Tseung Kwan O Desalination Plant

Ir CHAN Tak Yeung, Thomas

Chief Engineer / Consultants Management

Water Supplies Department, HKSARG

Dr. Srinivas (Vasu) Veerapaneni

Desalination Technology Leader

Black & Veatch Corporation

19 December 2016

The Hong Kong Institution of Engineers

2

Outline

• Uprising Challenges and Strategic Measures

• Global Desalination Perspective

• The Desalination Plant Project

• Overview of Typical Desalination Plant Design

3

Uprising Challenges and

Strategic Measures

4

Is

Hong Kong a

WATER-SCARCE city?

5

Water Rationing in the 1960s

6

Three-pronged Supply

Local Yield199mcm(16%)

Dongjiang Water

772mcm(62%)

Seawaterfor Flushing

274mcm(22%)

2015 Demand

1245mcm

Dongjiang Water

Local Yield

Seawater

7

WATER SECURITY “the capacity of a population to safeguard sustainable

access to adequate quantities of acceptable quality

water for sustaining livelihoods, human well-being, and

socio-economic development, for ensuring protection

against water-borne pollution and water-related

disasters, and for preserving ecosystems in a climate

of peace and political stability.”

(UN-Water, 2013)

8 Photo source: Hotblack/Morguefile

Who’s Next?

Climate Change Is

Happening

Thailand:

July 2015 California,

USA:

April 2015

Taiwan:

April 2015

9

How Sensitive is our Water Resources?

10

How Sensitive is our Water Resources?

11

Hong Kong’s Challenge in Water Supply

Fluctuating local yield and Donjiang

water supply due to climate change

Keen competition for the

Dongjiang water resource

Increasing water demand and arising from

population and economic growth

12

Total Water Management

Demand Management

- Water Conservation

Supply Management

- New Water Sources

13

Water Conservation

Total Water Consumption

2%

8% 5%

31%

Non-domestic “Water Conservation

Starts from Home”

School Talk

Water: Learn and

Conserve – Teaching Kit

for Liberal Studies

“Save Water. Cherish the

World” Mobile Showroom

Roving Exhibition

Water Efficiency

Labelling Scheme

(WELS)

Flow Regulator

14

Best Practice Guidelines for

– Catering

– Hotel

– Laundry Industry

Water Conservation

Total Water Consumption

2%

8% 5%

31%

Non-domestic

15

New Water Sources

Local Yield(10-25%)

Dongjiang Water(41-56%)

Seawater for Flushing

(26%)

Desalination(6%)

Reclaimed Water(~1.5%)

Grey Water Recycling(~0.5%)

Note: Chart drawn based on average local yield of 295mcm

Seawater Desalination

(5% - 10%)

Proposed

Desalination Plant

Local Yield

Dongjiang Water

Seawaterfor Flushing

Three

Pronged

Supply

Six

Pronged

Supply

Water Reclamation

(2%+)

Grey Water Recycling

(~0.5%) Desalination

Water Reclamation

Grey Water Recycling

16

Global Desalination

Perspective

17

Global Desalination Trend

Proven: 150 countries have installed desalination plants around the world

18

Desalination Technologies

Currently Available

Primarily two types:

Thermal Desalination

Membrane Desalination

19

Principle of operation – Evaporate water and condense the vapors

Oldest desalination technology

One of thermal technologies - Multi-Stage Flash (MSF)

Thermal Desalination

B&V - 19

20

Lok On Pai Desalination Plant

• Commissioned in October 1975

• Adopted multi-stage flash distillation

• Decommissioned in 1982 due to high operation cost.

21

Pure water migrates from low conc.

vessel to high conc. vessel

Flow stops when

hydraulic head on

high conc. vessel is

equal to solution’s

osmotic pressure

If external P

greater than

osmotic pressure is

applied, “Reverse

Osmosis” occurs

(desalination).

Semi permeable membrane

Start with equal

volumes of

fresh water and

saline water

Saline waterFresh water

Natural

osmosis

Saline waterFresh water

water

Osmotic

equilibrium

osm

otic

pre

ssu

reP

Reverse

Osmosis

water

(a) (b) (c) (d)

Membrane Desalination

Reverse Osmosis (RO): Principle

22

• , Aus

Gold Coast, Australia

Melbourne desalination plant, Australia

Examples of SWRO Plants

Source: Suez Environment

Source: Veolia

23

• New water source not susceptible to climate

change

• Latest reverse osmosis technology

Seawater Desalination by RO

24

The Desalination Plant

Project

25

The Proposed Desalination Plant

2007 Pilot Plant Study

confirmed technical

feasibility of

desalination

technologies as a

reliable freshwater

source

2008 The HK Government

promulgated the Total

Water Management

Strategy which

recommended

seawater desalination

as a new alternative

water source

2015 Funding

was

approved

from the

LegCo’s

FC in

Jun

2015.

2000 - 2002 Feasibility study

of developing

desalination in

HK. Pilot Plant

Study

commenced in

2002.

2012 - 2015 Planning and investigation study

confirmed the technical and

environmental viability of

constructing a seawater reverse

osmosis desalination plant at TKO

Area 137

Nov 2015 Investigation Review,

Design and Construction

Consultancy Agreement

for the first stage of the

desalination plant

commenced.

2015 Environmental

Permit was

granted by

EPD

26

Site Selection Considerations

Oceanic current with stable seawater quality in the eastern waters

Strategic supply network to other parts of the territory

TKO Area 137 is currently a public fill bank zoned “Other Specified Uses (Deep Waterfront Industry)”

High turbidity in the western waters due to tidal effects in the Pearl River Delta

Environmental impacts assessed to be acceptable

27

9.5 km long fresh water

trunk main to convey the

fresh water produced at

the proposed

desalination plant

Tseung Kwan O Desalination Plant

-First Stage: 135 MLD = ~5% of the

daily fresh water demand in HK

-- Second Stage: expansion to 270

MLD = ~10% of the daily fresh water

demand in HK

Existing TKO fresh

water primary

service reservoir

350m

Submarine

outfall

250m

Submarine

intake

TKO Area 137

The Proposed Desalination Plant

28

Overview of Typical

Desalination Plant Design

29

Seawater RO Process Schematic

30

Intake • One of the important components of the

desalination plant. In fact, treatment starts with

a well designed intake

• Two types of intakes possible: Open intake or

Subsurface Intake

– Subsurface intake – high water quality, but

not always feasible

– Submerged open intake selected for the

project due to its feasibility

• Most commonly used around the world

• Capable of providing large flows

• Good pretreatment essential as water

quality is influenced by many factors

• Off the littoral zone of the coast to

minimize environmental impacts

• Low influent velocity to prevent

impingement

31

Open submerged intake at Fujairah, UAE

Open Submerged Intake

32

2 tunnels (2.5 km long and 3.4 m diameter)

Intake at Sydney Desalination Plant

Source: Veolia

33

2 tunnels – (2.2 km influent and 2 m effluent); 2.8 m ID

Open intake (submerged pipe, tunnel on land); Gold Coast

Source: Veolia

34

Environmental Considerations for Intake

Intake structure of Perth Desalination Plant, Australia (Source:Water Corporation)

Intake Overseas Example (Perth Desalination Plant, Australia)

Seawater Intake

•Submarine pipe to be constructed by micro-tunnelling

•Design of intake structure to minimise potential impingement and entrainment of fish and larvae

35

Environmental Considerations for Outfall

Marine life around brine discharge diffuser of Perth Desalination Plant, Australia (Source:Water Corporation)

Discharge Diffusers

•Submarine pipe to be constructed by micro-tunnelling

•Rapid dilution of brine to ambient level

•Confined mixing zone resulting in minimal impact to seawater quality

36

Intake and Outfall of TKO Desalination Plant

37

Objectives of Pretreatment

• Biofouling control

• Remove turbidity, suspended solids

– RO membranes are good at removing dissolved constituents. Particulate material can plug up membranes

• Address the following if present

– Oil and grease – RO membranes are not tolerant

– Algae – Can plug up pretreatment and foul RO membranes

• Typically, efficacy of pretreatment is measured in terms of silt density index (SDI)

• However, not all foulants captured by SDI

38

• Most common issue for open intake system

• Shock chlorination most widely practiced

• Newer practices being tested

• Change in pH (if feasible for offshore line also)

• Biofilm monitors

• Use of newer oxidants that do not damage membranes such as chloride dioxide

• Use of biocides such as DBNPA*

• Osmotic backwash of RO membranes

Biofouling Control

*2,2-dibromo-3-nitrilopropionamide

39

• Coagulation + Filtration (Perth, Ashkelon, Fujairah, Sydney, Gold Coast, etc.)

• Clarification used as necessary (Trinidad, Singapore, Hamma)

• Second stage filtration is also used in some facilities (Okinawa, Eni Gela-Sicily)

• Most commonly used coagulant is iron salt

• Attributed to broader pH range, discharge limitations

• Polymer – Almost all facilities used it at some point; Continuous usage not preferred – can irreversibly damage RO membranes

Pretreatment - Traditional

Iron coagulants have lower solubility over a broad pH range compared to Al

Pressure filters at Perth SWRO Source: water Corporation

40

• Singapore – Coagulation, flocculation, dissolved air flotation/filtration (DAFF) to address algae and oil & grease

• Barcelona, Spain – Coagulation, flocculation, DAF, two stage filtration

• Beckton, UK – Coagulation, flocculation, lamella clarifiers, pressure filters and UF

• Fujairah II – coagulation, flocculation, DAF and media filtration

Recent Pretreatment Configurations

In-Filter DAF at a SWRO facility Source: Black & Veatch

Additional processes primarily to address severe water quality issues

41

Algae

• Requires use of DAF

• Algal blooms occur periodically

• Need for treatment dependent on degree of reliability needed and also type and concentration of algae

– Not all are created equal

– Variations in morphology could have significant implications for treatment

– Not all algae concentrations can be estimated by chlorophyll measurements

– Dinoflagellates could be as large as 100 um and contribute minimally for chlorophyll

Source: Harmful algal blooms in coastal upwelling systems, Oceanography, 2005

42

• MF/UF as SWRO pretreatment on the rise

• They are polymeric membranes with absolute pore sizes;

• Primary benefits

• No coagulant needed for several, depending on water quality

• Consistently good water quality

• Design issues

• Ability to deal with varying water quality

• Strainers (type and size) to be selected carefully

• Algae

• Interchageability between different suppliers

Microfiltration/Ultrafiltration (MF/UF) pretreatment

43

• Cost still an issue

• Membrane life and replacement costs

• Largest plants with MF/UF are procured under alliance style agreement or DBO contractor has a UF product

• Adelaide, Perth II – Alliance style DBO plants in Australia

• Tuas II, singapore; Magta and Tlemcen, Algeria and Tianjin china – DBO contractor's own the product

MF/UF pretreatment

44

UF pretreatment at 318,000 m3/day (84 MGD) SWRO

Source: Hyflux

45

• Primary process for removal of ions

• Significant developments in membranes over last few decades

Reverse Osmosis

• In other words, an element with today’s rejection and permeability would have cost 150 times more 30 years ago

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1975 1980 1985 1990 1995 2000 2005 2010Year

Salt

pas

sa

ge (

%)

& M

em

bra

ne C

ost

($/g

allo

ns/d

ay)

0

3

6

9

12

15

18

21

24

Ele

men

t p

rod

ucti

vit

y (

gp

d/f

t2)

Salt passage Membrane Price/Flow Productivity (gpd/ft2)

Reference: Based on data by Truby et al., 2007

46

RO Design parameters

• Recovery – Percent of water converted to permeate

• Flux – Quantity of water pushed through unit membrane

area

• Skid Size/Pumping arrangement

• Number of passes – how many times the water is treated

• Energy recovery devices

47

Second pass • Typically required to meet specific water quality goals

– Boron concentration typical reason outside US • WHO guideline revised from 0.5 mg/L to 2,4 mg/L. • 2nd pass operated at pH of ~10 to convert uncharged boric acid to

charged borate

– Bromide • Formation of brominated DBPs when the desalinated water is mixed

with other water sources

– TDS limits (Chloride, sodium, etc.)

– Examples: • Perth:

– 90% of the SWRO permeate treated by 2nd pass – 0.1 mg/L bromide limit; Recently relaxed to 0.2 mg/L

• Ashkelon – 100% of the SWRO permeate treated by additional passes – 20 mg/L chloride and 0.4 mg/L boron limits

• Tuas – 80% of SWRO permeate at pH of 10 – boron limit of 0.5 mg/L

– Concentrate from second pass typically recycled to SWRO feed

48

Boron speciation B rejection

1st pass

2nd pass

Source : Dow chemical

49

Permeate collection for second

pass treatment

• Consider taking permeate from both ends of pressure

vessel

– Permeate from lead end of membrane can bypass second pass

treatment

– Permeate from lag end (higher concentrations of constituents)

further treated by second pass

– Depending on the water quality requirements, elements

separated (permeate tube blocked) after 2 or 3 elements

50

Feed water to second pass

FeedP

erm

ea

te 2

To post treatment

Pe

rme

ate

1

Feed

concentrate

to waste

Fe

ed

co

nc

Pe

rme

ate

co

nc Good quality -

to post treatment

Poor quality (wrt B)

send to second RO

Concentrate to

waste

Permeate2 for

further treatment

Permeate1 to

post treament

• Permeate from lag elements of the SWRO system

could be used as feed to second pass RO

51

Parameter Value

Boron ≤1.0 mg/L

Bromide ≤0.2 mg/L

RO of TKO Desalination Plant

• 2 passes RO to achieve the freshwater quality

objectives:-

• Low bromide concentration to ensure that disinfection

byproduct formation won’t increase when this water is

blended with other water that has organic carbon

52

• Two types of devices to recovery energy

• I: Hydro-Mechanical Conversion

– Hydraulic energy in concentrate is converted

to mechanical and then back to hydraulic

energy

• Pelton Wheel

• TurboCharger

• II: Positive Displacement

– Hydraulic energy in concentrate is transferred

to feed water directly

• Work Exchanger

• Pressure Exchanger

• Other devices

Energy Recovery:

HP PUMP

MEMBRANES

PELTON

TURBINE

HP PUMP

MEMBRANES

PXBOOSTER

PUMP

53

Post-treatment • RO permeate is corrosive

– low pH, low alkalinity, low TDS, low hardness, etc.

• Typical post-treatment: adjustment of pH,

alkalinity and hardness.

• Target: – match pH to that in distribution system – have reasonable alkalinity, positive LSI and

reasonable CCPP

• Raising pH: If feed water was acidified,

degassify to remove CO2. Add NaOH or Lime

• Typical chemicals: Lime, NaOH, CO2. Also,

use of corrosion inhibitors.

• Soda ash – not so common

• Calcite filters also an option

54

Green Energy Initiative

Use of Landfill Gas from South East New Territories (SENT) Landfill

• Processed gas from SENT available at night time

• On depletion till around 2030

• Technical and financial viability being explored

SENT Landfill

55

Moving Forward …

Ultimate Project Objective:

A state of the art desalination facility that provides a

strategic water source to Hong Kong at optimal cost

Save Water for the Future

Every Drop Counts

Thank You