the effects of sewage treatment works on watercourses - t.swain

NOTTINGHAM TRENT UNIVERSITY

THE EFFECTS OF SEWAGE TREATMENT EFFLUENTS ON WATERCOURSES.

by

THOMAS M. SWAIN

Dissertation submitted in partial fulfilment of the BSc (Honours) Degree in Environmental Science

2015

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Abstract

With the eutrophication of watercourses of primary concern at both UK and

European level, scrutiny has increased on sewage treatment works to improve levels

of treatment and demonstrate that they are not having a detrimental effect upon the

receiving watercourse. Therefore, the aim of this project was to investigate the

effects of sewage treatment effluents upon receiving watercourses to understand

whether significant differences occur between upstream and downstream samples.

Seven Severn Trent sewage treatment works of varying technology (Activated

Sludge Production, Membrane Bioreactor & Percolating Filter Bed) were sampled to

investigate their effects. River water samples were collected 200 metres upstream

and downstream as well as a final effluent sample for a range of 14 determinants

(ammonia, biological oxygen demand, boron, chloride, chemical oxygen demand,

conductivity, dissolved oxygen, nitrate, nitrite, orthophosphorus, pH, phosphorus,

sulphate & temperature) with an aim of understanding their effect upon the

watercourse. This project identified a significant decrease in pH between upstream

and downstream river water samples for pH at Site 4, a Membrane Bioreactor. All

other upstream and downstream river samples were not significant and therefore

demonstrated that STW effluents do not have a significant effect upon the receiving

watercourse. Further analysis into the pH result for Site 4 indicated that a more

likely cause for the decreased pH was the use of NaCl as a road salt as well as

increased nitrate inputs causing a eutrophic environment, thus reducing DO

concentrations as well as riverine pH. Flow was also correlated to individual

samples and demonstrated no-correlation between low pH in final effluent and

riverine pH levels. The results of this study demonstrates that sewage treatment

works are having a negligible effect upon watercourses. Technical improvements at

sewage treatment works have reduced determinant concentrations being

discharged by final effluent and are helping to achieve the WFD aim of achieving

‘good chemical and ecological status’ for all UK watercourses by 2015.

Keywords: Final Effluent; Membrane Bioreactor; Activated Sludge Process;

Percolating Filter Bed; WFD; UWWTD; eutrophication;

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Acknowledgement

There are a number of people whom without this project would not have been

possible. Firstly I would like to thank Dr Nicholas Ray who has provided supervision

and guidance throughout this project. Secondly, to Gail Pluckrose and Mark Garth,

Severn Trent Service Delivery Managers, for their assistance in the organisation of

funding and getting this project off the ground. Thanks should also be given to

Catherine Kendall and Rowan Luck, Severn Trent Treatment Process Advisers for

their technical advice throughout this study. I would also like to extend my gratitude

to Richard Hardy of the Environment Agency giving me his time in person and

openly discussing riverine pollution and the regulators viewpoint on sewage

treatment.

I also extend my gratitude to Lawrence Green and the team at National Laboratory

Service Nottingham for being so flexible in allowing me to deliver my samples in

person and providing results personally on a weekly basis as well as giving me a

tour of their facility to see the analysis process first hand.

I would like to give special thanks to Dr Joanna Varley-Campbell and John Barratt for

their advice, criticisms and support with this project.

Finally, I would like to thank my friends and in particular my family for their support

throughout my time at Nottingham Trent University.

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Table of Contents

Abstract II

Acknowledgement III

Table of Contents IV List of Figures VII List of Tables IX Acronyms X

1. Introduction 13 1.1. Water Quality Assessment. 13

1.1.1. Environment Agency General Quality Assessment (GQA) and Sampling regimes 14 1.2. Regulation 16

1.2.1. The EC Water Framework Directive (2000/60/EC) 16 1.2.2. The EC Urban Waste Water Treatment Directive (91/271/EEC) 17

1.2.2.1. Final effluent (FE) sampling 18 1.2.3. The EC Nitrates Directive (91/676/EEC) 19

1.3. Sources of pollution 19 1.3.1. Point pollution 19

1.3.1.1. Sewage Treatment Point Sources 19 1.3.1.2. Industrial Point Sources 20 1.3.1.3. Agricultural Point Sources 20 1.3.1.4. Misconnections 20 1.3.1.5. Storm Point Discharges 21

1.3.2. Diffuse pollution 21 1.3.2.1. Agricultural Practices 22

1.3.3. Eutrophication 23 1.3.3.1. Phosphorus 24 1.3.3.2. Nitrogen 25

1.4. Sewage Treatment works 26 1.4.1. Types of sewage treatment works 26

1.5. River water and effluent quality parameters 33 1.5.1. Physical Determinants 33

1.5.1.1. Temperature 33 1.5.1.2. Conductivity 34 1.5.1.3. Flow 34

1.5.2. Chemical Determinants 35 1.5.2.1. Ammonia 35 1.5.2.2. Biochemical Oxygen Demand (BOD) 35 1.5.2.3. Boron 35 1.5.2.4. Chloride 36 1.5.2.5. Chemical Oxygen Demand (COD) 36 1.5.2.6. Dissolved Oxygen (DO) 37 1.5.2.7. Nitrate 37 1.5.2.8. Nitrite 38 1.5.2.9. Orthophosphorus. 38 1.5.2.10. pH 39 1.5.2.11. Phosphorus 39 1.5.2.12. Sulphate 40

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1.5.3. Chemical Standards Report 40 1.6. Gaps in current studies 44 1.7. Aims and objectives 44

1.7.1. Hypotheses 44

2. Methodology and Equipment 45 2.1. Commercial Sensitivity 45 2.2. Site Selection 45

2.2.1. Sample locations 50 2.3. Sampling Timescales 50 2.4. Sample Technique 50

2.4.1. Bridge sampling technique 50 2.4.2. Riverbank sampling technique 51 2.4.3. Final Effluent sampling technique 51

2.5. Sample Analysis 51 2.5.1. In-situ data collection 51

2.5.1.1. Temperature and DO 51 2.5.1.2. Conductivity and on-site pH 52 2.5.1.3. Flow 52

2.5.2. Laboratory Analysis 52 2.5.2.1. Ammonia 52 2.5.2.2. Biological Oxygen Demand 53 2.5.2.3. Boron 53 2.5.2.4. Chemical Oxygen Demand 53 2.5.2.5. Chloride 53 2.5.2.6. Nitrate 54 2.5.2.7. Nitrite 54 2.5.2.8. Orthophosphate, Reactive as P 54 2.5.2.9. pH Laboratory 54 2.5.2.10. Phosphorus 54 2.5.2.11. Sulphate 55

2.6. Statistical analysis 55

3. Results 56 3.1. In-situ Results 56

3.1.1. Conductivity 56 3.1.2. Dissolved Oxygen 57 3.1.3. pH on-site 58 3.1.4. Temperature 59

3.2. Laboratory Results 60 3.2.1. Ammonia 60 3.2.2. Biological Oxygen Demand 61 3.2.3. Boron 62 3.2.4. Chemical Oxygen Demand 63 3.2.5. Chloride 64 3.2.6. Nitrate 65 3.2.7. Nitrite 66 3.2.8. Orthophosphate 67 3.2.9. pH Laboratory 68 3.2.10. Phosphorus 69 3.2.11. Sulphate 70

4. Discussion 71 4.1. Study findings 71

4.1.1. Ammonia 72 4.1.2. Biological Oxygen Demand (BOD) 73 4.1.3. Boron 74 4.1.4. Chemical Oxygen Demand (COD) 74 4.1.5. Chloride 75

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4.1.6. Conductivity 76 4.1.7. Dissolved Oxygen 77 4.1.8. Nitrate 77 4.1.9. Nitrite 78 4.1.10. Orthophosphate 78 4.1.11. pH 79 4.1.12. Phosphorus 80 4.1.13. Sulphate 81 4.1.14. Temperature 82

4.2. Further discussion 82 4.2.1. Difference between treatments 82

4.2.1.1. Activated Sludge Production (ASP) 83 4.2.1.2. Membrane Bioreactor (MBR) 83 4.2.1.3. Percolating Filter Works 84

4.2.2. Regulation 84 4.2.3. Criticisms of other literature 85

4.3. Study Limitations 86 4.4. Recommendations for further research. 86

5. Conclusion 88

References 89

Appendix 119

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List of Figures:

Figure 1.1: Diagram showing levels of treatment required in relation to PE.

Figure 1.2: Image showing multiple ASP lanes with aerobic and anoxic zones.

Figure 1.3: Diagram of the Activated Sludge Process

Figure 1.4: Image of a Zeeweed 500 hollow fibre MBR membrane used in

wastewater treatment.

Figure 1.5: Image of a percolating filter bed.

Figure 1.6: Diagram of a percolating filter bed.

Figure 1.7: A graph taken from EEA showing river orthophosphate levels from 1992

– 2012 in European rivers.

Figure 2.1: Site diagram showing layout of Site 1.

Figure 2.2: River course and sample point map for Site 1 showing upstream, final

effluent and downstream sample locations.

Figure 3.1: Mean conductivity values across all sites (Mean ± SE).

Figure 3.2: Mean DO values across all sites (Mean ± SE) (MRV=0.20 mg/l).

Figure 3.3: Mean on-site pH values across all sites (Mean ± SE) (MRV=0.05).

Figure 3.4: Mean on-site temperature values across all sites (Mean ± SE).

Figure 3.5: Mean ammonia concentrations across all sites (Mean ± SE)

(MRV=0.19mg/l).

Figure 3.6: Mean BOD concentrations across all sites (Mean ± SE) (MRV=1.0 mg/l).

Figure 3.7: Mean boron concentrations across all sites (Mean ± SE) (MRV=0.1mg/l).

Figure 3.8: Mean COD concentrations for across all sites (Mean ± SE) (MRV =10.0

mg/l).

Figure 3.9: Mean chloride concentrations across all sites (Mean ± SE)(MRV=0.9

mg/l).

Figure 3.10: Mean nitrate concentrations across all sites (Mean ± SE)(MRV=0.006

mg/l).

Figure 3.11: Mean nitrite concentrations across all sites (Mean ± SE) (MRV see

appendix 7).

Figure 3.12: Mean orthophosphate concentrations across all sites (Mean ±

SE)(MRV=0.008 mg/l).

Figure 3.13: Mean concentrations for laboratory pH across all sites (Mean ± SE)

MRV=0.05).

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Figure 3.14: Mean phosphorus concentrations across all sites (Mean ±

SE)(MRV=0.07 mg/l).

Figure 3.15: Mean sulphate concentrations across all sites (Mean ± SE) (MRV=1.0

mg/l).

Figure 4.1: Weekly ammonia concentrations for Site 5 (Mean ± SE)

(MRV=0.19mg/l).

Figure 4.2: Weekly ammonia concentrations for Site 7 (Mean ± SE) (MRV=0.19).

Figure 4.3: Weekly COD concentrations for Site 1 (Mean ± SE) (MRV =10.0 mg/l).

Figure 4.4: Photograph of Site 1 downstream showing agricultural (A) and surface

water (B) discharge

Figure 4.5: Marked scatter graph demonstrating flow vs. downstream pH for Site 4

with linear trend line.

Figure 4.6: FE phosphorus concentrations for all sites. (Mean ± SE)(MRV=0.07

mg/l).

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List of Tables:

Table 1.1: A table showing GQA parameters for river water quality.

Table 1.2: Phosphorus removal requirements in relation to PE.

Table 1.3: Target phosphorus concentrations for rivers in England and Wales, with

suggested applications to different river types.

Table 1.4: A table outlining the 3 primary sewage treatment technologies

implemented in this study.

Table 1.5: EA Chemical Standards report for UK and EU river chemical

concentrations.

Table 2.1: A table showing treatment methods employed at sampled STW.

Table 2.2: A table showing site descriptions for sampled STW.

Table 3.1: Multiple comparisons of means for conductivity including post-hoc

analysis.

Table 3.2: Multiple comparisons of means for DO including post-hoc analysis.

Table 3.3: Multiple comparisons of means for pH, including post-hoc analysis.

Table 3.4: Multiple comparisons of means for temperature, including post-hoc

analysis.

Table 3.5: Multiple comparisons of means for ammonia, including post-hoc analysis.

Table 3.6: Multiple comparisons of means for BOD including post-hoc analysis.

Table 3.7: Multiple comparisons of means for boron including post-hoc analysis.

Table 3.8: Multiple comparisons of means of COD including post-hoc analysis.

Table 3.9: Multiple comparisons of means for chloride including post-hoc analysis.

Table 3.10: Multiple comparisons of means for nitrate including post-hoc analysis.

Table 3.11: Multiple comparisons of means for nitrite including post-hoc analysis.

Table 3.12: Multiple comparisons of means for orthophosphate including post-hoc

analysis.

Table 3.13: Multiple comparisons of means for pH Laboratory including post-hoc

analysis.

Table 3.14: Multiple comparisons of means for phosphorus including post-hoc

analysis.

Table 3.15: Multiple comparisons of means for sulphate including post-hoc analysis.

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Acronyms ASP Activated Sludge Production

BOD Biological Oxygen Demand

COD Chemical Oxygen Demand

CSO Combined Sewer Overflow

DEFRA Department for Environment, Farming and Rural Affairs

DO Dissolved Oxygen

EA Environment Agency

EC European Commission

ECSFDI England Catchment Sensitive Farming Delivery Initiative

EEA European Environment Agency

FE Final Effluent

FST Final Settlement Tank

GQA General Quality Assessment

ICPOES Inductively Coupled Plasma Optical Emission Spectrometer

MBR Membrane Bio-reactor

MRV Minimum Reporting Value

NLS National Laboratory Service

nm Nanometres

NPK Nitrogen, phosphorus, and potassium.

NSA Nitrate Sensitive Area

NSAF Nitrifying Submerged Aerated Filter

NVZ Nitrate Vulnerable Zone

OECD Organisation for Economic Cooperation and Development

OSM Operator Self-Monitoring

P-stripping Phosphorus Stripping

PARIS Phosphorus from Agriculture: Riverine Impact Study (PE1226)

PE Population Equivalent

PoM Programme of Measures

PST Primary Settlement Tank

RAS Returned Activated Sludge

RBMP River Basin Management Plan

SAS Surplus Activated Sludge

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SRP Soluble Reactive Phosphorus

STW Sewage Treatment Works

UK United Kingdom

UN United Nations

UWWTD EC Urban Waste Water Treatment Directive (91/271/ECC)

WFD EC Water Framework Directive (2000/60/EC)

Chemical elements and compounds B Boron

C Carbon

C6H8O7 Citric Acid

Cl Chlorine

Cl- Chloride

CO2 Carbon Dioxide

H2O Water

H2SO4 Sulphuric Acid

HCl- Hydrochloric Acid

K Potassium

KCl Potassium Chloride

N Nitrogen

NaCl Sodium Chloride

NH3 Ammonia

NO2- Nitrite

NO3- Nitrate

O Oxygen

P Phosphorus

PO43– Orthophosphorus

SO42- Sulphate

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Units of measurement

l/s Litres per second

M3/d Metres cubed per day

mg/l Milligram per litre

mS/cm Millisiemens per centimetre

nm Nano Metres

µg/l Microgram per litre

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1. Introduction

River basins have long been associated with high levels of population density due to

their fertile lands and water for irrigation, industrial processes or potable supply

(Vega et al., 1998; Petts, 1998; Acreman, 2000). This makes them the lifeblood of

many of the UK’s largest towns and cities (Rivett et al., 2011; Vörösmarty et al.,

2010). In addition, rivers also assimilate a large amount of municipal wastewater

(DeBruyn et al., 2002), agricultural discharge and highways run off which can have a

polluting effect upon even the largest of watercourses (Aitken, 2003). These

polluting inflows mean that effective and efficient water management is critical,

therefore reliable water quality information is a necessity (Neal et al., 2008).

Urban wastewater (sewage) is a combination of domestic waste flows (baths, sinks,

washing machines and toilets), wastewater from industry and highway rainwater

run off (European Council, 1991). Without treatment, the discharge of wastewater

effluents into the UK’s rivers would adversely affect the riverine environment as

well as posing a serious issue to public health (Jarvie et al., 2006). Untreated sewage

contains organic matter, bacteria and chemicals that cannot be broken down by the

riverine bacteria (DEFRA, 2012). The purpose of a sewage treatment works (STW) is

to treat the wastewater to a suitable level so that it can be discharged to

watercourses with little or no effect on the environment and/or aquatic life (Singh et

al., 2004).

1.1. Water Quality Assessment.

Water quality analysis is an important part of any water management strategy

(European Commission, 2012). Water quality is graded on chemical,

biological/ecological and aesthetic parameters in line with pre-defined limits and

regulations (Norfolk County Council, 2010; Environment Agency, 2002; DEFRA,

2012). The national regulatory body in England, the Environment Agency (EA), often

carries out this work (DEFRA, 2012). National sampling regimes are the only way to

make comparisons between water bodies and also take steps to improve water

quality and reduce pollutants (DEFRA, 2014; European Commission, 2012).

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1.1.1. Environment Agency General Quality Assessment (GQA) and

Sampling regimes

From 1988, the Rivers Authority began the General Quality Assessment (GQA) of

rivers across the UK with the aim of providing an accurate and consistent

assessment of the UK’s water quality and its changes over time (Nixon et al., 1995;

Coquery et al., 2005; Foster et al., 2010). The GQA scheme sampled and observed a

number of parameters to understand the state of the UK’s river systems. GQA

Parameters can be found in Table 1.1 (Nixon et al., 1995; Furse et al., 2009).

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Table 1.1: A table showing GQA parameters for river water quality (Nixon et al., 1995; Furse et al., 2009).

GQA Parameter Measures Graded from Comment

Aesthetic quality Litter, foam, odour and

colour

1 = Good to 4 = Bad Taken from first observations of the river in terms of site

and smell with the aim of giving our overall perceptions of

the river (DEFRA, 2012a; Norfolk County Council, 2010)

Biological quality Analysis of macro-

invertebrates.

A = Very good to F = Bad Biological quality data is used as a health check for the river

system. Macro-invertebrates are grouped into 83 taxa and

given scores of between 1 (pollution-tolerant taxa) and 10

(pollution-sensitive taxa) (DEFRA, 2012a; Environment

Agency, 2002)

Chemical quality Dissolved oxygen,

biochemical oxygen

demand (BOD) and

ammonia

A = Very good to F = Bad Chemical quality data was used as a test of river pollution

levels and the effects of sewage treatment, industrial and

agricultural discharges into watercourses (Norfolk County

Council, 2010; DEFRA, 2012a)

Nutrient status Phosphate and nitrate

analysis

Graded from Very Low to

Excessively High

Nutrient status is an aid to identifying anthropogenic

sources of pollution due the majority of nitrate and

phosphate discharges coming from sewage treatment

effluent and agricultural sources (Neal et al., 2010; Bowes et

al., 2010; Jarvie et al., 2006)

Key: Department for Environment Rural Affairs, DEFRA;

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The GQA programme involved monthly sampling at 7000 monitoring sites across

over 40,000 kilometres of rivers and canals in England and Wales (DEFRA, 2012a;

Environment Agency, 2002). In 1996, with the establishment of the EA,

responsibility for the GQA was passed from the Rivers Authority to the EA. The EA

continued the GQA scheme until 2009 at which point it moved to focus river water

sampling based on the EC Water Framework Directive (2000/60/EC)(Logan &

Furse, 2002; DEFRA, 2012a; Environment Agency, 2002).

1.2. Regulation

Since 1996, the English regulator for the environment has been the EA

(Environment Agency, 2015) sponsored by the UK governmental Department for

Environment, Food and Rural Affairs (DEFRA) (DEFRA, 2015). The EA has the

mandate of protecting and enhancing the environment (DEFRA, 2014). Within

England this includes responsibility for (Environment Agency, 2015):

• Regulating major industry and waste

• Treatment of contaminated land

• River quality and resources

• Fisheries

• Inland river, estuary and harbour navigations

• Conservation and ecology

1.2.1. The EC Water Framework Directive (2000/60/EC)

The EC Water Framework Directive (WFD) (2000/60/EC) was introduced in 2000

with the primary aim to protect, enhance and restore ‘good’ ecological status in

aquatic ecosystems (European Commission, 2012). The WFD has ambitious

objectives to protect and restore aquatic ecosystems for the long-term sustainable

use of water for people, business and nature (Neal & Jarvie, 2005; Correljé et al.,

2007).

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The WFD looks to categorise rivers by chemical and ecological status of surface

waters with the primary aim of surface waters attaining ‘good chemical and

ecological status’ by 2015 (European Commission, 2012; Neal et al., 2008).

The WFD also stipulates the introduction of River Basin Management Plans (RBMP)

and accompanied Programme of Measures (PoM) (Natural England, 2012; European

Commission, 2012). The RBMP was introduced to allow for a cross-boundary

approach to the classification, assessment and monitoring of surface waters across

central Europe (Ulén & Weyhanmeyer, 2007).

It is recognised that in some cases it may not be feasible (either technically feasible

or disproportionally costly) to bring all watercourses to ‘good’ status by 2015

(DEFRA, 2014; Hering et al., 2010). Therefore, the WFD allow member states to

apply an exemption rule on the basis of natural conditions of the watercourse and

extend the deadline to 2027 or beyond (European Commission, 2012; DEFRA, 2014).

The WFD also implements the precautionary principle (Correljé et al., 2007), which

was adopted by the UN conference on the Environment and Development 1992

(Hering et al., 2010). The precautionary principle states “where there are threats of

serious or irreversible damage to the environment, lack of full scientific certainty

should not be used as a reason for postponing cost-effective measures to prevent

environmental degradation” (Correljé et al., 2007).

1.2.2. The EC Urban Waste Water Treatment Directive (91/271/EEC)

The EC Urban Waste Water Treatment Directive (91/271/ECC) (UWWTD) is the

primary legislation regulating the discharge of effluents from industry and STW

(European Council, 1991). Regulated by the EA, the UWWTD has a primary aim of

working alongside the WFD to improve the quality of surface waters by 2015

(DEFRA, 2012).

The UWWTD states that sewage treatment facilities must be provided for flows that

meet or exceed 2000 population equivalent (PE) (Neal et al., 2009) and puts in place

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specific treatment criteria in relation to PE (DEFRA, 2012) for example, tertiary

phosphorus stripping (P-stripping) for PE over 10,000 as demonstrated in table 1.2

(Bowes et al., 2009; Neal et al., 2009). Phosphorus is one of the primary limiting

factors for eutrophication (Mainstone & Parr, 2002) and therefore is closely

regulated by the UWWTD (Farmer, 2001). The UWWTD, in conjunction with the EA

Asset Management plans that have set out numerical consents in relation to

phosphorus discharge (Environment Agency, 2000).

Table 1.2: Phosphorus removal requirements in relation to PE (Neal et al., 2010).

Population Equivalent Phosphorus removal required.

10,000 – 100,000 2000µg/l

100,000 and above 1000µg/l

As well as setting discharge limits of phosphorus, the UWWTD also sets out

eutrophication sensitive areas where more stringent treatment processes should be

employed (DEFRA, 2012; European Council, 1991). These sensitive areas are to

protect against the discharge of nitrogen and phosphorus (Mainstone & Parr, 2002).

The UWWTD works alongside both the EC Nitrates Directive (91/676/EEC) and the

EC Drinking Water Directive (98/83/EC) in stipulating that nitrogen concentrations

in river water should not exceed 50 mg/l if to being used for potable abstraction

(Europa, 1998).

1.2.2.1. Final effluent (FE) sampling

The creation of the UWWTD has introduced the idea of regulation and prosecution

(DEFRA, 2012). Because of this, STW are now regularly sampled to ensure that the

quality of their FE is of standard. Water companies are sampled in two ways. Firstly

by operator self-monitoring (OSM) spot samples that are taken by the water

company and reported to the EA. Secondly, UWWTD samples which are 12-hour

composite samples are taken by the EA. The frequency of samples is determined by

PE and also the sensitivity of the receiving watercourse (Water Monitoring

Association, 2008).

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1.2.3. The EC Nitrates Directive (91/676/EEC)

The EC Nitrates Directive (91/676/EEC) works alongside the WFD to regulate and

improve the quality of surface waters in relation to nitrogen (DEFRA, 2014; Ulén &

Weyhenmeyer, 2007). The Nitrate directive is a key tool for the UK to regulate both

agriculture and sewage discharges to watercourses (Jarvie & Neal., 2005; Goodchild,

2008; Van Grinsven et al., 2012). As well as the implementation of the 50mg/l river

water nitrogen concentration limit for surface waters used for abstraction, the

Nitrate Directive has also implemented the creation of Nitrate Vulnerable

Zones/Nitrate Sensitive Areas (Vinten & Dunn, 2001; Jordan & Smith, 2005).

1.3. Sources of pollution

Rivers have always been the primary source of waste of disposal with medieval

towns allowing raw sewage and household wastes to run through the streets before

discharging into rivers (Sterner, 2008). This continues today in 3rd world countries

that lack suitable sewer infrastructure with rivers assimilating raw human and

agricultural wastes as well as household discharges (Elhance, 1999). Pollution of

watercourses is split into two categories, point and diffuse, depending on how it

enters the watercourse (Singh et al., 2004; Jarvie et al., 2006; Bowes et al., 2006).

1.3.1. Point pollution

Point discharges are defined as discharges that enters the watercourse at one

specific point (Bowes et al., 2006; Neal et al., 2008). Point discharges are primarily

caused by STW, industrial inputs, slurry overflows, sewer misconnections and storm

overflows (Bowes et al., 2010; Neal et al., 2010a). Point source pollutants can often

cause more harm to rivers than diffuse pollutants due to the lack of dilution in the

immediate area of the discharge (Hunt et al., 2010; Singh et al., 2004).

1.3.1.1. Sewage Treatment Point Sources

STW are one of the largest point source discharges for both phosphate and nitrate

pollution to the UK’s surface waters (Singh et al., 2004; Wade et al., 2002). Because

STW discharges FE at a specific point, it usually causes high levels of both nitrate

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and phosphorus concentration over a short section of the river (Hunt et al., 2010;

Jarvie et al., 2006; Bowes et al., 2008). This can be combatted by tertiary P-stripping

as well as an effective on-site biological treatment process to aid removal of nitrates

(Mainstone & Parr, 2002; Neal et al., 2005).

1.3.1.2. Industrial Point Sources

Industrial point sources are also a major cause of pollutant release into UK surface

waters (Foster et al., 1978; Amisah & Cowx, 2000). As with STW, industrial inputs

are often high in phosphorus and nitrates as well as other heavy metals and

nutrients (Neal et al., 2005; Neal et al., 2010; Wakida & Lerner, 2005). Discharges

depend upon on-site process so regulation and analysis is often tailored to specific

determinants (DEFRA, 2012; Environment Agency, 2015; DEFRA, 2010).

1.3.1.3. Agricultural Point Sources

Agriculture is one of the primary sources of riverine eutrophication (Jarvie et al.,

2006). Agricultural point sources include slurry overflows that discharge raw slurry

into watercourses causing spikes in both phosphorus and nitrates (Vega et al., 1998;

Sharpley et al., 2004; Kleinman et al., 2011). Careful pre-planning of application and

slurry storage can help keep these discharges to a minimum, as the effects of raw

slurry discharge can be catastrophic to small surface waters (Jarvie et al., 2006).

1.3.1.4. Misconnections

Misconnections are common across the UK and are often caused by the

misconnection of white goods (Dishwashers and washing machines) as well as

toilets (Faulkner et al., 2000; Broadhead et al., 2013). Misconnections happen when

instead of a connection to the foul sewer network, items are accidentally connected

to the surface water sewer, causing run-off directly to watercourses (Chandler,

2014).

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Misconnections can often cause dramatic pollution events and eutrophication to

small surface waters due to a lack of dilution (Chandler, 2014) and a prolonged

discharge over weeks or months, often unspotted (Baker et al., 2003).

1.3.1.5. Storm Point Discharges

Across the country, our sewer network has a number of Combined Sewer Overflows

(CSOs) installed to deal with hydraulic overloading of the sewer system (Gasperi,

2008). Discharge often occurs when combined surface and foul sewers experience

high levels of hydraulic loading during weather events. CSOs are designed to release

raw sewage to river to relieve the pressure on the sewer system and prevent

flooding events (Lau, 2002; Suarez, 2005).

Although CSOs discharge raw sewage directly into surface waters, the increased

levels of dilution both within the river itself when in spate, and an increase in

surface water runoff internally in the sewer means that the effects of these point

discharges are negligible (Baker et al., 2003; Gasperi et al., 2008).

As well as CSOs, STW also discharge raw sewage in times of high hydraulic load. In

adverse weather events, when STW cannot treat the full flow of the incoming

influent, the excess will be stored in storm tanks for later treatment, thus reducing

the effect upon the environment. However, when these tanks become full, they

discharge directly into the watercourse having the same effect as CSOs (Metcalf et

al., 1986; DEFRA 2012).

1.3.2. Diffuse pollution

Diffuse pollution is where pollutants enter the watercourse from multiple points

across the length of a section of river (Arheimer et al., 2004; Faulkner, et al., 2000).

Often individually minor, diffuse pollutants are cumulatively significant and can

have dramatic effects on watercourses. Diffuse pollutants are agriculturally

dominated, entering watercourses along the full contact area with fields via surface

water run off or via leachate (Bowes et al., 2008; Neal et al., 2008a)

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1.3.2.1. Agricultural Practices

Agriculture is one of the most intense sources of diffuse pollution across the UKs

river network with studies suggesting that around 50% of the phosphorus and 70%

of the nitrate loads delivered to rivers are as a result of agricultural sources (Neal &

Jarvie, 2005; RPA, 2003). This leachate from intensive agricultural practices across

the length of a river means that rivers can receive diffuse nitrate and phosphate

loads, often higher than a point source, along their full length causing an

accumulation in the water column (Neal et al., 2008; Jarvie et al., 2008; Withers &

Lord, 2002).

1.3.2.1.1. Fertiliser application timings

Often, one of the biggest issues causing the run off of phosphorus and nitrates is the

incorrect timing of the use of artificial NPK fertilisers (Hills et al.,1978; Sharpley et

al., 1994). If artificial fertilisers are sprayed prior to a weather event for example

rainfall or snow, this can cause a surface run off of phosphorus and nitrogen into the

watercourse (Neal & Jarvie, 2005; Withers & Lord, 2002; Jarvie et al., 2008; Vega et

al., 1998). If enough time has not passed for the crops to absorb the nitrates and

phosphates provided in the fertilizer, the excess hydraulic loading from rain running

through the soil causes surplus nutrients to be washed into watercourses (Vega et

al., 1998; Smith et al., 2001).

1.3.2.1.2. Research into effects of agriculture

One of the most informative projects into the effects of diffuse agricultural pollution

is the Phosphorus from Agriculture: Riverine Impact Study (PARIS) (PE1226) which

was investigated from 2003-2008 to look at the impacts that agricultural

phosphorus has upon riverine systems (DEFRA, 2008b). The PARIS study has been

working to reduce the agricultural impacts of phosphorus and soluble reactive

phosphorus (SRP) on UK river systems to ensure that the WFD directive target of

‘good ecological status’ by 2015 is met (DEFRA, 2012; DEFRA, 2008b).

The PARIS study has made a number of recommendations for changes to farming

practice, e.g. changes in mode of fertilisation, move towards natural fertilisation, and

23

the use of planning to ensure suitable fertilisation times (Haygarth et al., 2005;

DEFRA, 2008b). The study also identifies that in the subject streams, light and flow

were the main limiting factors of community algal growth. However, changes must

be made in riverine phosphorus content to reach the WFD good ecological status

marker for UK surface waters (DEFRA, 2008b; Mainstone & Parr, 2002).

In addition, the England Catchment Sensitive Farming Delivery Initiative (ECSFDI)

has also been set up by DEFRA to work as a tool to target the aims of the WFD

(DEFRA, 2008; DEFRA, 2008a). The ECSFDI works with farmers across the country

providing advice and seminars on soil, nutrient and manure management as well as

pesticides with the aim of tackling diffuse pollution. Although this advice and

support if voluntary, it is being shown to have a significant effect with a predicted

10-40% reduction in disuse pollution in the catchment areas. This education is

helping to reduce riverine concentrations of both phosphorus and nitrate (DEFRA,

2008; DEFRA, 2008a).

1.3.3. Eutrophication

Eutrophication occurs when an increase in the availability of nutrients causes an

increase in the biological activity of plant life, primarily, algae (Neal et al., 2002;

Bowes et al., 2008; Neal at al., 2008). Algal blooms caused by increases in riverine

nutrients can cause decreased levels of dissolved oxygen (DO) in the watercourse,

therefore reducing the ecological quality of the water (Miranda et al., 2001). One of

the biggest issues is anthropogenic eutrophication caused by nutrient rich

discharges into our watercourses (Mainstone et al., 2002). Discharges from STW,

industrial plants and agriculture have all caused eutrophication to increase over the

past 100 years (Morrison et al., 2001; Neal et al., 2005). This loading of our

watercourses with anthropogenic nutrient inputs has caused record levels of

phosphorus and nitrates concentrations that have the potential to damage the

ecological status of the UK’s watercourses (Bowes et al., 2008; Jarvie et al., 2006).

Eutrophication is one of the pillars of the WFD and is deeply embedded in UK

governmental policy through both DEFRA and the EA (Hering et al., 2010; DEFRA,

24

2012; European Commission, 2012). The EA has a specific eutrophication task force

that works to reduce UK riverine nutrient levels and prevent eutrophication events

(Mainstone et al., 2002). EA riverine SRP target levels can be found in Table 1.3.

Table 1.3: Target phosphorus concentrations for rivers in England and Wales (Environment Agency, 2000), with suggested applications to different river types (Mainstone et al., 2002).

Target Mean SRP (mgl -1) Suggested application

1 0.02 Upland watercourses and

headwaters

2 0.06 Rivers on chalk, hard

sandstone and limestone

3 0.1 Lowland rivers on clay

and alluvium

4 0.2 Interim target for heavily

enriched rivers

Eutrophication is an intrinsically seasonal process that is highest during the spring

and summer plant growing seasons (Neal & Jarvie, 2005). Eutrophication risk is

particularly high during summer months when baseline river flow conditions are

low and there will be low dilution of effluents into the watercourse (Hunt et al.,

2010). These conditions are ideal for algal blooms and eutrophication of smaller

watercourses (Arheimer et al., 2004).

1.3.3.1. Phosphorus

Phosphorus (P) is often seen as the limiting factor for eutrophication (Mainstone &

Parr, 2002) in the UK’s watercourses and is discharged by a number of

anthropogenic sources, i.e. STW, agriculture, industrial effluents into the UK’s rivers

(Bowes et al., 2008; Jarvie et al., 2006). Phosphorus is a vital compound for plants

providing aid for growth, photosynthesis, aid to cell division and the development of

new tissue. Phosphorus is also important for complex energy transformations in

plants (Richardson, 2001).

25

Phosphorus is often deficient is many plants hence the use of phosphorus based

fertilisers which add phosphorus artificially to aid plant growth (Beaton & Nelson,

2005). With phosphorus often being the limiting factor to eutrophication (Mainstone

& Parr, 2002), the rate of plant growth is directly linked to phosphorus inputs into

watercourses, meaning management of phosphorus is critical in controlling

eutrophication in UK river systems (Jarvie et al., 2008; Neal et al., 2010a). This is

why so much emphasis is placed upon controlling phosphorus inputs in both the

WFD and UWWTD (Ricci et al., 2012; Hering et al., 2010). A reduction in phosphorus

discharges and thus in riverine phosphorus concentrations can help to limit

eutrophication levels in UK rivers and aid the WFD to achieving ‘good ecological

status’ for all UK watercourses (Brouwer, 2008; Coquery et al., 2005; Foster et al.,

2005).

One of the most dangerous types of phosphorus to watercourses is soluble reactive

phosphorus (SRP) otherwise known as orthophosphate (Richardson, 2001; Bowes

et al., 2010; Correll, 1998). Orthophosphate is readily available phosphorus that is

found in solution in the water column and is readily absorbed by plants to aid

growth. High levels of Orthophosphate are common causes of eutrophication (Jarvie

& Neal, 2005; Neal et al., 2009; Wade et al., 2002).

1.3.3.2. Nitrogen

Nitrogen (N) is a key nutrient for plants and a limiting factor in eutrophication

(Anderson et al., 2002; Neal & Jarvie, 2005). Nitrogen is a key constituent in amino

acids, the building blocks of proteins and can be added to agricultural crops to

increase yield (Richards, 2000). Plants absorb nitrogen in the form of nitrate or

ammonia, both soluble in water that are present in NPK fertilisers, agricultural

slurries and are discharged to watercourses by STW and industrial discharges

(Goodchild, 1998).

In addition to anthropogenic inputs, nitrogen is also naturally occurring in the form

of nitrate and nitrite. The breakdown of organic matter containing organic nitrogen

can form ammonia, which is toxic to fish and aquatic organisms at high

26

concentrations (Hickley & Vickers, 1994). As part of the nitrogen cycle, ammonia is

also converted back to the less harmful form nitrate via nitrification from riverine

algae and plant life, thus removing ammonia from the water column (Galloway et al.,

2008).

Ammonia inputs to watercourses can come from a variety of sources, primarily

agriculture and sewage treatment (Ruiz et al., 2003). Sewage treatment, if

successful, should remove ammonia concentrations to a negligible level before

discharging to watercourses (Wagner et al., 1996). This ammonia is present as a

result of the sewage influent to the treatment works. However, low temperatures at

treatment works can cause reduced levels of nitrification in the treatment process,

thus increasing the concentration of ammonia discharged (Shammas, 1986).

Agriculture also has a large part to play in ammonia discharges. The discharge of

liquid manure to watercourses via leachate, surface run off, or storm overflow

discharge can cause catastrophic effects to watercourses due to toxic levels of

ammonia being discharged (Randall & Tsui, 2002).

1.4. Sewage Treatment works

STW are the critical link in returning sewage and grey water back into our

environment in a safe and minimally invasive way. (DEFRA, 2012) Sewage

treatment has taken great strides forward in improving the levels of treatment

achieved; this is directly improving the quality of our watercourses (DEFRA, 2014).

Varying in size, STW can take flows from one property to the discharges of a whole

city (DEFRA, 2012). Without STW, raw sewage would be discharged to the UK’s

watercourses, increasing pollution levels and reducing the possibility of potable

abstraction for safe drinking water as well as reducing the amenity value of the UK’s

watercourses.

1.4.1. Types of sewage treatment works

During this project, 3 different types of sewage treatment process will be

investigated to understand their effects on river water quality. Activated sludge

production (ASP), Percolating Filter Bed and Membrane Bioreactor (MBR) treatment

27

works are in current operation and have been specified to meet specific consents

and PE.

All STW follow a similar process, with a different choice of primary, secondary and

tertiary treatment being used in each different process (Metcalf et al., 1972).

Specification of STW technology links directly to the UWWTD as shown in Figure 1.1.

Figure 1.1: Diagram showing levels of treatment required in relation to PE (DEFRA, 2012).

28

Table 1.4: A table outlining the 3 primary sewage treatment technologies implemented in this study.

Key: Activated Sludge Process, ASP; biological oxygen demand, BOD; chemical oxygen demand, COD; Final Settlement Tank, FST;

Treatment Basic principle Benefits Drawbacks Additional points

Activated

Sludge

Process

(ASP)

ASP is the process of treating sewage effluents

using microorganisms held in suspension to break

down the organic matter in the effluent (Osada et

al., 1991). Microorganisms in the Activated

Sludge, commonly known as mixed liquor, are

mixed with incoming effluents in a number of ASP

lanes as shown in Figure 1.2 (Tomlinson et al.,

1966; Metcalf et al., 1972; Gerardi, 2005). ASP

lanes are split into aerobic and anoxic zones via

the placement of diffusers to provide the

breakdown of organic and carbonaceous material

and nitrification (Gerardi, 2005; Kim et al., 2005).

Once the effluent has passed through the ASP

lanes, it then pass forward to a secondary clarifier

or final settlement tank (FST) that settles the

excess mixed liquor before the final treated

effluent is discharged to the watercourse (Metcalf

et al., 1972)

Suitable for high PE sites.

High removal of

suspended solids, BOD &

COD

Biological nitrification

and phosphorus removal

Self-regulating with

reseeding from Returned

Activated Sludge (RAS)

shown in Figure 1.3

High levels of sludge are

produced which is

suitable for anaerobic

digestion (Metcalf et al.,

1972; Liu et al., 2000)

Energy intensive

High capital installation

costs

Requires regular

maintenance and

adjustment

High levels of sludge are

produced which requires

disposal (Metcalf et al.,

1972; Liu et al., 2000)

ASP is the most

common type of

sewage treatment

in the UK (DEFRA,

2012)

29


Key: Activated Sludge Process, ASP; biological oxygen demand, BOD; chemical oxygen demand; COD; Final Settlement Tank, FST;


Membrane

Bioreactor

(MBR)

Membrane Bioreactor (MBR) is a

combined treatment method utilising

both ASP and a membrane unit to treat

effluent. MBR treatment plants work by

passing effluent through 6, 3 and 1mm

screens before moving to a traditional

ASP stage (Judd, 2004). Once the

effluent has passed through the ASP, it

moves into a membrane plant where

Zeeweed 500 membranes (Figure 1.4)

are submerged in tanks of effluent from

the ASP (Noble, 2006; Buer & Cumin,

2010). Negative pressure then draws

the effluent through a 0.04nm pore

membrane that removes solid particles

(Buer & Cumin, 2010). The membrane

in a MBR plant replaces the FST in a

standard ASP plant (Judd, 2010)

Low site footprint

Very high effluent quality

Very high suspended-

solids, BOD and COD

removal

High levels of effluent

disinfection

Ease of automation (Noble,

2006; Buer & Cumin, 2010)

Technically complex

High initial install capital

required

Requires highly trained

technicians

Requires screening to 1mm

High energy usage

Chloride discharge can occur

if recovery clean and back

pulses are not completed

fully (Judd, 2004; Buer &

Cumin, 2010)

Site provides

membrane cleaning

and de-ragging via 1-

minute back pulses

of final effluent at 30-

minute intervals

Maintenance cleans

using citric acid

(C₆H₈O₇) and

recovery cleans

using Hydrochloric

acid (HCl-) are

completed weekly

and 6 monthly

respectively

30


Key: Activated Sludge Process, ASP; biological oxygen demand, BOD; chemical oxygen demand, COD; Membrane Bioreactor, MBR;


Percolating

(Trickling)

Filter Bed

A Percolating Filter treatment works uses

circular or rectangular tanks filled with

treatment media (Figure 1.5), often gravel or

broken rocks onto which effluent can be

sprayed via a rotating spray arm as shown in

Figure 1.6 (Metcalf et al., 1972). Highly

aerobic conditions cause bacteria that break

down the nitrates and phosphates of the

incoming effluent as it passes over the media.

This produces a treated effluent that exits the

bottom of the filter bed (Boller & Guier,

1986). Once the effluent has passed through

the filter beds, it will then pass through to a

humus settlement tank allowing any final

organic compounds that haven’t been

digested in the beds to be settled before

discharge to the watercourse (Metcalf et al.,

1972; Grady et al., 2012)

Low cost form of

treatment

Low maintenance

required

Low energy costs for

gravitational systems

Suitable for low flow

treatment (Metcalf et

al., 1972; Boller &

Guier, 1986)

Large footprint for large flow

treatment

Fly and odour issues can

occur. Fly dosing may be

required

Can have low BOD, COD and

suspended-solid removal

(Boller & Guier, 1986; Grady

et al., 2012)

Percolating Filter Bed

is often seen as a

traditional form of

treatment. Other

treatment methods

such as ASP or MBR

are often now

favoured for high

flow sites

31

Figure 1.2: Image showing multiple ASP lanes with aerobic and anoxic zones

(Swain, 2015).

Figure 1.3: Diagram of the Activated Sludge Process (Pipeline, 2003).

32

Figure 1.4: Image of a Zeeweed 500 hollow fibre MBR membrane used in

wastewater treatment (GE Power & Water, 2014).

Figure 1.5: Image of a percolating filter bed (Pure Water Gazette, 2014).

33

Figure 1.6: Diagram of a percolating filter bed (Pitocchelli, 2001).

1.5. River water and effluent quality parameters

River water and effluent parameters are tested to understand the underlying

chemical composition of the watercourse. The ability to understand the baseline

chemical composition of the watercourse allows for pollutants and toxins to be

identified. This study has set out to identify 14 individual determinants and the

effects that ASP, MBR and Percolating Filter effluents have upon water chemistry.

1.5.1. Physical Determinants

1.5.1.1. Temperature

Temperature has a dramatic impact upon riverine biological activity and growth,

defining the number, type and species of organisms that can thrive (Hester et al.,

2011). Temperature is a defining factor in river water chemistry; this is due to an

increase in temperature causing an increase in biological activity and the rate of

riverine chemical reactions (Chitluri, 2015).

34

Temperature is also critically linked to conductivity. With an increase in river

temperature, the mineral concentrations from ground rocks that are dissolved into

the water column increase therefore increasing conductivity (Vega et al., 1998).

Temperature can also change conductivity via water viscosity. An increase in a

waters viscosity, which is directly related to temperature, increases the mobility of

the ions in water causing an increase in conductivity. An increase of 1oC can cause a

2-3% increase in conductivity (Hayashi, 2004).

Finally, there is also a negative correlation between river water temperature and

DO. As temperature increases, the oxygen saturation levels in the water column

decrease causing a decrease in biological activity and growth (Sánchez et al., 2007).

1.5.1.2. Conductivity

Conductivity is a measure of the dissolved ions dissolved in the water column

(Chitluri, 2015). Measured in Siemens, conductivity relates to the amount of ions,

usually in the form of minerals from ground rock or salts that are found in

watercourses (Hill et al., 1997). Conductivity increases linearly with ion

concentrations meaning that with conductivity readings, ion concentrations in

solution can be extrapolated (Daniel et al., 2002).

Industrial discharges, STW and road run off can have a large effect upon the

conductivity of a watercourse, loading the water with charged ions that can disrupt

biological processes (Daniel et al., 2002; Morrison et al., 2001) and also disrupt

aquatic non-visual prey detection (Maciver et al., 2001).

1.5.1.3. Flow

The flow of a river is important as flow has a direct relationship to dilution and

assimilative capacity. With an increase in flow, the dilution rate of pollutants and

toxins increases (Hunt et al., 2010). This has a direct effect on the assimilative

capacity of a river, the ability of a river to transport harmful pollutants and toxins

without having affect upon aquatic life or potable water supplies

35

(Farhadian et al., 2014). Therefore, flow will regulate the amount of discharges

possible to a watercourse whilst keeping it of sound ecological status.

1.5.2. Chemical Determinants

1.5.2.1. Ammonia

Ammonia (NH3) is a highly toxic waterborne form of nitrogen that is formed during

the decomposition of organics (Worrall et al., 2009; O'Riordan et al., 2003). The

toxicity of ammonia is directly correlated to both pH and temperature. An increase

in pH or decrease in temperature can cause a dramatic rise in the toxicity of

ammonia, especially in highly alkaline watercourses (Hickey, 1994; Morrison et al.,

2001). Although a requirement for life, plants have a higher resistance to the toxicity

of ammonia than fish or other aquatic life (Randall, 2002).

1.5.2.2. Biochemical Oxygen Demand (BOD)

BOD is a measure of how much DO is being consumed as microorganisms break

down organic matter (European Environment Agency, 2014). A high BOD therefore

is indicative of high levels of biological activity that may cause a fall in DO

concentrations of rivers (Daniel et al., 2002).

High levels of BOD can be caused by organic pollution, often caused by sewage

inputs into watercourses causing a spike in biological activity (Figuerola et al., 2012;

Singh et al., 2004). High levels of BOD can also be caused by phosphorus or nitrate

spikes, both of which can be limiting factors to plant growth, this increase in plant

growth and organic matter causes a decrease in DO levels (Neal et al., 2008).

1.5.2.3. Boron

Boron (B) is a water-soluble non-metallic substance that is mined to create

substances such as boroniated fibreglass and borosilicate glass. Boron has also been

used as a whitening agent in detergents (Weinthal et al., 2005; Neal et al., 2002).

36

Due to the use of Boron in detergents and low reactivity in the hydrosphere as well

as its lack of natural inputs, boron has become a primary sewage tracer for water

quality analysis in relation to sewage inputs (Neal et al., 2010b; Neal et al., 2006).

Jarvie et al., (2006) has shown a direct correlation between riverine boron levels

and levels of sewage in watercourses demonstrating that boron can be used to

identify the presence of sewage and its dilution factor in watercourses. This has

however been questioned by Nestler et al., (2011) due to the decrease in boron use

in detergents over the past decade.

1.5.2.4. Chloride

Chloride (Cl-) is a naturally occurring ion present in fresh water. Chloride is formed

when substances such as sodium chloride (NaCl) or potassium chloride (KCl)

dissolve in water and separate to form separate ions (Green et al., 2001).

Chloride can be found in increased concentrations in watercourses due to

anthropogenic inputs for example an increase in surface water runoff from grit salt

used as a road de-icer into watercourses (Hunt et al., 2012; Godwin et al., 2003) as

well as agricultural discharges (Kelly et al., 2010). Chloride can also have an effect on

the reproductive rates of freshwater organisms and plants and if found in high

enough concentrations, as well as being toxic to aquatic life (Newman & Aplin, 1992;

Williams & Eddy, 1986).

1.5.2.5. Chemical Oxygen Demand (COD)

COD is the measurement of the total oxygen required to oxidise the chemicals in the

water column into carbon dioxide (CO2) and water (H2O) (Clair et al., 2003). High

levels of COD in effluents can cause riverine hypoxia during decomposition of

aquatic organics (Vega, et al., 1998).

37

1.5.2.6. Dissolved Oxygen (DO)

DO is the measure of the free, non-compound oxygen (O2) that is dissolved in water.

DO is measured in mg/l-1 with the maximum amount of oxygen the water can hold

being called the saturation point (Daniel, 2002).

DO has a direct correlation with temperature, with an increase in temperature

causing an inverse relationship to the DO water can retain (Wilcock et al., 1998). DO

is inputted into the water column via surface atmospheric diffusion or as a by-

product of plant photosynthesis (Cox, 2003).

Surface atmospheric diffusion increases when water is mixed through aeration via

rapids, waterfalls or other moving water bodies. This movement of water increases

the diffusion rate of O2 into the water column (Cox, 2003).

DO is as a result of the respiration of plants during photosynthesis. This DO input

from photosynthesis will peak during daytime and is seasonal with most inputs

coming during summer months (Auer & Effler, 1999; Schurr & Ruchti, 1977).

DO is also a primary indicator of pollution events, with low levels of DO being

indicative of an organic pollution from a sewage or agricultural discharge. This is

caused by microbial bacteria assimilating the available oxygen to break down the

organic pollutant (Daniel et al., 2002; Tsai, 1973). This reduction in DO can cause

very low DO levels and lead to aquatic fatalities via hypoxia (San Diego-McGlone et

al., 2008). The conventional threshold for hypoxia in river water is 2mg O2/l, with

first larval zoea stage of crustaceans, some of the most sensitive aquatic organisms,

having a hypoxic threshold of 8.6mg 02/l (Vaquer-Sunyer & Duarte, 2008).

1.5.2.7. Nitrate

Nitrate (NO3-) is a naturally occurring oxidised form of nitrogen, caused by the

nitrification of ammonia in the water column from organic breakdown first

transferring to nitrite and then finally to nitrate. (DEFRA, 2002). Excess levels of

38

nitrates in watercourses can lead to anoxia. This is a lack of DO in the water column

due to excessive nutrients generating algal blooms (Justić et al., 2003).

1.5.2.8. Nitrite

Nitrite (NO2-) is formed by the breaking down of ammonia in the water column (Kim

et al., 2006) and is highly toxic to aquatic organisms (Tilak et al., 2007). Nitrite can

cause hypoxia in fish by bonding with the haemoglobin in the fish blood stream and

replacing oxygen with methemoglobin; nitrite bonded with haemoglobin. This can

prove fatal for fish and other aquatic organisms (Williams & Eddy, 1986; Tilak et al.,

2007).

1.5.2.9. Orthophosphorus.

Orthophosphorus, (PO43–) is a measure of the forms of inorganic phosphorus that

are deposited in watercourses via the run off of fertilisers from agricultural practices

or sewage treatment (Bowes et al., 2008; Jarvie et al., 2006).

Orthophosphorus is vital for the survival of aquatic plant life but can also cause

eutrophic algal blooms causing a decrease in riverine DO levels (San Diego-McGlone

et al., 2008). As you can see from the graph in Figure 1.7, the levels of

orthophosphorus in European rivers has been reducing since 1992 (European

Environment Agency, 2015). This is due to a reduction in anthropogenic inputs via

increases in technology at STW and increase understanding of orthophosphorus

inputs by the agricultural community (Mainstone & Parr, 2002; Neal et al., 2010a).

39

Figure 1.7: A graph taken from EEA showing river orthophosphate levels from 1992 – 2012 in European rivers (European Environment Agency, 2015).

1.5.2.10. pH

pH is a numerical value given to how acidic or alkali a substance or body of water is

by measuring the concentration hydrogen (H+) ions. pH is a logarithmic scale

ranging from 0-14 with pH 7 neutral (Chitluri, 2015).

pH has a direct correlation with the solubility of nutrients. A minor increase in pH

can increase the solubility of nutrients such as phosphorus and nitrate making them

readily available for plants and thus causing a growth boom in aquatic plant

populations (Hill & Neal., 1997; Seybold et al., 2002).

1.5.2.11. Phosphorus

Phosphorus (P) is a measurement of the total phosphorus inputs, both organic and

inorganic, into a riverine system (Bowes et al., 2008; Chenet al., 2014). A limiting

factor in plant and algal growth, phosphorus can often be seen as a pollutant as it is

commonly discharged to watercourses in high quantities leading to eutrophication

(Correll, 1998).

40

Phosphorus is primarily discharged by STW as well as by industrial and agricultural

activities and natural processes (DEFRA, 2008b; Jarvie et al., 2006; Mainstone &

Parr, 2002).

1.5.2.12. Sulphate

Sulphate (SO42-) is a non-metallic element that is found in many industrial processes

and discharged by industrial processes that use sulphates or sulphuric acid (H2SO4)

for example mining and smelting operations, paper mills, textiles and tanneries

(Delisle & Schmidt, 1977; Ciardelli & Ranieri, 2001), and natural decomposition.

Sulphate is also discharged via agricultural runoff, being a constituent of agricultural

fertilisers and pesticides (Weston et al., 2004). At high concentrations, sulphate is

toxic to aquatic life, however the levels required for toxicity are incredibly high

(Stumm & Morgan, 2012).

1.5.3. Chemical Standards Report

The EA Chemical Standard report is a set of statutory standards at UK and European

level for surface water quality setting concentration limits (Environment Agency,

2011a). Chemical Standards for determinants in this project can be found in Table

1.5.

41

Table 1.5: EA Chemical Standards report for UK and EU river chemical concentrations (Environment Agency, 2011a).

Key: ammonia, NH3; European Union, EU; oxygen, O2;

Determinant Type of

Standard

Environmental

Medium

Legal Status

of standard

Standard Values Notes

Ammonia UK Standard

Freshwater Statutory Salmonid and cyprinid waters: < /= 0.025 mg NH3/l

Based on 95% of samples taken over a 12 month period Values for non-ionised ammonia may be exceeded in the form of minor peaks in the daytime

BOD UK Standard

Freshwater Statutory Salmonid Waters: < /= 3 mg O2/l Cyprinid Waters: < /= 6 mg O2/l

Based on 95% of samples taken over a 12 month period. These are guide values

Boron UK Standard

Surface Water Statutory Protection of sensitive freshwater aquatic life (e.g. salmonid fish): 2000 ug/l

Protection of other freshwater aquatic life (e.g. cyprinid fish): 2000 ug/l

Protection of saltwater life: 7000 ug/l

These values are for total boron and represent the annual average

COD EU Standard

Surface Water Intended for Abstraction for Drinking Water

Statutory No statutory value for surface water concentrations. 30 mg O2/l to be used as a guide for abstraction values

42


Key: chlorine, Cl; Environmental Quality Standard, EQS; European Union, EU; nitrate, NO3; oxygen, O2; sulphate, SO4;

Determinant Type of

Standard

Environmental

Medium

Legal Status of

standard


Chloride UK Non-statutory EQSs

Surface Water Non-Statutory Freshwater annual average:

250,000 ug/l

Total anions of 250,000 ug/l (annual average) also proposed. Total anion concentration 'normalised' to Cl- by Cl- = SO4-/1.5 = NO32-/1.8

Conductivity UK

Standard

Protection of Surface Waters Intended for the Abstraction of Drinking Water

Statutory Guide: 1000 uS/cm at 20°C Imperative: none set

In December 2007, the Directive through which these standards were established was repealed under the Water Framework Directive (2000/60/EC). Now values as guidance

DO UK

Standard

Freshwater Statutory Salmonid waters: 50% > /=

9 mg O2/l

Cyprinid waters: 50% > /= 7

mg O2/l

(1) When the oxygen concentration falls below 6 mg/l, the Environment Agency shall establish whether this is the result of chance, a natural phenomenon or pollution and shall adopt appropriate measures. The Environment Agency must prove that this situation will have no harmful consequences for the balanced development of the fish population

Nitrate UK Standard

Protection of Surface Waters Intended for the Abstraction of Drinking Water

Statutory 50mg NO3/l Compliance with these standards may be waived under exceptional meteorological or geographical conditions. Based on 95% of samples.

43


Key: chlorine, Cl; Environmental Quality Standard, EQS; European Union, EU; nitrate, NO3; oxygen, O2; sulphate, SO4;

Determinant Type of

Standard

Environmental

Medium

Legal Status of

standard


Nitrites EU Standard

Freshwater Statutory

Salmonid Waters: < /= 0.01 mg NO2/l Cyprinid Waters: < /= 0.03 mg NO2/l

Based on 95% of samples taken over a 12-month period. These refer to nitrites and are guide values

Ortho-

phosphorus

No Standard

N/A N/A N/A N/A

pH UK Standard

Freshwater Statutory Salmonid and cyprinid waters: 6-9

Based on 95% of samples taken over 12-month period.

Phosphorus EU Standard

Freshwater Non-Statutory No imperative or guide values are set.

Applies to total phosphorus

Sulphate UK Standard

Surface Water Intended for Abstraction for Drinking Water

Statutory 250 mg SO4/l

Compliance with this standard may be waived under exceptional meteorological or geographical conditions

Temperature UK Standard

Freshwater Statutory Salmonid waters: < /= 1.5°C increase < /= 21.5°C Cyprinid waters: < /= 3°C increase < /= 28°C

Thermal discharges must not cause the temperature downstream of the point of thermal discharge (at the edge of the mixing zone) to exceed the stated amount for times other than the breeding season or for waters that do not contain fish that need cold water to breed

44

1.6. Gaps in current studies

There have been a number of studies into the effects of sewage treatment effluents

on watercourses, specifically the UK based work by Jarvie and Neal. However, these

studies have only been based on river water samples and have not had access to FE

samples. The only study with FE sample access identified was Morrison et al., (2001)

who looked at FE discharges into wetlands in the Keiskamma River in South Africa.

To date, there are no studies into UK river water quality that have access to FE data.

It is believed that this is due to commercial sensitivity, with water companies not

wanting to release sensitive FE data for fear of prosecution from the regulator.

1.7. Aims and objectives

The aim of this study is to determine the effects that sewage treatment effluents

have upon the receiving watercourse by analysing both in-situ and chemical

determinants from 7 sewage treatment sites across the midlands area. The study

will look to address the following hypothesis:

1.7.1. Hypotheses

H0 - The discharge of sewage treatment effluent does have a significant effect upon

the receiving watercourse.

H1- The discharge of sewage treatment effluent does not have a significant effect

upon the receiving watercourse.

45

2. Methodology and Equipment

2.1. Commercial Sensitivity

Due to the commercial sensitivity of the water industry, site anonymity was

maintained to allow FE data to be collected and used. All site names have therefore

been removed from this study and replaced with site 1-7. Ensuring anonymity for

the sites met Severn Trent Waters criteria for allowing this project to take place. An

email confirming commercial sensitivity can be found in appendix 1.

2.2. Site Selection

All sites sampled were based in the Midlands region served by Severn Trent Water.

Site selection was made based upon a number of criteria to include, a mix of

technologies, size of treatment works, and access to the watercourse approximately

200 metres upstream and downstream of the FE sample point. Site treatment

technologies can be found in Table 2.1.

Characteristics for the 7 sampled sites vary dramatically. A mix of urban and rural

sites has been selected to provide contrast. The size of the receiving watercourse

also varies across sites with some sites discharging to small brooks and others to

large rivers. Full breakdown of site descriptions can be found in Table 2.2.

A site layout and sample point map is included for each site. Site 1 layout is

demonstrated in Figure 2.1 with a sample point map demonstrated in Figure 2.2.

Due to commercial sensitivity, only river course data is shown in sample point maps

to retain site anonymity. Site layouts and sample point maps for all sites can be

found in appendix 2 and 3.

46

Table 2.1: A table showing treatment methods employed at sampled STW.

Site

Number

Preliminary

Treatment

Primary

Treatment

Secondary

Treatment

Tertiary

Treatment

Consented

flow pass

forward

Population

Equivalent

(PE)

Notes

Site 1 Primary screening to 6 & 3mm

4 primary settlement tanks

4 rectangular Percolating Filter beds

4 Humus tanks and P-stripping

95 l/s 36,000

Site 2 Primary screening to 6mm


4 circular Percolating Filter beds

4 Humus tanks 17 l/s 5,500



2-lane ASP plant

7 Percolating Filter beds and 3-lane Humus tank, P-stripping

50 l/s 25,000 Percolating Filter works in place due to ASP not providing nitrification

Site 4 Primary screening to 6, 3 & 1mm

N/A 2-lane ASP plant

Membrane Bioreactor (MBR) plant

85 l/s 2,300



Multi-lane ASP plant

15 final settlement tanks, P-stripping

225 l/s 400,000



Multi – lane ASP plant

3 final settlement tanks, P-stripping

125 l/s 47,000

Site 7 Primary screening to 6mm

N/A 10 Percolating Filter beds

Nitrifying NSAF 95 l/s 22,000 NSAF provides nitrification and suspended solids removal

Key: Activated Sludge Process, ASP; Membrane Bioreactor, MBR; Nitrifying Surface Aerated Filter, NSAF;

47


Site

Number

Setting location Watercourse

characteristics

Influent Flows

to treatment

works

Sample Location

Other features

Site 1 Rural with high levels of agriculture and local industry

Small, fast flowing brook. Book regularly bursts its banks in high flow.

Residential and industrial

Upstream taken from the riverbank, downstream taken from road bridge

Dairy herd have direct access to brook between FE and downstream point. Agricultural runoff and surface water discharge evident downstream of FE point

Site 2 Very rural, located outside small town. High levels of agriculture in local area

Medium sized river Residential Upstream sample taken from road bridge, downstream taken from the riverbank

Flows can be seasonal due to high levels of tourism in the local area. Site is also prone to high flows during wet weather events and regularly discharges to storm

Site 3 Outskirts of a medium sized rural industrial town

Medium sized river that flows through the town itself before reaching the treatment works


Both upstream and downstream samples are taken from the riverbank. Upstream sample point is located in the valley with arable fields adjacent

River flows through the town itself before reaching the treatment works. Other industrial inputs are known and regulated upstream of STW

Site 4 Outskirts of medium sized rural town

Small, fast flowing river. Watercourse is classified as sensitive


Upstream sample taken from footbridge, downstream sample taken from the riverbank

Watercourse is sensitive with high EA interest and high recreational value

Key: Environment Agency, EA; Final Effluent, FE;

48


Key: Final Effluent, FE; Environment Agency, EA;

Site

Number

Setting location Watercourse

characteristics

Influent Flows

to treatment

works

Sample Location

Other features

Site 5 Located on the edge of large urban city

Discharge to a loop branch of a large river (See sample point map in appendix 3.5)

Very high levels of industry and high residential flows

Upstream samples are taken from a road bridge and downstream from the riverbank

Site influent takes flow from heavy industry. Heavy metals are common in influent

Site 6 Located on the edge of a large town

Small, fast flowing river


Upstream sample taken from the riverbank and downstream taken from road bridge

High levels of agriculture. Dairy herd are grazed and have access along the length of the watercourse

Site 7 Located outside a small rural town with high levels of agriculture

Medium sized fast flowing river with high natural aeration downstream


Upstream sample is taken from a road bridge. Downstream is taken from the riverbank

Flows can be seasonal due to high levels of tourism

49

Figure 2.1: Site diagram showing layout of Site 1.

Figure 2.2: River course and sample point map for Site 1 showing upstream, final effluent and downstream sample locations.

50

2.2.1. Sample locations

Three spot samples were taken at each site to provide an overview of the effect

sewage treatment effluent has upon a watercourse. An upstream sample was taken to

act as a reference of river water quality, a FE sample was taken to give a reference of

the inputs from the STW, and a downstream sample was taken to understand the

effects that the FE sample has upon the watercourse. A 200m radius from both FE and

storm outfalls was used with samples being taken as close to this 200m radius as

possible. This was to allow for the upstream sample to be representative of non-

sewage inputs and satisfactory dilution to occur downstream (Hunt et al., 2010).

2.3. Sampling Timescales

Sampling for this project took place during a 10-week period between November

2014 and January 2015. Sample collections during weeks 7 and 8 were slightly

amended due to the Christmas shut down of NLS Laboratories.

2.4. Sample Technique

To collect samples for analysis, a standardised sampling regime was used in line with

the EA standard operating procedures. Personal protective equipment was provided

by Severn Trent to be worn on-site as per site regulations. A full list of equipment is

found in appendix 4.

Two different sample bottles were used to store and transport water prior to analysis.

Due to analytical requirements, samples were collected in both PET 1L and MET

125ml bottles for each sample point to allow for a full range of analysis. A list of

analysis and bottle requirements can be found in appendix 5.

2.4.1. Bridge sampling technique

Samples are taken from the middle of the watercourse. A 1-litre food grade stainless

steel sampling can was attached to 10 metres of stainless steel chain and lowered into

the watercourse. Care was taken on both lowering and raising the sampling can to

prevent contact between the chain and the bridge as this may dislodge contaminants

51

into the sample can. Stainless steel chain was preferred to blue rope due to

contamination issues with water absorption of rope. The sample can was rinsed in

river water prior to every sample being taken to reduce the chance of cross

contamination. Analysis and bottling was completed at bridge level (Environment

Agency, 2014a).

2.4.2. Riverbank sampling technique

A safe access point was chosen to allow easy access to water level. A telescopic

sampling pole was be used and extended to its maximum 3m length to allow for reach

into the central stream of the watercourse. The sample can was rinsed in river water

prior to a sample being collected. Once collected, samples were then analysed and

bottles bankside (Environment Agency, 2014a).

2.4.3. Final Effluent sampling technique

To collect FE samples, site protocols for access to FE sample point were followed. The

sample container was rinsed in FE prior to a sample being collected. Analysis and

bottling was completed at FE point.

2.5. Sample Analysis

2.5.1. In-situ data collection

2.5.1.1. Temperature and DO

Temperature and DO readings were taken using a HACH (HQ30d) probe. The probe

was submerged 6-8cm into the sample and held in suspension until the reading had

stabilised using the inbuilt stabilisation (HACH, 2013). All readings were taken in

triplicate and strictly followed the EA Operational Standards 529_06 & 530_06

(Environment Agency 2010a; Environment Agency 2010b).

52

2.5.1.2. Conductivity and on-site pH

Conductivity and pH readings were taken using a Hanna Combo pH & EC HI98130

probe. The probe was submerged 6-8cm into the sample and held in suspension until

the reading had stabilised for 10 seconds (Hanna, 2005). All readings were taken in

triplicate and follow the EA Operational Standards 351_06 & 528_06 (Environment

Agency, 2010c; Environment Agency, 2014b). The Hanna Combo pH & EC was

calibrated before every sample day using pH 4 & 7 buffer solution

2.5.1.3. Flow

Flow measurements were taken from MCERT flow meters installed on the FE outfall.

These flow measurements are required for consented flow rates.

2.5.2. Laboratory Analysis

Samples were collected and bottled on-site before being transported to NLS. After

delivery to NLS, samples were stored in refrigerators to keep them in a dark cool

environment to inhibit photosynthesis thus preventing algal growth and

orthophosphate uptake (Jarvie et al., 1999). Analysis was completed within 2 days of

receipt. The following determinants have limited methodological information as the

analysis was conducted by NLS. Due to commercial sensitivity, detailed

methodological information is not available. However, the same laboratory was used

for all sample analysis and internal NLS and external quality assurances would have

ensured analysis consistency.

2.5.2.1. Ammonia

A Kone Discrete analyser was used to test for Ammonia. Ammonia reacts with

salicylate and dichloroisocyanurate in the presence of sodium nitroprusside to form a

blue colour, the intensity of which is proportional to the amount of ammonia present.

Sodium citrate is then added to mask possible interference from cations and the

colour produced was measured at 660nm (National Laboratory Service, 2015c).

53

2.5.2.2. Biological Oxygen Demand

Do was tested using robotic probe that self-cleans in deionised water. The BOD is

defined as the mass of DO required by a specified volume of liquid for the process of

biochemical oxidation over 5 days at 20oC in the dark (National Laboratory Service,

2015a).

2.5.2.3. Boron

An Inductively Coupled Plasma Optical Emission Spectrometer (ICPOES) was used to

test for Boron. Samples are digested in a mixture of concentrated nitric and

hydrochloric acid in an oven at 90oC for 16 hours, filtered and the metals

concentration determined by ICPOES (National Laboratory Service, 2015e).

2.5.2.4. Chemical Oxygen Demand

A Spectrophotometer was used to analyse for COD. Samples were oxidised by

refluxing with sulphuric acid and potassium dichromate with a silver salt to catalyse

the oxidation of alcohol and low molecular weight acids. Mercuric sulphate and excess

silver salt suppresses chloride interference and with it the effect due to ammonia. The

mixture was refluxed for two hours and the residual dichromate was determined

photometrically. The appearance of the green colour of Cr3+ is used for the

measurement. The amount of dichromate reduced is expressed in the form of

milligrams of oxygen consumed per litre of sample (National Laboratory Service,

2015b).

2.5.2.5. Chloride

A Kone Discrete analyser was used to test for chloride. Chloride reacts with mercuric

thiocyanate forming a mercuric chloride complex. Released thiocyanate reacts with

iron (III) forming a red ferric thiocyanate complex. The intensity of colour produced,

measured at 510nm, is proportional to the chloride concentration (National

Laboratory Service, 2015c).

54

2.5.2.6. Nitrate

Kone Discrete analyser was used to test for nitrate. Nitrate was reduced to nitrite by

hydrazine under alakaline conditions. The total nitrite is then treated with

sulphanilamide and N-1- naphthylethylene diamine dihydrochloride under acidic

conditions to form a pink azodye. The intensity of this dye is directly proportional to

the concentration of total oxidised nitrogen (National Laboratory Service, 2015c).

2.5.2.7. Nitrite

A Kone Discrete analyser was used to test for nitrite. Nitrite ions, when reacted with a

reagent containing sulphanilamide and N-(1-naphthyl)-ethylenediamine

dihydrochloride, in the presence of acid, produce a highly coloured azo dye that was

measured photometrically at 540nm (National Laboratory Service, 2015c).

2.5.2.8. Orthophosphate, Reactive as P

A Kone Discrete analyser was used to test for orthophosphate. Orthophosphate reacts

with ammonium molybdate and antimony potassium tartrate under acidic conditions

to form a complex which, when reduced with ascorbic acid produces an intense blue

colour, the absorbance of which is measured at 880nm (National Laboratory Service,

2015c).

2.5.2.9. pH Laboratory

An automated pH probe was used to test pH. The equipment is calibrated using buffer

solutions of known pH (National Laboratory Service, 2015d).

2.5.2.10. Phosphorus

An Inductively Coupled Plasma Optical Emission Spectrometer (ICPOES) was used to

test for phosphorus. Samples were digested in a mixture of concentrated nitric and

hydrochloric acid in an oven at 90oC for 16 hours, filtered and the metals

concentration determined by ICPOES (National Laboratory Service, 2015c).

55

2.5.2.11. Sulphate

A Dionex ICS-90 ion chromatograph was used to test for sulphate. Ions in a sample

were separated by being passed through a chromatography column containing a low

ion exchange capacity resin. The sample was eluted by using a weak solution of

sodium carbonate as a mobile phase. Eluent from the column was passed through a

continuous regeneration suppressor, where cations such as sodium and potassium

were replaced with hydrogen ions thus producing a low conductivity background. The

anions were detected using an electrical conductivity detector (National Laboratory

Service, 2015e).

2.6. Statistical analysis

Statistical analysis was completed using IBM SPSS V.22 statistics software. SPSS was

used to define normality with the dataset being defined as normally distributed.

Because of this, ANOVA was chosen as a comparison of means, and Tukey was used

for post-hoc analysis (Ennos, 2007; Dytham, 2010). Full mean results can be found in

appendix 6.

56

3. Results

3.1. In-situ Results

3.1.1. Conductivity

Mean conductivity values across the three testing locations are displayed in Figure

3.1. Differences between site testing locations for conductivity are displayed in Table

3.1.

Figure 3.1: Mean conductivity values across all sites (Mean ± SE) (MRV=0.00 mS/cm) Table 3.1: Multiple comparisons of means for conductivity including post-hoc analysis (n=10).

Site Between Groups Between

Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=0.213, P=0.810, P=0.793 P=0.937 P=0.949

Site 2 F2,29=95.770,

P<0.001*,

P<0.001* P=0.990 P<0.001*

Site 3 F2,29=21.595, P<0.001* P<0.001* P=0.983 P<0.001*

Site 4 F2,29=13.393, P<0.001* P<0.001* P=0.385 P=0.003*

Site 5 F2,29=83.071, P<0.001* P<0.001* P=0.885 P<0.001*

Site 6 F2,29=0.941, P<0.001* P=0.373 P=0.702 P=0.844

Site 7 F2,29=10.314, P<0.001* P<0.001* P=0.743 P=0.004*

*Indicates significance at the 0.05 level.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7

Co

nd

uc

tiv

ity

(m

S)

Site Number

Upstream

Final Effluent

Downstream

57

3.1.2. Dissolved Oxygen

Mean DO values across the three testing locations are displayed in Figure 3.2.

Differences between site testing locations for DO are displayed in Table 3.2.

Figure 3.2: Mean DO values across all sites (Mean ± SE)(MRV=0.20 mg/l). Table 3.2: Multiple comparisons of means for DO including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=57.946,

P<0.001*

P<0.001* P=0.980 P<0.001*

Site 2 F2,29=53.289,

P<0.001*

P<0.001* P=0.999 P<0.001*

Site 3 F2,29=45.466,

P<0.001*

P<0.001* P=0.379 P<0.001*

Site 4 F2,29=8.217, P=0.002* P=0.002* P=0.544 P=0.020*

Site 5 F2,29=187.841,

P<0.001*

P<0.001* P=0.408 P<0.001*

Site 6 F2,29=1.697, P=0.202 P=0.818 P=0.461 P=0.186

Site 7 F2,29=169.918,

P<0.001*

P<0.001* P=0.115 P<0.001*

* Indicates significance at the 0.05 level.

0

2

4

6

8

10

12

14


Dis

solv

ed

Ox

yg

en

(m

g/

l)

Site Number

Upstream

Final Effluent

Downstream

58

3.1.3. pH on-site

Mean pH values across the three testing locations are displayed in Figure 3.3.

Differences between site testing locations for pH are displayed in Table 3.3.

Figure 3.3: Mean on-site pH values across all sites (Mean ± SE) (MRV=0.05 pH) Table 3.3: Multiple comparisons of means for pH, including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=15.986, P<0.001* P<0.001* P=0.515 P<0.001*

Site 2 F2,29=20.422, P<0.001* P<0.001* P=0.113 P<0.001*

Site 3 F2,29=60.671, P<0.001* P<0.001* P=0.379 P<0.001*

Site 4 F2,29=199.541,

P<0.001*

P<0.001* P<0.001* P<0.001*

Site 5 F2,29=143.106,

P<0.001*

P<0.001* P=0.969 P<0.001*

Site 6 F2,29=161.631,

P<0.001*

P<0.001* P=0.517 P<0.001*

Site 7 F2,29=180.301,

P<0.001*

P<0.001* P=0.115 P<0.001*

*Indicates significance at the 0.05 level.

6.4

6.6

6.8

7

7.2

7.4

7.6

7.8

8

8.2

8.4

8.6


pH

on

-sit

e

Site Number

Upstream

Final Effluent

Downstream

59

3.1.4. Temperature

Mean temperature values across the three testing locations are displayed in Figure

3.4. Differences between site testing locations for temperature are displayed in Table

3.4.

Figure 3.4: Mean on-site temperature values across all sites (Mean ± SE). Table 3.4: Multiple comparisons of means for temperature, including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29= 10.018, P=0.001 P=0.003* P=0.928 P<0.001*

Site 2 F2,29 = 3.721, P=0.037 P=0.093 P=0.942 P=0.047*

Site 3 F2,29= 23.623, P=0.00 P<0.001* P=0.688 P<0.010*

Site 4 F2,29 =23.090, P=0.00 P<0.001* P=0.994 P<0.001*

Site 5 F2,29 = 52.284, P=0.00 P<0.001* P=0.798 P<0.001*

Site 6 F2,29= 7.598, P=0.02 P=0.022* P=0.655 P=0.186

Site 7 F2,29=19.680, P=0.00 P<0.001* P=0.687 P<0.001*


0

2

4

6

8

10

12

14

16


Te

mp

era

ture

(oC

)

Site Number

Upstream

Final Effluent

Downstream

60

3.2. Laboratory Results

3.2.1. Ammonia

Mean ammonia concentrations across the three testing locations are displayed in

Figure 3.5. Differences between site testing locations for ammonia are displayed in

Table 3.5.

Figure 3.5: Mean ammonia concentrations across all sites (Mean ± SE) (MRV=0.19mg/l).

Negative error bars are present on sites 1 and 6 as although the mean value was low

for FE ammonia over the 10 sample weeks, the range was large; therefore negative

error bars were reported.

Table 3.5: Multiple comparisons of means for ammonia, including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=0.092, P=0.913 P=0.906 P=0.985 P=0.964

Site 2 F2,29=10.540,

P<0.001*

P<0.001* P=1.000 P<0.001*

Site 3 F2,29=7.508, P=0.003* P=0.006* P=1.000 P=0.006*

Site 4 F2,29=2.227, P=0.127 P=0.161 P=0.991 P=0.202

Site 5 F2,29=8.667, P<0.001* P=0.003* P=1.000 P=0.004*

Site 6 F2,29=0.828, P=0.448 P=0.479 P=0.991 P=0.556

Site 7 F2,29=32.820,

P<0.001*

P<0.001* P=0.795 P<0.001*


-0.5

0

0.5

1

1.5

2

2.5

3

3.5


Am

mo

nia

(m

g/

l)

Site Number

Upstream

Final Effluent

Downstream

61

3.2.2. Biological Oxygen Demand

Mean BOD concentrations across the three testing locations are displayed in Figure

3.6. Differences between site testing locations for BOD are displayed in Table 3.6.

Figure 3.6: Mean BOD concentrations across all sites (Mean ± SE) (MRV=1.0 mg/l). Table 3.6: Multiple comparisons of means for BOD including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=2.298, P=0.120. P=0.101 P=0.620 P=0.465

Site 2 F2,29=70.680, P<0.001* P<0.001* P=1.000 P<0.001*

Site 3 F2,29=11.053, P<0.001* P<0.001* P=1.000 P<0.001*

Site 4 F2,29=0.338, P=0.716 P=0.772 P=0.999 P=0.746

Site 5 F2,29=7.453, P=0.003* P=0.009* P=0.977 P=0.005*

Site 6 F2,29=5.000, P=0.014* P=0.019* P=0.931 P=0.044*

Site 7 F2,29= 224.393,

P<0.001*

P<0.001* P=0.347 P<0.001*


0

1

2

3

4

5

6

7

8

9


Bio

log

ica

l O

xy

ge

n D

em

an

d (

mg

/l)

Site Number

Upstream

Final Effluent

Downstream

62

3.2.3. Boron

Mean boron concentrations across the three testing locations are displayed in Figure

3.7. Differences between site testing locations for boron are displayed in Table 3.7.

Figure 3.7: Mean boron concentrations across all sites (Mean ± SE) (MRV=0.1mg/l). Table 3.7: Multiple comparisons of means for boron including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=1.000, P=0.381 P=0.449 P=1.000 P=0.449

Site 2 F2,29=0.959, P=0.396 P=0.478 P=0.450 P=0.999

Site 3 F2,29=0.777, P=0.470 P=0.958 P=0.468 P=0.638

Site 4 F2,29=0.000, P=1.000 P=1.000 P=1.000 P=1.000

Site 5 F2,29=6.684, P=0.004* P=0.010* P=1.000 P=0.010*

Site 6 F2,29=2.764, P=0.081 P=0.123 P=1.000 P=0.123

Site 7 F2,29=0.000, P=1.000 P=1.000 P=1.000 P=1.000


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16


Bo

ron

(m

g/

l)

Site Number

Upstream

Final Effluent

Downstream

63

3.2.4. Chemical Oxygen Demand

Mean COD concentrations across the three testing locations are displayed in Figure

3.8. Differences between site testing locations for COD are displayed in Table 3.8.

Figure 3.8: Mean COD concentrations for across all sites (Mean ± SE) (MRV =10.0 mg/l). Table 3.8: Multiple comparisons of means of COD including post-hoc analysis (n=10).


0

10

20

30

40

50

60

70


Ch

em

ica

l O

xy

ge

n D

em

an

d (

mg

/l)

Site Number

Upstream

Final Effluent

Downstream


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=9.179, P<0.001* P<0.001* P=0.671 P=0.009*

Site 2 F2,29=19.940, P<0.001* P<0.001* P=0.798 P<0.001*

Site 3 F2,29=9.391, p<0.001* P<0.001* P=1.000 P=0.005*

Site 4 F2,29=2.121, P=0.139 P=0.121 P=0.704 P=0.440

Site 5 F2,29=0.653, P=0.529. P=0.606 P=0.999 P=0.574

Site 6 F2,29=2.665, P=0.088 P=0.074 P=0.648 P=0.357

Site 7 F2,29=39.037, P<0.001* P<0.001* P=0.637 P<0.001*

64

3.2.5. Chloride

Mean chloride concentrations across the three testing locations are displayed in

Figure 3.9. Differences between site testing locations for chloride are displayed in

Table 3.9.

Figure 3.9: Mean chloride concentrations across all sites (Mean ± SE) (MRV=0.9 mg/l). Table 3.9: Multiple comparisons of means for chloride including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=0.248, P<0.001* P=0.834 P=0.671 P=0.009*

Site 2 F2,29=47.696, P<0.001* P<0.001* P=0.958 P<0.001*

Site 3 F2,29=65.582, P<0.001* P<0.001* P=0.995 P<0.001*

Site 4 F2,29=3.273, P=0.053 P=0.057 P=0.879 P=0.149

Site 5 F2,29=103.825,

P<0.001*

P<0.001* P=0.999 P<0.001*

Site 6 F2,29=506.505,

P=0.300

P=0.336 P=0.990 P=0.407

Site 7 F2,29=25.031, P<0.001* P<0.001* P=0.868 P<0.001*


0

20

40

60

80

100

120

140


Ch

lori

de

(m

g/

l)

Site Number

Upstream

Final Effluent

Downstream

65

3.2.6. Nitrate

Mean nitrate concentrations across the three testing locations are displayed in Figure

3.10. Differences between site testing locations for nitrate are displayed in Table 3.10.

Figure 3.10: Mean nitrate concentrations across all sites (Mean ± SE) (MRV=0.006 mg/l). Table 3.10: Multiple comparisons of means for nitrate including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=9.346, P<0.001* P=0.002* P=0.930 P=0.004*

Site 2 F2,29=483.336,

P<0.001*

P<0.001* P=0.968 P<0.001*

Site 3 F2,29=61.948, P<0.001* P<0.001* P=0.991 P<0.001*

Site 4 F2,29=100.556,

P<0.001*

P<0.001* P=0.166 P<0.001*

Site 5 F2,29=68.903, P<0.001* P<0.001* P=1.000 P<0.001*

Site 6 F2,29=17.819, P<0.001* P<0.001* P=0.879 P<0.001*

Site 7 F2,29=126.566,

P<0.001*

P<0.001* P=0.658 P<0.001*


0

2

4

6

8

10

12

14

16

18


Nit

rate

(m

g/

l)

Site Number

Upstream

Final Effluent

Downstream

66

3.2.7. Nitrite

Mean nitrite concentrations across the three testing locations are displayed in Figure

3.11. Differences between site testing locations for nitrite are displayed in Table 3.11.

Figure 3.11: Mean nitrite concentrations across all sites (Mean ± SE) (MRV see appendix 7). Negative error bars are present on sites 2, 4, 6 and 7 as although the mean value was

low for upstream, FE and downstream nitrite concentrations over the 10 sample

weeks, the range was large; therefore negative error bars were reported.

Table 3.11: Multiple comparisons of means for nitrite including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=0.045, P=0.956 P=0.952 P=0.985 P=0.990

Site 2 F2,29=44.370, P<0.001* P<0.001* P=0.999 P<0.001*

Site 3 F2,29=21.925, P<0.001* P<0.001* P=0.999 P<0.001*

Site 4 F2,29=6.980, P=0.004 P=0.006* P=0.919 P=0.015*

Site 5 F2,29=9.897, P<0.001 P=0.002* P=0.993 P=0.002*

Site 6 F2,29=18.995, P<0.001* P<0.001* P=0.871 P<0.001*

Site 7 F2,29=126.556,

P<0.001*

P<0.001* P=0.740 P<0.001*


-0.1

0

0.1

0.2

0.3

0.4

0.5


Nit

rite

(m

g/

l)

Site Number

Upstream

Final Effluent

Downstream

67

3.2.8. Orthophosphate

Mean orthophosphate concentrations across the three testing locations are displayed

in Figure 3.12. Differences between site testing locations for orthophosphate are

displayed in Table 3.12.

Figure 3.12: Mean orthophosphate concentrations across all sites (Mean ± SE) (MRV=0.008 mg/l). Negative error bars are present on site 5 as although the mean value was low for FE

orthophosphate over the 10 sample weeks, the range was large; therefore negative


Table 3.12: Multiple comparisons of means for orthophosphate including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=13.095, P<0.001* P<0.001* P=0.802 P<0.001*

Site 2 F2,29=312.049,

P<0.001*

P<0.001* P=1.000 P<0.001*

Site 3 F2,29=167.751,

P<0.001*

P<0.001* P=0.998 P<0.001*

Site 4 F2,29=15.836, P<0.001* P<0.001* P=0.998 P<0.001*

Site 5 F2,29=2.320, P=0.118 P=0.154 P=0.994 P=0.185

Site 6 F2,29=44.977, P<0.001* P<0.001* P=0.737 P<0.001*

Site 7 F2,29=77.390, P<0.001* P<0.001* P=0.907 P<0.001*


-0.5

0

0.5

1

1.5

2

2.5


Ort

ho

ph

osp

ha

te (

mg

/l)

Site Number

Upstream

Final Effluent

Downstream

68

3.2.9. pH Laboratory

Mean pH concentrations across the three testing locations are displayed in Figure

3.13. Differences between site testing locations for pH are displayed in Table 3.13.

Figure 3.13: Mean concentrations for laboratory pH across all sites (Mean ± SE) (MRV=0.05 pH). Table 3.13: Multiple comparisons of means for pH Laboratory including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=5.823, P=0.008* P=0.014* P=0.978 P=0.022*

Site 2 F2,29=38.368, P<0.001* P<0.001* P=0.726 P<0.001*

Site 3 F2,29=89.139, P<0.001* P<0.001* P=0.999 P<0.001*

Site 4 F2,29=99.493, P<0.001* P<0.001* P=0.003* P<0.001*

Site 5 F2,29=414.636,

P<0.001*

P<0.001* P=0.979 P<0.001*

Site 6 F2,29=124,415,

P<0.001*

P<0.001* P=0.962 P<0.001*

Site 7 F2,29=199.507,

P<0.001*

P<0.001* P=0.188 P<0.001*


6.4

6.6

6.8

7

7.2

7.4

7.6

7.8

8

8.2

8.4


pH

La

b

Site Number

Upstream

Final Effluent

Downstream

69

3.2.10. Phosphorus

Mean phosphorus concentrations across the three testing locations are displayed in

Figure 3.14. Differences between site testing locations for phosphorus are displayed in

Table 3.14.

Figure 3.14: Mean phosphorus concentrations across all sites (Mean ± SE) (MRV=0.07 mg/l). Table 3.14: Multiple comparisons of means for phosphorus including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=13.822, P<0.001* P<0.001* P=0.724 P<0.001*

Site 2 F2,29=267.715,

P<0.001*

P<0.001* P=1.000 P<0.001*

Site 3 F2,29=206.568,

P<0.001*

P<0.001* P=0.984 P<0.001*

Site 4 F2,29=17.178, P<0.001* P<0.001* P=0.942 P<0.001*

Site 5 F2,29=10.152, P<0.001* P<0.001* P=0.960 P=0.002*

Site 6 F2,29=34.580, P<0.001* P<0.001* P=0.937 P<0.001*

Site 7 F2,29=97.023, P<0.001* P<0.001* P=0.682 P<0.001*


0

0.5

1

1.5

2

2.5

3


Ph

osp

ho

rus

(mg

/l)

Site Number

Upstream

Final Effluent

Downstream

70

3.2.11. Sulphate

Mean sulphate concentrations across the three testing locations are displayed in

Figure 3.15. Differences between site testing locations for sulphate are displayed in

Table 3.15.

Figure 3.15: Mean sulphate concentrations across all sites (Mean ± SE) (MRV=1.0 mg/l). Table 3.15: Multiple comparisons of means for sulphate including post-hoc analysis (n=10).


Upstream &

FE

Between

Upstream &

Downstream

Between FE &

Downstream

Site 1 F2,29=1.735, P=0.196 P=0.295 P=0.985 P=0.228

Site 2 F2,29=89.356, P<0.001* P<0.001* P=0.895 P<0.001*

Site 3 F2,29=42.831, P<0.001* P<0.001* P=0.997 P<0.001*

Site 4 F2,29=53.232, P<0.001* P<0.001* P=0.778 P<0.001*

Site 5 F2,29=265.445,

P<0.001*

P<0.001* P=1.000 P<0.001*

Site 6 F2,29=1.907, P=0.168 P=0.197 P=0.982 P=0.266

Site 7 F2,29=40.152, P<0.001* P<0.001* P=0.873 P<0.001*


0

20

40

60

80

100

120

140

160


Su

lph

ate

(m

g/

l)

Site Number

Upstream

Final Effluent

Downstream

71

4. Discussion

Overall, scientific literature posts a negative view of STW and their effects upon the

environment. The view that phosphate and nitrate discharges from STW are having a

dramatic and negative effect upon the UKs watercourses is well publicised in scientific

journals (Bowes et al., 2010; Jarvie et al., 2006; Neal et al., 2005; Neal et al., 2010). The

works of Jarvie (2002; 2006), Neal (2005; 2005a; 2008; 2008a; 2010) and Mainstone

(2002) have all been critical of the detrimental effects of sewage treatment effluents,

particularly in relation to phosphorus and nitrate and their eutrophic effects upon

watercourses.

The introduction of two key pieces of legislation, the WFD and UWWTD, has meant

that sewage treatment discharge is now more regulated than ever before. The scrutiny

that water companies are put under by regulators to ensure the quality and reliability

of effluents is high. The OSM and UWWTD sampling regime means that water

companies have to keep consistently high standards throughout the year to ensure

they avoid prosecution.

This study has built upon well-publicised works into the effects of sewage treatment

effluents on watercourse by adding another dimension to the analysis by integrating

FE data into the study. This allows us to analyse the discharge from treatment works

and examine whether these have a significant effect upon the receiving watercourse.

This data has not previously been available and therefore allows a new standpoint of

whether STW are in fact causing the significant detrimental effects that many people

believe. Analysis into the significant difference between upstream and downstream

river water samples has allowed understanding of whether FE does or does not have

an impact upon the receiving watercourse.

4.1. Study findings

From the analysis of river water and FE samples taken in this study, it has been

possible to gain an understanding of the effects that sewage treatment effluents have

upon their receiving watercourses. From the analysis, there are a number of notable

sample readings that will be explored in further detail.

72

4.1.1. Ammonia

Analysis showed that none of the sites have a significant difference in ammonia

concentrations between upstream and downstream samples, therefore demonstrating

that sewage treatment effluents are not having a significant effect upon riverine

ammonia concentrations. However, there are a number of high FE results that warrant

further investigation.

Site 5 shows high mean FE ammonia concentrations of 2.859 mg/l which is abnormal

for an ASP treatment that usually has high levels of nitrification (Tomlinson et al.,

2008). Further analysis of individual samples shown in Figure 4.1 demonstrates plant

malfunction from weeks 2-7 with a maximum spike of 7.67 mg/l. This was identified

during the study and fed back to Severn Trent who re-seeded the ASP between weeks

7-8. Reseeding had a dramatic reduction on FE ammonia concentrations with a drop

from 6.75mg/l in week 7 to 0.19 mg/l, the MRV, in week 8 as shown in Figure 4.1.

Throughout the sample period, riverine ammonia levels did not exceed the statutory

level of 0.025 mg NH3/l (Environment Agency, 2011a).

Figure 4.1: Weekly ammonia concentrations for Site 5 (Mean ± SE) (MRV=0.19mg/l).

-2

0

2

4

6

8

10

1 2 3 4 5 6 7 8 9 10

Am

mo

nia

(m

g/

l)

Sample Weeks

Upstream

Final Effluent

Downstream

73

Negative error bars are present in Figure 4.1 for weeks 1, 8 and 10 as although the

mean concentration was low for FE ammonia, the range was large; therefore negative


Site 7 also indicated high mean ammonia concentrations of 2.1 mg/l in FE. As

demonstrated in Figure 4.2, ammonia concentrations ranged from 0.984 mg/l to

4.16mg/l. This demonstrates insufficient levels of treatment from the on-site NSAF

tertiary ammonia treatment unit in relation to load and influent (Hu et al., 2011).

Throughout the sample period, Site 7 did not exceed its consent limits and mean

upstream and downstream concentrations of 0.19 mg/l and 0.245 mg/l respectively

are within statutory levels for riverine ammonia (Environment Agency, 2011a).

Figure 4.2: Weekly ammonia concentrations for Site 7 (Mean ± SE) (MRV=0.19mg/l).

4.1.2. Biological Oxygen Demand (BOD)

Analysis demonstrated that none of the sites have a significant difference in BOD


that sewage treatment effluents are not having a significant effect upon riverine BOD

concentrations. There are a number of outlying results that warrant further

investigation.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 2 3 4 5 6 7 8 9 10

Am

mo

nia

(m

g/

l)

Sample Weeks

Upstream

Final Effluent

Downstream

74

Both Site 2 and 7 are demonstrating high FE BOD concentrations, 5.984 mg/l and

7.387 mg/l respectively. This demonstrates the inherent issue with the Percolating

Filter Beds at these sites. Percolating Filter Beds have an inherent issue with BOD

removal due to low residence times and bacteria availability to break down the

suspended organic matter inside the sewage (Boller & Guier, 1986; Grady et al., 2012).

Although FE samples taken may have seemed high, both sites were well inside

consented limits for BOD and background river samples for all were all below the

statutory level of 3mg/l (Environment Agency, 2011a).

4.1.3. Boron

Analysis showed that none of the sites have a significant difference in boron


that sewage treatment effluents are not having a significant effect upon riverine boron

concentrations. Site 2 is of interest however with upstream boron concentrations of

0.1295 mg/l. This demonstrates that an upstream industrial discharge is occurring

(Jarvie et al., 2006) which may alter background river concentrations upstream of the

STW. FE and downstream concentrations are 0.1 mg/l, the MRV, which demonstrates

the high assimilation factor that Site 2’s receiving watercourse achieves due to its high

flow (DeBruyn & Rasmussen, 2002).

4.1.4. Chemical Oxygen Demand (COD)

Analysis showed that none of the sites have a significant difference in COD


that sewage treatment effluents are not having a significant effect upon riverine COD

concentrations. Analysis has shown Site 1 to be demonstrating high levels of

background and FE COD. FE COD was recorded at 60.4 mg/l, which although within

consent, is high. Further investigation into individual samples shown in Figure 4.2

demonstrates that FE concentrations were fluctuating between 29mg/l and 111 mg/l

over the sample period. This fluctuation indicates that Site 1’s Percolating Filter Beds

cannot cope with changes in COD load in the influent, an inherent problem with

Percolating Filters (Boller & Guier, 1986; Grady et al., 2012).

75

Figure 4.3: Weekly COD concentrations for Site 1 (Mean ± SE) (MRV =10.0 mg/l).

Upstream and downstream COD concentrations are also high at 31.5mg/l and 37.6

mg/l respectively. This may be a result of high levels of agriculture in the vicinity

depositing high levels of organic matter into the watercourse via slurry and arable run

off (Vega et al., 1998; Sharpley et al., 2004). Between Site 1 FE and downstream

sample points, a dairy herd have access to the watercourse, thus having the possibility

to cause the downstream increase in COD.

4.1.5. Chloride

Analysis showed that none of the sites have a significant difference in chloride



chloride concentrations. Analysis has however identified Site 1 as having high FE and

background chloride concentrations. Site 1 has FE concentrations of 113.68 mg/l,

which is high in comparison to other treatment works. This is due to a mixture of

increased levels of road run off to foul sewers in addition to high local trade levels

affecting the influent (Kelly et al., 2010). It should be noted that chloride levels are

expected to be seasonal due to an increased usage of NaCl over the winter months as a

road de-icer (Amrhein et al., 1992; Kelly et al., 2007) .

0

20

40

60

80

100

120

140

1 2 3 4 5 6 7 8 9 10

Ch

em

ica

l O

xy

ge

n D

em

an

d (

mg

/l)

Sample Weeks

76

Upstream and downstream riverine levels of chloride are also high for Site 1 at 105.08

mg/l and 104.14 mg/l respectively. This is primarily as a result of road surface water

(Hunt et al., 2012) and agricultural run off (Kelly et al., 2010) which are both evident

actively discharging into the watercourse as shown in Figure 4.4.

Figure 4.4: Photograph of Site 1 downstream showing agricultural (A) and surface

water (B) discharge

4.1.6. Conductivity

Analysis showed that none of the sites have a significant difference in conductivity



conductivity concentrations. Analysis also demonstrated that all FE discharges were

within normal levels. Background concentrations however were high for Site 1 & 6

(Site 1: 1.054 mg/l & 1.010 mg/l; Site 6: 0.869 & 0.824 mg/l). This can be attributed to

the high levels of agricultural activity at both sites causing an increase in riverine

B

A

77

conductivity (Morrison et al., 2001). All sites were within EA guidance concentrations

(Environment Agency, 2011a).

4.1.7. Dissolved Oxygen

Analysis showed that none of the sites have a significant difference in DO


that sewage treatment effluents are not having a significant effect upon riverine DO

concentrations. All background samples had DO concentrations above 8.6mg 02/l, the

level required to sustain the first larval zoea stage of crustaceans, some of the most

sensitive aquatic organisms (Vaquer-Sunyer & Duarte, 2008) as well as the 9mg O2/l

statutory level for salmonid waters (Environment Agency, 2011a).

4.1.8. Nitrate

Analysis showed that none of the sites have a significant difference in nitrate



nitrate concentrations.

Although FE nitrate concentrations are all within normal parameters, background

concentrations at sites 1 and 6 show increased nitrate concentrations. This is likely

correlated to both sites having dairy herds in adjacent fields and with access to the

watercourse (Singleton et al., 2007) and poor agricultural practices being in place

(DEFRA, 2002; Mainstone & Parr, 2002). This is contrasted by other sites in high

agricultural areas for example sites 2 and 7, where good agricultural practices are

being followed and the ECSFDI is being implemented, leading to low riverine nitrate

concentrations (DEFRA, 2008). This demonstrates the effect the ECSFDI is having on

reducing riverine nitrate concentrations in areas where farmers are implementing the

strategy. Background nitrate levels for all sites were below statutory levels for nitrate

concentrations (Environment Agency, 2011a).

78

4.1.9. Nitrite

Analysis showed that none of the sites have a significant difference in nitrite



nitrite concentrations.

Although background levels were consistently low and below statutory levels

(Environment Agency, 2011a), both sites 3 and 7 displayed a high FE nitrite

concentration. This is primarily down to a failure of the Percolating Filter Beds at both

sites not providing sufficient nitrification (Boller & Guier, 1986). At site 3, Percolating

Filter Beds provide tertiary nitrification after the ASP. This obviously is unsuccessful

and is leading to increased FE concentrations. Site 7 uses a NSAF for tertiary

nitrification as well as filter beds and has already been identified by ammonia

concentrations to be working below standard.

4.1.10. Orthophosphate

Analysis showed that none of the sites have a significant difference in orthophosphate



orthophosphate concentrations.

Withstanding this, FE orthophosphate concentrations are particularly high at Site 2

with concentrations of 2.099 mg/l. This demonstrates a low level of treatment from

Site 2, a Percolating Filter Works. Low levels of orthophosphate removal are primarily

linked to the residence time of the sewage in the filter bed. A low residence time does

not allow for sufficient treatment to occur before the effluent passes out as FE (Boller

& Guier, 1986). Because of the low flows of Site 2, tertiary p-stripping would not be

cost effective considering the volume and assimilation factor of the receiving

watercourse. Even with high levels of orthophosphate in the FE, both upstream and

downstream samples are at MRV (0.08 mg/l) showing no significant effect from FE.

79

4.1.11. pH

Analysis of pH concentrations showed that for sites 1, 2, 3, 5, 6 and 7, there was not a

significant difference between upstream and downstream samples, therefore

demonstrating that sewage treatment effluents for these sites did not have a

significant effect upon riverine pH. However, for Site 4 there was a significant

difference between samples at P=0.003* with a decrease in pH from 7.808 upstream to

7.64 downstream with FE at pH 7.274. There are a number of possible reasons for this

decrease in riverine pH in addition to sewage effluents.

One cause of river acidification, a reduction in pH, is aquatic respiration and the

breakdown of organic matter. In eutrophic watercourses, as phytoplankton die and

sink, the organic matter they contain is reminerialized to CO2 by aquatic respiration.

This respiration consumes O2 and can lead to hypoxia and lower riverine pH levels

(Feely et al., 2010; Baldigo et al., 2001; Gergel et al., 2002).

Site 4 is shown to have a dramatically increased downstream nitrate (1.592mg/l

upstream; 3.475 mg/l downstream) and DO concentrations (downstream 10.031

mg/l) that could provide suitable nutrients and O2 for eutrophication to occur. This

may lead to algal blooms and acidification (Jarvie et al., 2006).

Another possible answer to a decrease in pH is NaCl pollution from surface water

runoff. During the sampling period (November to January) high amounts of NaCl were

applied to roads in the vicinity of site 4 due to its upland rural nature and the high

probability of ice forming on roads. The receiving watercourse for Site 4 runs parallel

with the main access road to the local town. This parallel stretch of river and road

runs approximately 125 metres from FE discharge point to the downstream sampling

point. Upstream the river moves into a rural setting and would not be subjected to

surface water discharge. The stretch of river between the FE and downstream sample

points would therefore take large concentrations of NaCl from road spray and run off

directly into the watercourse. NaCl has been shown to have acidifying effects on

surface waters (Löfgren, 2001; Hindar et al., 1995) and would therefore lower the pH

of the watercourse as the samples demonstrate. Use of NaCl is also shown to cause

increases in riverine chloride (Green et al., 2001). This is demonstrated at Site 4 with

80

downstream increases in chloride concentration (upstream: 34.14 mg/l; downstream

39.97 mg/l) which would also demonstrate the effects of NaCl runoff.

The critical aspect to understand whether Site 4 FE is causing a change to pH levels in

the watercourse is to understand the FE flow to pH correlation. As we can see in

Figure 4.5, there is non-correlation between increased flow and a decrease in riverine

pH that we would expect to see if FE pH was the significant contributor to

acidification, in fact Figure 4.5 demonstrates the opposite. This would lead to

concluding that an increase in nitrate concentrations from agriculture causing

eutrophication and NaCl run off from road salt would be the primary cause of a

decrease in Site 4 downstream pH. Mean flow for all sites can be found in appendix 8.

Figure 4.5: Marked scatter graph demonstrating flow vs. downstream pH for Site 4

with linear trend line.

4.1.12. Phosphorus

Analysis showed that none of the sites have a significant difference in phosphorus



phosphorus concentrations.

0.000

50.000

100.000

150.000

200.000

250.000

300.000

7.45 7.5 7.55 7.6 7.65 7.7 7.75 7.8 7.85 7.9

Flo

w (

l/s)

Downstream pH

81

The effect of p-stripping is shown dramatically in the sample analysis with the two

sites without p-stripping indicating notably increased FE phosphorus concentrations.

Sites 2 and 7 both do not implement p-stripping due to their PE and discharge flow

rates. As you can see in Figure 4.6, Sites 2 and 7 both show increased FE phosphorus

concentrations of 2.302 mg/l and 1.853 mg/l respectively. Figure 4.6 also

demonstrates the effect ASP treatment has upon phosphorus removal. Sites 4, 5 and 6

all implement ASP and have notably reduced phosphorus discharges.

Figure 4.6: FE phosphorus concentrations for all sites. (Mean ± SE)

(MRV=0.07 mg/l).

Phosphorus discharge from all sites was acceptable and within consented limits.

Although no statutory limit exists for phosphorus, all background levels were

considered low at levels less than 0.5 mg/l (Environment Agency, 2011a).

4.1.13. Sulphate

Analysis showed that none of the sites have a significant difference in sulphate



sulphate concentrations.

0

0.5

1

1.5

2

2.5

3


Ph

osp

ho

rus

(mg

/l)

Site Number

82

A number of sites however did show elevated concentrations of sulphate both at

background concentrations and FE. Both sites 1 and 6 showed highly elevated

background levels of sulphate in comparison to the rest of the sites. This may be down

to a mixture of high levels of agriculture and high levels of trade discharge that occurs

to both receiving watercourses (Weston et al., 2004). The cumulative effect of this

causes background concentrations to increase. Both Site 1 and 6 suffer from poor

agricultural practices leading to large concentrations of leachate being discharged to

the watercourse, thus causing the increased concentrations.

Although being rural, both sites also have large trade influents that increase FE

sulphate levels. This is shown dramatically by site 5. Although background

concentrations are low (upstream: 37.12 mg/l; downstream: 37.10 mg/l) because of

the high amounts of heavy industry and trade in the catchment area, the influent and

therefore FE is high in sulphate (136.00 mg/l). This is a demonstration of how trade

influent can affect FE. All background samples were below the statutory limit of 250

mg SO4/l (Environment Agency, 2011a)

4.1.14. Temperature

Regulatory consents are also based upon temperature. It is understood that if FE is

less than 5oC, nitrification is inhibited during treatment. This means that an

exceptional circumstances clause is put into effect and consents are not enforced.

Analysis showed that none of the sites have a significant difference in temperature

between upstream and downstream samples, therefore demonstrating that sewage

treatment effluents are not having a significant effect upon riverine temperatures.

4.2. Further discussion

4.2.1. Difference between treatments

This study has used the 3 primary technologies that are implemented at medium and

large STW across the UK; ASP, Percolating Filter Bed and MBR. Each form of

technology has been seen to have its benefits and drawbacks and can be implemented

in different situations.

83

4.2.1.1. Activated Sludge Production (ASP)

ASP technology has become prevalent over the past 30 years and been shown to work

well in high flow environments providing high levels of treatment (DEFRA, 2012;

Metcalf et al., 1986; Cote et al., 1995). This is evident in Site 5 that discharges on

average in excess of 2000 l/s. All ASP sites in this study have demonstrated high levels

of ammonia, BOD, COD, phosphorus and orthophosphate treatment. They produce

high quality effluents often on both a medium and large scale, however there are some

drawbacks to ASP technology. Because of the aeration required, ASP plants are highly

energy intensive that leads to high running costs (Osada, 1991). They are also highly

sensitive and require high levels of maintenance and monitoring. This was shown

with the ammonia spike in Site 5. However once the ASP was reseeded, Site 5

produced low ammonia FE.

4.2.1.2. Membrane Bioreactor (MBR)

MBR technology is a new technology to the UK for wastewater treatment and Site 4 is

one of only 4 plants in the country. MBR demonstrates high levels of ammonia,

phosphorus and orthophosphate treatment from the ASP process as well as high

suspended-solids removal from the membrane process producing low BOD and COD

FE.

The MBR is energy efficient, has a low site footprint and is fully automated, controlling

flow levels and FE back-pulses to de-rag the membranes. This means it can be run

with lower manpower unlike ASP STW.

Although the MBR process produces a high quality effluent, it is both capital and

maintenance intensive. Zeeweed membranes require replacement every 12 years and

require regular cleaning with both citric and hydrochloric acid (Noble, 2006).

Therefore, MBR will only be suitable for a number of unique situations where FE

quality is critical.

84

4.2.1.3. Percolating Filter Works

Percolating Filter Works are the oldest form of technology used across the 3 sites

having been used since the early 1900s. Although technology has moved on, the basic

principle has stayed the same throughout (Metcalf et al., 1986; Boller & Guier, 1986).

As technology has moved on, ASP has replaced Percolating Filter Works as the

primary form of treatment for high PE environments; therefore Percolating Filter

Works are now mainly confined to small and medium sized STW. Percolating Filter

Works do have issues with levels of treatment. High BOD, COD, nitrite, phosphorus

and orthophosphate levels are common in FE due to lack of retention times inside the

filter bed (Boller & Guier, 1986; Grady et al., 2012). They are often used in tandem

with tertiary treatment for example NSAF to try and reduce phosphorus and nitrate

concentrations. Percolating Filter Works are a simple and low maintenance way of

serving low and medium PE areas. Because of the gravitational design of many works,

they use very small amounts of energy and are therefore highly cost effective forms of

treatment (Metcalf et al., 1986; Logan et al., 1987).

4.2.2. Regulation

Since 1991, the wastewater industry has come under higher levels of scrutiny

regarding the concentrations of many determinants in its FE. The introduction of the

WFD and UWWTD has set out provision for protection of surface waters and has

highlighted nitrate and phosphate discharges as primary causes of eutrophication

(DEFRA, 2014; European Commission 2012). The WFD aim of bringing surface waters

to ‘good ecological and chemical status’ by 2015 has been a driver for the UWWTD

and has resulted in tighter regulatory consents and the introduction of on-site p-

stripping for works with PE of 10,000+ (DEFRA, 2012).

There are high socioeconomic effects with complying with wastewater regulation.

From 1995 – 2010, £950 million was spent on effluent clean up in the UK alone (Neal

et al., 2010), demonstrating why reducing FE concentrations and working towards the

WFD objectives is critical.

85

Regulation has driven forward the wastewater industry demanding ever-higher levels

of treatment, this has worked in tandem with improvements in agricultural practices

to reduce riverine levels of phosphorus and nitrate and reduce the number of

eutrophic watercourses in the UK. The UK looks set to be succeeding with the WFD

aim of bringing all surface waters to ‘good ecological and chemical status’ by 2015

(Ulén & Weyhenmeyer, 2007; Foster et al., 2010).

4.2.3. Criticisms of other literature

There are a number of criticisms of the literature surrounding the effects of sewage

treatment effluents on watercourses, especially research based on UK watercourses.

Jarvie and Neal have compiled the majority of research into this field. Both have been

investigating the effects of phosphorus and nitrate discharges from both STW and

agricultural sources for a number of years. The on-going theme running through their

research suggests that both STW and agriculture have a large detrimental effect upon

watercourses and require large-scale investment to be brought up to standard. Their

analysis suggests large-scale capital investment in the UK’s wastewater infrastructure,

however this approach would have a number of knock on effects. Firstly, the money

water companies have is finite; an increase in infrastructure spending would directly

affect customer’s bills, which is currently a politically charged topic.

Jarvie and Neal also are not looking at the cost-effectiveness of tertiary p-stripping. P-

stripping is only cost effective on large scale works as it is inherently expensive.

Installing p-stripping on smaller works would have little effect upon riverine

phosphorus concentrations as demonstrated in this study, due to the assimilation

factor of the receiving watercourse. Money would be better invested improving

infrastructure and transferring flows away from small STW to larger STW where a

higher level of treatment can be achieved.

The work of Jarvie and Neal is also critically flawed. Without FE data, it is impossible

to determine whether STW effluent is at fault for any statistical change in riverine

concentrations. As their studies use only upstream and downstream data, their

dataset is exposed to external variables for example diffuse agricultural pollution or

86

trade discharges. Without visibility of FE data, it is impossible to demonstrate

whether it is the FE alone that is having a significant effect upon the watercourse.

4.3. Study Limitations

A primary limitation of this study was the sample collection period. Samples were

collected over a 3-month period from November to January. This may have allowed

seasonal bias to affect the dataset.

The number of upstream and downstream sample points that were used also limited

this study. The collection of 3 samples, upstream, FE and downstream gave a limited

dataset and allowed only a snapshot into whether sewage treatment effluents were

significantly affecting the entire receiving watercourse. Only one downstream sample

point at 200 metres made it difficult to make assumptions regarding the assimilation

of pollutants into the watercourse and their possible effects further downstream.

4.4. Recommendations for further research.

Although the effects of sewage treatment effluents on watercourses are a well-

documented, there are a number of areas for further research. The introduction of FE

data has allowed this study to see the specific effect that effluent have upon the

receiving watercourse. This approach should be taken forward and used on previous

geographical areas of study to see whether initial indications of detrimental sewage

treatment effects were indeed correct with the visibility of FE data. In addition to this,

future studies should look to increase the number of upstream and downstream

points. This will allow the assimilation factor of watercourses to be investigated with

relation to STW effluents.

This study should also be continued with further sample collection and analysis. This

study used a limited collection period of 3 months from November to January. To be

representative, future studies should look to collect samples over a 12 or 24-month

period to reduce seasonal bias.

87

This study has also highlighted the need for further research into the effects of MBR

technology on riverine pH. This study detected a significant difference between

upstream and downstream riverine pH concentrations for the MBR technology;

further researched should be completed to see if this pH change could be replicated in

other locations.

88

5. Conclusion This study set out to assess whether sewage treatment effluents had a significant

effect upon their receiving watercourse, with the purpose of investigating a number of

determinants associated with sewage treatment discharge and surface water

pollution. This study revealed that sewage treatment effluents do not have a

significant effect upon the receiving watercourse thus contradicting the popular

scientific standpoint.

Of the 98 statistical tests carried out in this study, only Site 4 pH was deemed to be

significantly different from analysis of upstream and downstream samples. A number

of factors have been discussed that could have caused this significant difference;

therefore it cannot be assumed that the significant difference is caused uniquely by

the STW FE. This allows us to accept the alternative hypothesis and reject the null

hypothesis of this study.

As mentioned, the results of this study have gone against current scientific literature

and open up the possibility of STW taking a step back from agriculture as the primary

cause of riverine eutrophication. The reduction in riverine determinant

concentrations shows that the WFD and associated UWWTD are having a significant

effect upon FE concentrations, especially phosphate and nitrate and that new

technology such as MBR and improvements in ASP technology are raising the bar for

treatment levels across the board.

89

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Appendix

Appendix 1: Email from Gail Pluckrose, Waste Water Service Delivery Manager confirming commercial sensitivity for the project.

120

Appendix 2: Site layout diagrams

Appendix 2.1: Site diagram showing layout of Site 1.


121



122

Appendix 2.5.1: Site diagram showing primary treatment at Site 5.

Appendix 2.5.2: Site diagram showing secondary treatment at Site 5.

123

Appendix 2.5.3: Site diagram showing tertiary treatment at Site 5.

Appendix 2.6.1: Site diagram showing preliminary and primary treatment for Site 6.

124

Appendix 2.6.2: Site diagram showing secondary and tertiary treatment for Site 6.


125

Appendix 3: Sample point maps

Appendix 3.1: River course and sample point map for Site 1 showing upstream, final effluent and downstream sample locations.

126


127


128


129

Appendix 3.5: River course and sample point diagram for site 5 showing upstream, final effluent and downstream sample locations

130


131


132

Appendix 4: Equipment list.

Equipment Source of equipment

PPE: Severn Trent Water

Challenger 2 life jacket

Eye protection

Hard Hat

High Visibility Jacket

Latex examination gloves

Severn Trent “Blues” work trousers

Severn Trent Soft-Shell jacket

Steel Toe-cap work boots

Yellow road line marking spray paint

Sample Collection: Severn Trent Water

10m stainless steel chain

1L food grade stainless steel sample can

Sample collection pot 70cl

Telescopic sample pole 3 metres

Sample Analysis: NTU Brackenhurst Labs

De-ionised water

HACH (HQ30d) probe

Hanna Combo pH & EC HI98130

pH buffer solutions

Bottles: NLS Laboratory

GEN Bottle (1L Clear PET)

MET Bottle (125ml Polypropylene)

Key: Personal Protective Equipment, PPE;

133

Appendix 5: National Laboratory Service bottle guide for multi determinant sampling (National Laboratory Service, 2015).

Bottle Picture Analysis Sampling

technique

GEN Bottle (1L

Clear PET)

Ammonia, BOD,

chloride, COD,

orthophosphate,

pH suspended

solids, sulphate,

T.O.N as nitrogen

Fill to top leave

no air gap

MET Bottle

(125ml

Polypropylene)

Boron,

phosphorus.

Fill to neck of

bottle.

Key: biological oxygen demand, BOD; chemical oxygen demand, COD; total organic

nitrogen, T.O.N;

134

Appendix 6.1: Mean values for upstream samples (n=10)

Key: Degree Celsius, oC; Milligram per litre, mg/l; Millisiemens, mS;

In situ Results - Upstream Laboratory Results - Upstream

DO

(mg/l)

Conductivity

(mS)

pH – on site

(pH Units)

Temperature

(oC)

Ammonia

(NH3) (mg/l)

BOD

(mg/l)

Boron

(B) (mg/l)

COD

(mg/l)

Site 1 10.160

1.054

7.856

8.650

0.253

1.972

0.100

31.500

Site 2 11.116

0.260

8.012

8.280

0.190

1.104

0.126

20.400

Site 3 11.371

0.463

8.225

7.570

0.190

1.180

0.100

16.500

Site 4 10.406

0.358

7.949

8.830

0.190

1.177

0.100

23.200

Site 5 11.143

0.512

8.215

8.050

0.190

1.405

0.100

19.600

Site 6 9.846

0.869

7.905

8.860

0.229

1.710

0.100

29.200

Site 7 11.300

0.419

8.256

7.810

0.190

1.103

0.100

15.000

135

Appendix 6.2: Mean values for upstream samples (n=10)

Key: Milligram per litre, mg/l;

Laboratory Results - Upstream

Chloride

(Cl-) (mg/l)

Nitrate

(NO3-) (mg/l)

Nitrite

(NO2-) (mg/l)

Ortho-P

(PO43-) (mg/l)

pH – Lab

(pH Units)

Phosphorus

(P) (mg/l)

Sulphate

(SO42-) (mg/l)

Site 1 105.080

5.811

0.077

0.306

7.827

0.373

123.360

Site 2 14.240

1.673

0.006

0.080

7.895

0.072

21.340

Site 3 26.320

3.225

0.016

0.085

8.074

0.101

35.210

Site 4 34.140

1.592

0.006

0.080

7.808

0.073

19.520

Site 5 27.160

3.489

0.019

0.088

8.068

0.121

37.120

Site 6 71.540

9.344

0.083

0.262

7.791

0.330

100.450

Site 7 20.300

2.761

0.008

0.080

8.123

0.071

27.400

136

Appendix 6.3: Mean values for final effluent samples (n=10)

In situ Results – Final Effluent Laboratory Results – Final Effluent

DO

(mg/l)

Conductivity

(mS)

pH – on site

(pH Units)

Temperature

(oC)

Ammonia

(NH3) (mg/l)

BOD

(mg/l)

Boron

(B) (mg/l)

COD

(mg/l)

Site 1 5.342

0.982

7.669

11.850

0.290

3.779

0.114

60.400

Site 2 7.941

0.524

7.653

9.600

0.865

5.984

0.101

38.700

Site 3 8.534

0.627

7.513

11.380

0.924

2.425

0.103

27.100

Site 4 9.039

0.641

7.180

11.600

0.715

1.084

0.100

14.800

Site 5 5.476

1.000

7.225

13.400

2.859

2.133

0.116

23.300

Site 6 9.640

0.793

7.295

11.210

0.190

1.129

0.120

20.500

Site 7 5.639

0.580

7.399

11.510

2.100

7.387

0.100

41.500


137

Appendix 6.4: Mean values for final effluent samples (n=10)

Key: Milligram per litre, mg/l;

Laboratory Results – Final Effluent

Chloride

(Cl-) (mg/l)

Nitrate

(NO3-) (mg/l)

Nitrite

(NO2-) (mg/l)

Ortho-P

(PO43-) (mg/l)

pH – Lab

(pH Units)

Phosphorus

(P) (mg/l)

Sulphate

(SO42-) (mg/l)

Site 1 113.680

11.905

0.066

0.983

7.659

1.207

98.250

Site 2 41.860

12.281

0.236

2.099

7.522

2.302

37.780

Site 3 75.120

14.123

0.384

1.208

7.274

1.308

55.480

Site 4 63.220

14.785

0.182

0.363

7.176

0.363

47.760

Site 5 81.080

11.347

0.065

0.156

7.175

0.293

136.000

Site 6 84.440

15.313

0.019

0.750

7.221

0.788

87.380

Site 7 58.450

8.220

0.376

1.404

7.288

1.853

49.050

138

Appendix 6.5: Mean values for downstream samples (n=10)


In Situ Results - Downstream Laboratory Results - Downstream

DO

(mg/l)

Conductivity

(mS)

pH – on site

(pH Units)

Temperature

(oC)

Ammonia

(NH3) (mg/l)

BOD

(mg/l)

Boron

(B) (mg/l)

COD

(mg/l)

Site 1 10.259

1.016

7.905

8.330

0.267

2.767

0.100

37.600

Site 2 11.131

0.257

8.180

8.080

0.190

1.098

0.100

18.100

Site 3 11.155

0.468

8.130

8.070

0.190

1.193

0.114

17.800

Site 4 10.031

0.434

7.738

8.880

0.226

1.183

0.100

19.900

Site 5 11.600

0.488

8.199

7.650

0.209

1.359

0.100

19.400

Site 6 10.255

0.824

7.863

8.130

0.225

1.638

0.100

25.800

Site 7 10.805

0.447

8.154

8.340

0.254

1.571

0.100

18.000

139

Appendix 6.6: Mean values for downstream samples (n=10)

Key: Milligram per litre, mg/l

Laboratory Results - Downstream

Chloride

(Cl-) (mg/l)

Nitrate

(NO3-) (mg/l)

Nitrite

(NO2-) (mg/l)

Ortho-P

(PO43-) (mg/l)

pH – Lab

(pH Units)

Phosphorus

(P) (mg/l)

Sulphate

(SO42-) (mg/l)

Site 1 104.140

6.376

0.071

0.397

7.816

0.504

126.040

Site 2 15.140

1.769

0.007

0.080

7.859

0.070

20.690

Site 3 26.780

3.366

0.019

0.090

8.071

0.113

35.410

Site 4 39.970

3.475

0.026

0.083

7.640

0.091

21.590

Site 5 27.380

3.494

0.020

0.092

8.075

0.133

37.100

Site 6 72.780

9.838

0.077

0.304

7.780

0.352

99.110

Site 7 23.350

3.099

0.031

0.131

8.040

0.191

28.750

140

Appendix 7: Minimum-reporting values (MRV) for determinants analysed by National Laboratory Service (National Laboratory Service, 2015).

Key: Milligrams per litre, mg/l; Millisiemens per centimetre, mS/cm

Determinant Units Minimum reporting

value (MRV)

Ammonia mg/l 0.19

Biological Oxygen Demand

(BOD) 5 Day AUT

mg/l 1

Boron mg/l 0.1

Chemical Oxygen Demand mg/l 10

Chloride mg/l 0.9

Conductivity mS/cm

0.00

DO mg/l 0.20

Nitrate mg/l 0.006

Nitrite mg/l Calculated as TON (MRV

0.29mg/l) less Nitrite.

Orthophosphate (As

reactive P)

mg/l 0.08

pH pH Units 0.05

Phosphorus mg/l 0.07

Sulphate at SO4 mg/l 1

141

Appendix 8: Mean final effluent flow levels across all sites.

1.000

10.000

100.000

1000.000

10000.000


Flo

w (

l/s

)

Sample Weeks

Week 1

Week 2

Week 3

Week 4

Week 5

Week 6

Week 7

Week 8

Week 9

Week 10

the effects of sewage treatment works on watercourses - t.swain

Documents

sewage treatment works

severn trent sewage

levels of treatment

decreased ph

low ph

ph result

downstream samples

riverine ph levels