and far field dispersion modelling applied a logarithmic velocity profile to the hydrodynamic data to produce a dispersion field which varied across the water column, as it would in reality. Therefore three datasets were produced for each parameter modelled to illustrate the variation in dispersion through the water column and the impact on each of these zones.

These layers were:

• Surface layer of 5m thickness

• Central layer extending from 5m below the surface to a depth of 20m

• Seabed layer of thickness 1m

8.4.3 Dispersion Characteristics

Previous RPS Consulting Engineers experience of modelling and dye release studies in the Irish Sea showed that discharges become rapidly mixed through the water column and the primary source of horizontal advection is due to tidal currents. Therefore standard dispersion coefficients were derived for use within the model.

The dispersion coefficients used in the numerical model are a function of grid spacing, model time-step and flow conditions. In addition, the amount of dispersion is varied according to orientation with regards to the flow direction. A series of dye test within the Irish Sea indicate that the dispersion in the longitudinal flow direction is typically around three to four times that of the traverse direction. The vertical dispersion through the water column was found to be one tenth of the traverse direction dispersion. The coefficient relating to flow conditions was derived from a series of calibration tests documented by DHI. These flow conditions being a function of water depth, mean current speed, grid spacing and model time-step.

8.4.4 Dispersion Model Simulations

The dispersion modelling was carried out for four parameters namely suspended sediment, coagulant, antiscalant and the brine itself. In the case of the suspended sediment two models were used; firstly applying the assumption that the sediment remains in suspension and secondly modelling discharge with the inclusion of settlement.

The results are presented in the form of maximum and average plume envelopes. The maximum plume envelope displays (for each 45m cell) the largest concentration which is experienced during the simulation period in that cell. These plots therefore show the greatest impact that the discharge will have on the domain. However, these concentrations will not be experienced simultaneously and may only occur at that particular location for a short period of time. In order to asses the duration of the elevated concentration levels average plume envelopes are presented. These show the average concentrations in each cell over the course of the simulation. To aid visualisation typical plume excursion plots have been included for the suspended sediment results.

8.5 DISPERSION MODELLING RESULTS

8.5.1 Initial Dilution

The initial dilution modelling has been undertaken using a diffuser with 10 ports of 0.4m diameter and the flow characteristics given in Section 8.1. The diffuser ports were at 10m centres with the port exits discharging vertically. The UM3 model was run for the rms value of spring and neap flow conditions to simulate the initial dilution over the tidal cycle.


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The brine will initially sink down to the seabed due to the density of the brine solution. The initial trajectory will depend on the tidal velocity. The resulting trajectories for rms spring and rms neap tidal velocities are presented in Figure 8.6. The plume in red relates to the rms spring velocity of 0.368 m/s while the plume in blue relates to the rms neap tidal velocity of 0.2 m/s.

Figure 8.6 Brine plume dimensions per outlet

The brine will be diluted as the outlet jets spread out with distance from the outfall. Figure 8.7 shows the corresponding initial dilution for the two tidal velocities outlined previously. At 0.2 m/s tidal velocity the initial dilution will be x46 at about 10 m from the outfall which corresponds to a salinity of 35.8 g/l at the point where the plume reaches the seabed. At 0.386 m/s tidal velocity the initial dilution will be x115 at about 20 m from the outfall with a salinity of 35.3 g/l.

Figure 8.7 Initial dilution prediction


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8.5.2 Medium and Far Field Brine Dispersion

8.5.2.1 Suspended sediment Dispersion – Excluding settlement

Figure 8.8 Typical Suspended Sediment Plume Excursion over Tidal Cycle - Surface 5m layer


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Figure 8.9 Maximum Plume Envelope Suspended Sediment–Surface 5m layer (no settlement)

Figure 8.10 Average Plume Envelope Suspended Sediment – Surface 5m layer (no settlement)


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Figure 8.11 Maximum Plume Envelope Suspended Sediment – Central 15m layer (no settlement)

Figure 8.12 Average Plume Envelope Suspended Sediment – Central 15m layer (no settlement)


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Figure 8.13 Maximum Plume Envelope Suspended Sediment – Seabed 1m layer (no settlement)

Figure 8.14 Average Plume Envelope Suspended Sediment – Seabed 1m layer (no settlement)


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8.5.2.2 Suspended Sediment Dispersion – with settlement

Figure 8.15 Maximum Sediment Deposition

Figure 8.16 Average Sediment Deposition


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Figure 8.17 Maximum Plume Envelope Suspended Sediment – Surface 5m layer (settlement)

Figure 8.18 Average Plume Envelope Suspended Sediment – Surface 5m layer (settlement)


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Figure 8.19 Maximum Plume Envelope Suspended Sediment – Central 15m layer (settlement)

Figure 8.20 Average Plume Envelope Suspended Sediment – Central 15m layer (settlement)


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Figure 8.21 Maximum Plume Envelope Suspended Sediment – Seabed 1m layer (settlement)

Figure 8.22 Average Plume Envelope Suspended Sediment – Seabed 1m layer (settlement)


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8.5.2.3 Coagulant Dispersion

Figure 8.23 Maximum Plume Envelope Iron – Surface 5m layer

Figure 8.24 Average Plume Envelope Iron – Surface 5m layer


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Figure 8.25 Maximum Plume Envelope Iron – Central 15m layer

Figure 8.26 Average Plume Envelope Iron – Central 15m layer


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Figure 8.27 Maximum Plume Envelope Iron – Seabed 1m layer

Figure 8.28 Average Plume Envelope Iron – Seabed 1m layer


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8.5.2.4 Antiscalant dispersion

Figure 8.29 Maximum Plume Envelope Phosphonate – Surface 5m layer

Figure 8.30 Average Plume Envelope Phosphonate – Surface 5m layer


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Figure 8.31 Maximum Plume Envelope Phosphonate – Central 15m layer

Figure 8.32 Average Plume Envelope Phosphonate – Central 15m layer


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Figure 8.33 Maximum Plume Envelope Phosphonate – Seabed 1m layer

Figure 8.34 Average Plume Envelope Phosphonate – Seabed 1m layer


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8.5.2.5 Brine Dispersion

Figure 8.35 Maximum Plume Envelope Salt (above background) – Surface 5m layer

Figure 8.36 Average Plume Envelope Salt (above background) – Surface 5m layer


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Figure 8.37 Maximum Plume Envelope Salt (above background) – Central 15m layer

Figure 8.38 Average Plume Envelope Salt (above background) – Central 15m layer


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Figure 8.39 Maximum Plume Envelope Salt (above background) – Seabed 1m layer

Figure 8.40 Average Plume Envelope Salt (above background) – Seabed 1m layer


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8.6 DISCUSSION OF DISPERSION RESULTS

8.6.1 Initial Dilution

The initial dilution results show that with a the brine jetted up into the water column using the 10 port diffuser design outlined in this study, there will generally be sufficiently dilution of the brine before it sinks to the seabed to avoid a significant increase in salinity at the seabed around the outfall. Only for very short periods around slack water will the salinity increase locally above 37 g/l at the seabed.

8.6.2 Medium and Far Field Dispersion

Generally the plume excursion characteristics showed that dispersion levels in the region of the outfall were high due to the high current speeds in the vicinity; specifically around the Skerries to the north and to the south at Rogerstown Inlet. The plume excursion is shown in Figure 8.8.

Suspended sediment assuming no sedimentation shown in Figure 8.9 to Figure 8.14 illustrates that levels of sediment within the water column fall below a maximum of 1mg/l away from the immediate vicinity of the outfall. The EPA prescribes that the maximum allowable impact is a 30% rise in background levels. Although no specific sampling was undertaken for this study these limits are unlikely to have been exceeded in this case.

Sedimentation is included in the next series of results presented. Figure 8.15 and Figure 8.16 show the sedimentation levels experienced during the discharge cycle which in are in general very low. Sedimentation occurs to a depth of 1mm in the vicinity of the outfall during slack water. This material is re-suspended and dispersed as current speeds increase through the tidal cycle. This is demonstrated in the suspended sediment plots, Figure 8.17 to Figure 8.22, which show the greatest levels at the bed with a reduction towards the surface with the material being dispersed as it progresses through the water column.

The dispersion modelling of the coagulant (Figure 8.23 to Figure 8.28), the antiscalant (Figure 8.29 to Figure 8.34) and the brine discharge (Figure 8.35 to Figure 8.40) show the same discharge patterns. Smaller extents are exhibited at the bed as the pollutant is dispersed through the water column due to the logarithmic nature of the velocity profile. The maximum coagulant level is 3 mg/l outside the immediate vicinity of the discharge. This level is only experienced for a small part of the tidal cycle as the average value demonstrates – this is less than one sixth of the maximum value. The EPA limit on iron is 1 mg/l. A specific allowable level for the phosphonate used as an antiscalant is not prescribed by the EPA but the peak maximum values outside of the immediate area of the outfall are below 12 µg/l.

For brine discharge the allowable increase is limited to a 10% increase in background levels. With maximum values less than 1.5 g/l and a background of 35g/l, discharges are well within the acceptable levels.

8.7 COSTING

An estimate of costs for an intake and outfall to serve the possible desalination plant was made based on discussions with specialist marine contractors regarding present market factors. Given that detailed design parameters and site conditions were not known at this time the following assumptions were made. The intake would be twin 1800mm diameter pipelines of the order of 3km length constructed in a single tunnel which will also house the brine discharge pipework. The offshore end will be placed in 20m water depth (Lowest Astronomical Tide – LAT) with all construction except the intake structure to be buried below the seabed. The outfall would be approximately 2km in length constructed of twin


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1400mm diameter HPPE pipeline. The diffuser end would be located in a water depth of 15m at LAT with the outfall buried throughout its length. Scour/anchoring protection would be required around the diffusers. Seawater abstraction would be facilitated by the construction of a seawater pumping station to be installed in two phases to supply the desalination plant efficiently for the maximum demand of each phase – 477Mld (phase 1) and 715 Mld (phase 2).

The construction cost was estimated around €73.6M for abstraction and discharge pipelines. The civil engineering costs include mobilisation and demobilisation, temporary works, surveys, butt fusion and testing, intakes, diffusers etc. These costs are outlined in greater detail in Section 11 – Economic Assessment.

8.8 SUMMARY & CONCLUSIONS

The discharge of brine and pollutants associated with the operation of a desalination plant were modelled using numerical modelling techniques. The dispersion levels were high due to the tidal regime and high current speeds in the vicinity of the proposed discharge site.

The levels of suspended solids, iron and salt were found to be within acceptable levels outside of the immediate vicinity of the discharge site. Sedimentation levels resulting from the sludge dispersal were found to be very low. With very limited settlement occurring during slack water, which is subsequently re-suspended and dispersed as current speeds increase as the tidal cycle progresses.

An estimation of the cost of such a scheme was made (section 8.7). This cost assumes that ground conditions are reasonably favourable.


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9 ENERGY REQUIREMENTS

9.1 INTRODUCTION

Preliminary examination of the energy requirements and associated production of greenhouse gases has identified that desalination would have a considerable overall energy demand and high footprint during the operational phase of the project. The following is an outline of the anticipated operational energy demand of a desalination facility and the potential sources of energy available to fuel the technology.

9.2 ENERGY DEMAND OF DESALINATION TECHNOLOGIES

A report titled ‘Energy Consumption of Reverse Osmosis (RO) Plants’ (see Appendix D) was produced by Veolia as a part of the overall examination of the desalination technology options. Previous study has identified Reverse Osmosis as the most practicable option for desalination in Ireland. This was arrived at following a review of the various desalination technologies available (including those only at pilot stage) across a range of criteria including:

• Energy Demand

• Plant Availability

• Health and Safety

• Environmental Impact

• Maturity of technology

The two most relevant examples of RO technology in operation today are the Ashkelon Plant in Israel and the Perth Desalination plant in Australia. Both are among the largest currently in operation (Ashkelon at 320 Mld and Perth at 250Mld). The electrical demand of these plants ranges from 4.0 to 3.8 kWh per 1000 Litre (or m3) of treated water produced, with Ashkelon ranging from 4.0 to 3.9 dependent on salinity and Perth largely maintaining a 3.8kWh per 1000 Litre (or m3) demand. Extrapolated directly to the Dublin project this would see 300Mld per day produced at an average electrical demand of approximately 3.9 kWh per 1000 litres treated water, or 1,170MWh per day. An initial examination of local conditions with regard to salinity and turbidity (along with a trade-off between capital and operational costs in plant design) has been conducted and as a result a more defined estimate for the Dublin plant has been calculated as 3.77 kWh per 1000 litres treated water, accounting for seawater abstraction and reverse osmosis treatment (see Appendix D).

300 Mld at 3.8kWh per 1000 litres would see an overall daily demand of approximately 1140MWh per day. If an assumption is made that the operation at the plant will be on an uninterrupted 24hr per day basis then the normal operating electrical demand would be in the region of 47.5 MW. This would be comparable to the quantity of electricity supplied by a small power generation station.

9.3 EXISTING ENERGY AND PRIMARY FUEL SOURCES

As detailed in Section 7, the preferred location for the desalination plant and abstraction point is in North County Dublin. This was arrived at following an initial review of onshore topography, tidal regime and bathymetry of locations both North and South of Dublin City. Also investigated were energy availability, access and the ease of integrating water supplies into the Dublin Region network.


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9.3.1 Natural Gas

The north Fingal preferred location is straddled by the Ireland to UK gas interconnectors. Pressure reducing regulator skids are present North of Balbriggan and at Loughshinny with a major Above Ground Installation (AGI) present in Ballough to the South-west of the location. Generally speaking, there is a significant quantity of gas available in the area and the supply is robust, considering the proximity of both the interconnectors and the Ballough AGI connecting to the Gas Pipeline to the West, which in turn will connect to the Corrib Gas Field. With such a quantity of gas in the area it is likely that there would be sufficient Natural Gas available should on-site generation be considered for the desalination process. For a generation plant of this size however the connection cost would likely be significant.

9.3.2 Direct Supply from Local Grid

Another possibility would be the direct supply of electricity from the local grid to the facility. Both HV and MV networks extend close to the sites with the potential for connection to 10/20 kV power lines and also 38kV power lines. However, considering the magnitude of demand at the site it is possible that this infrastructure would not be able to support the facility. The proximity of Huntstown Power Station in Meath, currently under expansion, may provide a solution. It is situated approximately 40km from the site of the power station and is supported by the 220kV network. It is likely that connection to Huntstown or another point along the 220kV network in the area would entail a significant cost and reflecting on recent opposition to HV line expansion, would more than likely be subject to a protracted planning and connection process. In addition to this, ongoing operational costs associated with purchase of electricity from the grid might establish this option as being prohibitively expensive. The need for this connection will be particularly relevant should any form of renewable energy be considered for the site, where frequent back-up and peak demand power (supplemented from the National Grid) may be required up to full plant demand.

9.4 POTENTIAL FOR ALTERNATIVE ENERGY SUPPLY OPTIONS There are many alternative electricity generation technologies in use and in development worldwide. These can broadly be separated into a number of categories such as Wind, Wave, Tidal, Hydro, Solar and Biofuel.

9.4.1 Wind Electricity generation from wind is a mature technology both in terms of on-shore and off-shore generation. Two major considerations in the utilisation of wind energy to supply the desalination option would be the scale of windfarm (and consequent cost) necessary to support the facility and the intermittent nature of wind generation which would require a back-up supply either directly from the grid or by on-site generation. This back-up would more than likely be an expensive and largely redundant piece of equipment.

The scale of wind-farm necessary to supply a constant 47.5 MW of power would be (taking an onshore turbine size of 1MW) in the region of 47 Turbines. This is assuming that they all produce electricity to their installed capacity, 24 hours per day, 365 days per year. In general it is assumed that wind turbines will produce approximately 30-35% of their installed capacity once generation efficiency and wind regime are taken into consideration. Taking this best case (100%) scenario of 47 Turbines the likely cost would be €75 million including grid connection and the turbines would be spread across an area of approximately 429 Hectares (assuming a spacing grid of 350m). Should an offshore facility be considered, then the closest suitable area currently identified as a potential site for development (by Airtricity) is 40km distant to the South-east of Dundalk.


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Assuming a turbine size of 3.6MW (similar to the Arklow Development), this would see an offshore development of 14 Turbines spread over 312 hectares. There would also be a significant development and connection cost associated with this, possibly in the region of €150 million.

Should the empirical and evidence-based estimate of 32.5% electricity production compared to installed capacity be used then onshore a windfarm to support the desalination plant could require 145 turbines spread over 1320 Hectares with a potential cost of €230 million; while an offshore installation could require 43 turbines spread over an area of 1000 hectares with a cost of €461 million.

9.4.2 Wave, Tidal and Hydropower Technologies

Both wave and tidal technologies are not considered to be mature at this point in time. They do however represent good potential for energy generation in Ireland for the longer term. While both technologies have a number of pilot projects in existence utilising a variety of proprietary mechanisms for generation (OpenHydro tidal turbine, Wavebob, Pelamis inter alia), it is unlikely that any of these will be proven at the scale required for the desalination plant in the short to medium term. In the case of Hydro-electricity, there are insufficient resources available in the area to provide a reliable and significant power supply to the desalination option. In general terms, it is highly unlikely that any large-scale hydro-electricity generation facility will be developed in Ireland due to the significant environmental impact caused by same.

9.4.3 Solar Photovoltaic and Thermal/Steam Turbine Technologies

Solar technologies are applied in a number of different scenarios in Ireland. By far the most prevalent is that of Solar Thermal technology where daylight only is needed for the efficient harnessing of solar energy. Far less common is the utilization of Solar Photovoltaic technologies which produce electricity from direct sunlight, with most of these installations being in isolated areas for small demand such as emergency phones and low-level emergency lighting. Newer configurations of solar technology also utilise mirror arrays to concentrate solar energy to a point, superheating water into steam, which is then used to produce electricity. While these electricity production technologies are and will be successful elsewhere it is highly unlikely considering the quantity of direct insulation experienced in the Irish climate that it would ever be economically feasible to support an installation with a demand of 47.5 MW.

9.4.4 Biomass and Biofuel Technologies

Biomass and liquid biofuel energy technologies are considered to be relatively mature in the current energy market. The weakness in their development and utilisation is normally due to country specific barriers and often relates to taxation, level of incentivisation and most importantly, level of fuel availability and the supply chain for same. In the case of a proposed desalination plant at the scale mentioned above, calculations on the quantities of fuel and storage required have yielded the following results – refer table 9.1.


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Table 9.1 Quantities of fuel and storage requirements for various biomass and biofuel technologies

kWh/tonne Tonnes/yr Tonnes/day Storage (m

3/yr)

Monthly Storage Requirement

(m3)

Chips 1,250 332,880 912 1,331,520 110,960

Pellets 1,563 266,304 729.6 1,065,216 88,768

Biodiesel 10,347

(9.105kWh/l)

40,215

(45,700,165 l/yr)

110

(125,206 l/day)

45,700 3808.3

The physical storage of these quantities, the logistics associated with delivery and movement of raw materials and storage & disposal of waste ash could have a significant impact on the operation of the facility. It is also important to put these quantities into the context of the current Irish Biomass and Biofuel Markets. The utilisation of either woodchip or wood-pellet would necessitate a growth in the wood-fuel market of in excess of 100% (going by Ireland’s published 2006 Energy Balance figures – Sustainable Energy Ireland). The utilisation of biodiesel as the primary fuel would necessitate in excess of a tenfold increase in the current Irish biofuel market to satisfy the demand of the desalination plant.

9.5 SINGLE ENERGY MARKET

The Irish regulatory framework for the electricity market is dependent on the power required by the consumer, as shown on Figure 9.1. When the power required is < 5 Megawatts, consumers can buy energy directly from an energy supplier located anywhere in Ireland. The Irish National Grid can be used to deliver this energy.

On the contrary, when the power requirements are > 5 MW, no direct contract is allowed between the consumer and the independent generator. Eirgrid deals with energy supply to the consumer, using a mix of different sources of energy. The price fixed by Eirgrid will integrate production costs, delivery cost and also an Eirgrid mark-up for risk.

Figure 9.1 Electricity market regulatory framework

Energy Delivered via National Grid

Energy

Consumer

Independent

Generator(oil, gas, wind, biofuels etc.)

Direct Contract

< 5 MW

Eirgrid

Energy

Consumer

Independent

Generators(oil, gas, wind, biofuels etc.)

Contract

> 5 MW


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In the case of wind generated power there are regulatory constraints under which all electricity produced at a site of >5MW capacity will have to be dispatched to the national grid. The energy requirements for a desalination facility of this scale are 47.5MW as outlined in the previous section. This electricity would then be subject to the Single Energy Market and cost drivers, instead of allowing the desalination plant to avail of direct supply from independent generators.

9.6 CARBON FOOTPRINT MODEL

9.6.1 Energy Consumption

The energy consumption of desalination was assessed taking into account the annual growth of water supplies. The minimum operational production of the plant has been established at 50Mld. Desalination requires energy principally for the reverse osmosis process (high pressure pumps). Figure 9.2 illustrates the annual energy consumption to 2040 for the proposed desalination plant. The trend shows energy consumption increasing in direct proportion to the water supply.

Figure 9.2 Annual Energy Consumptions

Annual Energy Consumption

0

50,000,000

100,000,000

150,000,000

200,000,000

250,000,000

300,000,000

350,000,000

400,000,000

450,000,000

2010 2015 2020 2025 2030 2035 2040 2045

Year

E (kWh/year)

Figure 9.3 illustrates the energy requirements per cubic metre of water delivered until the year 2040. The total energy requirement is sub-divided into energy required for abstraction and reverse osmosis and energy required for transmission of treated water.


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Figure 9.3 Annual Energy Consumptions per m3 delivered

Annual Energy Consumption per m3 Delivered

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

2010 2015 2020 2025 2030 2035 2040 2045

Year

E (kWh/year/m

3) TOTAL

Abstraction+RO

Transmission

RO

Abstraction

9.6.2 Carbon Footprint Model Development

The Carbon Footprint Model enables the assessment and comparison of different energy supply scenarios, including: energy supply from the national grid, oil and gas independent power generation, energy generation from biofuels (wood chips, pellets and biodiesel) and wind power. For each scenario, the model calculates the energy cost (excluding carbon tax), carbon emissions and carbon tax based upon current market prices and technologies.

The current primary fuel (oil, gas, biofuels) prices and company retail prices (grid and wind power suppliers) have been used (€/kWh), with the former weighted by their respective process efficiency factors (%).

For each of the energy sources, the CO2 emission factors (kgCO2/kWh) have also been included in the model to calculate the annual carbon emissions for any scenario. Finally, the annual CO2 emissions are converted into anticipated future carbon taxes using dedicated website information (pointcarbon).

A detailed example of Carbon Footprint Model simulation is given in Appendix E.

9.6.3 Energy Supply Scenarios

In order to assess the energy supply possibilities for desalination, the different available energy sources have been compared in terms of cost, carbon emissions and associated carbon tax. For simplicity and consistency with the economic assessment detailed in Section 11, no inflation was taken into account in the results shown in Figures 9.4, 9.5 and 9.6.


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Figure 9.4 Annual Cost for Different Energy Sources

Annual Energy Cost

€0

€20,000,000

€40,000,000

€60,000,000

€80,000,000

€100,000,000

€120,000,000

€140,000,000

2010 2015 2020 2025 2030 2035 2040 2045

Year

€/year

100% oil

100% biofuels

100% wind

100% gas

100% grid

Figure 9.5 Annual CO2 Emissions for All Energy Supply Scenarios

Annual Carbon Emissions

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

2010 2015 2020 2025 2030 2035 2040 2045

Year

CO2 tonnes/year

100% oil

100% biofuels

100% wind

100% gas

100% grid


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Figure 9.6 Annual Carbon Tax for All Energy Supply Scenarios

Annual Carbon Tax

€0

€1,000,000

€2,000,000

€3,000,000

€4,000,000

€5,000,000

€6,000,000

€7,000,000

€8,000,000

€9,000,000

€10,000,000

2010 2015 2020 2025 2030 2035 2040 2045

Year

€/year

100% oil

100% biofuels

100% wind

100% gas

100% grid

9.6.4 Summary

Figure 9.7 gives a summary of the total annual cost of the energy supply predicted for the year 2040, including both the energy production cost and the carbon tax without inflation projection. Figure 9.7 Desalination Summary – Total Annual Cost of Energy Supply

Desalination Energy Cost and Carbon Tax (2040)

€0

€20,000,000

€40,000,000

€60,000,000

€80,000,000

€100,000,000

€120,000,000

€140,000,000

100% grid 100% gas 100% wind 100% biofuels 100% oil

Type of Energy Supply

Cost (€)

Carbon Tax

Energy Cost


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9.6.5 Anticipated Supply Scenarios

Two costing tables (Table 9.2 and 9.3) were designed with regard to the type of fuel that would be used to power the desalination plant including the origins of that fuel and carbon footprint. These tables were compiled using the Carbon Footprint Model simulation that is given in Appendix E.

9.6.5.1 Option 1 - Fossil Fuel and Renewable Fuel Mix

The fuel used for Option 1 is the expected fuel mix between fossil fuels and renewables from now until 2040. At present, the mix includes 7% renewables. While there was a target set in the White Paper for Energy of 33% renewables by 2020, “an achievable target” is said to be 20%. With the reduction in fossil fuels expected to heighten over the coming decades an increase in the percentage of renewables is expected, with 40% renewables by 2040 being a reasonable estimate.

The cost of the fuel is based on the current prices being quoted with a 4% inflation rate for every year. The amount of carbon produced is based on the electricity fuel mix only and not from the renewable source. The carbon tax quoted is based on the European market price in €/tonne. Future predictions were based on detailed surveys of users of a dedicated carbon market website, pointcarbon.com. When the price of carbon reaches €40/tonne it is expected to level off.

Table 9.2: Option 1 – Off-site Fossil Fuel and Renewable Fuel Mix – Energy Cost Projections

2008 2016 2021 2026 2031 2036 2040

Mix of Fuel Type (%Fossil / %Renewable)

93/7 85/15 80/20 75/25 70/30 65/35 60/40

Cost of Power from Fuel

7.7m€ 11.0m€ 26.6m€ 46.4m€ 70.9m€ 94.7m€

Carbon Production (Tonnes of CO2)

47,778 52,189 99,245 138,895 171,547 190,725

Carbon Tax (€/Tonne CO2)

25 30 35 40 40 40 40

Total Carbon Cost (€)

1.4m 2.2m 5.6m 8.9m 12.3m 14.9m

Total Cost (Fuel + Carbon)

9.1m 13.2m 32.2m 55.3m 83.2m 109.6m

9.6.5.2 Option 2 - Desalination plant powered directly from a gas fired station

The fuel used for Option 2 comes directly from a gas fired station and is converted to electricity on site. This cuts out the need for supplying Eirgrid and then receiving it from an electricity supplier. There will be no extra charges added to the fuel as there is no “middle man”, i.e. Eirgrid and suppliers. However, there would be the added capital cost of building a gas fired station and O&M costs which aren’t included in this table.


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While gas isn’t as efficient as electricity, 100% (grid) versus 58% (gas), it is cheaper. The carbon produced from burning the gas is significantly less than that of the electricity mix, however by 2041 there is less of a difference between the amounts of carbon being produced between the two options as the amount of renewables used increases over time in Option 1.

The cost of the fuel is based on the current prices being quoted with a 4% inflation rate for every year. The amount of carbon produced is based on the electricity fuel mix only and not from the renewable source. The carbon tax quoted is based on the European market price in €/tonne. Future predictions were based on detailed surveys of users of a dedicated carbon market website, pointcarbon.com. When the price of carbon reaches €40/tonne it is expected to level off.

Table 9.3: Option 2 – On-site gas fired power station – Energy Cost Projections

2008 2016 2021 2026 2031 2036 2040

Mix of Fuel Type (%)

100 100 100 100 100 100 100

Cost of Power from Fuel

3.5m€ 4.9m€ 11.5m€ 19.8m€ 29.6m€ 38.8m€

Carbon Production (Tonnes of CO2)

24,728 28,699 58,213 87,290 116,103 139,840

Carbon Tax (€/Tonne CO2)

25 30 35 40 40 40 40

Total Carbon Cost (€)

742k 1.2m 3.3m 5.6m 8.4 11.0m

Total Cost (Fuel + Carbon)

4.2m 6.1m 14.8m 25.4m 38.0m 49.8m

9.7 RECOMMENDATIONS

Desalination is a very energy intensive process and in an Irish context the cost of oil/gas for energy generation is a key issue for consideration. Due to the import requirements there were long term security of supply considerations to be evaluated as part of the assessments of a desalination facility.

To reduce risks associated with supply security a dedicated power station may provide some solutions. However the impacts of construction of such a station (sized to guarantee supply of 47.5 MW and located in close proximity to the plant) may be considerable.

In terms of alternative energy as outlined in section 9.4.1.1 for any wind energy project there are regulatory constraints under which all electricity produced at a site of >5MW capacity will have to be dispatched to the national grid. This electricity would then be subject to the Single Energy Market and cost drivers, instead of allowing the desalination plant to avail of direct supplies from independent generators. Since the plant requires 47.5 MW this option becomes less desirable in terms of lower energy costs associated with using alternative energy sources.


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From the review above it is apparent that the most practicable options for powering the desalination facility would be Natural Gas (as a primary fuel for electricity production on-site) or direct electrical supply from the National Grid. This is considered to be the case from a number of perspectives including:

• The scale of investment required;

• Area required for on-shore and off-shore wind technologies and regulatory controls regarding electricity supply for same;

• On-site storage, fuel management and ash disposal and management for solid and liquid biofuels;

• Quantity of primary fuel required with regard to solid and liquid biofuels and the current market size and consequent sensitivity.

• Maturity of technologies in the case of wave and tidal.


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10 ENVIRONMENTAL CONSIDERATIONS

10.1 INTRODUCTION

A qualitative and quantitative assessment of the likely significant effects of constructing a desalination facility on each aspect of the environment has been carried out in order to identity key issues. These assessments were based on the likely magnitude of the impact and the sensitivity of the environmental aspect, national and international legislation and other relevant plans and programmes.

(Tables 11.16 and 11.18 of the Environmental Report, tabled for public consultation under the Strategic Environmental Assessment Phase 2 (SEA Ph 2) process provides a summary of the qualitative and quantitative assessments respectively).

10.2 ACTIVITIES ARISING FROM THE IMPLEMENTATION OF WATER TREATMENT BY DESALINATION

In brief the water abstracted from the Irish Sea will need to be conveyed to a facility on land where it will be treated prior to transmission to the distribution network in the Dublin Region. A facility to store the treated water will be required prior to release to the distribution network. For the Irish Sea/Desalination, the existing reservoir at Ballycoolin may be suitable to act as the storage reservoir.

A preliminary abstraction point, treatment facility location and transmission route has been identified in order to assess the feasibility of desalination and to identify the likely key environmental issues which relate to this treatment process. Primary data sources such as OSI mapping, the Heritage Service and NPWS data bases of (Record of Monuments and Places (RMP) and National and European (natural heritage) sites were used to select these preliminary locations and transmission routes so as to avoid major known sensitive receptors.

10.3 ENVIRONMENTAL ASSESSMENTS

This section of the report outlines the environmental aspects and key issues which were considered and assessed for the study area covered by the Desalination Plant in North Dublin.

10.3.1 Biodiversity, Flora and Fauna

The primary habitat covered by the Desalination Plant is the marine environment and the proposed site is located on or in proximity to sites with the following designations:

• Special Areas of Conservation (SAC) (Designated under the Habitats Directive 92/43/EC)

• Special Protection Areas (SPA) (Designated under the Birds Directive 79/409/EEC)

• Natural Heritage Areas (NHA) (Designated under the Wildlife Act 1976)

The proposed area of abstraction to the north of Dublin has no national or European natural heritage designation and the volume of water to be abstracted will have no impact in terms of available water resources in the Irish Sea and was not seen as a key issue.


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Similarly, there are no national or European sites in the general vicinity of the proposed treatment works. Given the proximity of the treatment works to the sea, an option for the removal of wastewater from the works which was considered was discharge to the sea after treatment. Given the potential dilution available this is not seen as a key issue.

The brine dispersion model examined the impact of the option of returning the sludge to the sea via the plant outfall. No significant impact was anticipated. However, as part of the design of the treatment works the sludge produced by the treatment process would be collected and thickened at the works and would be removed from site for disposal.

The transmission route will only be approximately 24km long but given the existing development along the route, the location of the route is not entirely flexible. However, it is likely that the route would be able to avoid any site of National or European Importance and is therefore not seen as a key issue.

An existing reservoir at Ballycoolen is likely to be used for storing treated water which an as such is not anticipated to have any adverse impact.

As shown in Table 10.1, there are a number of designated sites within a 5km radius of the proposed site but the desalination study area itself does not fall within the boundaries of any designated area.

Table 10.1 Designated areas close to Loughshinny

Designated area Site code Distance from Loughshinny

Loughshinny Coast pNHA (002000) 1km North

Skerries Islands

Shenick Island, St. Patricks Island, Colt Island

SPA (004122) /pNHA

(001218)

2.5km North

Lambay Island SPA (004069)/pNHA (000204) ~5 km south east

Rogerstown Estuary SPA (004015)/ SAC (000208) 3.5km South

It was deemed that overall no significant adverse impact would be anticipated from the construction of a desalination facility at north Fingal on biodiversity, flora and fauna.

10.3.2 Population and Human Health

The approximate number of people that the treatment plant can provide water for was used here as a gauge of positive impact on communities.

The population of Ireland was over 4.2 million in 2006. Though the population growth has been accelerating, the population density in Ireland is still low from a European perspective and the population still remains below that of the island in the early 19th century.

Population projections for the GDA as a whole were undertaken in great detail in the Greater Dublin Strategic Drainage Study and reported on in population and land use Report 2003. The Dublin Region (Water Supply Area) population projections are outlined in Table 2.1 of this report. The largest population centres are located south of the M50 in the Dublin City area and along the east coast. Northern Fingal County is sparsely populated by comparison.


MDW0158RP0080F01 176 F01

An adequate secure water supply is a basic need of society; it is essential to ensure public health and sustain social, environmental and economic conditions appropriate in a modern European City. Currently there is an adequate drinking water supply in the Dublin Region but it is forecast that as early as 2014 the demand in the area could exceed supply.

The Strategic Planning Guidelines in 2002 recognised that a secure water supply for the GDA would be the most significant factor determining its long-term capacity to accommodate growth. The National Spatial Strategy promotes higher housing densities in the Dublin Region to promote vibrant sustainable communities and to make the best use of infrastructure.

Here there are concerns over the security of a desalinated water supply as a result of its energy requirements. As desalination is highly energy intensive and would most likely rely on offshore gas supplies for energy there are concerns over the security of the supply. Should there be a reduction or loss in supply for any reason this process could struggle to maintain a water supply.

The cost of energy is also likely to be a factor here. Desalination is economically unfavourable due to the high energy costs which is considerably more expensive than costs for conventional treatment processes.

Finally, there is also a perceived and potential lack of security of the quality of the source due to its vulnerability in terms of exposure to gross and chronic pollution in the Irish Sea. The security of providing an adequate and good quality supply would be at risk as a result of poor source water quality.

It must therefore be recognised that desalination may have a negative impact on population and human health.

10.3.3 Water

The Irish Sea stretches between Ireland and the UK and is connected to the Atlantic Ocean through St. George's Channel and the Celtic Sea to the south, and by the North Channel between Northern Ireland and Scotland to the north. The stretch of coastline along North County Dublin, in the vicinity of the proposed desalination plant site is a combination of rocky and sedimentary habitats.

The phytoplankton population dynamics in the Irish Sea varies depending on whether the water column stratifies or not. Where it does stratify the pattern is one with major productivity peak in spring/early summer, and a smaller peak in the autumn, while in areas of constant mixing there is only one peak in productivity in early summer (Marine Institute, 1999). The zooplankton of the Irish Sea is dominated by copepods, which mainly feed on the phytoplankton (Marine Institute, 1999) and, in-line with the phytoplankton, are also most abundant during the spring and summer.

The Irish Sea falls within ICES (International Council for the Exploration of the Sea) area VIIa for the purposes of fisheries management, and it is an important area for fish in terms of fisheries and conservation. Many inshore areas of the Irish Sea are regarded as notable spawning and/or nursery systems for several commercially important fish species including cod (Gadus morhua), whiting (Merlangius merlangus), plaice (Pleuronectes platessa), lemon sole (Microstomus kitt), herring (Clupea harengus) and sprat (Sprattus sprattus), with the most important areas being in the Western Irish Sea between Strangford and Dublin (Coull et al., 1998, Marine Institute, 1999). The large estuaries bounding the western Irish Sea also support velvet crab, lobster, whelk, razor fish and scallop fisheries. As such, the Fingal coastal area is highly important in terms of fishery (both commercial and non-commercial) spawning, nursery and feeding functions.

In terms of marine mammals, both cetaceans (whales and dolphins) and seals have been recorded in the inshore waters of North Dublin.


MDW0158RP0080F01 177 F01

As there was insufficient suitable and recent water quality data available for the Irish Sea at north Fingal a water sampling survey was carried out (refer to Appendix B for results of water sampling survey). This included a wide range of physical and chemical parameters and also silt density index measurements (SDI). The data collected from the water quality analysis was used as a baseline for water quality in the Irish Sea at this location. In conjunction with the results of the brine dispersion modelling study (refer section 8.0 of this report) which examined the currents along the north Fingal coast no significant potential changes to water quality as a result of brine dispersion were anticipated.

In relation to assessing any impacts on achieving the objectives of the Water Framework Directive the only adverse impact may be the dispersion of sludge which could potentially lead to enhanced phytoplankton growth in turn leading to algal blooms occurring at certain times of the years. As outlined in section 10.2.1 no significant impact is anticipated.

10.3.4 Air and Climate

In 2006, measured sulphur dioxide, nitrogen dioxide, carbon monoxide, lead and benzene concentrations in Ireland were all below their individual limits, as designated under the 2002 Air Quality Standards Regulations. In addition, particulate matter (PM10) concentrations in 2006 were similar to those measured in 2005, with all stations compliant with the standard introduced from 2005.

However, ozone concentrations measured in Ireland in 2006 were higher than recent years.

Met Eireann measure various climatological parameters on a rolling 30 year period. Over a 30 year period data recorded from Dublin Airport showed a mean temperature of 9.6ºC, mean relative humidity of 82%, mean daily sunshine duration of 3.9 hours, mean monthly rainfall of 732.7 mm and mean wind speeds of 9.9 knots.

Greenhouse gases contribute to global warming/climate change and the most important greenhouse gases are carbon dioxide, methane and nitrous oxide. The sources of emissions can be divided up into two broad categories, energy related and non-energy related. Carbon dioxide makes up a very large percentage of greenhouse gas emissions and the estimation of carbon dioxide is one of the best methods there is of calculating impacts on climate change.

Desalination is a highly energy intensive process due to the pumping requirements for reverse osmosis and would have an adverse effect on greenhouse gases and climate change.

In the assessment of energy consumption of a reverse osmosis plant several parameters are taken into account including sea water characteristics which determine the extent of the pre-treatment required and the number of RO passes required. In the case of Loughshinny an extensive pre-treatment facility is required in addition to a 2nd pass RO process to remove the high SDI and boron levels respectively. These factors in addition to the energy requirements for both sea water and treated water pumping and feed pumping for the RO unit are considerable (255.7 millions kWh per year for the year 2031).

The anticipated CO2 emissions using energy from the grid at the current emission rate of 0.000776 tons CO2 per kWh would produce 198,422 tons CO2 per annum (taking the figure for the year 2031). The carbon emission figures up to the year 2040 are included in the carbon model in Appendix E.

Desalination would therefore be anticipated to have a very negative impact on air and climate.


MDW0158RP0080F01 178 F01

10.3.5 Cultural Heritage (including Archaeology and Architecture)

There is a potential negative indirect impact on cultural heritage for the location selected for the desalination plant. The northern Fingal (Loughshinny) location was selected over a site in Balbriggan - another technically feasible location - on the grounds that the Balbriggan location was considered highly unsuitable due to the presence of an important prehistoric complex. A southern Loughshinny site was also considered, but was deemed highly unsuitable due to its proximity to a promontory fort of National Monument status. The northern Loughshinny location may impact indirectly on the setting of the promontory fort.

Baseline work was completed for the Irish Sea / Desalination plant as part of (SEA Phase l). Full details of this work are provided in the Environmental Report. Coastal landscapes are considered to have an intrinsically significant archaeological potential unless proved otherwise by archaeological investigation. As with rivers, the coast has always been a focus for human activity, with the sea providing a source of food and raw materials as well as a means of travel and communication and a place to build communities. Flint and stone artefactual evidence found along the shoreline from Loughshinny to Rogerstown (the latter being a particularly rich source) have indicated that this part of Dublin has witnessed human activity as early as the Mesolithic period.

National monuments within the study area include a prehistoric promontory fort, Drumanagh which is a recorded monument and is also subject to a preservation order. This is located within an area to the south of Loughshinny village. The fort has not been taken into State Care as a National Monument but the DoEHLG require that any site covered by a preservation order must be described as a National Monument.

10.3.6 Landscape

The area selected is characterised by beaches, islands and headlands that together create a sensitive and important landscape of high amenity and landscape value.

The most significant impact on the landscape will occur during the construction phase and will be temporary. While the treatment plants, pump stations and storage reservoirs will have some potential impact on landscape this was considered to be a secondary key issue and is not expected to have a significantly adverse impact on landscape.

10.3.7 Material Assets (including Landuse)

The main issues in relation to material assets are the temporary impacts on land and services during the construction phase, the permanent impact on land due to the sanitation of lands in the immediate vicinity of the transmission line from certain landuse/development activities and the energy used to treat the abstracted water and transmit it to the distribution system.

Landuse to be affected at north Fingal is horticulture and mixed agriculture as the footprint of the infrastructure will require the necessary land acquisition (see Appendix G for proposed site layout) with the plant covering an area of approximately 15 hectares at its ultimate capacity. This will constitute a minor negative impact.

10.3.8 Soil

In order to assess the impact on soils details of material quantities would need to be specified. As these details are determined at project level they cannot be used as a quantitative comparison at this stage. Therefore no significant adverse impact is expected.


MDW0158RP0080F01 179 F01

10.4 CONCLUSIONS

Due to the high amount of energy that would be required for the desalination process and the resultant emissions of green house gases when compared with conventional treatment methods it is anticipated that desalination would have a considerable negative impact in the environment.

The proposed preliminary design contains a substantial pre-treatment facility and requires a second pass RO system to be incorporated. This is required to treat both the high SDI (silt density index) and boron levels present in the source water. In the case of boron a reduction to 1mg/l is required in order to comply with current legislation while SDI’s >5 have a high potential to cause fouling of the RO membrane (levels in source water were recorded as >30 SDI). These factors contribute to the already anticipated high energy requirement for this treatment process.

In terms of the impacts on population and health the vulnerability of the Irish Sea source to acute or chronic pollution events exposes the treatment process to risks in terms of security of supply and poor quality treated water.


MDW0158RP0080F01 180 F01

11 ECONOMIC ASSESSMENT

This section contains summary details of economic assessments. Full details of economic assessments are available in Appendix F.

11.1 CAPITAL COSTS

11.1.1 Seawater Abstraction Intakes and Brine Discharge Outfalls

Twin 1800mm diameter pipelines are needed to abstract seawater efficiently at maximum capacity (715Mld). The required pipeline length is 3km in order to provide a sufficient water depth – 20m – for the intake structures. A minimum elevation above seabed is needed for water quality purpose as well as a minimum depth below water level for navigation safety.

Similarly, twin 1400mm diameter pipelines will enable the discharge of brine in an optimised manner at maximum flow rate (415Mld). In this case the pipeline length will only be 2km since brine dispersion modelling demonstrated that this would provide suitable dilution patterns for avoidance of sensitive coastal areas (see modelling results Section 8)

The engineering works involved in the construction of these pipelines are complex and expensive. It is difficult to assess accurately the construction costs without extensive seabed site investigations. The construction methodology will be:

• tunnelling from the desalination plant

• sand dredging between tunnel exit and pipeline extremities (seawater intakes / brine outfalls)

Hydraulic calculations show that pipelines will have to remain at least 7m below the minimum sea level in order to provide a suitable hydraulic profile. Therefore, from the desalination plant shafts the pipelines will be tunnelled to a point which must be at least 7m below the minimum sea level. The anticipated length of such a tunnel is about 800m, subject to site conditions.

For cost reduction purpose, intakes and outfalls will be laid through a single tunnel, which will be the most expensive part of the construction works (22k€/m to 28k€/m). From the tunnel’s exit to the intakes/outfalls, pipelines will be dredged into sand with a minimum cover of 1.6m. Abstraction and discharge pipelines will be dredged in separate trenches from the tunnel in Easterly and South-Easterly directions for the outfalls and intakes, respectively.

The construction costs are summed up in the following Table 11.1


MDW0158RP0080F01 181 F01

Table 11.1 Abstraction and Discharge Pipelines CAPEX

Diameter Total length Unit price (k€/m) Cost

Intake pipelines (supply)

1800mm 4km (2x2km) 1.5 6 m€

Discharge pipelines (supply)

1400mm 6km (2x3km) 1 6 m€

Tunnelling 6m 0.8km 28 22 m€

Dredging - 3.4km (1.2km + 2.2km)

4.7 16 m€

Mob/demob contractors, temporary works, surveys, butt fusion and testing, intakes, diffusers, mechanical joints, anchorweights, pipestrings, connections, etc.

14 m€

Contingencies for Site Conditions

15% of total 9.6 m€

Total 73.6 m€

11.1.2 Desalination Treatment Plant

11.1.2.1 Sea water abstraction

The seawater pumping station would be based upon large capacity submerged pumps placed in the sump. The pumps would be installed in two phases to supply the desalination plant efficiently for the maximum demand of each phase – 477Mld (Phase 1) and 715Mld (Phase 2). The capital costs of the seawater pumping facilities for each phase are summed up in the following table.

Table 11.2 Abstraction Pumping Station CAPEX – Phase 1 and 2

Installed Power

M&E Civil Works ESB Total

Phase 1 3.7 MW 8.1 m€ 7.1 m€ 1.9 m€ 17.1 m€

Phase 2 2.4 MW 4.1 m€ 3.6 m€ 1.2 m€ 8.9 m€

Total 6.1 MW 12.2 m€ 10.7 m€ 3.1 m€ 26.0 m€

11.1.2.2 Pre-Treatment

Due to the fouling capacity of Irish Sea water, significant pre-treatment is needed for satisfactory membrane filtration operation. This pre-treatment will consist of the following steps:

• Shock chlorination

• Coagulation with ferric chloride

• Acidification with sulphuric acid

• Flocculation with anionic polymer

• Dissolved air floatation

• Dual media filtration (anthracite and sand)


MDW0158RP0080F01 182 F01

The produced sludge will be dewatered on site before disposal.

The overall capital cost of the seawater pre-treatment and sludge treatment processes is shown in the following table:

Table 11.3 Pre-Treatment CAPEX

M&E Civil Works Total

Phase 1 29.6 m€ 22.2 m€ 51.8 m€

Phase 2 14.8 m€ 11.1 m€ 25.9 m€

Total 44.4 m€ 33.3 m€ 77.7 m€

11.1.2.3 Reverse Osmosis Treatment

The cartridge filters, high-pressure pumps, energy recovery systems, booster pumps, membrane filtration units, cleaning and flushing systems, as well as the post-treatment and disinfection, are all accounted for in an overall CAPEX assessment of the RO process, whose costs are given in the following table:

Table 11.4 Reverse Osmosis CAPEX

Installed Power

ESB M&E Civil Works Membranes Total

Phase 1 42.1 MW 21.1 m€ 42.4 m€ 48.6 m€ 20.6 m€ 132.7 m€

Phase 2 21.0 MW 10.5 m€ 21.2 m€ 24.3 m€ 10.3 m€ 66.3 m€

Total 63.1 MW 31.6 m€ 63.6 m€ 72.9 m€ 30.9 m€ 199.0 m€

11.1.3 Drinking Water Transmission

The transmission pipeline and associated facilities are designed for a termination point at Ballycoolen Reservoirs, in North Dublin. These will consist of twin 1100mm diameter pipelines laid in Phase 1.

Table 11.5 Transmission Pipelines Cost

Diameter (mm) Total length (km) Unit price (k€/m) Cost

Transmission pipelines 1100 48.7 (2x24.35km) 1.06 51.8 m€

Roads Rivers Railways Cost

Crossings 1.5 m€ 2.8 m€ 0.3 m€ 4.6 m€

Total 56.4 m€


MDW0158RP0080F01 183 F01

In terms of pumping, the drinking water transmission capital costs are as follows:

Table 11.6 Clear Water Pumping Station

Installed Power

M&E Civil Works ESB Storage Tank

Total

Phase 1 3.8 MW 3.7 m€ 3.0 m€ 1.9 m€ 5.4 m€ 14.0 m€

Phase 2 3.6 MW 2.0 m€ 1.5 m€ 1.8 m€ 2.7 m€ 8.0 m€

Total 7.4 MW 5.7 m€ 4.5 m€ 3.7 m€ 8.1 m€ 22.0 m€

11.1.4 One-off items

Other typical costs associated with the implementation of the Capital Works will be design fees, supervision costs, land purchase and wayleaves. Also, some provision is made for overheads and contingencies. A summary of these one-off costs is given in the following table.

Table 11.7 One-off Items

Investment Design & Supervision

Land Purchase

Wayleaves & Legal

Preliminaries & Overheads

Total

Phase 1 345.5 m€ 17.3 m€ 1.5 m€ 2.4 m€ 51.8 m€ 418.6 m€

Phase 2 109.1 m€ 5.5 m€ 0 m€ 0 m€ 16.4 m€ 130.9 m€

Total 454.7 m€ 22.7 m€ 1.5 m€ 2.4 m€ 68.2 m€ 549.5 m€

11.2 CAPITAL RENEWALS

Capital renewals provisions have also been assessed for the scheme based upon the various asset lifetimes detailed in the following table. These provisions represent the annual money required to make up the initial capital cost of an investment once its lifetime is over. Renewals are different from maintenance costs, which are needed to keep the capital investment in a good state of repair and maintaining it in a suitable operating condition until the full completion of its lifetime.

Table 11.8 Asset lifetime and renewal annual provisions

Asset Class

Civil Works Pipelines

Civil Works Structures

M&E Membranes

Lifetime 80 years 50 years 15 years 7 years Total

Phase 1 1.5 m€ 1.7 m€ 5.6 m€ 2.9 m€ 11.7 m€

Phase 2 1.5 m€ 2.6 m€ 8.4 m€ 4.4 m€ 16.9 m€


MDW0158RP0080F01 184 F01

11.3 OPERATING COSTS

Operating costs have been assessed on an annual basis over 25 years (2016-2040) in order to reflect the gradual water supply growth and to allow for an accurate assessment of the project whole life cost over a representative period of time for this scale of investment.

11.3.1 Maintenance

The maintenance costs are assessed as a percentage of the CAPEX. This percentage and the annual maintenance expenses during each phase are indicated in the table below. Due to the highly corrosive environment created by seawater and brine, the maintenance percentage allocated for mechanical and electrical investments is higher than that used for fresh water treatment plants.

Table 11.9 Maintenance Annual Costs

Capital class Civil Works M&E

Type Pipelines Pumping Stations

Pre-Treatment

RO Pumping Stations

Pre-Treatment

RO

CAPEX % 1% 1% 1% 1% 3% 3% 3% Total

Phase 1 1,158 k€ 156 k€ 219 k€ 489 k€ 352 k€ 886 k€ 1,274 k€ 4.5 m€

Phase 2 1,158 k€ 234 k€ 329 k€ 733 k€ 539 k€ 1,328 k€ 1,912 k€ 6.2 m€

11.3.2 Energy

11.3.2.1 Installed Power Capacity Demand Charge

The installed capacity demand charges for each phase are summed up in the following table

Table 11.10 Power Capacity Charge

Installed Power Charging Rate Total

Phase 1 49.6 MW 223 k€/annum

Phase 2 76.6 MW 4.5 k€/MW/annum

345 k€/annum

11.3.2.2 Annual Power Consumption

The annual consumption is assessed annually in accordance with the growth of the water supply. With a fixed power consumption unit cost of 0.1€/kWh for grid supply, the annual energy cost illustrated on the following graph is obtained-:


MDW0158RP0080F01 185 F01

Figure 11.1 Annual Energy Cost for Grid Supply

Annual Energy Cost

€0

€5,000,000

€10,000,000

€15,000,000

€20,000,000

€25,000,000

€30,000,000

€35,000,000

€40,000,000

€45,000,000

2015 2020 2025 2030 2035 2040

Year

€ / year

11.3.3 Chemicals and Standing Charges

11.3.3.1 Chemicals

Again, the estimated chemicals annual cost is reflecting the water demand projections, as illustrated in the following graph-:

Figure 11.2 Chemicals Annual Cost

Annual Chemicals Cost

€0

€1,000,000

€2,000,000

€3,000,000

€4,000,000

€5,000,000

€6,000,000

2015 2020 2025 2030 2035 2040

Year

€ / year


MDW0158RP0080F01 186 F01

11.3.3.2 Staff

The staff costs for each phase are summarized in the following table:

Table 11.11 Staff Cost

Staff Number Rate Total

Phase 1 8 360 k€/annum

Phase 2 12 45 k€/person/annum

540 k€/annum

11.3.3.3 Overheads

Overheads and contingencies have been accounted for as 5% of the total OPEX

11.3.4 Opex summary

The following figure illustrates the annual OPEX increasing over 25 years and its breakdown into energy consumption, power charge, maintenance, chemicals, sludge disposal, staff and overheads.

Figure 11.3 OPEX summary

OPEX

€14,232,870

€28,310,891

€57,332,095

€0

€10,000,000

€20,000,000

€30,000,000

€40,000,000

€50,000,000

€60,000,000

€70,000,000

2010 2015 2020 2025 2030 2035 2040 2045

Year

€ / year

Total Opex

Energy Consumption

Maintenance

Chemicals

Overheads

Sludge

Staff

Power Charge


MDW0158RP0080F01 187 F01

11.4 WHOLE LIFE COST

The simplified method of calculating Whole Life Costs (WLC) consists of discounting all of the investments and renewal provisions for CAPEX, together with OPEX over an operational period and adding the discounted CAPEX and OPEX costs to arrive at a Net Present Value for the scheme (NPV). The NPV of the scheme can then be divided by the total water volume delivered by the scheme over its lifetime to give an indicative cost in €/m3. The NPV has been estimated over a 3-year construction period – from 2013 to 2015 followed by a 25-year operating period – between 2016 and 2040.

The calculations are made at constant 2007 prices, i.e. inflation is not taken into consideration. Also, the NPV of the residual value of the Capital Works in 2040 has been deducted from the NPV of the scheme before calculating the volumetric cost of water in €/m3.

Whole life costs have been estimated at three different discount rates, with a base rate at 5% and sensitivity tests at 3% and 7%.

The following table presents the Whole Life Cost results

Table 11.12 Whole Life Costs of the Scheme at 3%, 5% and 7% Discount Rates

Discount rate 3% 5% 7%

NPV CAPEX (k€) 706,560 611,287 539,281

Investment 394,127 362,067 334,946Renewals 228,253 170,755 130,736One off items 84,180 78,465 73,600

NPV RESIDUAL VALUE (k€) 192,933 110,458 63,908

NPV OPEX (k€) 469,496 336,024 246,329

Maintenance 86,029 64,529 49,535Energy Capacity charge 4,544 3,386 2,582Energy Consumption 300,553 212,219 153,394Chemicals 41,460 29,316 21,220Sludge disposal 7,353 5,199 3,763Personnel 7,200 5,374 4,105Overheads 22,357 16,001 11,730

Volume delivered (Ml) 1,311,080 1,311,080 1,311,080

NPV Capex + Opex (k€) 1,176,057 947,312 785,610

NPV Capex + Opex - Residual Value (k€) 983,124 836,854 721,702

NPV Capex + Opex - Residual Value / Volume (€/m3) 0.75 0.64 0.55

NPV Capex - Residual Value / Volume (€/m3) 0.39 0.38 0.36NPV Opex / Volume (€/m3) 0.36 0.26 0.19


MDW0158RP0080F01 188 F01

12 CONCLUSIONS

The principal conclusion which has arisen from this Study is that Desalination is technically feasible as a major water supply option which has the capacity to deliver a high quality, sustainable product capable of secure operation with the necessary flexibility to meet changes in demand and water quality standards during the life of the project. Due to significant commercial growth in desalination technology reverse osmosis is now used as a viable water supply option in many water stressed parts of the world including many tourist zones in Europe.

In the Irish context desalination has to be evaluated with more commonly employed water treatment processes. Although great improvements have been made in recent years in membrane performances which have in turn led to greater efficiencies and reduced energy consumption, desalination remains an intensive energy process by comparison with more traditional water supply sources and technologies. High energy consumption entails high installed power capacity demand charges. As a consequence the anticipated CO2 emissions from a plant powered by the national grid would have a considerable negative impact on the environment compared to non-desalination technologies. In addition there are risks associated with security of power supply, quality of source water and impacts to the marine environment from possible poor brine dispersion management.

Economically, the Whole Life Cost of the scheme at a 5% discount rate over the assumed 25 year operating period is calculated at €947M which translates as €0.64/m3 of water delivered over the 25 year operational lifetime.

APPENDIX A

TRACKING DESALINATION COSTS

Water Supply Project – Dublin Region Appendix A Desalination Study Report

MDW0158RP0080F01 A1 F01

Inauguration Capacity

City Country YearCapacity

(m³/d)

(CAPEX)

Project

Cost

(mUS$)

Water Cost

(US$/m³)

RO system

Energy

Consumption

(kWh/m³)

Total Energy

consumption

(kWh/m³)

Feed Water

Salinity

(mg/l)

Producted

Water

Salinity

(mg/l)

Number

of stages

Feed

Pressure

(bar)

Recycling

(y/n)

Overall Water

Recovery (%)Membrane

Energy recovery

system

High-pressure

pumps

Operation Tuas Singapure 2005 136380 200

0.49 (first year

operation) - 0,78

4.1 - 4,35 Up to 35000 < 500 2 5845% in the first stage, 90% in

the second stage

SWRO - High Boron Rejection Membrane (up to

95%)

Calder DWEER model 1100 ( 97%

of efficiency according to Calder)

Operation Ghalilah UAE 2005 13650 < 4.0 35% - 41% SWROERI PX-220

(95% efficiency)

Operation Tampa Bay USA 200595000

(expandable to 132000)

1500.497 - 0.659

18000 - 32000 2 43 to 72,4 57%SWRO (operation

problemes - clogging)

Energy recovery turbine (45% efficiency)

horizontal split case high

pressure (RO feed pump)

Operation Ashkelon Israel 2005 320000 250 0.523,2 for ALL stages (2)

< 4.0 40750 < 40 2 62

45% in the first stage and 90 % in the second

stage

SWRO - Three center design

DWEER (96% efficiency)

three plus one 5.5MW (close to 90% of efficiency)

OperationKwinana - Perth 1

Australia 2006143700


287 0,75 - 1

2,6 for the first stage ONLYaround 3.5 for ALL stages

3,8 Kwh/m3 TOTAL COST

35000 - 37000 < 30 2 > 58 Yes43% - 45% first

stage total 80% - 90%

SWRO - Film Tech Membrane Technology -

spiral-wound RO module

ERI PX - 220 (96,8% efficiency)

First pass: 2,5 MW High

Pressure Pumps, Second Pass:

Weir variable high speed drive high pressure pumps

Final Construction

Perth II Australia November 2007 123300 SWRO

Water quality Operational parameters Technology

Status

Location Expected Costs / Costs Energy consumption

APPENDIX B

WATER QUALITY ANALYSIS

555555555444 44 4444

333333333222222222111 11 1111

666666666 777777777

999999999888888888

101010101010101010111111111111111111121212121212121212

131313131313131313

1 41 41 41 41 41 41 41 41 4

Scale: NTS

Notes

Approved:

Checked:

Title

Project

Issue Details

Drawn:

1. This drawing is the property of RPS Group Ltd. It is a confidential document and must not be copied, used, or its contents divulged without prior written consent.2. All levels are referred to Ordnance Datum, Malin Head.3. Ordnance Survey Ireland Licence No. EN 0005008 Copyright Government of Ireland.

Figure

Loughshinny Bathymetry and Water Sampling

Areas

Water Supply Project - Dublin Region

Rev.

File Ref.

Date: 02/10/2008

G. Geoghegan

E. McAuliffe

A02

A.A/SK Project No. MDW0158

Drawing No.

Mi0133

MDW0158Mi0133A02

+353 (0)1 2884499+353 (0)1 [email protected] www.rpsgroup.com/ireland

West Pier Business Campus, Dun Laoghaire,Co DublinIreland

LEGEND

Water SamplingArea

Bathymetric Contours

TFEW

Water Supply Project – Dublin Region Appendix B Desalination Study Report

MDW0158RP0080F01 B2 F01

Date of Sampling: 16/08/07 – Sites A, B and C

High Water

Parameter Units PV Value Surface Mid Bottom Surface Mid Bottom Surface Mid Bottom

1 TDS mg/l - 31400 28000 32700 31400 30400 30600 30900 30000 379002 pH pH Units 6.5 - 9.5 8.14 8.13 8.13 8.12 8.07 8.16 8.08 8.70 8.073 Conductivity µs/cm at 20ºC 2500 µs/cm at 20ºC 60800 57700 61300 60900 60800 61000 67000 61100 611004 Turbidity NTU NAC & ATC 3.50 1.35 5.00 2.20 3.20 1.48 1.43 1.45 2.305 Alkalinity as HCO3 mg/l - 154 144 146 143 143 152 144 145 1346 COD mg/l - <5 <5 <5 <5 <5 <5 <5 <5 <57 Ammonia as N mg/l 0.23 mg/l <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.18 Ammonia as NH4 mg/l 0.30 mg/l <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 <0.139 Phosphorus mg/l - <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.110 Nitrate as N03 mg/l 50 mg/l <8.77 <8.77 <8.77 <8.77 <8.77 <8.77 <8.77 <8.77 <8.7711 Hardness mg/l - 5479.00 5372.00 5554.00 6016.00 5763.00 5596.00 5802.00 5912.00 5908.0012 Faecal Coliforms cfu/100ml - 31 35 40 52 48 24 5 2 213 Calcium mg/l - 280.0 271.0 280.0 298.0 292.0 282.0 290.0 297.0 297.014 Magnesium, Total mg/l - 1150.0 1130.0 1170.0 1270.0 1210.0 1180.0 1220.0 1250.0 1240.015 Sodium mg/l 200mg/l 9160.000 8900.000 9440.000 10300.000 9780.000 9370.000 9780.000 10100.000 10000.00016 Potassium mg/l - 466.00 473.00 467.00 563.00 487.00 522.00 492.00 508.00 505.0017 Strontium mg/l - 8.400 8.200 8.500 9.500 8.900 8.600 9.000 9.200 9.20018 Barium, Total as Ba mg/l - 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.00719 Boron, Total mg/l 1000 µs/l 3.50 3.40 3.40 3.80 3.70 3.50 3.60 3.70 3.7020 Total Chlorine mg/l - 0.06 0.05 0.06 0.04 0.05 0.04 0.04 0.04 0.0421 Sulphate mg/l 250 mg/l 1512.5 1532.2 1782.7 1249.4 1583.9 1411.1 1401.3 1627.2 1367.322 Flouride mg/l 0.8 mg/l 0.9 0.9 0.09 0.9 0.9 0.9 0.8 0.9 0.923 Silica (Molybdate Reactive) mg/l - <3 <3 <3 <3 <3 <3 <3 <3 <3

Sample 1 28.70Sample 2 24.40Sample 3 28.50

Silt Density Index24

A B C


MDW0158RP0080F01 B3 F01


Low Water

Parameter Units PV Value SURFACE MID BOTTOM SURFACE MID BOTTOM SURFACE MID BOTTOM

1 TDS mg/l - 39000 35000 29400 34200 35000 31100 37200 33000 301002 pH pH Units 6.5 - 9.5 8.08 8.07 8.18 8.10 8.11 7.93 8.07 8.09 8.013 Conductivity µs/cm at 20ºC 2500 µs/cm at 20ºC 61200 61400 61500 61000 61000 61300 60900 60900 608005 Turbidity NTU NAC & ATC 1.30 1.22 6.40 4.50 1.01 6.50 6.3 6.00 5.606 Alkalinity as HCO3 mg/l - 152 146 146 137 145 150 146 148 1567 Alkalinity as CaCO3 mg/l - 125 120 120 112 119 123 120 121 1288 COD mg/l - <5 <5 <5 <5 <5 <5 <5 <5 <59 Ammonia as N mg/l 0.23 mg/l <0.1 <0.1 0.12 0.1 <0.1 <0.1 <0.1 <0.1 <0.110 Ammonia as NH4 mg/l 0.30 mg/l <0.13 <0.13 0.15 0.13 <0.13 <0.13 <0.13 <0.13 <0.1311 Phosphorus mg/l - <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.112 Nitrate as N03 mg/l 50 mg/l <8.77 <8.77 <8.77 <8.77 <8.77 <8.77 <8.77 <8.77 <8.7713 Hardness mg/l - 5565 5675.00 5811.00 5908.00 5551.00 5455.00 5562.00 5268.00 5473.0014 Faecal Coliforms cfu/100ml - 56 61 79 23 34 29 52 62 501 Calcium mg/l - 292.0 287.0 300.0 294.0 281.0 272.0 274.0 265.0 270.02 Magnesium, Total mg/l - 1160.0 1190.0 1220.0 1250.0 1170.0 1150.0 1180.0 1110.0 1160.03 Sodium mg/l 200mg/l <5 9610.000 9.000 9760.000 9120.000 9020.000 9230.000 8560.000 9200.0004 Potassium mg/l - 457.00 474.00 503.00 519.00 478.00 475.00 489.00 451.00 486.005 Strontium mg/l - 8.400 8.700 9.000 9.300 8.600 8.600 8.800 8.200 8.8006 Barium, Total as Ba mg/l - 0.008 0.008 0.008 0.008 0.007 0.007 3.600 0.007 0.0077 Boron, Total mg/l 1000 µs/l 3.70 3.60 3.80 3.80 3.60 3.50 3.60 3.40 3.508 Total Chlorine mg/l - 0.07 0.09 0.08 0.07 0.09 0.09 0.08 0.08 0.079 Sulphate mg/l 250 mg/l 1288.7 1541.2 1352.6 1775.3 1371.3 1208.0 1481.6 1597.0 1105.410 Flouride mg/l 0.8 mg/l 0.7 0.9 0.9 0.9 0.8 0.9 0.9 0.8 0.811 Silica (Molybdate Reactive) mg/l - <3 <3 <3 <3 <3 <3 <3 <3 <3

Sample 1 31.30Sample 2 70.00Sample 3 30.60

A B C

12 Silt Density Index


MDW0158RP0080F01 B4 F01


High Water

Depth (m) Conductivity Salinity Conductivity Salinity Conductivity Salinity

1 60400 138.9 61000 140.3 61100 140.52 60600 139.3 60800 139.8 61000 140.33 61000 140.3 61000 140.3 61100 140.54 60800 139.8 60900 140 61200 140.75 60900 140 60700 139.6 61100 140.56 61000 140.3 60900 140 61200 140.77 61100 140.5 61300 140.98 61100 140.5 61000 140.39 61000 140.310 62100 142.811 61200 140.712 61200 140.7131415

Low Water

Depth (m) Conductivity Salinity Conductivity Salinity Conductivity Salinity

1 60700 139.6 61100 140.5 61100 140.52 61000 140.3 61800 142.1 61000 140.33 61100 140.5 61000 140.3 60900 140.04 67000 154.1 60800 139.85 61300 140.9 61200 140.76 60900 140.07 61000 140.08 60600 139.39 61200 140.7101112131415

Units

µs/cm at 20ºC%

Parameter PV Value

2500 µs/cm at 20ºC -

Conductivity

Salinity

A B C

A B C


MDW0158RP0080F01 B5 F01

Site HW max depth HW Mid depth LW Max depth LW Mid Depth

A (200m) 6.8 3.4 (3.5) 3.5-3.6 1.8 (2)B (500m) 9 4.5 5.8 2.9 (3)C (1km) 13 6 9.8 4.9 (5)

ID Tide Site location Site Depth Temp F Temp C

HWA-S1 HW 200m A 1 58 14.5HWA-S2 HW 200m A 2 58 14.5HWA-S3 HW 200m A 3 58 14.5HWA-S4 HW 200m A 4 58 14.5HWA-S5 HW 200m A 5 58 14.5HWA-S6 HW 200m A 6 58 14.5

HWB -S1 HW 500m B 1 59 15HWB -S2 HW 500m B 2 59 15HWB -S3 HW 500m B 3 59 15HWB -S4 HW 500m B 4 58 14.5HWB -S5 HW 500m B 5 58 14.5HWB -S6 HW 500m B 6 58 14.5HWB -S7 HW 500m B 7 58 14.5HWB -S8 HW 500m B 8 58 14.5

HWC -S1 HW 1000m C 1 60 15.5HWC -S2 HW 1000m C 2 60 15.5HWC -S3 HW 1000m C 3 60 15.5HWC -S4 HW 1000m C 4 60 15.5HWC -S5 HW 1000m C 5 60 15.5HWC -S6 HW 1000m C 6 60 15.5HWC -S7 HW 1000m C 7 60 15.5HWC -S8 HW 1000m C 8 60 15.5HWC -S9 HW 1000m C 9 60 15.5HWC -S10 HW 1000m C 10 60 15.5HWC -S11 HW 1000m C 11 60 15.5HWC -S12 HW 1000m C 12 60 15.5

ID Tide Site Location Site Depth (m) Temp F Temp C

LWA -S1 LW 200m A 1 59 15LWA -S2 LW 200m A 2 59 15LWA -S3 LW 200m A 3 58 14.5

LWB -S1 LW 500m B 1 59 15LWB -S2 LW 500m B 2 59 15LWB -S3 LW 500m B 3 58 14.5LWB -S4 LW 500m B 4 58 14.5LWB -S5 LW 500m B 5 58 14.5

LWC-S1 LW 1000m C 1 59 15LWC-S2 LW 1000m C 2 58 14.5LWC-S3 LW 1000m C 3 58 14.5LWC-S4 LW 1000m C 4 58 14.5LWC-S5 LW 1000m C 5 58 14.5LWC-S6 LW 1000m C 6 58 14.5LWC-S7 LW 1000m C 7 58 14.5LWC-S8 LW 1000m C 8 58 14.5LWC-S9 LW 1000m C 9 58 14.5

Bracketed figure indicates depth that mid water sample was

taken at


MDW0158RP0080F01 B6 F01

Date of Sampling: 19/10/07 – Site C

Low Water Site C (1000m)

Parameter Units PV Value MID

1 TDS mg/l - 390002 pH pH Units 6.5 - 9.5 8.163 Conductivity µs/cm at 20ºC 2500 µs/cm at 20ºC 557005 Turbidity NTU NAC & ATC 1.606 Alkalinity as HCO3 mg/l - 1507 Alkalinity as CaCO3 mg/l - 1248 COD mg/l - -9 Ammonia as NH3 mg/l 0.23 mg/l 0.6910 Ammonia as NH4 mg/l 0.30 mg/l 0.7411 Phosphorus mg/l - <0.112 Nitrate as N03 mg/l 50 mg/l 9.1713 Hardness mg/l - 6049.0014 Faecal Coliforms cfu/100ml - -15 Calcium mg/l - 320.016 Magnesium, Total mg/l - 1270.018 Sodium mg/l 200mg/l 11100.00019 Potassium mg/l - 476.0020 Strontium mg/l - 6.50021 Barium, Total as Ba µg/l - <0.122 Boron, Total mg/l 1000 µs/l 4.2023 Total Chlorine mg/l - -24 Sulphate mg/l 250 mg/l 2480.925 Flouride mg/l 0.8 mg/l 0.726 Silica (Molybdate Reactive) mg/l - <0.327 Chloride mg/l - 15034.0028 TSS mg/l - 161.0029 Kjeldahl Nitrogen mg/l - <531 Total Nitrogen as N mg/l - <732 Total Organic Carbon mg/l - 0.7033 Iron, Total mg/l - <0.0534 Chlorophyll A µg/l - 7.5735 Ortho-phosphate mg/l <0.536 Salinity mg/l - 35200.0037 Pheophytine A µg/l 1.08

17.7017.7017.1016.8016.90

38 Silt Density Index

APPENDIX C

POTENTIAL DESALINATION SITES

3

7

4

8

2

5

6

1

File Ref.

Approved: G. Geoghegan

XX.X

Notes

Project No.

Project

Title

Issue Details

Drawn:

Checked:

Scale:

Date:

Figure Water Supply Project - Dublin Region

Areas Investigated - Desalination Potential Sites

E. Laurinaviciute

C. Cole

1:150,000 @ A3

20/08/2008

MDW0158

1. This drawing is the property of RPS Consulting Engineers. It is a confidential document and must not be copied, used, or its contents divulged without prior written consent.2. All levels are referred to Ordnance Datum, Malin Head.3. Ordnance Survey Ireland Licence No. EN 0005008 Copyright Government of Ireland.

Drawing No. Rev.

Mi0136 A01

MDW0158Mi0136A01

Ph: 01-2884499Fax: 01-2835676E: [email protected] W: www.rpsgroup.com/ireland

RPS Consulting Engineers West Pier Business Campus, Dun Laoghaire,Co Dublin

Desalination Potential Sites

LEGEND

APPENDIX D

ENERGY CONSUMPTION OF DESALINATION PLANTS

Water Supply Project – Dublin Region Appendix D Desalination Study Report

MDW0158RP0080F01 D1 F01

Energy Consumption of RO Desalination Plants


MDW0158RP0080F01 D2 F01

1. INTRODUCTION.......................................................................................................................................3

2. ENERGY CONSUMPTION OF RO PLANTS: MAIN FACTORS..............................................................4

2.1. REPARTITION OF THE ENERGY CONSUMPTION FOR THE WHOLE PLANT.............................................................4

2.2. RO SYSTEM: FACTORS INFUENCING THE ENERGY CONSUMPTION.................................................................5

2.3. LOCAL CONDITIONS ......................................................................................................................................6

2.3.1. Impact of salinity ............................................................................................................................. 6

2.3.2. Temperature ................................................................................................................................... 7

2.4. RO CONFIGURATION/DESIGN........................................................................................................................7

2.4.1. Conversion rate (Y)......................................................................................................................... 8

2.4.2. required feed pressure and membrane permeability ...................................................................... 8

2.4.3. conlcusion ..................................................................................................................................... 10

2.5. PUMPING UNITS .........................................................................................................................................11

2.5.1. high pressure pumps (hp pumps) ................................................................................................. 11

2.5.2. Energy recovery device ................................................................................................................ 11

3. CASE STUDY .........................................................................................................................................14

3.1. IMPACT OF THE PUMPING UNIT-1-PASS RO PLANT .........................................................................................14

3.2. ASHKELON PLANT ......................................................................................................................................16

3.3. PERTH PLANT ............................................................................................................................................17

3.4. CONCLUSION.............................................................................................................................................18

4. APPLICATION TO THE DUBLIN PROJECT .........................................................................................19

5. CONCLUSION ........................................................................................................................................22

APPENDICES : TRAKING ON DESALINATION PLANT PERFORMANCE ........................................................23


MDW0158RP0080F01 D3 F01

1. INTRODUCTION

Energy costs impact for about 50% of overall operational costs of a desalination plant

using reverse osmosis technology. Assessment and optimization of power

consumption is then a key issue in the feasibility and the financial and environmental

evaluation of a new project.

This document aims at assessing the future electrical consumption of a possible

desalination plant in the area of Dublin, taking into account the local conditions, the

state of the art and the expected technical development.

In each particular case, assessment of energy consumption of a RO plant should be

as exhaustive as possible and take into account several parameters: sea water

characteristics, values taken for RO sizing, electromechanical components efficiency

(high pressure pumps and energy recovery device) to end up in a realistic result.

Values published are often partial results corresponding only to a specific step (first

pass) of the RO system and must be cautiously analysed and should not be taken as

representative of the whole electrical consumption in the plant.

Then, it is important to firstly list any parameters playing a part in the energy

consumption of a RO plant in order to understand how it changes and how it can be

assessed in the case of Dublin.

These parameters will be listed in the first part of this document. Three case studies

will be then presented before the last chapter addresses the question of a possible

desalination plant in the area of Dublin.


MDW0158RP0080F01 D4 F01

2. ENERGY CONSUMPTION OF RO PLANTS: MAIN FACTORS

2.1. REPARTITION OF THE ENERGY CONSUMPTION FOR THE

WHOLE PLANT.

The energy consumption of a desalination plant using Reverse Osmosis (RO) is the

sum of the energy used in all segments of the plant with this following typical

distribution:

� Sea water pumping 6-10 %

� Pre and post –treatment unit + auxiliary equipment 1-2 %

� RO unit : feed pumping unit 76-86 %

� Treated water pumping 7-12%

RO system

pre/post treatment

sea water pumping

treated water pumping

Figure 1 : Repartition of electric consumption in a RO plant

The RO system accounts for the largest part of electrical consumption in a RO plant.

Pre and post treatment and auxiliary equipments (chemicals plant) play a minor part in

the energy consumption.

The next section focuses on the parameters influencing the electrical consumption of

the RO system in order to understand where this consumption comes from and how it

can be assessed and optimised.


MDW0158RP0080F01 D5 F01

2.2. RO SYSTEM: FACTORS INFUENCING THE ENERGY

CONSUMPTION

The main power consumers in a RO system are:

� sea water pumping unit to reach the required feed pressure at the inlet of the

membrane

� chemical dosing system

� cleaning of membrane

� auxiliary electrical equipment (as on-line analyser)

Around 99% of the electrical consumption of the RO system comes from the sea water

pumping. Hence the parameters influencing the total consumption are related to the

required feed pressure and sea water flow (conversion rate).

Then, the energy needed to produce 1 m3 of fresh water depends mainly on:

� the required feed pressure

� the energy needed to reach this required feed pressure

� the conversion rate of the RO system

AS a result of the above, the electrical consumption depends on:

� Local condition : raw water quality - temperature and salinity.

� Feed pressure

� RO system design : head loss through RO units, number of passes, type of

membrane (membrane permeability), configuration of the system.

�Feed pressure, conversion rate

� Characteristic of the pumping units: efficiency of high pressure pumps,

efficiency of energy recovery device.

� Energy needed to reach the feed pressure


MDW0158RP0080F01 D6 F01

2.3. LOCAL CONDITIONS

2.3.1. IMPACT OF SALINITY

The next figure schematizes what is occurring in a membrane module.

In the above figure, the application of an external pressure to the salt solution side

(High TDS1) which is equal to the osmotic pressure will cause the equilibrium. This

pressure is a solution property independent on the membrane. Additional

pressure (to reach the feed pressure) will raise the chemical potential of the water in

the salt solution and cause a solvent flow to the pure water side.

As shown on next figure, osmotic and feed pressures increase with salinity.

Figure 2 : Impact of sea water salinity on osmotic pressure and feed pressure (on

brackish water) – source: “The guidebook of membrane desalination technology”-

Balaban collection

1 TDS is the total dissolved solids, most of then being dissolved salts.


MDW0158RP0080F01 D7 F01

Salinity and temperature impact the required feed pressure. Most of the energy

required for the RO system is used to pump water up to this pressure.

2.3.2. TEMPERATURE

Water temperature influences the osmotic pressure and the required feed pressure.

An increase of water temperature leads to a decrease of required feed pressure (see

Figure 3). It actually increases the difference between the osmotic pressure and the

required feed pressure.

Figure 3 : Impact of sea water temperature on required feed pressure – source: “The

guidebook of membrane desalination technology”-Balaban collection

Temperature and salinity are the two main sea water characteristics which impact the

power consumption. Then it is important to know the range of temperature and salinity

of the sea water to be processed in order to estimate correctly the electrical

consumption of the plant. Most of the time, these values are given in the literature for

the existing plants.

2.4. RO CONFIGURATION/DESIGN

When designing RO systems, several parameters shall be combined to reach the best

balance between the performance of the system and its costs (CAPEX, OPEX):

� Conversion rate of one membrane module for each pass

� Feed pressure

� Number of passes


MDW0158RP0080F01 D8 F01

2.4.1. CONVERSION RATE (Y)

The conversion rate of a membrane is the part of the sea water entering a membrane

module which flow through the membrane. This is the permeate flow.

The overall conversion rate of the RO system depends on the configuration and

results from an economic optimization. The reverse osmosis step can be composed of

several passes, 2 or more can be necessary when:

� The sea water salinity is too high to be reduced with 1 pass in the local

conditions

� The sea water contains Boron exceeding the standard (1mg/L in Europe).

The conversion rate of the second pass is usually between 70% and 90 %, whereas

the first one is between 35 % and 50 %. A 2 pass configuration will modify the

conversion rate of the RO system.

2.4.2. REQUIRED FEED PRESSURE AND MEMBRANE PERMEABILITY

Whereas the osmotic pressure depends only on the seawater characteristics, the

required feed pressure depends on many parameters, including:

� The conversion rate of the RO system (Figure 4)

� The membrane permeability (Figure 5), which characterizes the membrane

ability to transmit water and depends on temperature, salinity and fouling of

the membrane.

Figure 4 : Relation between conversion rate in RO unit and required feed pressure –

Source: “The guidebook of membrane desalination technology”-Balaban collection


MDW0158RP0080F01 D9 F01

The required feed pressure increases with the conversion rate and decreases with the

membrane permeability. The type of membrane chosen for a RO unit and the current

research on membrane are important factors which will influence the electrical

consumption, as well as the conversion rate chosen during RO sizing.

50

55

60

65

70

75

0,8 1 1,2 1,4 1,6 1,8 2

membrane permeability in L/m2/h/bar

required feed pressure in bar

5°C 10°C

possible future development

Figure 5 : Relation between membrane permeability and required feed pressure

For each particular case, these parameters are set at values resulting from an

optimization between CAPEX and OPEX which is performed for each case. High feed

pressure leads to higher energy consumption (OPEX) but smaller membrane area

(CAPEX). Low feed pressure leads to low energy consumption (OPEX) but high

membrane area (CAPEX).

Another optimization must be found between the permeability and the salt rejection of

the membrane (part of salts which are retained by the membrane). The higher the

permeability is, the lower the feed pressure (�OPEX). But in the same time,

membrane salt rejection is often lower (see Table 1) and the design needed to reach

the same final permeate salinity can lead to higher CAPEX.


MDW0158RP0080F01 D10 F01

PermeabilityL/m2/h/bar

Acetate cellulose membrane

High salt rejection

Low salt rejection

0,5

1

Composite membrane

High salt rejection

Low salt rejection

1,2

1,4

Table 1 : permeability of different types of membrane

2.4.3. CONLCUSION

The type of membrane chosen for a RO unit and the current researches on membrane

are important factors which will influence the electrical consumption, as well as the

conversion rate chosen during RO sizing. However these parameters are not often

published and are hold only by the membrane suppliers or plant operators.

On the other hand, to decrease the costs, following parameters shall be optimized:

� membrane permeability (increase is needed)

� couple feed required pressure / conversion rate

� couple permeability / permeate water quality

During the last years, membranes permeability has increased, but the membranes

having such permeability have lowest salt rejection (�decline of permeate quality). In

the next years, new membrane may appear with higher permeability, perhaps also

with a good salt rejection. Anyway, decreasing electrical cost might be at the expense

of treated water quality.


MDW0158RP0080F01 D11 F01

2.5. PUMPING UNITS

2.5.1. HIGH PRESSURE PUMPS (HP PUMPS)

Feed pump used in commercial RO systems are either centrifugal or positive

displacement type.

In large capacity RO systems, centrifugal type pumps are used almost exclusively.

The hydraulic efficiency of high pressure pumps used in large plants are then around

84%-88% and do not exceed 88,5 % (high pressure pump of SULZER)

Hydraulic

efficiency

Output capacity maintenance

Centrifugal type 84-88% High output capacity:

practically unlimited (up to

2500 m3/h)

�used in large plants

correct

Positive

displacement type

95 % Limited output capacity

(<200 m3/h)

� used in small capacity

plants

More frequent

maintenance than

centrifugal type

Pumps and motors have reach efficiencies which cannot significantly increase now.

The final Power consumption will also depend on the efficiency of the drive motor (94-

96%)

2.5.2. ENERGY RECOVERY DEVICE

There are several pressure recovery device types being used currently in RO

applications:

� Reverse running pump (not implemented any more)

� Pelton wheel

� Turbocharger

� Pressure exchanger (isobaric device)


MDW0158RP0080F01 D12 F01

Hydraulic

efficiency

Output capacity principle

Pelton wheel

Up to 90 % 10 to 900 m3/h Hydraulic power of the

brine is used to drive the

HP pump (common shaft

with electric motor and

HP pump)

Turbocharger

Up to 60% < 200 m3/h Hydraulic power of the

brine is used to drive a

second pump

(downstream HP pump)

Pressure

exchanger

(isobaric

device)

95-97% 100 to 250

m3/h

Hydraulic pressure of

the brine is used to

pressurize (1-Y)Q2 and

YQ is pressurized by the

HP pump � decrease

HP pumps capacity

The energy recovery devices which are gaining increased acceptance recently in RO

sea water system are pressures exchanger (also called isobaric devices) of various

configurations. The most famous types are DWEER (Calder Corporation, see Figure

6) and PX (Energy Recovery Device Inc.). As an example, DWEER are used in the

plant of Ashkelon and PX in the plant of Perth.

2 Y is the conversion rate of the RO system in % and Q is the seawater feeding flow / sea water pumped flow in m3/h


MDW0158RP0080F01 D13 F01

Figure 6 : DWEER type work exchanger (Calder Corporation)

Great advances have been made on High pressure and energy recovery devices for

the last years. But now, the efficiencies of theses components are close to the

maximum limit and are unlikely to evolve much. High efficiency devices are now

available and should be used in large plants where energy recovery make really

sense, as concentrate flow is very high (much hydraulic energy available on the plant).


MDW0158RP0080F01 D14 F01

3. CASE STUDY

3.1. IMPACT OF THE PUMPING UNIT-1-PASS RO PLANT

This section presents a theoretical example of one pass RO plant processing

Mediterranean type water. The local parameters and the main design parameter which

have been considered for the energy calculations are summarized in the Table 2. The

RO step design is a single pass system.

Salinity g/L 40,6

Water temperature 22°C

Conversion rate of the

RO system

50 %

Flux L/m2/h 14

membrane Hydranautics SWC5

Table 2 local condition and RO design.

Different configurations of pumping units have been considered and compared:

� First configuration (Figure 7): Pump and power recovery Turbine. Hydraulic

power of the brine is used to drive the HP pump (common shaft with electric

motor and HP pump).

Figure 7 : First configuration

� Second configuration (Figure 8): High efficiency pump+ Pelton Wheel. The

hydraulic power of the brine is used to drive a second pump added

downstream the HP pump.


MDW0158RP0080F01 D15 F01

Figure 8 : 2nd configuration

� Third configuration (Figure 9): High efficiency pump + work exchanger.

Hydraulic pressure of the brine is used to pressurize (1-Y)Q3 and YQ is

pressurized by the HP pump. This configuration allows to decrease HP pumps

capacity.

Figure 9 : 3rd configuration

The energy consumptions (kWh per m3 of produced water) of these 3 configurations

are presented in the following table. These values result from theoretical calculations

which are comparable to electrical consumption of the first pass ONLY (in RO system)

in existing plants. These data clearly show the influence of the pumping unit on the

total electric consumption in a one-pass RO plant.

3 Y is the conversion rate of the RO system in % and Q is the seawater feeding flow / sea water pumped flow in m3/h


MDW0158RP0080F01 D16 F01

1rst configuration

Pump + power

recovery Turbine

2nd Configuration

High efficiency pump+

Pelton Wheel

3rd configuration

High efficiency pump+

pressure exchanger

Pump efficiency % 82 88 88,5

Electric motor efficiency 94 96 96

Energy recovery device

efficiency

82 88 94

Feed pressure 64 64 64

Pre and post treatment +

auxiliary equipment

0,05 0,05 0,05

Sea water pumping 0,30 0,28 0,28

HP pumps 4,34 4,14 2,08

Power recovery -1,37 -1,45 +0,19

RO system 2,97 (= 4,34-1,37) 2,69 (= 4,14-1,45) 2,27 (=2,08+0,19)

Treated water pumping 0,36 0,35 0,35

Total 3,68 3,37 2,95

Table 3 : Impact of different pumping units configuration on electrical energy of a RO plant (in kWh)

In this case study, 0,5 kWh can be saved with the high efficiency pumping unit:

� high pressure pumps : 88,5% efficiency

� energy recovery devices : 96 %

3.2. ASHKELON PLANT

This plant has got a capacity of 320 MLD and is the current largest RO desalination

plant in operation. Operational costs are quite low cost for this type of project.

The local condition in Ashkelon and the RO sizing are presented in the following table.

This plant is composed of 2 RO passes.


MDW0158RP0080F01 D17 F01

Salinity g/L 41

Water temperature 15-30 °C

Overall conversion rate

of the RO system

40%

Number of passes 2

membrane SWRO

pumps High efficiency : 88,5%

Energy recovery

device

Work exchanger

DWEER (96%)

The corresponding electrical consumption of each step of the plant is as follows:

RO system Sea water

pumping HP pumps Power

recovery

Treated water

pumping

Total

6,8 -3,6 Electrical

consumption in

kWh per m3 of

produced water

0,45

3,2 (=6,8-3,6)

0,33 4

The total electrical cost of the plant includes raw water and treated water pumping

costs and is often less than 4 kWh per m3 of produced water (it can be as low as 3,9

kWh)

3.3. PERTH PLANT

This plant has a final capacity of 250 MLD (end 2007) and is one of the largest

desalination plants in operation. Electrical costs of this plant are the lowest costs for

this type of project for now.

The local conditions in Perth are presented in the following table. This plant is

composed of 2 passes.

Salinity g/L 36

Water temperature 15-30


MDW0158RP0080F01 D18 F01

Conversion rate of the

RO system

41%

Number of passes 2

membrane SWRO

pumps High efficiency : 88%

Energy recovery

device

Work exchanger PX

(96%)

The salinity is lower than in the sea water processed by Ashkelon. The overall

conversion rate can be higher than the one for Ashkelon. The electrical cost in Perth is

then a bit lower than in Ashkelon. It is mostly due to better local condition in Perth.

The corresponding electrical consumption of each step of the plant are the following

one:

RO system Sea water

pumping HP pumps Power

recovery

Treated water

pumping

Total

5,25 -2 Electrical

consumption

in kWh

0,33

3,33 =(5,25-2)

0,32 3,8

The total electrical cost of the plant includes raw water and treated water pumping

costs and is 3,8 kWh per m3 of produced water.

3.4. CONCLUSION

In the 2 last case studies, the electrical consumptions are close:

� For the RO system : 3,2 – 3,3 kWh

� For the whole plant : 3,9-4 kWh

Both plants use high efficiency pumps and energy recovery devices of the same type.

They use the best technology available on the market today. Exact membrane

characteristics are unpublished data (like permeability).


MDW0158RP0080F01 D19 F01

4. APPLICATION TO THE DUBLIN PROJECT

The local conditions in the Dublin area, as estimated during the sampling round

performed in August are:

Salinity 40 g/L

Water temperature 15 °C

Boron 3-4 mg/L

(European standards in

drinking water = 1mg/L)

The salinity is around 40 g/L according to the first sea water analysis (performed in

August 2007), which is close to the salinity of water processed in Perth and Ashkelon.

On the other hand, the temperature is lower than in Australia or Israel. The first value

measured in Irish sea is 15°C, but it might reach 10 °C or less during the winter.

Design hypothesis:

membrane SWRO

Number of passes 2 for boron removal

pumps High efficiency : 88,5%

Energy recovery

device

Work exchanger : 96%

An estimation of electrical costs can be made, using the following hypothesis:

� Minimum temperature during the year : 10°C

� RO Conversion rate of 1rst pass: 50%

� RO Conversion rate of 1rst pass: 90%: with the current membrane

technologies, 2 pass will be needed for boron removal.

� Membrane permeability between 1,2 and 1,5 L/m2/h


MDW0158RP0080F01 D20 F01

Membrane permeability

L/m2/h/bar

1

(ashkelon

membrane)

1,4

(current

maximum)

Estimated Required feed pressure 68 63

10°C 10°C Estimated electrical consumption

For a ONE-pass configuration

- RO system

- Whole plant

2,93

3,7

2,63

3,4

10°C 10°C Estimated electrical consumption

For a TWO-pass configuration

- RO system

- Whole plant

3,3

4,07

3

3,77

The whole electrical consumption of a desalination plant located in the area of Dublin

can be estimated at 3,77 kWh per cubic meter of produced water, with the

technologies available on the market for now (membrane and pumping units). In spite

of low temperature in Irish sea, the electrical consumption is similar to those of

Ashkelon and Perth, mostly thanks to new membranes recently made available (with

higher permeability and good salt rejection)

Further membrane development could enable a one pass RO system (with high boron

rejection) and then bring down this cost to 3,4 kWh/m3 or less (Figure 10).


MDW0158RP0080F01 D21 F01

1

1,5

2

2,5

3

3,5

4

0,8 1 1,2 1,4 1,6 1,8 2

perméabilité membranaire en LMH/bar

couts en kWh

1 pass - 5°C 2 passes - 5°C1 pass -10°C 2 passes - 10°C

todayashkelon membrane

possible future developpments

Perth andAshkelon

Figure 10 : Evolution of electrical costs depending on the minimum water temperature, the number of RO passes and the membrane permeability (including possible

development)

However, in order to asses a realistic value (representative of what the plant would

really be) the calculation should be performed again after the final design of the plant.

The feed pressure and the overall conversion rate will depend on the RO system

design, as explained in the section 2.4.


MDW0158RP0080F01 D22 F01

5. CONCLUSION

Various parameters are involved in the electrical consumption of a RO plant. Hence,

any assessment of power consumption of a RO plant should be performed

independently, taking into account the local conditions, the RO sizing of the plant and

the electromechanical components efficiency. Most of the time, values published are

not representative of the whole electrical consumption of the plant, and are partial

results corresponding only to the first pass of the RO system.

It is then crucial to list any parameters impacting the power consumption in order to

assess a realistic value for the existing largest plants (Ashkelon and Perth) and a plant

in the area of Dublin.

Efficiency of electromechanical equipment has been greatly improved in the past

years mainly at the energy recovery stage.. This helped saving electricity for the

desalination plants built during the last three years. These equipments efficiency are

close to a maximum limit (88,5% for HP pumps and 96% for energy recovery devices)

and are unlikely to improve during the next years.

Concerning the RO design, it mostly depends on the local conditions, the targeted

treated water quality and the available membrane on the market to reach this water

quality. The electrical consumption of RO system is lower when high membrane

permeability is used. Much advance has been made concerning the membrane

characteristics. The permeability has increased and may still increase during the next

years. But for now this evolution has been performed at the expense of the membrane

salt rejection (then of the permeate quality).

As a result of the above, the overall electrical consumption of a desalination plant

located in the area of Dublin can be estimated at 3.77 kWh per cubic meter of

produced water, with the technologies available on the market for now (membrane

and pumping units). In spite of low temperature in Irish sea, the electrical consumption

is similar to those of Ashkelon and Perth, mostly thanks to new membranes recently

made available (with higher permeability and good salt rejection)

Further membrane development could enable a one pass RO system (with high boron

rejection) and then bring this cost down to around 3.4 kWh/m3 or less.


MDW0158RP0080F01 D23 F01

APPENDICES : TRAKING ON DESALINATION PLANT PERFORMANCE

Year Capacity (m³/d)

(Expected)

Costs

electrical

consumption

Water Cost

(US$/m³)

Total Energy consumption

(kWh/m³)

Feed Water

Salinity (mg/l)

Feed Water Temperature

(°C) Membrane Provider

Energy recovery

system Provider

2001 120000 0,7 4.08 - 4.25 38500 14 to 24 °CSWC3 Spiral

WoundHydranautics

Pelton Turbines

(80% of efficiency) CALDER

2002 136000 0,71 4.0 15000-35000

First pass SWRO Toray SWHR-380

; Second Pass BWRO Toray SUL-G20F

TorayPelton Turbines

30- 40 % efficiency

2006 200000 Toray

2003 170000 0.70-0.90 4,5 38500 22 to 35 °C

1 Pass: SWC3 2 Pass: ESPA1 low energy membranes

HydranauticsPelton Turbines

88-89% effciciencyCALDER

1998 1280001.774 (capital

cost)43764

module Hollosep HM10255FI

Toyobo

2005 1363800.49 (first year operation) -

0,784.1 - 4,35

29000 -

35000

SWRO - High Boron Rejection

Membrane (up to 95%)

Toray

work exchanger DWEER

up to 97% of efficiency

CALDER

2005 13650 < 4.0 SWROWork exchanger ERI PX-220 95% efficiency

ERI

200595000


0.497 - 0.6718000 - 32000

SWC4 (obs: operation problemes - clogging)

HydranauticsPelton Turbine 45% efficiency

CALDER

2005 320000 0,52 < 4.0 40750SWRO - Three center design

Dow Chemical Company

Work

exchangerDWEER(96% efficiency)

1994 113600 43300 module Hollosep HM10255FI:

1480 pcs

Toyobo

2006 190000 Hydranautics

2006143700

(expandable to

250000)

0,75 - 1 3,8 Kwh/m3

TOTAL COST

35000 -

37000 16 to 24 °C

SWRO - Film Tech Membrane Technology -

spiral-wound RO module

Dow Chemical

Company

ERI PX - 220

(96,8% efficiency)ERI

TechnologyWater quality

Ashkelon - Israel

Jeddah

Huntington Beach, CA - USA

Kwinana - Perth - Australia

Medine/Yanbu -Saudi Arabia

(hybrid SWRO/MSF)

Tuas - Singapure

Ghalilah - UAE

Tampa Bay, Florida - USA

Carboneras Spain

Point Lisas -Trinidad and Tobago

Hamma (Algerie)

Fujairah (UAE)

Location

APPENDIX E

CARBON FOOTPRINT MODEL

Water Supply Project – Dublin Region Appendix E Desalination Study Report

MDW0158RP0080F01 E1 F01

Last Updated 01/07/2008

Treatment/Route H-Desalination

Energy Source Cost per unit % Energy Use

% Energy

Efficiency

Carbon Intensity C02

Tonnes per kWh

Electricity(grid) €0.10 100 100 0.000776Gas €0.03 58 0.000198Wind €0.15 100 0Wood Chips €0.02 88 0Pellets €0.12 90 0Biodiesel €0.35 81 0Oil €0.06 38 0.000249

100

Annual Inflation

Rate (%) 0

Carbon Intensity

C02 Tonnes per

kWh €28.70 www.pointcarbon.com Date: 01/07/2008

Water Demand

Energy Demand

(kWh)

Total Energy

from Primary

Fuel (kWh) Energy Cost Carbon Intensity Carbon Cost

2016 50.00 72,434,478 72,434,478 €7,243,448 56209.15 €1,613,2032017 50.00 72,434,478 72,434,478 €7,243,448 56209.15 €1,613,2032018 50.00 72,434,478 72,434,478 €7,243,448 56209.15 €1,613,2032019 50.00 72,434,478 72,434,478 €7,243,448 56209.15 €1,613,2032020 50.00 72,434,478 72,434,478 €7,243,448 56209.15 €1,613,2032021 58.00 84,067,069 84,067,069 €8,406,707 65236.05 €1,872,2742022 70.00 101,549,130 101,549,130 €10,154,913 78802.12 €2,261,6212023 82.00 119,076,979 119,076,979 €11,907,698 92403.74 €2,651,9872024 93.00 135,190,141 135,190,141 €13,519,014 104907.55 €3,010,8472025 105.00 152,824,545 152,824,545 €15,282,455 118591.85 €3,403,5862026 117.00 170,524,350 170,524,350 €17,052,435 132326.90 €3,797,7822027 128.00 186,812,366 186,812,366 €18,681,237 144966.40 €4,160,5362028 140.00 204,656,316 204,656,316 €20,465,632 158813.30 €4,557,9422029 151.00 221,087,788 221,087,788 €22,108,779 171564.12 €4,923,8902030 163.00 239,100,586 239,100,586 €23,910,059 185542.05 €5,325,0572031 174.00 255,698,157 255,698,157 €25,569,816 198421.77 €5,694,7052032 185.00 272,383,171 272,383,171 €27,238,317 211369.34 €6,066,3002033 196.00 289,160,808 289,160,808 €28,916,081 224388.79 €6,439,9582034 207.00 306,036,246 306,036,246 €30,603,625 237484.13 €6,815,7942035 218.00 323,014,667 323,014,667 €32,301,467 250659.38 €7,193,9242036 229.00 340,101,248 340,101,248 €34,010,125 263918.57 €7,574,4632037 240.00 357,301,169 357,301,169 €35,730,117 277265.71 €7,957,5262038 251.00 374,619,611 374,619,611 €37,461,961 290704.82 €8,343,2282039 262.00 392,061,751 392,061,751 €39,206,175 304239.92 €8,731,6862040 273.00 409,632,769 409,632,769 €40,963,277 317875.03 €9,123,013Totals 3592.00 5,297,071,255 5,297,071,255 €529,707,125 4110527.29 €117,972,133

Total Cost €647,679,259

Water Supply Project – Dublin Region Appendix E Desalination Study Report

MDW0158RP0080F01 E2 F01

Last Updated 01/07/2008

Treatment/Route H-Desalination

Energy Source Cost per unit % Energy Use

% Energy

Efficiency

Carbon Intensity C02

Tonnes per kWh

Electricity(grid) €0.10 100 0.000776Gas €0.03 100 58 0.000198Wind €0.15 100 0Wood Chips €0.02 88 0Pellets €0.12 90 0Biodiesel €0.35 81 0Oil €0.06 38 0.000249

100

Annual Inflation

Rate (%) 4

Carbon Intensity

C02 Tonnes per

kWh €40.00 www.pointcarbon.com Date: 01/01/2040

Water Demand

Energy Demand

(kWh)

Total Energy

from Primary

Fuel (kWh) Energy Cost Carbon Intensity Carbon Cost

2016 50.00 72,434,478 124,887,031 €3,496,837 24727.63 €989,1052017 50.00 72,434,478 124,887,031 €3,636,710 24727.63 €1,028,6692018 50.00 72,434,478 124,887,031 €3,776,584 24727.63 €1,068,2342019 50.00 72,434,478 124,887,031 €3,916,457 24727.63 €1,107,7982020 50.00 72,434,478 124,887,031 €4,056,331 24727.63 €1,147,3622021 58.00 84,067,069 144,943,222 €4,870,092 28698.76 €1,377,5402022 70.00 101,549,130 175,084,707 €6,078,941 34666.77 €1,719,4722023 82.00 119,076,979 205,305,137 €7,358,136 40650.42 €2,081,3012024 93.00 135,190,141 233,086,450 €8,614,875 46151.12 €2,436,7792025 105.00 152,824,545 263,490,595 €10,033,722 52171.14 €2,838,1102026 117.00 170,524,350 294,007,499 €11,525,094 58213.48 €3,259,9552027 128.00 186,812,366 322,090,286 €12,986,680 63773.88 €3,673,3752028 140.00 204,656,316 352,855,717 €14,622,341 69865.43 €4,136,0342029 151.00 221,087,788 381,185,841 €16,223,269 75474.80 €4,588,8682030 163.00 239,100,586 412,242,389 €18,006,748 81623.99 €5,093,3372031 174.00 255,698,157 440,858,891 €19,750,478 87290.06 €5,586,5642032 185.00 272,383,171 469,626,157 €21,565,233 92985.98 €6,099,8802033 196.00 289,160,808 498,553,116 €23,451,939 98713.52 €6,633,5482034 207.00 306,036,246 527,648,701 €25,411,561 104474.44 €7,187,8422035 218.00 323,014,667 556,921,839 €27,445,108 110270.52 €7,763,0452036 229.00 340,101,248 586,381,462 €29,553,626 116103.53 €8,359,4542037 240.00 357,301,169 616,036,499 €31,738,200 121975.23 €8,977,3772038 251.00 374,619,611 645,895,880 €33,999,959 127887.38 €9,617,1312039 262.00 392,061,751 675,968,536 €36,340,068 133841.77 €10,279,0482040 273.00 409,632,769 706,263,396 €38,759,735 139840.15 €10,963,468Totals 3592.00 5,297,071,255 9,132,881,474 €417,218,726 1808310.53 €118,013,297

Total Cost €535,232,023

APPENDIX F

ECONOMIC ASSESSMENT DETAILS

Water Supply Project

Dublin RegionAppendix F Desalination Study Report

CAPEX Assessment

Phase 1 Phase 2

Capital cost Capacity 200 Abstract. 476.4 Capacity 300 Abstract. 714.6 Capacity 100 Abstract. 238.2

PipelinesDiameter

(mm)

Length

(km)

Unit cost

(k€/m)Cost (k€)

Diameter

(mm)

Length

(km)

Unit cost

(k€/m)

Cost

(k€)

Diameter

(mm)

Length

(km)

unit cost

(k€/m)

Cost

(k€)

Intakes 1800 6 7.2 43200 1800 6 7.2 43200 1800 0 7.2 0

Outfalls 1400 4 5.2 20800 1400 4 5.2 20800 1400 0 5.2 0

Contingency (surveys) 15% 9600 15% 9600 15% 0

Transmission pipelines 1100 48.68 1.1 51796 1100 48.68 1.1 51796 1100 0 1.1 0

Transmission Crossings Type noUnit cost

(k€/cros.)

Cost

(k€)Type no

Unit cost

(k€/cros.)

Cost

(k€)Type no

Unit cost

(k€/cros.)

Cost

(k€)

National 2 275 550 National 2 275 550 National 0 275 0

Regional 8 50 400 Regional 8 50 400 Regional 0 50 0

Secondary 16 35 560 Secondary 16 35 560 Secondary 0 35 0

Railways 1 275 275 1 275 275 0 275 0

Major 2 275 550 Major 2 275 550 Major 0 275 0

Medium 7 200 1400 Medium 7 200 1400 Medium 0 200 0

Minor 12 75 900 Minor 12 75 900 Minor 0 75 0

Canals 0 200 0 0 200 0 200 0

Water Treatment Plant TypePower

(k€/MW)

Capacity

(k€/Mld)

Cost

(k€)Type

Power

(k€/MW)

Capacity

(k€/Mld)

Cost

(k€)Type

Power

(k€/MW)

Capacity

(k€/Mld)

Cost

(k€)

Power 3,700 kW Power 6,100 kW Power 2,400 kW

M&E 120 16 8067 M&E 120 16 12166 M&E 120 16 4099

Civil 15 7146 Civil 15 10720 Civil 15 3573

ESB 500 1850 ESB 500 3050 ESB 500 1200


M&E 360 72000 M&E 360 108000 M&E 360 36000


Memb 103 20600 Memb 103 30900 Memb 103 10300

ESB 500 21050 ESB 500 31550 ESB 500 10500


M&E 120 16 3656 M&E 120 16 5688 M&E 120 16 2032


ESB 500 1900 ESB 500 3700 ESB 500 1800

Water StorageVolume

(Ml)

Unit cost

(k€/Ml)

Volume

(Ml)

Unit cost

(k€/Ml)

Volume

(Ml)

Unit cost

(k€/Ml)

Tanks 18.12 300 5436 27.18 300 8154 9.06 300 2718

Sub-Total 345536 454658 109123

Design&Supervision 5% of total 17277 5% of total 22733 5% of total 5456

Land Purchase 100 k€/ha 15 1500 100 k€/ha 15 1500 100 k€/ha 0 0

Wayleaves&legal 100 k€/km 24.34 2434 100 k€/km 24.34 2434 100 k€/km 0.0 0

Preliminaries and Overheads 15% of total 51830 15% of total 68199 15% of total 16368

Total (k€) 418577 549524 130947

Phase 1 Phase 2 Upgrading Cost

Clear PS

Roads

Rivers

Reverse Osmosis

Raw PS

MDW0158Rp0080F01 F1 F01

Water Supply Project

Dublin RegionAppendix F Desalination Study Report

CAPEX-OPEX Assessments

2013-2040

coef UNIT Unit Price 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 TOTAL

VOLUME Average annual flow Dublin Mld 50 50 50 50 50 58 70 82 93 105 117 128 140 151 163 174 185 196 207 218 229 240 251 262 273

Average annual flow Local Mld 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Instantaneous average raw water flow 2.382 l/s 1,379 1,379 1,379 1,379 1,379 1,599 1,930 2,261 2,564 2,895 3,226 3,529 3,860 4,163 4,494 4,797 5,101 5,404 5,707 6,011 6,314 6,617 6,920 7,224 7,527

Instantaneous average clear water flow l/s 579 579 579 579 579 671 810 949 1,076 1,215 1,354 1,481 1,620 1,748 1,887 2,014 2,141 2,269 2,396 2,523 2,650 2,778 2,905 3,032 3,160

CAPEX

Intake and Sump

Pipe ND 1800 ml 7,200 2,000 2,000 2,000

Pipe ND 1400 5,200 1,333 1,333 1,333

Transmission

Pipe ND 1100 ml 1,064 16,227 16,227 16,227

TOTAL ml 19,560 19,560 19,560 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Total Cost 103 Euros 38,599 38,599 38,599 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 115,796

Crossings 103 Euros 1,545 1,545 1,545 4,635

Contingency for Marine Site Results 15% 103 Euros 3,200 3,200 3,200

Raw Water Pumping Station kW 3,700 6,100

M&E 103 Euros 8,067 4,099 12,166

Civil 103 Euros 7,146 3,573 10,720

ESB 103 Euros 1,850 1,200 3,050

RO kW 42,100 63,100

M&E 103 Euros 72,000 36,000 108,000

Civil 103 Euros 70,800 35,400 106,200

Memb 103 Euros 20,600 10,300

ESB 103 Euros 21,050 10,500 31,550

Clear Water Pumpin Station kW 3,800 7,400

M&E 103 Euros 3,656 2,032 5,688

Civil 103 Euros 3,000 1,500 4,500

ESB 103 Euros 1,900 1,800 3,700

Total Cost 103 Euros 0 0 210,069 0 0 0 0 0 0 0 0 0 106,405 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 316,474

M&E ? 103 Euros 0

Civil 103 Euros 5,436 2,718 8,154

Total Cost 103 Euros 0 0 5,436 0 0 0 0 0 0 0 0 0 2,718 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8,154

103 Euros 43,344 43,344 258,849 0 0 0 0 0 0 0 0 0 109,123 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 454,658

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 454,658

103 Euros 24,347 24,347 24,347 0 0 0 0 0 0 0 7,275 7,275 7,275 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 94,866

Design&supervision 5% 103 Euros 5,759 5,759 5,759 1,819 1,819 1,819

Land purchase 103 Euros 500 500 500

Wayleaves&legal 103 Euros 811 811 811

Preliminaries&overheads 15% 103 Euros 17,277 17,277 17,277 5,456 5,456 5,456

Pipelines 80 103 Euros 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 1,447 36,186

M&E 15 103 Euros 5,582 5,582 5,582 5,582 5,582 5,582 5,582 5,582 5,582 5,582 8,390 8,390 8,390 8,390 8,390 8,390 8,390 8,390 8,390 8,390 8,390 8,390 8,390 8,390 8,390 181,669

Civil 50 103 Euros 1,728 1,728 1,728 1,728 1,728 1,728 1,728 1,728 1,728 1,728 2,591 2,591 2,591 2,591 2,591 2,591 2,591 2,591 2,591 2,591 2,591 2,591 2,591 2,591 2,591 56,149

Membranes 7 103 Euros 2,943 2,943 2,943 2,943 2,943 2,943 2,943 2,943 2,943 2,943 4,414 4,414 4,414 4,414 4,414 4,414 4,414 4,414 4,414 4,414 4,414 4,414 4,414 4,414 4,414 95,643

Total Cost 103 Euros 0 0 0 11,699 11,699 11,699 11,699 11,699 11,699 11,699 11,699 11,699 11,699 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 369,647

103 Euros 67,691 67,691 283,196 11,699 11,699 11,699 11,699 11,699 11,699 11,699 18,974 18,974 128,097 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 16,843 919,171

OPEX

1% 103 Euros 0 0 0 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 1,158 28,949

M&E 3.0% 103 Euros 0 0 0 352 352 352 352 352 352 352 352 352 352 536 536 536 536 536 536 536 536 536 536 536 536 536 536 536 11,551

Civil 1% 103 Euros 0 0 0 156 156 156 156 156 156 156 156 156 156 234 234 234 234 234 234 234 234 234 234 234 234 234 234 234 5,064

M&E 3.0% 103 Euros 0 0 0 2,160 2,160 2,160 2,160 2,160 2,160 2,160 2,160 2,160 2,160 3,240 3,240 3,240 3,240 3,240 3,240 3,240 3,240 3,240 3,240 3,240 3,240 3,240 3,240 3,240 70,200

Civil 1% 103 Euros 0 0 0 708 708 708 708 708 708 708 708 708 708 1,062 1,062 1,062 1,062 1,062 1,062 1,062 1,062 1,062 1,062 1,062 1,062 1,062 1,062 1,062 23,010

103 Euros 0 0 0 4,533 4,533 4,533 4,533 4,533 4,533 4,533 4,533 4,533 4,533 6,229 6,229 6,229 6,229 6,229 6,229 6,229 6,229 6,229 6,229 6,229 6,229 6,229 6,229 6,229 138,774

103 Euros 4.5 0 0 0 223 223 223 223 223 223 223 223 223 223 345 345 345 345 345 345 345 345 345 345 345 345 345 345 345 7,403

103 Euros 0.1 0 0 0 7,243 7,243 7,243 7,243 7,243 8,407 10,155 11,908 13,519 15,282 17,052 18,681 20,466 22,109 23,910 25,570 27,238 28,916 30,604 32,301 34,010 35,730 37,462 39,206 40,963 529,707

Desalination (RO process including RW pumping)

Flow m3/year 18,250,000 18,250,000 18,250,000 18,250,000 18,250,000 21,170,000 25,550,000 29,930,000 33,945,000 38,325,000 42,705,000 46,720,000 51,100,000 55,115,000 59,495,000 63,510,000 67,525,000 71,540,000 75,555,000 79,570,000 83,585,000 87,600,000 91,615,000 95,630,000 99,645,000

Electric consumption 3.74 kWh/year 68,238,725 68,238,725 68,238,725 68,238,725 68,238,725 79,156,921 95,534,215 111,911,509 126,924,028 143,301,322 159,678,616 174,691,136 191,068,430 206,080,949 222,458,243 237,470,763 252,483,282 267,495,802 282,508,321 297,520,841 312,533,360 327,545,880 342,558,399 357,570,919 372,583,438

Transmission ( 2 pipes 1100 mm)

Flow m3/year 18,250,000 18,250,000 18,250,000 18,250,000 18,250,000 21,170,000 25,550,000 29,930,000 33,945,000 38,325,000 42,705,000 46,720,000 51,100,000 55,115,000 59,495,000 63,510,000 67,525,000 71,540,000 75,555,000 79,570,000 83,585,000 87,600,000 91,615,000 95,630,000 99,645,000 1,311,080,000

Head 24.3 km m 62.0 63.3 63.3 63.3 63.3 63.3 63.8 64.8 65.9 67.0 68.4 69.9 71.4 73.2 74.9 77.0 79.0 81.1 83.4 85.7 88.2 90.8 93.5 96.3 99.3 102.3

Electric consumption 3.63 kWh/year 4,195,753 4,195,753 4,195,753 4,195,753 4,195,753 4,910,148 6,014,915 7,165,470 8,266,112 9,523,223 10,845,733 12,121,230 13,587,886 15,006,838 16,642,342 18,227,394 19,899,888 21,665,006 23,527,925 25,493,826 27,567,888 29,755,290 32,061,211 34,490,832 37,049,331

Chemicals 103 Euros 20.3 0 0 0 1,015 1,015 1,015 1,015 1,015 1,177 1,421 1,665 1,888 2,132 2,375 2,598 2,842 3,065 3,309 3,532 3,756 3,979 4,202 4,425 4,649 4,872 5,095 5,319 5,542 72,918

Sludge disposal 103 Euros 3.6 0 0 0 180 180 180 180 180 209 252 295 335 378 421 461 504 544 587 626 666 706 745 785 824 864 904 943 983 12,931

Staff 103 Euros 45 0 0 0 360 360 360 360 360 360 360 360 360 360 540 540 540 540 540 540 540 540 540 540 540 540 540 540 540 11,700

Overheads 5% 103 Euros 0 0 0 678 678 678 678 678 745 847 949 1,043 1,145 1,348 1,443 1,546 1,642 1,746 1,842 1,939 2,036 2,133 2,231 2,330 2,429 2,529 2,629 2,730 38,672

0 0 0 14,233 14,233 14,233 14,233 14,233 15,655 17,792 19,933 21,901 24,054 28,311 30,297 32,472 34,473 36,666 38,685 40,713 42,750 44,798 46,857 48,927 51,009 53,104 55,211 57,332 812,105

103 Euros 1.59 0 0 0 28,974 28,974 28,974 28,974 28,974 33,610 40,564 47,518 53,892 60,846 67,799 74,174 81,128 87,502 94,456 100,830 107,204 113,579 119,953 126,327 132,701 139,076 145,450 151,824 158,199

5% 103 Euros 0 67,691 67,691 283,196 -3,042 -3,042 -3,042 -3,042 -3,042 -6,255 -11,072 -8,610 -13,016 91,305 -22,645 -27,033 -31,812 -36,185 -40,946 -45,302 -49,648 -53,985 -58,311 -62,627 -66,931 -71,223 -75,503 -79,770 -84,023 -454,658

Tanks

Other Costs

TOTAL CAPEX

NPV

Renewal

Standing charges

TOTAL OPEX

SALES

Pipelines

Network Maintenance

Pumping Stations Maintenance

WTP

Total investment

RO Maintenance

Total Maintenance

Power Capacity Cost

Electrical consumption

Pumping Stations & RO

MDW0158Rp0080F01 F2 F01

Water Supply Project – Dublin Region Appendix F Desalination Study Report

MDW0158RP0080F01 F3 F01

WHOLE LIFE COST

Discount rate 3% 5% 7%

NPV CAPEX (k€) 706,560 611,287 539,281

Investment 394,127 362,067 334,946Renewals 228,253 170,755 130,736One off items 84,180 78,465 73,600

NPV RESIDUAL VALUE (k€) 192,933 110,458 63,908

NPV OPEX (k€) 469,496 336,024 246,329

Maintenance 86,029 64,529 49,535Energy Capacity charge 4,544 3,386 2,582Energy Consumption 300,553 212,219 153,394Chemicals 41,460 29,316 21,220Sludge disposal 7,353 5,199 3,763Personnel 7,200 5,374 4,105Overheads 22,357 16,001 11,730

Volume delivered (Ml) 1,311,080 1,311,080 1,311,080

NPV Capex + Opex (k€) 1,176,057 947,312 785,610

NPV Capex + Opex - Residual Value (k€) 983,124 836,854 721,702

NPV Capex + Opex - Residual Value / Volume (€/m3) 0.75 0.64 0.55

NPV Capex - Residual Value / Volume (€/m3) 0.39 0.38 0.36NPV Opex / Volume (€/m3) 0.36 0.26 0.19

APPENDIX G

DESALINATION PLANT LAYOUT

desalination study report - website

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