Effect of UV on the Chemical Composition of Water including DBP …dwi.defra.gov.uk/research/completed-research/reports/DWI... · 2015-06-03 · Version Control Table Version number

WRc Ref: Defra 10459.04

March 2015

Effect of UV on the Chemical Composition of

Water including DBP Formation: Final Report

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Effect of UV on the Chemical Composition of

Water including DBP Formation: Final Report

Report No.: Defra 10459.04

Date: March 2015

Authors: David Shepherd, Rowena Gee, Tom Hall, Paul Rumsby, Glenn Dillon

Project Manager: Glenn Dillon

Project No.: 16164-0

Client: DWI

Client Manager: Annabelle May

Version Control Table

Version

number Purpose Issued by

Quality Checks

Approved by Date

V.01 Draft final report issued to DWI Representative for PSG meeting.

Glenn Dillon, Project Manager

Glenn Dillon 21/11/2014

V.02 Draft final report issued to DWI Representative for review.


Tom Hall 29/12/2014

V.03 Revised final report issued to DWI Representative for review


Tom Hall 03/02/2015

V.04 Final report issued. Glenn Dillon, Project Manager

Simon Blake 04/03/2015

Acknowledgement

This project was funded by Defra and managed by DWI.

The authors gratefully acknowledge the assistance given by water companies in England and Wales in

providing data and other information.

Disclaimer

Defra and DWI assume no responsibility for the content of this report. Any views expressed are those

of the authors and not necessarily those of Defra or DWI.

Contents

Summary .................................................................................................................................. 1

1. Introduction .................................................................................................................. 3

1.1 Objectives .................................................................................................................... 3

1.2 Background ................................................................................................................. 3

1.3 Résumé of contents .................................................................................................... 4

2. Literature Review ........................................................................................................ 5

2.1 Introduction .................................................................................................................. 5

2.2 Effect of UV used for disinfection ................................................................................ 5

2.3 Effect of UV in advanced oxidation processes .......................................................... 11

2.4 Conclusions ............................................................................................................... 24

3. UV Treatment in Public Supplies .............................................................................. 26

3.1 Introduction ................................................................................................................ 26

3.2 Results ...................................................................................................................... 26

3.3 Conclusions ............................................................................................................... 26

4. Effect of UV Dosage and/or Pre-oxidation on Chemical Composition and DBP Formation ................................................................................................... 31

4.1 Introduction ................................................................................................................ 31

4.2 Selected works and results ....................................................................................... 31

4.3 Conclusions ............................................................................................................... 34

5. UV Treatment in Private Supplies ............................................................................. 35

5.1 Introduction ................................................................................................................ 35

5.2 2011 data .................................................................................................................. 35

5.3 2012 data .................................................................................................................. 36

5.4 2013 data .................................................................................................................. 38

5.5 Nitrate and bromate .................................................................................................. 38

5.6 Conclusions ............................................................................................................... 43

6. Health Significance.................................................................................................... 44

6.1 Introduction ................................................................................................................ 44

6.2 Cytotoxicity and genotoxicity studies ........................................................................ 44

6.3 Derivation of guidance values ................................................................................... 54

6.4 Conclusions ............................................................................................................... 55

7. Future Research........................................................................................................ 57

7.1 Public supplies .......................................................................................................... 57

7.2 Private supplies ......................................................................................................... 62

8. Conclusions ............................................................................................................... 63

8.1 Literature review ........................................................................................................ 63

8.2 Public supplies .......................................................................................................... 63

8.3 Private supplies ......................................................................................................... 64

8.4 Health effects ............................................................................................................ 64

References ............................................................................................................................. 65

Glossary of Terms .................................................................................................................. 69

Appendices

Appendix A Literature Review ..................................................................................... 71

Appendix B UV Treatment in Public Supplies: Returned Questionnaires .................. 85

Appendix C Site Visit Data ........................................................................................ 107

List of Tables

Table 2.1 Summary of UV effects ........................................................................... 14

Table 3.1 Summary of UV treatment by function and source ................................. 28

Table 3.2 Summary of UV treatment by upstream treatment, dose and DBPs detected ......................................................................................... 30

Table 5.1 Summary of UV treated private supplies by water source (2011) ...................................................................................................... 35

Table 5.2 Summary of UV treated private supplies by water use (2011) ................ 36

Table 5.3 Summary of UV treated private supplies by water source (2012) ...................................................................................................... 37

Table 5.4 Summary of UV treated private supplies by water use (2012) ................ 37

Table 5.5 Private supplies: Nitrate (mg/l) ................................................................ 39

Table 5.6 Private supplies: Bromate (µg/l) .............................................................. 42

Table 6.1 Toxicity for different treatment processes ............................................... 47

Table 6.2 Summary of cytotoxicity and genotoxicity studies ................................... 50

Table 6.3 Guideline values for DBPs identified in the literature review .................. 54

Table 7.1 Summary of proposed small-scale investigations ................................... 61

Table C.1 Works A5: Effect of prechlorination on bromate formation ................... 114

List of Figures

Figure 7.1 Upland surface waters and treatment ..................................................... 58

Figure 7.2 Lowland surface waters and treatments.................................................. 59

Figure 7.3 Groundwater and treatment .................................................................... 60

Figure C.1 Works A2: Schematic ............................................................................ 109

Figure C.2 Works A2: Final water THMs ................................................................. 110

Figure C.3 Works A2: UV254 absorbance after preozonation .................................. 111

Figure C.4 Works A2: UV254 absorbance after GAC ............................................... 111

Figure C.5 Works A2: Final water bromate and bromide ........................................ 112

Figure C.6 Works A5: Schematic ............................................................................ 113

Figure C.7 Works A5: Final water THMs ................................................................. 114

Figure C.8 Works A5: Bromate formation due to sunlight ....................................... 115

Figure C.9 Works B1: Schematic ............................................................................ 117

Figure C.10 Works B1: Final water THMs ................................................................. 119

Figure C.11 Works B1: SR1 THMs ........................................................................... 119

Figure C.12 Works B1:SR2 THMs ............................................................................ 120

Figure C.13 Works B1: Filtered water THMs ............................................................ 120

Figure C.14 Works B1: Raw water algal counts ........................................................ 121

Figure C.15 Works B1: Raw and final water TOC..................................................... 121

Figure C.16 Works B1: SR1 THMs (2010-12) ........................................................... 122

Figure C.17 Works B2: Schematic ............................................................................ 123

Figure C.18 Works B2: Final water THMs (April-September 2013) .......................... 125

Figure C.19 Works B2: Final water THMs (April-September 2014) .......................... 125

Figure C.20 Works B2: SR1 THMs (2013) ................................................................ 126

Figure C.21 Works B2: SR1 THMs (2014) ................................................................ 126

Figure C.22 Works B2: TOC (2013) .......................................................................... 127

Figure C.23 Works B2: TOC (2014) .......................................................................... 127

Figure C.24 Works B2: Raw water colour (2013) ...................................................... 128

Figure C.25 Works B2: Raw water colour (2014) ...................................................... 128

Figure C.26 Works D2: Schematic ............................................................................ 129

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WRc Ref: Defra 10459.04/16164-0 March 2015

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Summary

i Reasons

Ultraviolet (UV) disinfection has been used in water treatment for many years and its

implementation in the UK is increasing for general disinfection or specifically to deal with

Cryptosporidium. In addition, advanced oxidation processes (AOPs) incorporating UV at much

higher doses than used for disinfection have been developed over recent years for destruction

of organic micropollutants such as pesticides and algal metabolic products.

Whilst the risk of formation of disinfection by-products (DBPs) from the use of UV is believed

to be low, this work will identify the implications of UV treatment for changing water chemistry,

particularly in relation to DBP formation.

The results of this work will be used to further inform the use of UV in water treatment.

ii Objectives

The aim of this project was to increase DWI‟s understanding of the impact of UV disinfection

on the chemical composition of water, with specific reference to potential formation or removal

of DBPs.

iii Résumé of Contents

This report presents a review of the literature on the effects of UV disinfection on the chemical

composition of water (Section 2), a review of UV treatment in public supplies (Section 3), the

effect of UV dosage and/or pre-oxidation as evidenced from selected treatment works

(Section 4), a review of UV treatment in private supplies (Section 5), a review of the health

significance of DBPs identified as being formed by UV (Section 6), and suggested areas for

future research to fill knowledge gaps regarding DBP formation as a result of UV treatment

(Section 7). Conclusions are presented in Section 8.

iv Conclusions

The potential formation of DBPs as a result of treatment by appropriately designed and

maintained UV systems is low. The most significant DBPs are nitrite (formed from nitrate) and

bromate (formed from prechlorinated supplies containing bromide); the formation of both can

be minimised by appropriate water treatment and UV system design.

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A survey of water companies in England and Wales (73% response) identified 89 UV plants

(existing and proposed) with a total treatment capacity of 1,492 Ml/d used mostly at small

groundwater sites for general disinfection and where there is a Cryptosporidium risk.

The full extent of UV treatment of private supplies is unclear from Local Authority (LA) returns

to DWI. UV treated private supplies used for commercial purposes appear to account for

around 90% of persons served and 97-98% of water capacity. Whilst it is unlikely that

formation of DBPs is a significant risk for private supplies, the risk might be greater for

supplies used for commercial purposes where water treatment might include prechlorination

or the UV system might incorporate medium pressure (MP) lamps.

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1. Introduction

1.1 Objectives

The aim of this project was to increase DWI‟s understanding of the impact of ultraviolet (UV)

disinfection on the chemical composition of water, with specific reference to potential

formation or removal of disinfection by-products (DBPs).

1.2 Background

Whilst UV disinfection has been used in water treatment for many years, its implementation in

the UK is increasing for general disinfection or specifically to deal with Cryptosporidium. In

addition, advanced oxidation processes (AOPs) incorporating UV at much higher doses than

used for disinfection have been developed over recent years for destruction of organic

micropollutants such as pesticides and algal metabolic products. Disinfection doses for UV

are typically about 40 mJ/cm2, whereas AOP doses are at least an order of magnitude higher.

The risk of formation of DBPs from the use of UV is believed to be low. Two basic types of UV

lamp are used: low pressure (LP) and medium pressure (MP). LP lamps emit UV almost

entirely at the germicidal wavelength of 254 nm, whereas MP lamps emit UV at a wider range

of wavelengths, e.g. 200-300 nm. The DBP most associated with the use of UV is nitrite,

which is formed from reduction of nitrate at a wavelength of less than 230 nm. The formation

of nitrite by MP lamps is minimised by the incorporation of quartz sleeves to remove the lower

wavelength UV. Similarly, absorption of UV by natural organic compounds in water may also

occur at lower wavelength, and any changes to water chemistry from this mechanism may

influence DBP formation. There have been recent reports in the UK of bromate formation

when prechlorinated water is dosed with UV at doses of above 100 mJ/cm2 or when exposed

to natural sunlight. Bromate had not previously been identified as significant from the use of

UV.

The overall objective of this work was to identify the implications of UV treatment for changing

water chemistry, particularly in relation to DBP formation, through its use on public and private

water supplies. The implications for DBPs should include not only those for which standards

exist, specifically the trihalomethanes (THMs), chlorate/chlorite, nitrite and bromate, but also

those without current standards which need to be minimised without compromising

disinfection. These would include haloacetic acids (HAAs), nitrogen-containing DBPs,

iodinated THMs/HAAs and nitrosamines.

The overall objective was met through the sub-objectives:

Identification of the possible mechanisms for changes in water chemistry and DBP

formation from UV use, through a review of published information, and the impact of UV

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type, dose, water quality and other treatments, particularly oxidation, upstream and

downstream to UV.

The implications of these changes for drinking water quality, health or aesthetic

considerations.

The potential scope and impact of these changes based on current UV implementation

for both public and private water supplies.

Evidence of whether or not these changes are significant for public supplies based on a

review of existing data from water treatment works monitoring.

A programme of further work needed to clarify the findings and fill knowledge gaps.

The results of this work will be used to further inform the use of UV in water treatment.

1.3 Résumé of contents

This report presents a review of the literature on the effects of UV disinfection on the chemical

composition of water (Section 2), a review of UV treatment in public supplies (Section 3), the

effect of UV dosage and/or pre-oxidation as evidenced from selected treatment works

(Section 4), a review of UV treatment in private supplies (Section 5), a review of the health

significance of DBPs identified as being formed by UV (Section 6), and suggested areas for

future research to fill knowledge gaps regarding DBP formation as a result of UV treatment

(Section 7). Conclusions are presented in Section 8.

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2. Literature Review

2.1 Introduction

The results of the literature review are summarised below; the detailed review is presented in

Appendix A.

The literature review has considered the use of UV irradiation in water treatment for

disinfection and in AOPs. Findings most relevant to conditions used for drinking water

treatment are summarised below for UV disinfection (Section 2.2) and for UV used in AOPs

(Section 2.3). A tabulated summary of the findings is given in Table 2.1.

2.2 Effect of UV used for disinfection

UV disinfection typically uses LP or MP lamps. LP lamps emit essentially monochromatic UV

at 254 nm, whereas MP lamps emit within the range 200-400 nm1. The UV dose for primary

disinfection will typically2 be 40 mJ/cm

2.

2.2.1 Effect of UV on organics

LP UV

Various investigations applying LP UV at doses of 40-200 mJ/cm2 reported no change in the

nature of dissolved organic carbon (DOC) as indicated by DOC concentration, UV254

absorbance and/or specific UV absorbance (SUVA) (Malley et al., 1995; Kashinkunti et al.,

2004; Chin and Berube, 2005; Ijpelaar et al., 2005; Choi and Choi, 2010). An increase in the

fraction of hydrophilic DOC was observed in some (generally low-coloured) waters but not

others (generally high-coloured) by Malley et al. (1995); however, Choi and Choi (2010) found

no change in this metric for the treated surface water used in their tests.

Choi and Choi (2010) investigated dual wavelength (185/254 nm) LP UV. At 40 mJ/cm2, there

was no change in the nature of the DOC, but at 150 mJ/cm2 the average molecular weight

was reduced, consistent with breakage of organic bonds at lower (<200 nm) wavelengths.

1 German (DVGW) and Austrian (ÖNORM) standards for validating performance of MP lamps for

disinfection require wavelengths below 240 nm to be blocked, but the equivalent American (USEPA)

validation protocol does not.

2 German (DVGW) and Austrian (ÖNORM) standards for validating performance of UV for disinfection

stipulate 40 mJ/cm2, but the equivalent American (USEPA) protocol validates performance in terms

of log inactivation of target pathogens (Cryptosporidium, Giardia and/or viruses). The dose applied

by a USEPA validated UV plant may therefore be less than or greater than 40 mJ/cm2.

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Various investigations applying LP UV at doses of 40–200 mJ/cm2 reported no change in

regrowth potential as indicated by assimilable organic carbon (AOC) concentration (Malley et

al., 1995; Kashinkunti et al., 2004; Chin and Berube, 2005; Ijpelaar et al., 2005; Choi and

Choi, 2010). An increase in biodegradable dissolved organic carbon (BDOC) was observed in

some (untreated surface) waters but not others (treated surface, ground) by Malley et al.

(1995).

MP UV

MP UV applied at 40 mJ/cm2 resulted in no change in the nature of DOC as indicated by DOC

concentration, UV254 absorbance, fraction of hydrophilic DOC or SUVA (Choi and Choi, 2010).

Over the course of a year, the average molecular weight was decreased for one season but

unchanged for the remainder. Choi and Choi noted that breakage of organic bonds by UV is

more likely at higher (>280 nm) wavelengths as well as lower (<200 nm).

Neither Kashinkunti et al. (2004), (doses 40-140 mJ/cm2) nor Choi and Choi (2010)

(40 mJ/cm2) observed any change in regrowth potential as indicated by AOC concentration.

However, Ijpelaar et al., (2005) reported that AOC increased with increasing UV dose (47-

91 mJ/cm2) and suggested that GAC should be installed after MP UV. Ijpelaar et al. (2007)

concluded that AOC formation is favoured by MP UV, although any increase is unlikely to

exceed 10 g/l for doses <100 mJ/cm2.

2.2.2 Formation of DBPs: Direct formation

Nitrogenated by-products

LP UV

No nitrophenols or nitrosamines were detected following UV irradiation of treated municipal

wastewater effluent (100-160 mJ/cm2) (Liberti et al., 2002). Mole et al. (1997) found some

evidence of the formation of unidentified N-containing compounds after applying a dose of

6,600 mJ/cm2 to an untreated surface water.

Aldehydes and carboxylic acids

LP UV

Formaldehyde (up to 10 μg/l) was formed in various water samples (treated and untreated

surface waters; coloured groundwaters) after a dose of 130 mJ/cm2; concentrations were

highest in coloured surface water and highly-coloured (50 ºH) groundwater, whereas no

formaldehyde was detected in low-coloured groundwater samples (Malley et al., 1995). Mole

et al. (1997) detected formaldehyde and acetaldehyde at concentrations <10 μg/l in untreated

surface water (110 mJ/cm2) and groundwater with added humic acid (220 mJ/cm

2); in both

cases the aldehyde concentration increased at higher UV doses. Liu et al. (2002) observed no

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aldehyde formation in synthetic drinking waters at doses 40-500 mJ/cm2, but some formation

(maximum 13 μg/l) as dose increased to 6,360 mJ/cm2.

Carboxylic acids were not formed as a result of UV irradiation of synthetic drinking water at

doses less than 1,000 mJ/cm2 (Liu et al., 2002).

MP UV

Aldehydes were not formed as a result of UV irradiation of synthetic drinking water at doses

less than 1,000 mJ/cm2 (Liu et al., 2002). However, formation was evident at higher doses

(maximum 37 μg/l at 6,360 mJ/cm2).

Carboxylic acids were not formed as a result of UV irradiation of synthetic drinking water at

doses less than 1,000 mJ/cm2 (Liu et al., 2002). However, 100-240 μg/l were formed

(primarily formic, acetic and oxalic acids) at 6,360 mJ/cm2.

Nitrite

LP UV

Malley et al. (2005), Mole et al. (1997) and Ijpelaar et al. (2005) did not detect nitrite after

applying doses up to 120 mJ/cm2 variously to groundwater, nitrate-spiked deionised water

and treated surface water samples. Ijpellar et al. (2007), however, detected nitrite following

irradiation of nitrate-containing waters: 2 μg/l nitrite at 25 mJ/cm2 with 50 mg/l NO3; and 7 μg/l

nitrite at 120 mJ/cm2 with 14 mg/l NO3. Mole et al. (1997) also observed nitrite after higher

doses (1,100-22,850 mJ/cm2), with formation increasing with UV dose and nitrate

concentration.

MP UV

Ijpellar et al. (2005) detected c. 40 μg/l nitrite following irradiation of a treated surface water at

100 mJ/cm2. Ijpellar et al. (2007) detected 20-40 μg/l nitrite following irradiation at 70 mJ/cm

2;

the lower formation corresponded to an initial nitrate concentration of 8 mg/l, and the higher to

15 mg/l. Ijpellar et al. (2007) also reported that fitting MP lamps with sleeves to block

wavelengths below 235 nm reduced nitrite formation from 150 μg/l to 30 μg/l (50 mJ/cm2,

50 mg/l nitrate). They noted that nitrate absorbs UV predominantly in the 200-240 nm

wavelength range3.

3 Hence it is expected that nitrite formation should not be an issue with MP UV units validated to the

DVGW or ÖNORM standards.

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Bromate

Ijpelaar et al. (2007) stated that neither UV nor UV/H2O2 are able to convert bromide to

bromate.

LP UV

Neither Malley et al. (1995) nor Kishimoto and Nakamura (2012) detected bromate formation

after UV irradiation of bromide-containing waters.

Benzene and toluene

LP UV

Zoeteman et al. (1982) detected benzene (0.9 g/l) and toluene (3 g/l) after UV irradiation of

stored River Rhine water at 120 mJ/cm2.

2.2.3 Formation of DBPs: Effect of UV upstream of chlorination

LP UV

Upstream UV irradiation at doses used for disinfection has little, if any, effect on subsequent

formation of THMs (Malley et al., 1995; Liu et al., 2002; Kashinkunti et al., 2004; Chin and

Berube, 2005; Reckhow et al., 2010; Lyon et al., 2012; Linden et al., 2012). However, Liu et

al. (2006) dosed 7 mg/l free chlorine to various waters after UV irradiation at 60 mJ/cm2;

chloroform formation increased by 20-100% in 3 waters but was unchanged in one. Choi and

Choi (2010) found 40 mJ/cm2 had no effect on chlorine demand of a treated surface water at

4°C but increased short-term chlorine demand at 15°C. They also observed that this UV dose

increased THM formation by c. 5-10% in summer and autumn but not in winter and spring.

Dotson et al. (2010) reported an increase in THMFP of c. 15% after applying a UV dose of

1,000 mJ/cm2 to treated river water. The 24-hour chlorine demand increased by c. 40%.

Generally, upstream UV irradiation at doses used for disinfection has little effect on

subsequent formation of HAAs (Malley et al., 1995; Kashinkunti et al., 2004; Chin and Berube,

2005; Reckhow et al., 2010; Lyon et al., 2012). However, Liu et al. (2006) reported 60 mJ/cm2

increased dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) by 10-50% in 3 waters

but had no impact on one.

Malley et al. (1995) reported UV dosed at 60–200 mJ/cm2 did not affect subsequent formation

of cyanogen chloride (CNCl). Conversely, Liu et al. (2006) reported increased (40-130%)

CNCl concentrations in chlorinated waters dosed upstream at 60 mJ/cm2 in three out of four

waters tested, but no change in the other one.

In a US study (Reckhow et al., 2010), LP UV dosed at 40–140 mJ/cm2

to raw and treated

water had no impact on formation of haloacetonitriles (HANs) and trichloropropanone (TCP).

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Shah et al. (2011) found that UV doses up to 1,000 mJ/cm2 had no effect on

halonitromethane formation after subsequent chlorination. Linden et al. (2012) observed some

additional formation of halonitromethane, at the single g/l level, after UV doses up to

186 mJ/cm2; greater increases were apparent at higher doses (186-1,000 mJ/cm

2).

Lyon et al. (2012) reported increased bromopicrin formation (40-186 mJ/cm2 in the presence

of nitrate and bromide). At a higher dose of 1,000 mJ/cm2, chloral hydrate formation

increased. Linden et al. (2012) observed some additional formation of chloral hydrate, at the

single g/l level, after UV doses up to 186 mJ/cm2; greater increases were apparent at higher

doses (186-1,000 mJ/cm2).

Chu et al. (2014) found doses of 19.5–585 mJ/cm2 did not influence haloacetamide formation.

Linden et al. (2012) concluded that nitrosamine formation after subsequent chloramination is

likely to be reduced to a small degree after UV doses of up to 186 mJ/cm2, with greater

reductions expected at higher doses (186-1,000 mJ/cm2).

MP UV

Upstream UV irradiation at doses used for disinfection has little, if any, effect on subsequent

formation of THMs (Liu et al., 2002; Kashinkunti et al., 2004; Reckhow et al., 2010; Lyon et

al., 2012). However, Liu et al. (2006) dosed 7 mg/l free chlorine to various waters dosed with

at 60 mJ/cm2; chloroform formation increased by 40-110% in 3 waters but was unchanged in

one. Choi and Choi (2010) found 40 mJ/cm2 had no effect on chlorine demand of a treated

surface water at 4°C but increased short-term chlorine demand at 15°C. They also observed

that this UV dose increased THM formation by c. 5-10% in summer and autumn but not in

winter and spring. Liu et al. (2002) observed a decrease of 9-29% in THM formation when

dose was increased to 5,000 mJ/cm2, whereas Lyon et al. (2012) reported THM formation

increased by 30-40% when dose was increased to 1,000 mJ/cm2. Dotson et al. (2010)

reported an increase in THMFP of c. 30-50% after applying a UV dose of 1,000 mJ/cm2 to

treated river water. The 24-hour chlorine demand increased by c. 60%.

Generally, upstream UV irradiation at doses used for disinfection has little effect on

subsequent formation of HAAs (Liu et al., 2002; Kashinkunti et al., 2004; Reckhow et al.,

2010; Lyon et al., 2012; Linden et al., 2012). However, Liu et al. (2006) reported 60 mJ/cm2.

increased formation of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) by c. 10-

90% in two waters tested but reduced it by 10-30% in two other waters. Liu et al. (2002)

observed a decrease of 15-44% in HAA formation when dose was increased to 5,000 mJ/cm2.

Liu et al. (2006) reported increased CNCl concentrations by 10-100% in four chlorinated

waters dosed upstream with 60 mJ/cm2. Lyon et al. (2012) reported the formation of CNCl

after subsequent chloramination doubled when UV was dosed at 186 mJ/cm2 in the presence

of nitrate.

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Reckhow et al. (2010) reported that UV dosed at 40–140 mJ/cm2

to raw and treated water

increased chloropicrin formation. Shah et al. (2011) found that doses <300 mJ/cm2 increased

chloropicrin formation by as much as an order of magnitude after chlorination. Similarly, Lyon

et al. (2012) reported chloropicrin formation increased by 3 to 6 times after UV doses of 40-

186 mJ/cm2, in the presence of nitrate; and bromopicrin formation increased by 4 to 10 times

after a UV dose of 40 mJ/cm2 in the presence of nitrate and bromide.

Reckhow et al. (2010) reported that UV dosed at 40–140 mJ/cm2

to raw and treated water

increased chloral hydrate formation. Lyon et al. (2012) reported chloral hydrate formation

increased by 20–40% after a UV dose of 40 mJ/cm2. Linden et al. (2012) observed some

additional formation of chloral hydrate, at the single g/l level, after UV doses up to

186 mJ/cm2; greater increases were apparent at higher doses (186-1000 mJ/cm

2).

Linden et al. (2012) observed some additional formation of halonitromethane, at the single

g/l level, after UV doses up to 186 mJ/cm2; greater increases were apparent at higher doses

(186-1,000 mJ/cm2).

Linden et al. (2012) concluded that nitrosamine formation after subsequent chloramination is

likely to be reduced to a small degree after UV doses of up to 186 mJ/cm2, with greater

reductions expected at higher doses (186-1,000 mJ/cm2).

2.2.4 Formation of DBPs: Effect of UV downstream of chlorination

Linden et al. (2012) concluded that UV doses <186 mJ/cm2 did not alter chlorine (or

chloramine) demand nor regulated DBP formation to any practical extent. However, they

noted that photolysis of chlorine species formed hydroxyl and chloride radicals, and

recommended that UV disinfection be installed upstream of secondary disinfection.

LP UV

Huang et al. (2008) reported formation of 10-15 ug/l bromate in chlorinated bromide-spiked

deionised water exposed to LP UV (200-1,000 mJ/cm2 for 5-25 minutes). Bromate formation

was greater at acidic pH (<6).

MP UV

Campbell (2011) reported elevated bromate concentrations at two groundwater sites

containing >100 ug/l bromide where UV >100 mJ/cm2 was dosed post chlorination.

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2.2.5 Effect of UV on pre-formed DBPs

Bromate

LP UV

Siddiqui et al. (1996) reported 3-38% decomposition of bromate to bromide (via bromite and

hypobromite) at doses of 22-228 mJ/cm2 using „tailored‟ LP UV at <200 nm. Smaller

conversions of bromate were measured at higher UV doses using standard LP UV.

MP UV

Siddiqui et al. (1996) reported 7-46% decomposition of bromate to bromide (via bromite and

hypobromite) at doses of 60-550 mJ/cm2.

Bensalah et al. (2013) reported 90% decomposition of bromate to at a dose of 1,000 mJ/cm2.

THMs

LP UV

Mole et al. (1997) reported removals of the regulated THMs (bromoform, chlorodibromoform

and bromodichloroform) from spiked groundwaters at LP UV doses of 1,100 and 6,600

mJ/cm2. Chloroform was not removed, indicating that photolysis of the Br-C bond occurs more

readily than the Cl-C bond.

Chang (2008) observed for UV doses of 0-2,200 mJ/cm2 minimal removal of chloroform but

removals of brominated THMs at rates which increased with bromine content.

HAAs

LP UV

Chang (2008) observed for UV doses of 0-4,400 mJ/cm2 negligible removal of chlorinated

HAAs (monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid

(TCAA)) and monobromoacetic acid (MBAA) but greater removals of brominated HAAs

(dibromoacetic acid (DBAA), tribromoacetic acid (TBAA)) at rates which increased with

bromine content.

2.3 Effect of UV in advanced oxidation processes

UV may be used in conjunction with ozone (O3), hydrogen peroxide (H2O2) or titanium dioxide

(TiO2) in AOPs, with subsequent reactions strongly influenced by the presence of highly

reactive hydroxyl radicals. UV doses used in AOPs are typically an order of magnitude or

more greater than used for disinfection.

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2.3.1 Effect of UV on organics

A reduction in TOC was reported after UV/TiO2 photocatalytic treatment (Richardson et al.,

1996), but the magnitude of the reduction (40%) was likely have been enhanced by the

configuration of the experiment (the samples were recirculated for 24 hours).

Mineralisation of TOC by UV/O3 was observed by Chin and Berube (2005).

Increases in AOC in the range 27-131 mg/l have been reported following UV/H2O2 (MP UV

dose 540 mJ/cm2, H2O2 dose 4.0-6.9 mg/l). AOC formation was inversely related to nitrate

concentration; nitrate strongly absorbs UV at the wavelengths absorbed by natural organic

matter (NOM).

2.3.2 Formation of DBPs: Direct formation

Nitrite

Nitrite may be formed by photolysis of nitrate and is potentially greater at the higher UV doses

used for AOPs (Ijpelaar et al., 2007), for example 40-330 μg/l NO2- formed following UV/H2O2

(MP UV 540 mJ/cm2, H2O2 3.4-6.9 mg/l).

Bromate

Ozone reacts readily with bromide to from bromate. Collivignarelli and Sorlini (2004) reported

that LP UV/O3, with UV dose in the range 270-1,400 mJ/cm2 and ozone dose in the range 0.3

to 10 mg/l, reduced bromate formation by 40-50% relative to ozone alone provided UV dose

was less than 800 mJ/cm2 and/or CT (the product of ozone dose and contact time) was less

than 10 mg.min/l; above these thresholds UV did not reduce bromate formation. However,

Hofman et al. (2010) found that MP UV/O3 (600 mJ/cm2, 2 mg/l) did not reduce formation of

bromate relative to ozone alone.

Hydroxyl radicals can convert bromide to bromate via hypobromous acid (HOBr/OBr-), but in

the presence of H2O2 hypobromous acid is reduced to bromide. Hence bromate formation

from bromide is not expected from the UV/H2O2 process (Ijpelaar et al., 2007). Kishimoto and

Nakamura (2012) observed no bromate formation in experiments with UV/H2O2.

2.3.3 Formation of DBPs: Effect of UV upstream of chlorination

THMs and HAAs

Richardson et al. (1996) reported the formation of many halogenated DBPs after UV/TiO2 and

chlorination, but the number and concentrations were lower than when chlorine was used

alone.

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Kleiser and Frimmel (2000) reported an initial increase in THM formation potential following

UV/H2O2 (H2O2 8 mg/l) before declining at increased UV doses. DOC and UV254 absorbance

declined with UV dose. They concluded that molecular ozone is more effective than hydroxyl

radicals for decreasing halogenated organic DBP formation and that an ozone-based AOP is

advantageous if wanting to simultaneously remove micropollutants and reduce DBP

formation.

Collivignarelli and Sorlini (2004) performed bench-scale tests to determine performance of LP

UV/O3. The UV dose was in the range 270-1,400 mJ/cm2 and ozone dose 0.3-10 mg/l. THM

formation was typically 10-30% lower than ozone alone but there was considerable scatter in

their results, with some samples showing increased formation.

Chin and Berube (2005) compared UV/O3 with UV and O3 individually on precursors of

chlorinated DBPs. UV/O3 (130 mJ/cm2; 3 mg/l O3) reduced formation of chloroform and

chlorinated HAAs to a similar extent to that of O3 alone; increasing doses resulted in greater

reductions. UV alone had no impact on DBP formation.

Dotson et al. (2010) investigated DBP formation following UV/H2O2 treatment. Bench-scale

tests using LP and MP UV, with and without H2O2 addition, were carried out on treated water

sampled from a treatment works (river water source). Mean bromide in the treated water

measured 49 µg/l; mean TOC measured 1.51 mg/l in sand filtered water and 0.86 mg/l in

GAC filtered water. A UV dose of 1,000 mJ/cm2 with 10 mg/l H2O2 increased THMFP c. 100%

for both LP and MP UV. The 24-hour chlorine demand was approximately 0.6 mg/l higher

when the 10 mg/l H2O2 was used in combination with 1,000 mJ/cm2 UV, relative to

1,000 mJ/cm2 UV alone.

2.3.4 Effect of UV on pre-formed DBPs

THMs and HAAs

LP UV

Chang (2008) compared UV doses of 0-2,200 mJ/cm2 with and without 6 mg/l H2O2 for THM

removal. The addition of H2O2 did not affect reaction rates. Removal of chloroform was

minimal but removals of brominated THMs increased with bromine content.

Chang (2008) compared UV doses of 0-4,400 mJ/cm2 with and without 6 mg/l H2O2 for HAA

removal. The addition of H2O2 did not affect reaction rates. Removal of chlorinated HAAs

(MCAA, DCAA, TCAA) and MBAA was negligible but removals of brominated HAAs (DBAA,

TBAA) increased with bromine content.

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Table 2.1 Summary of UV effects

UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)

Medium Observed effect(s) Reference

Effect of UV used for disinfection

Effect of UV on organics

LP 40 Treated SW No change in DOC / hydrophilic DOC, UV254, SUVA or

AOC.

Choi and Choi, 2010

LP 40-140 Treated SW (clarified, filtered, GAC) No change in AOC. Kashinkunti et al., 2004

LP 47-91 Treated SW No significant change in AOC. Ijpelaar et al., 2005

LP 60-200 GWs, untreated SWs, treated (clarified or

filtered) SWs

No change in DOC or UV254 absorbance; AOC was

unchanged; BDOC increased in untreated SWs but

was unchanged in treated SWs and GWs; hydrophilic

DOC increased in treated SWs and low-coloured GWs

but was unchanged in high-coloured untreated SWs

and GWs.

Malley et al., 1995

LP 130-1,600 SW (untreated lake water) No effect on TOC at any dose. No effect on UV254

absorbance at 130 mJ/cm2; marginal reduction at 1600

mJ/cm2.

Chin and Berube, 2005

Dual LP (185/254 nm) 40 Treated SW No change in DOC / hydrophilic DOC, UV254, SUVA or

AOC.

Choi and Choi, 2010

150 No change in DOC / hydrophilic DOC, UV254, SUVA or

AOC. DOM molecular weight decreased in the “dry

season”, unchanged rest of the year.

MP (200-400 nm)

40 Treated SW No change in DOC / hydrophilic DOC, UV254, SUVA or



MP (185-400 nm) 40 No change in DOC / hydrophilic DOC, UV254, SUVA or



MP 40-140 Treated SW (clarified, filtered, GAC) No change in AOC. Kashinkunti et al., 2004

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UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)


MP 47-91 Treated SW AOC increased approximately in proportion to dose (c.

400% at 91 mJ/cm2).

Ijpelaar et al., 2005

Formation of DBPs: Direct formation - Mutagenicity

LP 47-91 Treated SW No significant change in mutagenicity. Ijpelaar et al., 2005

LP 120 Stored SW (River Rhine) No significant change to mutagenicity. Zoeteman et al., 1982

MP 47-91 Treated SW Mutagenicity increased. Ijpelaar et al., 2005

Formation of DBPs: Direct formation - Nitrogenated by-products

LP 100-160 Effluent from municipal wastewater plant No nitrophenols or nitrosamines detected. Liberti et al., 2002

LP 6,600 SW (with/without 50 mg/l added NO3-) Possible formation of unidentified N-containing

compounds.

Mole et al., 1997

Formation of DBPs: Direct formation - Aldehydes and carboxylic acids

LP 130 GWs, untreated SWs, treated (clarified or

filtered) SWs

Formation of formaldehyde in untreated, coloured

SWs, treated SWs and a highly-coloured GW; no

formaldehyde detected in other GWs.

Malley et al., 1995

LP 40-500 Synthetic drinking water (c. 3 mg/l TOC) No significant formation of aldehydes (formaldehyde

and acetaldehyde) or carboxylic acids (formic, acetic

and oxalic acids.

Liu et al., 2002

1,000-6,360 Formation of aldehyde (formaldehyde and

acetaldehyde) increased at doses above 500 mJ/cm2

to 13 μg/l at 6360 mJ/cm2.

LP 110-16,500 Untreated River Thames water Formation of aldehyde (formaldehyde and

acetaldehyde) increased from 9.7 μg/l at 110 mJ/cm2 to

85 μg/l at 16500 mJ/cm2.

Mole et al., 1997

220-16,500 10 mg/l humic acid dissolved in borehole

water

Formation of aldehyde (formaldehyde and

acetaldehyde) increased from 2.9 μg/l at 220 mJ/cm2 to

48.8 μg/l at 16500 mJ/cm2.

MP 40-500 Synthetic drinking water (c. 3 mg/l TOC) No significant formation of aldehydes (formaldehyde

and acetaldehyde) or carboxylic acids (formic, acetic

and oxalic acids).

Liu et al., 2002

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UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)


1,000-6,360 Formation of aldehyde (formaldehyde and

acetaldehyde) increased at doses above 500 mJ/cm2

to 37 μg/l at 6,360 mJ/cm2; carboxylic acids (formic,

acetic and oxalic acids) increased to 100-240 μg/l at

6,360 mJ/cm2.

Formation of DBPs: Direct formation - Nitrite

LP 130 GWs (nitrate 0.16-8.1 mg/l) No change in nitrate concentration and nitrite not

detected.

Malley et al., 1995

LP 60-120 Spiked deionised water (nitrate 10 & 50

mg/l)

Nitrite not detected (pH5-8) Mole et al., 1997

2,850-

22,850

At 2,850 mJ/cm2: 90 μg/l nitrite formed with 10 mg/l

nitrate; 290 μg/l nitrite formed with 50 mg/l nitrate

(pH7). At 22,850 mJ/cm2: 570 μg/l nitrite formed with

10 mg/l nitrate; 1,900 μg/l nitrite formed with 50 mg/l

nitrate (pH7).

1,100-6,600 Spiked deionised water (nitrate 50 mg/l) 161 μg/l nitrite formed at 1,100 mJ/cm2, pH8.1 but

<100 μg/l at pH5.1-7.2 (minimum formation at pH6.1).

Formation increased proportionately to dose to 6,600

mJ/cm2.

LP 47-91 Treated SW No significant formation of nitrite. Ijpelaar et al., 2005

LP 25-120

Not stated 2 μg/l nitrite at 25 mJ/cm2 (50 mg/l nitrate); 7 μg/l nitrite

at 120 mJ/cm2 (14 mg/l nitrate).


MP 70 Not stated 40 μg/l nitrite at 70 mJ/cm2 (15 mg/l nitrate); 20 μg/l

nitrite at 70 mJ/cm2 (8 mg/l nitrate).

MP 50 Not stated. 50 mg/l nitrate. 30 μg/l nitrite with sleeves to block wavelengths below

235 nm; 150 μg/l nitrite without sleeves.

MP 25-200 Treated SW c. 40 g/l nitrite formed at 100 mJ/cm2 (pilot scale);

BUT c. 800 g/l formed at 91 mJ/cm2 (bench scale).

Authors unable to explain discrepancy.


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UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)


Formation of DBPs: Direct-formation - Bromate

LP 130 GWs (bromide 50-250 μg/l) No change in bromide concentration and bromate not

detected.

Malley et al., 1995

LP Not stated Not stated (bromide 150 μg/l) No bromate formation after 30 minutes irradiation. Kishimoto & Nakamura, 2012

Formation of DBPs: Direct formation - Other

LP 120 Stored SW (River Rhine) Benzene increased to 1 μg/l; toluene increased to 3

μg/l.

Zoeteman et al., 1982

Not stated Not stated SW (reservoirs) Copper released into solution from copper-bound NOM

(copper sulphate used to control algae).

Parkinson et al., 2001

Formation of DBPs: Effect of UV upstream of chlorination

LP 19.5-585 Various No effect on haloacetamide formation. Chu et al., 2014

LP 40 Treated SW No effect on chlorine demand at 4°C but increased

chlorine decay rate at 15°C. THM formation increased

by c. 5-10% in summer and autumn, no change in

winter or spring.

Choi and Choi, 2010

LP 40-140 Treated SW (clarified, filtered, GAC) Sequential UV and chlorine (2 mg/l dose, 24 hr contact

time): no effect on chlorine demand or formation of

THMs, HAAs, TOX, carboxylic acids and aldehydes.

Kashinkunti et al., 2004

LP 40-140 Raw and treated water No effect on formation of THMs, HAAs, HANs or TCP. Reckhow et al., 2010

LP 60-200 Not stated No effect of UV prior to chlorination or chloramination

on formation of THM, HAA or CNCl.

Malley et al., 1995

LP 40-500 Synthetic drinking water (c. 3 mg/l TOC) No effect on THM or HAA formation. Liu et al., 2002

1,000-6,360 THM formation increased by 15% at 5,000 mJ/cm2. No

effect on HAA formation.

LP 60 Three synthetic waters (each 5 mg/l DOC)

and a raw SW (1.8 mg/l DOC)

Sequential UV and chlorine (7 mg/l free chlorine dose,

3 day contact time): Chloroform formation increased in

3 waters by c. 20-100%, unchanged in 1 water; DCAA

and TCAA formation increased in 3 waters by c. 10-

50%, unchanged in 1 water. Sequential UV and

Liu et al., 2006

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UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)


chlorine (7 mg/l free chlorine dose, 7 day contact time):

CNCl formation increased in 3 waters by c. 40-130%,

unchanged in 1 water.

LP Up to 1,500 Humic acid solution and “water samples” No effect of LP on halonitromethane formation. Shah et al., 2011

LP 40-186 “Water samples” spiked with bromide and

nitrate

No effect on THM and HAA formation. Bromopicrin

formation increased by 30-60% when both bromide

and nitrate spiked.

Lyon et al., 2012

1,000 THM formation increased by 30-40%. Chloral hydrate

formation increased.

LP <186 Not stated (various) Chlorine demand, THM and HAA formation unaffected.

Halonitromethane and chloral hydrate formation may

be increased, at single g/l level. Nitrosamine

formation likely reduced to small degree where

chloramination follows UV.

Linden et al., 2012

186-1,000 Chlorine/chloramine demand and corresponding DBP

concentrations increased. Halonitromethane and

chloral hydrate formation may be increased, at g/l

level. Nitrosamine formation likely reduced by

appreciable extent where chloramination follows UV.

LP 130-1,600 SW (untreated lake water ) Negligible reduction in formation potentials of

chloroform and chlorinated HAAs during subsequent

chlorination.


LP 500-1,000 Sand filtered river water (1.51 mg/l TOC);

GAC filtered river water (0.86 mg/l TOC)

c.15% increase in THM formation potential. Dotson et al., 2010

LP Not stated Filtered SW (River Ruhr) 7-13% reduction in THM formation potential after 30-

240 minutes; 13-24% reduction in AOX formation

potential in 30-240 minutes.

Kleiser and Frimmel, 2000

Dual LP (185/254 nm) 40 Treated SW No effect on chlorine demand at 4°C but increased



winter or spring.

Choi and Choi, 2010

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UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)


150 Increased chlorine decay rate at 4°C and 15°C. THM

formation increased by c. 5-15% in spring through

autumn, no change in winter.

MP 40-140 Treated SW (clarified, filtered, GAC) Sequential UV and chlorine (2 mg/l dose, 24 hr contact

time): no effect on chlorine demand or formation of

THMs, HAAs, TOX, carboxylic acids and aldehydes.

Kashinkunti et al., 2004

MP 40-140 Raw and treated water No effect on formation of THMs, HAAs, HANs or TCP;

chloral hydrate and chloropicrin increased with

increasing dose (chloropicrin also increased with

increasing nitrate).

Reckhow et al., 2010

MP <300 Humic acid solution and “water samples” Increased chloropicrin by an order of magnitude

(greater after chlorination than chloramination); MP

UV/chloramination increased HAN formation in the

humic acid solution but not in the water samples.

Shah et al., 2011

MP 40-500 Synthetic drinking water (c. 3 mg/l TOC) No effect on THM or HAA formation. Liu et al., 2002

1,000-6,360 THM formation decreased by 9- 29% at 5,000 mJ/cm2;

HAA formation decreased by 15-44% at >5,000

mJ/cm2.

MP 60 Three synthetic waters (each 5 mg/l DOC)

and a raw SW (1.8 mg/l DOC)

Sequential UV and chlorine (7 mg/l free chlorine dose,

3 day contact time): Chloroform formation increased in

3 waters by c. 40-110%, unchanged in 1 water; DCAA

and TCAA formation increased in 2 waters by c. 10-

90%, decreased in 2 waters by c. 10-30%. Sequential

UV and chlorine (7 mg/l free chlorine dose, 7 day

contact time): CNCl formation increased by c. 10-

100%.

Liu et al., 2006

MP 40 Treated SW No effect on chlorine demand at 4°C but increased



winter or spring.

Choi and Choi, 2010

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UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)


MP (185-400 nm) 40 Treated SW Increased chlorine decay rate at 4°C and 15°C. THM

formation increased by c. 5-16% in summer and

autumn, no change in winter or spring.

Choi and Choi, 2010

MP 40-186 “Water samples” spiked with bromide and

nitrate

No effect on THM and HAA formation. Chloropicrin

formation increased by a factor of 2 after

chloramination and by 3-6x after chlorination (nitrate 1-

10 mg/l N). Bromopicrin formation increased by 4-10x

at 40 mJ/cm2 in the presence of both bromide and

nitrate. Cyanogen chloride formation doubled at 186

mJ/cm2 after chloramination. Chloral hydrate formation

increased by 20-40% at 40 mJ/cm2.

Lyon et al., 2012

1,000 THM formation increased by 30-40%.

MP 500-1,000 Sand filtered river water (1.51 mg/l TOC);


c. 30-50% increase in THM formation potential. Dotson et al., 2010

MP <186 Not stated (various) Chlorine demand, THM and HAA formation unaffected.

Halonitromethane and chloral hydrate formation likely

to be increased, at single g/l level. Nitrosamine

formation likely reduced to small degree where

chloramination follows UV.

Linden et al., 2012

186-1,000 Chlorine/chloramine demand and corresponding DBP

concentrations increased. Halonitromethane and

chloral hydrate formation likely to be increased, at g/l

level. Nitrosamine formation likely reduced by

appreciable extent where chloramination follows UV.

Formation of DBPs: Effect of UV downstream of chlorination

Sunlight Sunlight Chlorinated sea water Increased chlorine decay rate and formation of

bromate (from hypobromite produced by the oxidation

of bromide ions by hypochlorite).

Wong, 1980

LP 40-2,000 Spiked (88 μg/l Br-) deionised water &

clarified/filtered river water (DOC=1.7 mg/l,

Br- = 53-151 μg/l)

Exposure to UV accelerated chlorine decay and

formation of bromate (10-15 μg/l in 5-25 min, and

greater at acidic pH (<6)).

Huang et al., 2008

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UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)


Not stated 186 Not stated (various) UV doses <186 mJ/cm2 did not affect chlorine or

chloramine demand nor regulated DBP formation; UV

able to photolyse chlorine and chloramine (producing

hydroxyl and chloride radicals); recommended UV

disinfection be installed upstream of secondary

disinfection.

Linden et al., 2012

Effect of UV on pre-formed DBPs: Bromate

LP (<200 nm) 23-228 3-38% decomposition of bromate to bromide (via

bromite and hypobromite).

Siddiqui et al., 1996

MP 60-550 7-46% decomposition of bromate to bromide (via

bromite and hypobromite).

MP 1,000 90% decomposition of bromate. Presence of DOC,

inorganic carbon or nitrate reduced reaction rate.

Bensalah et al., (2013)

Effect of UV on pre-formed DBPs: THMs

LP 0-2,200 Deionised water Minimal removal of chloroform. Removal of brominated

THMs increased with increasing bromine content.

Reaction rates first order with respect to UV dose.

Chang, 2008

LP 1,100 /

6,600

THM (50 mg/l) spiked GW At 1,100 mJ/cm2, 80% removal of bromoform, 50% of

chlorodibromoform, 20% of bromodichloroform.

At 6,600 mJ/cm2, 100% removal of bromoform and

chlorodibromoform, 50% of bromodichloroform.

No removal of chloroform.

Mole et al., 1997

Effect of UV on pre-formed DBPs: HAAs

LP 0-4,400 Deionised water Negligible removal of chlorinated HAAs (MCAA, DCAA,

TCAA) and MBAA. Removal of more brominated HAAs

(DBAA, TBAA) increased with increasing bromine

content. Reaction rates first order with respect to UV

dose.

Chang, 2008

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UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)


Effect of UV used in advanced oxidation processes

Effect of UV on organics

LP 130-1,610 SW (untreated lake water) UV/O3 oxidised organic material and to lesser extent

mineralised TOC.


MP 540 - AOC formation increased (by 27-131 mg/l) after

UV/H2O2 compared with UV disinfection alone; AOC

formation inversely related to nitrate (strongly absorbs

UV at wavelengths absorbed by NOM).


Not specified - Raw and ultrafiltered water 40% reduction in TOC after UV/TiO2 photocatalytic

treatment (recirculated in batch reactor for 24 hr).

Richardson et al., 1996

Formation of DBPs: Direct formation – Nitrite

MP 540 - UV/H2O2 plant 40-330 μg/l nitrite (nitrate 4.4-12.5 mg/l

NO3-.).


Formation of DBPs: Direct formation – Bromate

LP 270-1,400 SW (1.8 mg/l TOC) UV/O3: UV reduced bromate formation by 40-50%

relative to ozone alone provide UV dose <800 mJ/cm2

and ozone CT <10 mg.min/l.

Collivignarelli and Sorlini, 2004

LP Not stated Not stated (bromide 150 μg/l) UV/H2O2: No bromate formation after 30 minutes

irradiation.

Kishimoto & Nakamura, 2012

MP 600 Part-treated surface waters (0.24 and 1.75

mg/l DOC; bromide 170 μg/l)

UV/O3: After an O3 dose of 2 mg/l, UV increased

bromate formation from 28 to c. 55 g/l in the lower

DOC water but did not change formation in the higher

DOC water.

Hofman et al., 2010

Formation of DBPs: Effect of UV upstream of chlorination

LP 585 Various UV/H2O2 (10 mg/l H2O2): reduced formation of N-DBPs

(haloacetamides, haloacetonitriles, halonitromethanes).

Chu et al., 2014

LP 1,000 Sand filtered river water (1.51 mg/l TOC);


THMFP increased by c.15% as a result of UV alone,

and by c.100% as a result of UV/H2O2 (10 mg/l).

Dotson et al., 2010

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UV lamp type /

Wavelength (nm)

UV dose

(mJ/cm2)


LP 130-1,610 SW (untreated lake water) UV/O3 reduced formation of chloroform and chlorinated

HAAs by c. 40% at 3 mg/l O3/130 mJ/cm2.


LP 270-1,400 SW (1.8 mg/l TOC) UV/O3: UV typically reduced THM formation by 10-30%

relative to ozone alone but some samples showed an

increase.

Collivignarelli and Sorlini, 2004

MP 1,000 Sand filtered river water (1.51 mg/l TOC);


THMFP increased by c. 30-50% as a result of UV

alone, and by c.100% as a result of UV/H2O2 (10 mg/l).

Dotson et al., 2010

Not specified - Ultrafiltered water (with and without

secondary chlorination)

Many halogenated DBPs formed after UV/TiO2 and

chlorination, but less than when chlorine used alone;

possible formation of 3-methyl-2,4-hexanedione and

dihydro-4,5-dichloro-2(3H)furanone (recirculated in

batch reactor for 24 hr).

Richardson et al., 1996

- - Filtered river water (River Ruhr) UV/H202 initially increased THM formation before

decreasing with further increase in UV dose; small

reduction in DOC and UV254 absorbance.

Kleiser and Frimmel, 2000

Effect of UV on pre-formed DBPs: THMs

LP 0-2,200 Deionised water UV/H202: UV + 6 mg/l H2O2 did not change reaction

rates relative to UV alone. Minimal removal of

chloroform. Removal of brominated THMs increased

with increasing bromine content. Reaction rates first

order with respect to UV dose.

Chang, 2008

Effect of UV on pre-formed DBPs: HAAs

LP 0-4,400 Deionised water UV/H202: UV + 6 mg/l H2O2 did not change reaction

rates relative to UV alone. Negligible removal of

chlorinated HAAs (MCAA, DCAA, TCAA) and MBAA.

Removal of more brominated HAAs (DBAA, TBAA)

increased with increasing bromine content. Reaction

rates first order with respect to UV dose.

Chang, 2008

Note:

1. GW = groundwater, SW = surface water.

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2.4 Conclusions

UV is used in water treatment for disinfection at doses around 40 mJ/cm2 and in AOPs at

doses typically an order of magnitude greater.

At UV doses typically used for disinfection:

Organic DBPs (THMs, HAAs, aldehydes, carboxylic acids) do not appear to be formed

directly.

Nitrite formation may occur if nitrate is present. The likelihood, and extent of formation,

depend on the type of UV lamp, being greatest for MP lamps where wavelengths below

240 nm are not blocked and lowest for LP lamps.

Bromate is not formed by UV directly.

When UV at doses typically used for disinfection is followed by chlorination:

The formation of THMs and HAAs is unlikely to be affected but potentially may increase

by c. 10% (LP or MP).

The formation of aldehydes, carboxylic acids, TCP or HANs is unlikely to be affected.

The formation of chloropicrin and bromopicrin is likely to increase. The formation of

both is promoted by higher concentration of nitrate, while the formation of bromopicrin

is promoted by higher concentration of bromide.

The formation of cyanogen chloride is likely to increase.

The formation of chloral hydrate and halonitromethanes is likely to increase, at the

single g/l level (LP UV) or g/l level (MP UV).

The formation of nitrosamines is likely to be reduced.

When chlorination is followed by UV at doses typically used for disinfection:

There is potential for bromate formation if bromide is present.

Chlorine decay rate may increase but this effect is unlikely to be of practical

significance.

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© WRc plc 2015 25

When UV is applied as part of an AOP:

Some mineralisation of DOC may occur.

AOC is likely to increase.

Nitrite formation is likely to occur in the presence of nitrate.

Bromate formation will not occur with UV/H2O2 but will occur with UV/O3.

Conflicting results indicated an increase in THMFP following UV and UV/H2O2 - but also

a reduction in the formation of halogenated organic DBPs - after subsequent

chlorination.

Removal of pre-formed brominated THMs and HAAs is likely, the extent increasing with

UV dose and with bromine content. Removal of chloroform and HAAs containing only

chlorine will not occur to any appreciable extent at practicable UV doses.

DWI


© WRc plc 2015 26

3. UV Treatment in Public Supplies

3.1 Introduction

Information on UV treatment in public supplies was collected by a focussed questionnaire

survey of 22 water companies in England and Wales. The questionnaire was designed to

identify the main features of existing and proposed UV treatment plants, including details of

the plant, main function, upstream and downstream treatment, and any related DBP formation

(or degradation). The survey built on a previous survey carried out by WRc in 2007.

Questionnaires were returned by 16 water companies (73% response), including nil returns

from 6 water companies that reported not using UV treatment.

Six water companies failed to respond to the questionnaire and subsequent requests,

although one company confirmed having about 45 UV units (all on groundwater sites).

3.2 Results

Results of the survey are summarised in Tables 3.1 and 3.2; returned questionnaires are

presented in Appendix B. All details of water companies and treatment works have been

anonymised.

3.3 Conclusions

The questionnaire survey identified 894 UV plants (existing and proposed) from returns from

16 water companies (including 6 nil returns) with a total UV treatment capacity of 1,492 Ml/d.

The UV treatment capacity represents approximately 23% of the production capacity of the

ten companies utilising UV (between 3-100% of capacity) and approximately 17% of the

production capacity of all 16 companies.

The UV dose used for general disinfection is typically around 40 mJ/cm2. The UV dose used

in AOPs is typically around 500-600 mJ/cm2.

UV treatment is used mostly where there is a Cryptosporidium risk and for general

disinfection, with a much smaller usage in AOPs.

UV is used most widely at small groundwater sites, although a greater water volume is treated

by fewer large UV plants at lowland surface water sites. There is little implementation of UV

for upland water sources.

4 Excluding the c. 45 UV units reported by one company that failed to respond to the questionnaire.

DWI


© WRc plc 2015 27

Several DBPs were detected at sites incorporating UV: THMs, HAAs, bromate, nitrite,

chlorate, chlorite, and NDMA. Of these, only bromate (at Works A5) was directly attributed to

the use of UV.

DWI


© WRc plc 2015 28

Table 3.1 Summary of UV treatment by function and source

Water

company

No. UV

plants

Volume

treated

(Ml/d)

UV treatment by function1 (Ml/d)

(No. sites in brackets)

UV treatment by source2 (Ml/d)

(No. sites in brackets) Notes

D C M GW LSW USW

A 6 354 354

a

(6)

354a

(6) -

42b

(2)

342b

(5) -

a) Includes UV treatment at 6 sites for general

disinfection & Cryptosporidium risk.

b) Includes UV treatment at one site (30 Ml/d)

supplied by GW & LSW.

B 4 28.6 28.6

a

(4) -

12.2a

(1)

2.7

(2)

12.2

(1)

13.7

(1)

a) Includes UV treatment at one site (12.2 Ml/d) for

general disinfection and advanced oxidation.

C 2 134 - 134

(2) -

84

(1)

50

(1) -

D 8 187 47.4

a,b

(3)

148.4a

(4)

27.6b

(2)

101.3c

(6)

102.1c

(3) -

a) Includes UV treatment at one site (16.4 Ml/d) for

general disinfection & Cryptosporidium risk.

b) Includes UV treatment at one site (20 Ml/d) for

general disinfection & advanced oxidation.

c) Includes UV treatment at one site (16.4 Ml/d)

supplied by GW & LSW.

E 8 52.9 52.9

(8) - -

52.9

(8) - -

F 2 4.2 4.2

(2) - -

4.2

(2) - -

G 38 98.6a

74.8b

(28)

98.6b

(23) -

98.6

(38) - -

a) Total for 14 works.

b) Includes UV treatment at 10 sites (74.8 Ml/d) for


H 2 107.5 - 107.5

(2) -

17.5

(1)

90

(1) -

DWI


© WRc plc 2015 29

Water

company

No. UV

plants

Volume

treated

(Ml/d)

UV treatment by function1 (Ml/d)

(No. sites in brackets)

UV treatment by source2 (Ml/d)

(No. sites in brackets) Notes

D C M GW LSW USW

J 4 49.0 46.1

(3)

2.9

(1) -

49.0

(4) - -

K 15 476.4 476.4

a

(15)

151a

(4) -

161.4

(9)

300

(5)

15

(1)

a) Includes UV treatment at 3 sites (151 Ml/d) for


Totals 89 1,492 1,084

(69)

996.4

(42)

39.8

(3)

613.6

(73)

896.3

(16)

28.7

(2)

Notes:

1. D = General Disinfection; C = Cryptosporidium risk; M = Micropollutants (e.g. pesticide, with UV as part of an Advanced Oxidation Process (AOP)).

2. GW = Ground Water; LSW = Lowland Surface Water; USW = Upland Surface Water.

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© WRc plc 2015 30

Table 3.2 Summary of UV treatment by upstream treatment, dose and DBPs detected

Water

company

Upstream pre-oxidation by source UV dose by source (mJ/cm2) DBPs

1 detected by source

GW LSW USW GW LSW USW GW LSW USW

A Pre-chlorine Pre-chlorine

Pre-ozone - 40 (min) 40 (min) -

TTHMs

Bromate2

TTHMs

Bromate

Chlorate

Chlorite

-

B Nil Nil Nil 40 40 / 500 40

THMs

Bromate

HAAs

THMs

NDMA

THMs

HAAs

C Pre-chlorine Pre-chlorine - 60 40 - THMs THMs -

D Pre-chlorine Pre-ozone - 25 / 600 40 / 500 -

THMs

Bromate

Nitrite

Chlorate

NDMA

THMs

Bromate

Nitrite

Chlorate

NDMA

-

E Nil - - 40 - -

TTHMs

Bromate

Nitrite

- -

F Nil - - 40 - - THMs - -

G Pre-chlorine - - 40 - >42 - - -

THMs

Bromate

Nitrite

Chlorate

THMs

Bromate

Nitrite

Chlorate

H Nil Nil - 45 40 - THMs THMs

J ? - - 40 - - ? - -

K Nil Pre-chlorine Nil 40 / 48 40 / 48 48 Bromate Nil Nil

Notes: 1. DBPs detected in treatment, distribution or at customers‟ taps, by regulatory or operational monitoring. 2. DBP specifically associated with UV treatment.

DWI


© WRc plc 2015 31

4. Effect of UV Dosage and/or Pre-oxidation on Chemical Composition and DBP Formation

4.1 Introduction

Operating and monitoring data from a small number of water treatment works were analysed

to evaluate the effect of UV dosage and/or pre-oxidation on chemical composition and DBP

formation. Appropriate works were selected from the survey of public supplies taking into

account risk factors identified from the literature review and including:

Raw water quality (to include groundwaters and surface waters particularly containing

high levels of bromide).

Different UV sources (LP, MP, LPHO lamps) and location in the treatment stream.

Upstream and downstream treatment (particularly pre-oxidation (e.g. prechlorination)

which is likely to have the greatest impact on DBP formation).

Works were selected where data were available to evaluate effects of changes in UV dosage,

including:

Treatment streams before and after the installation of UV.

Treatment streams where UV is switched on and off.

Treatment streams where UV dose has been changed, e.g. from low dose to high dose

reflecting the installation of AOPs to remove micropollutants.

Parallel treatment streams with and without UV.

Whilst available DBP data was mostly for THMs, the following features were also sought:

Works where a more rigorous monitoring programme has been associated with the

implementation of UV (e.g. higher sampling frequencies, sampling for other DBPs such

as HAAs and bromate, etc.)

Works were UV absorbance and/or colour data (surrogate measures for chlorine

demand) are available before and after UV.

Chlorine dose/demand data are available.

A high frequency of total and individual THM data are available.

4.2 Selected works and results

Five water treatment works were visited to inspect installed UV plant and collect operating

data, to elucidate the formation of DBPs. Full reports of the site visits are included in Appendix

C; summaries of the findings are presented below.

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© WRc plc 2015 32

4.2.1 Works A2

Works A2 (design capacity 165 Ml/d) treats a high alkalinity canal water with moderate colour

(typically 30°H) and occasional high turbidity at around 100-110 Ml/d.

Raw water is stored prior to treatment and dosed with chlorine during April to September to

prevent zebra mussel growth; the storage tanks are aerated for THM removal. Further

treatment incorporates preozonation, coagulation (with polyaluminium chloride (PACl)),

sedimentation, RGF, ozonation, GAC, MP UV (typical dose 60-120 mJ/cm2), phosphate

dosing and final chlorination.

Precautions are taken to reduce DBP formation: sulphuric acid can be dosed upstream of

ozonation to reduce bromate formation; MP UV lamps are sleeved to reduce bromate

formation; on-site electrolytic generation of chlorine (OSEGC) uses low-bromide salt, and the

hypochlorite product is stored for no longer than 4 days.

THMs in final water show a seasonal variation, with highest concentrations in the summer –

possibly affected by changes in the nature of raw water DOC, temperature and

prechlorination. Generally, THM concentrations (<30 µg/l) have reduced since the installation

of UV in 2012, but this may reflect reduced chlorine use rather than an effect of UV.

Concentrations of bromate (up to 8 µg/l) are likely to be due to ozonation rather than UV, and

nitrite levels after UV are always low or non-detectable.

4.2.2 Works A5

Works A5 (design capacity 12 Ml/d) treats a high alkalinity, iron-rich groundwater at around 4

Ml/d. The raw water organic content is low (mean TOC 0.5 mg/l). Prior to 2013, treatment

incorporated prechlorination (for iron precipitation), contact tanks, RGF, LP UV, chlorination

and phosphate dosing. The design UV dose at 12 Ml/d is 48 mJ/cm2, but at the lower works

throughput is usually over 100 mJ/cm2.

Prior to 2013, bromate formation was an issue as a result of high-dose UV treatment of

prechlorinated water containing greater than 100 µg/l bromide. Small-scale tests showed

bromate concentrations up to 26 µg/l in post-UV treated water (raw water bromide 154 µg/l,

pre-chlorine dose 2 mg/l). Bromate in RGF filtered water measured 17 µg/l, formed as a result

of sunlight on the supernatant water. Prechlorination ceased in 2013 because of concerns

over bromate formation.

THM formation is low (typical TTHMs in final water <8 µg/l).

4.2.3 Works B1

Works B1 (design capacity 12 Ml/d) treats a low-coloured lowland reservoir water at around

8 Ml/d. The catchment is agricultural and nutrient levels in the reservoir are sufficient to cause

DWI


© WRc plc 2015 33

high algal levels during summer. Treatment incorporates pH adjustment, coagulation (ferric

sulphate), polyelectrolyte-aided sedimentation (LT22S), pH adjustment/chlorination (for

manganese removal), pressure filtration, H2O2/LP UV (for pesticide removal; typical UV dose

400 mJ/cm2), GAC, chlorination/dechlorination.

The raw water TOC shows seasonal variation up to 8 mg/l in the summer/autumn. Final water

THMs similarly show seasonal variation up to 55 µg/l, probably related to water temperature

rather than treated water TOC (which is relatively constant throughout the year). THMs

increased in distribution up to 75-85 µg/l.

A notable feature of the THM data is the very high proportion of brominated THMs in the final

water following peroxide/UV. For filtered water - and for final water prior to implementation of

peroxide/UV - trichloromethane is a higher proportion of the total THMs. Whilst the data

suggest peroxide/UV is enhancing the formation of brominated species, this cannot be stated

definitively because of the quality of the data (variation in operation and sample types).

Bromate concentrations in 2014 measured up to 3.1 µg/l at the GAC inlet, reducing to 1 µg/l in

the final water.

Single measurements for total HAAs in 2014 showed 13 µg/l leaving the works and 19 µg/l in

distribution.

4.2.4 Works B2

Works B2 treats a low-alkalinity, highly-coloured reservoir water at around 13 Ml/d. Treatment

incorporates pH adjustment, coagulation (PACl), polyelectrolyte-aided sedimentation (LT22S),

pH adjustment/chlorination (for manganese removal), RGF, chlorination. UV was installed in

2014 for general disinfection with a design dose of 40 mJ/cm2.

Comparison of DBP formation before and after the installation of UV suggests that THMs

have not increased since the installation. A single HAA measurement (55 µg/l) in 2014 was

higher than pre-UV values; bromate remained low (1.9-3.3 µg/l); and nitrite was not detected.

4.2.5 Works D2

Works D2 (design capacity 7.4 Ml/d) treats a groundwater from three borehole sources at

around 2.3-6.9 Ml/d. Water from Borehole 3 (maximum flow 3.0 Ml/d) contains pesticides and

is treated with high dose LP UV. UV treated water is blended with water from Boreholes 4 and

5 (combined maximum flow 6.2 Ml/d). A proportion of blended water is treated by ion

exchange for nitrate removal, before being blended back prior to chlorination.

Since implementation of UV, THM concentrations in distribution have been low (<20 µg/l) and

nitrite concentrations in the final water have been non-detectable (although any nitrite formed

DWI


© WRc plc 2015 34

by UV would be removed by chlorine). Initial pilot trials at the site highlighted potential

problems with nitrite from MP UV because of the high nitrate in the raw water.

No bromate data are available, but bromide in the raw water is very low and potential for

bromate formation would be expected to be negligible.

4.3 Conclusions

Operating and monitoring data from five water treatment works were analysed to evaluate any

effects of UV dosage and/or pre-oxidation. Generally, available data were limited and few

conclusions regarding effect on DBP formation can be made.

Works A2, A5 (historically) and B2 all dosed chlorine prior to UV. Bromate in excess of the

drinking water standard (10 µg/l) had been detected at Works A5 due to treatment of

prechlorinated water containing greater than 100 µg/l bromide with UV at over 100 mJ/cm2;

the high UV dose resulted from operation at less than the design flow rate. At Works B2, a

single HAA measurement (55 µg/l) exceeded values detected prior to installation of UV in

2014.

Works B1 and D2 both incorporated high-dose UV. No significant effects on DBP formation

were observed, although possible enhanced formation of brominated THMs was noted at

Works B1 (UV dose 400 mJ/cm2).

DWI


© WRc plc 2015 35

5. UV Treatment in Private Supplies

5.1 Introduction

Data on UV treatment in private supplies are collated by DWI based on returns from local

authorities (LAs). Data from 2011-2013 have been summarised below.

5.2 2011 data

In 2011, 261 LAs in England and Wales submitted data to DWI with regard to private water

supplies. In total, 22,503 regulated private supplies were identified, with the capacity to supply

247,155 Ml/yr (approximately 677 Ml/d) (DWI, 2012).

One-hundred-and-thirty-three LAs reported 2,472 private supplies incorporating UV treatment

(UVA and UVP), with the capacity to supply up to 111,474 persons with up to 143 Ml/d of

drinking water. Tables 5.1 and 5.2 provide a summary of these supplies based on the source

type and main activities for which the water is used, respectively.

Table 5.1 Summary of UV treated private supplies by water source (2011)

Water Source1,2

No. of Supplies Persons Served Capacity (m3/d)

BHW 850 (34.4%) 69,545 (62.4%) 37,099 (26.0%)

MMS 33 (1.3%) 3,391 (3.0%) 6,692 (4.7%)

MXW 130 (5.3%) 7,039 (6.3%) 86,699 (60.7%)

RNW 5 (0.20%) 75 (0.07%) 14 (0.01%)

SFW 115 (4.7%) 13,073 (11.7%) 3,371 (2.4%)

SPW 1,053 (42.6%) 15,239 (13.7%) 8,259 (5.8%)

UNK 87 (3.5%) 441 (0.40%) 128 (0.01%)

WEL 199 (8.1%) 2,671 (2.4%) 678 (0.47%)

Totals 2,472 111,474 142,940

Notes:

1. BHW = borehole; MMS = multiple sources which are a combination of borehole and spring (but not influenced by

surface water); MXW = borehole influenced by surface water; RNW = rainwater; SFW = surface water; SPW =

spring; UNK = unknown; WEL = well.

2. Not reported: EBW (estuarine or brackish water) or PMW (public supply (Regulation 8 supplies)).

DWI


© WRc plc 2015 36

Table 5.2 Summary of UV treated private supplies by water use (2011)

Main Activity for

Water Use1


COMM 1,195 (48.3%) 100,212 (89.9%) 139,630 (97.7%)

DOMS 1,062 (43.0%) 10,399 (9.3%) 3,015 (2.1%)

SDDW 193 (7.8%) 572 (0.51%) 233 (0.16%)

UNKN 22 (0.89%) 290 (0.26%) 61 (0.04%)

Totals 2,472 111,474 142,940

Note:

1. COMM = commercial purposes; DOMS = domestic purposes; SDDW = single domestic dwelling with no

commercial activity; UNKN = unknown.

Table 5.1 shows that the majority of private supplies incorporating UV treatment are sourced

from springs (42.6%; 1,053) and boreholes (34.4%; 850). Boreholes account for the largest

percentage of persons served (62.4%; 69,545) and the second largest percentage of water

capacity (26.0%; 37,099 m3/d), whereas springs account for 13.7% of persons served

(15,239) and 5.8% of water capacity (8,259 m3/d). Boreholes influenced by surface water

account for the largest percentage of water capacity (60.7%, 86,699 m3/d) supplied from 130

sources.

Table 5.2 shows that approximately equal numbers of private supplies incorporating UV

treatment are used for commercial purposes (48.3%; 1,195) and domestic purposes (43.0%;

1,062). However, private supplies used for commercial purposes account for substantial

percentages of persons served (89.9%; 100,212) and water capacity (97.7%; 139,630 m3/d).

5.3 2012 data


supplies. In total, 22,984 regulated private supplies were identified, with the capacity to supply

a permanent population of 1,022,209 (DWI, 2013).

One-hundred-and-forty-nine LAs reported 2,640 private supplies incorporating UV treatment

(UVA and UVP), with the capacity to supply up to 132,953 persons with up to 707 Ml/d of

drinking water. Tables 5.3 and 5.4 provide a summary of these supplies based on the source

type and main activities for which the water is used, respectively.

DWI


© WRc plc 2015 37

Table 5.3 Summary of UV treated private supplies by water source (2012)

Water Source1,2


BHW 1027 (38.9%) 84,367 (63.5%) 40,375 (25.6%)

MMS 39 (1.5%) 1,793 (1.3%) 6,665 (4.2%)

MXW 136 (5.2%) 7699 (5.8%) 86,791 (55.0%)

RNW 6 (0.23%) 75 (0.06%) 15 (0.01%)

SFW 161 (6.1%) 17,454 (13.1%) 17,236 (10.9%)

SPW 1033 (39.1%) 18,806 (14.1%) 5,968 (3.8%)

UNK 86 (3.3%) 521 (0.4%) 110 (0.07%)

WEL 152 (5.8%) 2,238 (1.7%) 601 (0.38%)

Totals 2,640 132,953 157,761

Notes:

1. BHW = borehole; MMS = multiple sources which are a combination of borehole and spring (but not influenced by

surface water); MXW = borehole influenced by surface water; RNW = rainwater; SFW = surface water; SPW =

spring; UNK = unknown; WEL = well.

2. Not reported: EBW (estuarine or brackish water) or PMW (public supply (Regulation 8 supplies)).

Table 5.4 Summary of UV treated private supplies by water use (2012)

Main Activity for

Water Use1


COMM 1,205 (45.6%) 119,443 (89.8%) 152,334 (96.6%)

DOMS 1,198 (45.4%) 12,719 (9.6%) 4,727 (3.0%)

SDDW 205 (7.8%) 412 (0.3%) 386 (0.24%)

UNKN 32 (1.2%) 379 (0.3%) 314 (0.20%)

Totals 2,640 132,953 157,761

Note:

1. COMM = commercial purposes; DOMS = domestic purposes; SDDW = single domestic dwelling with no

commercial activity; UNKN = unknown.

Table 5.3 shows that the majority of private supplies incorporating UV treatment are sourced

from springs (39.1%; 1,033) and boreholes (38.9%; 1,027). Boreholes account for the largest

percentage of persons served (63.5%; 84,367) and the second largest percentage of water

capacity (25.6%; 40,375 m3/d), whereas springs account for 14.1% of persons served

(18,806) and 3.8% of water capacity (5,968 m3/d). Boreholes influenced by surface water

account for the largest percentage of water capacity (55.0%; 86,791 m3/d) supplied from 136

sources.

DWI


© WRc plc 2015 38

Table 5.4 shows that approximately equal numbers of private supplies incorporating UV

treatment are used for commercial purposes (45.6%; 1,205) and domestic purposes (45.4%;

1,198). However, private supplies used for commercial purposes account for substantial

percentages of persons served (89.8%; 119,443) and water capacity (96.6%; 152,334 m3/d).

5.4 2013 data


supplies5; three LAs failed to respond. Subsequently, the 2013 dataset was supplemented

with data from 2011 or 2012 for these three LAs to provide a „complete‟ picture of the nature

and type of private supplies in the UK6 (DWI, 2014).

In total for England and Wales, 48,274 private supplies were identified [England 34,221;

Wales 14,053]. A large number of these private supplies served single domestic dwellings

(SDDWs) [England 18,976 (55%); Wales 11,571 (82%)].

Local authorities are not generally required to risk assess or monitor SDDWs, and so less is

known about these supplies. The remaining 17,035 supplies [England 14,553; Wales 2,482]

require risk assessment and monitoring. Data for these monitored supplies show that 567,007

people [England 494,759; Wales 72,248] were reliant on private supplies. Upwards of 8

million people [England 7,759,937; Wales 270,398] were exposed to temporary private

supplies when attending leisure events, such as shows, concerts, etc.

The private supplies data submitted to DWI for 2013 did not include details of treatment so it

was not possible to identify supplies using UV treatment.

5.5 Nitrate and bromate

Data were provided for 2011, 2012 and 2013 identifying private supplies containing nitrate

and bromate. Summaries of supplies where nitrate and bromate equalled or exceeded

regulatory standards7 are given in Tables 5.5 and 5.6.

5 Sixty-nine councils reported no private water supplies.

6 In total, 72,312 private supplies were identified for the UK including those serving single domestic

dwellings (SDDWs).

7 Nitrate 50 mg/l; bromate 10 µg/l (DWI, 2009).

DWI


© WRc plc 2015 39

Table 5.5 Private supplies: Nitrate (mg/l)

Local Authority 2011 2012 2013

Max Mean Max Mean Max Mean

Amber Valley 75.3 52.1 51.4 35.0 - -

Anglesey 123 24.7 80.5 22.3 80.9 17.6

Arun 85.1 55.2 77.1 31.1 - -

Babergh 113 11.3 52.9 5.96 68.2 10.5

Basingstoke & Deane - - 55.6 34.0 78.8 47.2

Braintree 83.0 27.1 150 37.5 84.0 29.3

Breckland 248 23.8 - - - -

Broadland 135 21.2 - - 86.9 18.5

Calderdale - - 65.6 7.55 73.1 6.70

Carmarthenshire 81.0 14.4 - - - -

Ceredigion 76.0 11.8 90.0 10.5 207 10.6

Cherwell 82.0 24.7 70.8 64.6 76.3 32.6

Cheshire East 78.7 13.5 108 15.6 70.4 12.7

Chichester 61.2 35.66 - - - -

Colchester - - 97.5 48.5 139 64.5

Cornwall 65.4 19.3 141 25.3 169 17.5

Cotswold 99.4 43.5 - - 104 30.4

Dacorum - - - - 63.4 36.3

Daventry 67.3 36.6 - - - -

Denbighshire 128 9.76 64.1 12.9 81.5 13.5

Derbyshire Dales 59.9 19.5 68.7 16.2 67.1 20.5

Doncaster - - 55.5 37.0 89.7 44.8

Durham 58.0 5.64 - - - -

East Devon 122 26.4 311 15.5 85.0 28.5

East Dorset - - - - 65.8 38.4

East Hampshire 54.2 27.0 62.0 22.6 129 32.6

East Hertfordshire - - 108 24.2 - -

East Lindsey 93.7 15.36 60.7 21.4 90.0 14.9

East Northamptonshire - - 56.9 21.2 - -

East Riding of Yorkshire 61.2 23.1 74.3 29.6 80.0 25.9

DWI


© WRc plc 2015 40



Eden 53.0 5.68 - - - -

Fareham - - 50.3 50.3 - -

Forest Heath - - 50.0 35.9 134 45.9

Gedling 72.2 24.3 - - 76.8 37.0

Guildford 67.0 67.0 65.4 63.9 67.1 49.9

Hambleton 53.2 9.55 - - - -

Harrogate 110 19.5 62.0 30.8 110 29.1

Herefordshire 176 33.0 177 35.2 168 35.5

Hertsmere 62.8 45.9 56.0 41.0 52.8 50.8

Horsham 55.0 31.3 - - 51.3 23.4

Kings Lynn & West

Norfolk

81.7 56.5 74.0 47.4 86.1 56.7

Leeds City - - 50.7 8.92 - -

Liverpool 66.8 54.7 - - - -

Malvern Hills 108 26.5 73.0 18.1 53.2 16.0

Melton - - - - 97.0 49.9

Mendip 61.0 23.0 51.0 22.4 54.0 23.9

Mid Sussex 62.9 56.4 53.5 53.5 - -

Neath & Port Talbot - - - - 150 20.6

Newcastle under Lyme - - 160 70.0 - -

New Forest - - - - 58.0 30.4

North Devon 63.9 12.3 55.4 13.9 53.2 12.4

North East Derbyshire 57.6 10.9 - - 51.0 10.1

North East Lincolnshire 55.6 22.2 - - 52.2 19.4

North Hertfordshire - - 80.4 31.0 - -

North Kesteven 64.6 10.9 - - - -

North Norfolk 129 18.6 121 19.0 130 18.7

North Somerset 64.0 23.8 - - - -

North Warwickshire - - - - 93.4 47.9

Northumberland - - - - 79.0 15.3

Norwich City 50.5 24.9 - - 53.2 25.8

NW Leicestershire 68.4 48.9 - - - -

DWI


© WRc plc 2015 41



Pembrokeshire 264 23.6 - - - -

Peterborough City 125 45.3 - - - -

Purbeck - - - - 83.4 25.6

Richmondshire - - 65.4 15.6 53.3 18.5

Rutland - - - - 89.1 59.3

Ryedale 60.9 30.5 81.2 38.8 54.2 36.4

Scarborough - - 64.0 11.2 51.0 6.62

Sedgemoor 64.3 21.3 198 46.3 80.6 33.4

Selby - - - - 98.0 11.1

South Cambridgeshire 53.0 40.1 51.7 39.5 50.8 41.6

South Derbyshire 80.0 55.0 - - - -

South Gloucestershire 75.0 33.5 - - - -

South Hams 76.5 28.4 81.0 29.2 87.3 25.9

South Norfolk 103 14.1 172 22.4 120 26.1

South

Northamptonshire

71.9 44.7 60.7 29.9 74.2 34.9

South Oxfordshire - - 116 30.1 123 34.8

South Somerset 160 50.2 140 45.4 120 52.5

St Edmundsbury 80.4 38.1 97.0 14.7 109 39.4

Stafford - - - - 92.0 48.5

Staffordshire Moorlands 85.0 19.8 - - - -

Stratford-on-Avon - - 75.1 34.7 75.1 25.4

Suffolk Coastal 150 42.3 240 56.1 110 27.3

Taunton Deane 108 28.9 54.0 17.2 157 28.7

Teignbridge - - 86.8 11.1 - -

Telford & Wrekin 127 82.9 145 42.6 192 40.4

Test Valley 93.6 39.9 89.0 39.8 100 43.5

Tewkesbury 74.7 20.1 82.7 28.0 70.5 32.0

Uttlesford - - 72.0 35.1 76.0 29.9

Vale of White Horse 120 47.5 68.4 26.7 86.7 28.4

Welwyn Hatfield 57.6 38.6 66.4 57.9 81.2 70.3

West Devon - - 120 12.9 70.5 9.27

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West Oxfordshire 70.0 47.5 51.0 37.8 108 34.4

West Somerset 58.0 27.0 59.0 32.9 - -

Wiltshire 65.9 17.4 131 23.0 169 25.0

Winchester City 77.5 38.1 75.7 33.6 79.7 39.9

Wolverhampton 98.1 84.2 99.2 98.9 99.0 89.7

Wychavon 65.5 43.6 50.4 28.6 - -

Wyre Forest 60.2 52.9 - - - -

Table 5.5 shows that over the period 2011 to 2013, ninety-nine LAs reported concentrations

of nitrate in private supplies above the drinking water standard. Whilst this in itself is a

concern, the number of these supplies that use UV treatment is unknown. There is a

possibility that nitrate in source waters could be converted to nitrite by MP UV, but MP lamps

are typically shrouded to avoid formation of nitrite, and MP UV is probably used rarely on

private supplies other than possibly on some larger commercial supplies.

Table 5.6 Private supplies: Bromate (µg/l)



Babergh 16.1 1.97 - - - -

East Hampshire - - - - 15.0 1.31

Horsham - - 17.7 2.70 11.4 1.91

Northumberland - - 12.0 2.07 - -

Powys - - 10.5 10.5 - -

South Oxfordshire - - 23.1 4.02 - -

Tunbridge Wells - - - - 14.7 7.45

Vale of White Horse - - - - 10.0 3.63

West Devon - - - - 10.7 10.0

Westminster 10.0 10.0 - - - -

Table 5.6 shows that over the period 2011 to 2013, ten LAs reported concentrations of

bromate in private supplies above the drinking water standard. Bromate is not generally found

in source waters but is formed by the oxidation of bromide. The literature shows that bromate

has been formed in chlorinated waters exposed to UV (either from UV lamps or natural

sunlight). It is unlikely that chlorine–UV is used on private supplies other than possibly on

some larger commercial supplies.

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5.6 Conclusions

UV treatment

In 2011 and 2012, less than 100% of LAs reported private supplies data to DWI. As a result -

and as identification of UV treatment was not compulsory - the data for this period

underestimates the full extent of UV treatment of private supplies.

The LA response to DWI gave no indication as to the design or performance of installed UV

treatment. If inadequately designed or maintained, UV units may be providing greater or

lesser than design doses. If UV doses lower than typical disinfection doses are applied

(including no dose), disinfection could be compromised which would be a greater concern

than the small risk of formation of DBPs.

In 2011 and 2012, around 55-60% of drinking water from UV treated private supplies was

sourced from boreholes influenced by surface water accounted for. Boreholes influenced by

surface water - and surface waters - are more susceptible to contamination, particularly from

microorganisms, organic precursors, nitrate and bromide (the latter two are also possible

contaminants of groundwaters). No respondents reported the use of estuarine or brackish

water sources.

Private supplies used for commercial purposes account for substantial percentages of

persons served and water capacity. In 2011 and 2012, UV treated private supplies for

commercial purposes accounted for 90% of persons served and 97-98% of water capacity.

In 2013, private supplies data submitted to DWI did not include details of treatment so it was

not possible to identify supplies using UV treatment.

Nitrate and bromate

Nitrate data for private supplies show that over the period 2011 to 2013, ninety-nine LAs

reported nitrate exceeding the drinking water standard (50 mg/l). These data were not

correlated to supplies treated by UV. Whilst exceedance of the nitrate standard is of concern,

it is unlikely that formation of nitrite (from nitrate) is a significant risk for private supplies

treated by UV.

Bromate data for private supplies show that over the period 2011 to 2013, ten LAs reported

bromate exceeding the drinking water standard (10 µg/l). These data were not correlated to

supplies treated by UV. Whilst exceedance of the bromate standard is of concern, it is unlikely

that formation of bromate (from bromide) is a significant risk for private supplies treated by

UV.

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6. Health Significance

6.1 Introduction

Toxicological implications for the DBPs identified in the literature review have been identified

and used to provide a measure of impact for UV treatment in public supplies and private

supplies.

There is, at present, little toxicological information on the vast majority of DBPs that have

been identified. However, the in vitro cytotoxicity and genotoxicity studies of Plewa et al.

(2012) and others have investigated the DBPs which have the potential to be formed by

reaction of chlorine and organic material with UV and these studies give an indication of

cytotoxic and genotoxic potential; increased cytotoxicity was demonstrated by the observation

of cell death in the cultured cells used in the in vitro assays, and increased genotoxicity was

demonstrated by the observation of DNA/genetic damage. These studies are described

below.

In addition, sufficient toxicological data have been located for the specific DBPs identified

through the literature review to be formed under conditions relevant for treatment in the UK,

enabling the derivation of guidance values.

6.2 Cytotoxicity and genotoxicity studies

Plewa et al. (2012) investigated whether mammalian toxicity varied in response to different

chlorination protocols, with and without LP UV (monochromatic low pressure UV) or MP UV

(polychromatic medium pressure UV) radiation (average dose 300 mJ/cm2 for both). Samples

were obtained from a pilot unit at the Ohio River Plant of the Greater Cincinnati Water Works

in the USA, and the transgenic Chinese Hamster Ovary (CHO) cell line AS52 was used for

both cytotoxicity and genotoxicity assays.

First the water quality of the samples was examined. Some nitrite formation occurred through

the MP UV unit. No difference was observed in the simulated distribution total organic

halogens (SD-TOX) between pilot influent and LP UV treated effluent (with or without

chlorine). SD-TOX of MP UV treated effluent was 30% higher than the pilot influent, where

this was increased by a further 19% when chlorine was added prior to MP UV treatment.

Cytotoxicity assays showed that, after chlorination, water samples were twice as cytotoxic as

those treated with GAC alone. Treatment with MP UV or LP UV alone reduced the cytotoxicity

(by 42 and 65%, respectively) and the authors concluded that the UV radiation degraded

some of the cytotoxic agents in the GAC-treated source water. Subsequent chlorination of UV

treated samples increased the cytotoxicity. The most cytotoxic sample of the entire study was

formed by the combination of LP UV followed by chlorination.

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There was a significant correlation (P<0.001) between cytotoxicity and genotoxicity. As with

cytotoxicity, chlorination of GAC-treated source water increased the genotoxicity and the

genotoxicity of the source water was reduced or eliminated with MP UV or LP UV,

respectively. Also as with cytotoxicity, chlorination in addition to UV treatment increased the

genotoxicity to above that of the GAC-treated source water. The highest level of genotoxicity

was observed with LP UV treatment and subsequent chlorination, where this level was higher

than that of chlorination alone. The authors concluded that UV plus chlorination-mediated

generation of specific classes of DBPs was the basis for the distribution of genotoxicity rather

than a general increase of TOX.

In conclusion, the lowest levels of cytotoxicity and genotoxicity were observed with

GAC-treated water exposed to UV treatment alone. With combined chlorination and UV

treatment, the lowest levels of cytotoxicity and genotoxicity were observed with

chlorination followed by MP UV radiation (Plewa et al., 2012).

In a study conducted by Lyon et al. (2014), the formation and cytotoxicity of DBPs in water

was investigated following treatment of natural organic matter (NOM) concentrates. The use

of concentrated NOM conserved volatile DBPs and allowed for direct analysis of the treated

water. Samples were treated with either MP UV radiation (dose 500 mJ/cm2; 550 W lamp)

followed by chlorine or chloramination, or with chlorination or chloramination alone, either with

or without nitrate or iodide spiking. Cytotoxicity assays were carried out using an in vitro

normal human colon cell (NCM460) assay. UV treatment prior to chlorination (unspiked

samples) did not affect cytotoxicity compared to chlorination alone, when toxicity was

expressed on the basis of dissolved organic carbon (DOC); this is contrary to the effects

observed by Plewa et al. (2012). However, nitrate-spiked UV and chlorination treated samples

were of greater cytotoxicity than nitrate-spiked samples treated with chlorine alone or

unspiked samples treated with UV and chlorine, on both a DOC and total organic halogen

basis. Cytotoxicity was also greater using samples treated with UV and chloramination

compared to chloramination alone, where the presence of iodide increased this further, using

either dose metric.

The authors concluded that the increased cytotoxicity observed was likely to be due to

a combination of factors, rather than a single DBP or class of DBPs. They also stated it

was likely that trichloronitromethane contributed to the increased cytotoxicity on the

basis of the DBPs analysed (Lyon et al., 2014).

Buchanan et al. (2006), investigated DBP formation, as well as the cytotoxicity and

mutagenicity of samples treated with UV or VUV (vacuum ultraviolet) photo-oxidation. Raw

surface water (SW) samples were collected from a reservoir system in Victoria, Australia.

Cytotoxicity assays were conducted using African green monkey kidney cells and

mutagenicity was examined using Ames assays in Salmonella typhimurium strains TA98,

TA100 and TA102. Cytotoxicity was not observed using samples treated with UV doses of

23-138 J/cm2 or with VUV doses of 16-160 J/cm

2, whilst cell death was reported in positive

controls. Similarly, mutagenicity was observed only in positive controls, other than one

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positive result in strain TA98 at a VUV dose of 16 J/cm2. This result was further investigated,

and various low doses of VUV (5, 11 and 16 J/cm2) did not lead to a mutagenic response. The

authors highlighted the fact that the radiation doses used in this study are much larger than

typical UV disinfection doses (40-100 mJ/cm2). In agreement with the results from this study,

Backlund (1992) reported that treatment of lake water (natural humic water) from Finland with

UV irradiation (254 nM) alone or in combination with hydrogen peroxide (H2O2) did not result

in mutagenic activity in Salmonella typhimurium strains TA97, TA98 and TA100 (Backlund,

1992; Buchanan et al., 2006).

In summary, no significant cytotoxicity or genotoxicity was observed with samples of

raw reservoir surface water treated with UV or VUV at doses of 23-138 and

16-160 J/cm2, respectively. The authors noted that the doses used in this study are

significantly higher than typical UV disinfection doses In a separate study, no

mutagenicity was observed with samples of lake water (natural humic water) treated

with UV or UV in combination with H2O2.

Martijn et al. (2014) attempted to trace nitrogenous DBPs (N-DBPs) formed after MP UV

treatment. Positive results were reported in an Ames test using strain TA98 without metabolic

activation, after MP UV/H2O2 treatment at a water treatment plant (WTP) in Heemskerk, The

Netherlands (doses not reported). Effluent from the first reactor showed a genotoxic response

2.5 times higher than influent treated with H2O2 alone. Effluent from subsequent reactors

(second to fifth) showed increasing positive responses, at levels slightly above those of the

positive control. A positive correlation was observed between the number of positive wells in

the Ames test and nitrite formation (due to photolysis of nitrate).

In a second study, bench-scale MP UV experiments were conducted using commercially

available artificial water (IHSS Pony Lake NOM) containing 2.5 mg C/l, either with or without

nitrate at a practical concentration of 10 mg NO3/l. In these experiments, UV doses of

40 mJ/cm2 (disinfection) or 600 mJ/cm

2 (UV/H2O2 treatment, with 6 ppm H2O2) were used,

and Ames tests were similarly carried out using strain TA98 without metabolic activation. The

response of MP UV treated water was similar to that of the blank, regardless of the treatment

protocol. However, the addition of nitrate led to an increase in the Ames response, where this

increase was greater with the UV AOP treatment (approximately 4-fold increase in response)

compared to the UV disinfection treatment (approximately 3-fold increase), although these

responses were still below that of the positive control.

In subsequent experiments, using the same artificial water (2.5 mg C/l) with 10 mg NO3/l

treated with MP UV at a dose of 600 mJ/cm2, many nitrogen-containing by-products were

detected following analysis by mass spectroscopy. The identities of three of these by-products

were confirmed to be 2-methyoxy-4,6-dinitrophenol, 4-nitrocatechol and 4-nitrophenol. Three

additional unconfirmed by-products were reported as 3-hydroxy-4-nitrobenzoic acid,

5-nitrovanillin and 2,4-dinitrophenol. Additional data showed that Ames response is increased

(both with and without metabolic activation) after MP UV treatment, but that after

“conventional” post-treatment the Ames response is reduced to below the level of that

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observed before MP UV treatment. This corresponds with an observed increase of nitrogen-

containing by-products after MP UV treatment, but a reduction in the level of by-products after

post-treatment (no further details available).

The data from this study indicate that the genotoxic responses observed in Ames

assays may be due to the sum of multiple nitrogen-containing by-products formed at

low concentrations after MP UV treatment of nitrate-containing waters. However,

conventional post-treatment appears to remove these genotoxic compounds that are

formed. Note that these results were reported at a conference presentation, and are not

yet available as a peer-reviewed publication, and therefore only limited details were

available.

Schmalz et al. (2014) investigated the effect of different treatment processes on DBP

formation, cytotoxicity and genotoxicity. Pilot swimming pool water (with added humic acid in

order to better simulate swimming pool conditions) was subjected to seven different treatment

protocols. These protocols and the results of the cytotoxicity and genotoxicity assays (assay

details not available) are shown in Table 6.1 (details of the assays used not reported).

Table 6.1 Toxicity for different treatment processes

Number Treatment protocol Cytotoxicity Genotoxicity

1 Coagulation (0.07 g/m

3 alum); Sand filtration;

GAC filtration; Chlorination (0.5 mg/l) - -

2 Coagulation; Sand filtration; LP UV (340 W/m

2);

Chlorination - +

3 Coagulation; Sand filtration; MP UV

(4,200 W/m2); Chlorination

(+) +

4 Coagulation; Ultrafiltration; LP UV; Chlorination + -

5 Coagulation; Ultrafiltration; MP UV; Chlorination + +

6 Coagulation; PAC (1.5 g/m

3, 40 seconds);

Ultrafiltration; Chlorination - -

7 Coagulation; PAC; Sand filtration; Chlorination - -

Notes:

- Negative; (+) Induction factor between 1.2 and 1.3; + Induction factor > 1.3

(control: tap water from Bad Elster, Germany).

No cytotoxicity or genotoxicity was observed with any of the control treatments, without UV.

Both cytotoxicity and genotoxicity were observed with the two protocols using MP UV (3 and

5; 4,200 W/m2) in combination with either sand filtration or ultrafiltration. With LP UV

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(340 W/m2), genotoxicity only was observed with protocol 2 (in combination with sand

filtration) and only cytotoxicity was observed with protocol 4 (in combination with

ultrafiltration). Levels of the DBP trichloramine were significantly increased using protocols 3

and 5, with MP UV (approximately 4-fold increase). Levels were also increased with

protocols 2 and 4, with LP UV treatment, but by a lower amount (approximately 3- and 1.5-

fold increases, respectively).

In summary, the use of UV treatment (particularly MP UV) led to an increase in the

cytotoxicity and genotoxicity of pilot swimming pool water, and in levels of the DBP

trichloramine. These results further elucidate the effects observed by Plewa et al.

(2012) with UV treatment and chlorination. Note that these results were reported at a

conference presentation, and are not yet available as a peer-reviewed publication, and

therefore only limited details were available.

Zoeteman et al. (1982) compared alternatives to chlorine for the disinfection of stored River

Rhine water in a pilot-plant study. Using the Ames assay and Salmonella typhimurium strain

TA98 (with and without metabolic activation), increased mutagenicity was observed after

treatment with either chlorine dioxide or chlorine, but ozonation reduced the mutagenic

activity. When UV was applied at a dose of 120 mJ/cm2, no significant change to mutagenicity

was observed relative to the untreated raw water, and no significant mutagenicity was

observed with any treatment using strain TA100.

A study by Heringa et al. (2011) aimed to investigate the genotoxicity of water following

UV/H2O2 treatment and GAC filtration. Pre-treated surface water from three locations (two in

The Netherlands and one in Ohio, USA) was treated with MP UV/H2O2 followed by GAC

treatment. Samples were taken before and after each treatment step, and genotoxicity was

examined (with and without metabolic activation) using the Comet assay in HepG2 human

liver cells and in the Ames II assay (a modified version of the classic Ames assay).

Pre-treatment protocols varied between locations: At the US site, pre-treatment consisted of

coagulation (aluminium sulphate and polyDADMAC8), sedimentation, pH correction (calcium

oxide) and rapid sand filtration; the first site in The Netherlands used coagulation (iron

sulphate), sedimentation, microsieves and rapid sand filtration, and the second site used a

2-6 day reservoir residence time followed by coagulation (iron chloride sulphate),

sedimentation and rapid sand filtration.

No genotoxicity was observed in any water sample following MP UV/H2O2 treatment in either

the Comet assay or the Ames II assay using the strain TAMix, which is a combination of six

different strains. However, significant increases in mutations (described as “low genotoxicity”)

were observed with the TA98 strain both with (one location) and without (all three locations)

metabolic activation. Genotoxicity was also observed using samples treated only with MP UV,

8 Cationic polymer (poly-diallyldimethylammonium chloride).

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to a higher level than those treated also with H2O2. The authors indicated that the observed

response in strain TA98 but not TAMix indicated that the compounds in the samples were

generating frame-shift mutations, rather than base-pair substitutions. Subsequent GAC

treatment of MP UV/H2O2 treated water reduced genotoxic activity to the level of the negative

control in samples from two of the three locations. Whilst a slight genotoxic response was still

observed in strain TA98 (with metabolic activation) using the sample from the third location,

this response was less than was observed in the sample which did not undergo GAC

treatment. Preliminary results using samples from two of the locations showed a much lower

or no genotoxic response following LP UV/H2O2 treatment, compared to MP UV/H2O2

treatment.

The authors concluded that the observed genotoxic response in water samples from

three different locations indicated that the genotoxic compounds were formed from

ubiquitous water components, such as NOM. It was also concluded that no health risks

are expected provided that UV/H2O2 treatment is followed by GAC filtration. The

authors also noted that the UV dose usually applied during disinfection is typically 10-

15 times lower than the dose used in this study (Heringa et al., 2011).

Micronucleus assays have also been used to characterise the mutagenic response following

UV treatment, although, mixed results have been reported. Helma et al. (1994) reported a

dose-dependent increase in micronuclei in the Tradescantia plant using groundwater exposed

to UV under laboratory conditions (highest dose, 1500 J/m2 (150 mJ/cm

2)), where this

clastogenic response was only observed transiently with a reported half-life of approximately

1 day. However, following treatment of groundwater samples (from different locations in

Austria) with LP UV radiation (254 nm; 800 J/m2 (80 mJ/cm

2)), no genotoxic effects were

observed in micronucleus assays with the Tradescantia plant or primary rat hepatocytes. Only

one weak positive result was reported in an Ames assay with strain TA98 without metabolic

activation (negative in strains TA100 and TA102) (Haider et al., 2002).

The results discussed above are summarised in Table 6.2.

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Table 6.2 Summary of cytotoxicity and genotoxicity studies

Treatment protocol UV dose

(mJ/cm2)

Sample details Assay(s) Results Reference

UV 23-138 Raw SW from a

reservoir system in

Victoria, Australia

African green monkey

cells (cytotoxicity)

Ames assays in

Salmonella

typhimurium strains

TA98, TA100 and

TA102 (genotoxicity)

No cytotoxicity or genotoxicity in

treated samples.

Buchanan et al.,

2006

VUV 16-160 No cytotoxicity in treated samples.

One positive genotoxicity result in

strain TA98. When investigated

further, no positive results

observed at various low doses (5,

11, 16)

UV 120 Stored River Rhine

water

not reported No significant change in

mutagenicity, compared to

untreated water

Zoeteman et al.,

1982

GAC + MP UV or LP

UV

300 (average) From a pilot unit at the

Ohio River Plant

(Greater Cincinnati

Water Works, USA)

Chinese Hamster

Ovary cell line AS52

(cytotoxicity and

genotoxicity)

Reduced cytotoxicity and

genotoxicity compared to GAC

treatment alone

Plewa et al., 2012

GAC + Cl2

GAC + MP UV + Cl2

GAC + LP UV + Cl2

Increased cytotoxicity and

genotoxicity compared to GAC

treatment alone

Most cytotoxic sample:

GAC + LP UV + Cl2

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(mJ/cm2)


MP UV + Cl2

(unspiked)

500 NOM concentrates normal human colon

cell (NCM460) assay

(cytotoxicity only)

No effect on cytotoxicity compared

to Cl2 alonea.

Lyon et al., 2014

MP UV + Cl2

(nitrate-spiked)

Greater cytotoxicity than unspiked

samples, or nitrate-spiked

samples with Cl2 aloneb.

MP UV + chloramine Greater cytotoxicity compared to

chloramine alone; further

increased by iodide spiking.

UV (254 nm)

UV + H2O2

not reported Lake water (natural

humic water) from

Finland

Ames assays in

Salmonella

typhimurium strains

TA97, TA98 and

TA100

No mutagenic activity with either

treatment condition

Backlund, 1992;

cited in Buchanan

et al., 2006

MP UV + H2O2 not reported WTP in Heemskerk,

The Netherlands

Ames assays in

Salmonella

typhimurium strain

TA98 (without

metabolic activation)

Increasing genotoxic response

with effluent from 1st-5th reactors;

greater than influent treated only

with H2O2

Martijn et al., 2014

MP UV

MP UV + H2O2

40

600

Artificial water (IHSS

Pony Lake NOM)

Genotoxic response on the

addition of nitrate

MP UV 600 Genotoxic response reduced

following post-treatment

Coagulation + sand

filtration + LP UV +

chlorination

340 W/m2 Pilot swimming pool

water (with added

humic acid)

No details reported Increased genotoxicity

Negative for cytotoxicity

Schmalz et al.,

2014

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(mJ/cm2)


Coagulation +

ultrafiltration + LP UV

+ chlorination

Increased cytotoxicity

Negative for genotoxicity

Coagulation + sand

filtration/ultrafiltration

+ MP UV +

chlorination

4,200 W/m2 Increased genotoxicity and

cytotoxicity

No cytotoxicity or genotoxicity

when using the three protocols

without UV

MP UV/H2O2 400 (Ohio site);

550 or 560 (two

sites in The

Netherlands,

respectively)

Pre-treated SW from

three locations (two in

The Netherlands and

one in Ohio, USA)

Comet assay in

HepG2 human liver

cells and Ames II

assay using strains

TA98 and TAMix

(genotoxicity)

No genotoxicity in comet assay or

TAMix. Low genotoxicity in TA98

Heringa et al.,

2011

MP UV only Genotoxicity observed, to a higher

level than with H2O2 treatment

MP UV/H2O2 + GAC Reduced genotoxicity compared

to samples without GAC treatment

LP UV/H2O2 (two

locations only)

Lower or no genotoxic response

compared to MP UV/H2O2

treatment.

UV (laboratory

conditions)

1,500 (highest

dose)

GW Micronucleus assay in

the Tradescantia

plant.

Transient dose-dependent

increase in micronuclei (half-life of

approximately 1-day).

Helma et al., 1994

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(mJ/cm2)


LP UV (254 nm) 800 GW from various

locations in Austria

Micronucleus assay in

the Tradescantia plant

and primary rat

hepatocytes; Ames

assay in strains TA98,

TA100 and TA102

No micronuclei formation

observed.

Weak positive genotoxic response

in strain TA98 without metabolic

activation (negative in strains

TA100 and TA102).

Haider et al., 2002

UV 23-138 J/cm2 Raw SW from a

reservoir system in

Victoria, Australia

African green monkey

cells (cytotoxicity)

Ames assays in

Salmonella

typhimurium strains

TA98, TA100 and

TA102 (genotoxicity)

No cytotoxicity or genotoxicity in

treated samples.

Buchanan et al.,

2006

VUV 16-160 J/cm2 No cytotoxicity in treated samples.

One positive genotoxicity result in

strain TA98. When investigated

further, no positive results

observed at various lower doses

(5, 11 and 16 J/cm2)

Notes:

a: When expressed on the basis of dissolved organic carbon (DOC).

b: On both a DOC and total organic halogen basis.

NOM: Natural organic matter.

VUV: Vacuum ultraviolet.

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6.3 Derivation of guidance values

In addition to searching for studies investigating the changes in cytotoxicity and mutagenicity

upon using different UV treatment protocols, guidance values have also been derived for

specific DBPs of concern that were identified through the literature review (Task 1) to be

formed under conditions relevant for treatment in the UK (Table 6.3). The specific DBPs

identified were bromate, chloral hydrate, chloropicrin, cyanogen chloride and nitrite.

Standards are available in the UK for bromate and nitrite, and so these have been used as

the respective guideline values. The World Health Organization (WHO) has set health-based

values for both chloral hydrate and cyanogen chloride. These are not formal guidelines, but

can nevertheless be used for guidance purposes, to give an indication of the levels below

which adverse health effects are not anticipated.

There are currently no drinking water standards available for chloropicrin in the UK, and WHO

has not derived a Guideline for Drinking-water Quality (GDWQ) or any health-based values.

However, in 2011 the European Food Safety Authority (EFSA) derived an Acceptable Daily

Intake (ADI) for chloropicrin in food. Using this ADI as a Tolerable Daily Intake (TDI), a

guidance value for chloropicrin can be derived, assuming a 60 kg adult drinking 2 litres of

water per day and allocating 20% of the TDI to water. The use of 20% allocation is similar to

the lifetime exposure usually used in standards and guideline values derived by authoritative

bodies such as WHO.

Table 6.3 Guideline values for DBPs identified in the literature review

DBP Reference value TDI Guidance value

(µg/l)

Bromate - - 10 (UK standard;

DWI, 2012)

Chloral hydrate LOAEL

13.5 mg/kg bw/day

Based on a 2-year

drinking water study in

mice

0.0045 mg/kg bw/day

Derived by WHO

100 (WHO health-

based value but not

a formal guideline)a

Chloropicrin NOAEL

0.1 mg/kg bw/day

(EFSA, 2011)

Based on a 2-year

(chronic) rat study

0.001 mg/kg bw/day

(1 µg/kg bw/day)

(EFSA, 2011)

ADI derived by EFSA

6

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DBP Reference value TDI Guidance value

(µg/l)

Cyanogen chloride NOAEL

4.5 mg/kg bw/day

(cyanide)

Based on a 13-week

drinking water study in

rats

0.045 mg/kg bw/day

(as cyanide)

reported to correspond

to 0.11 mg/kg bw/day

as cyanogen chloride

600 (as cyanogen

chloride; WHO

health-based value

but not a formal

guideline)b

Nitrite - - 500 (UK standard;

DWI, 2012)c

Notes:

a: In 2005, WHO calculated a health-based value of 100 µg/l for chloral hydrate based on 80% allocation of the TDI

to water (since most exposure to chloral hydrate is from drinking water). However, since they reported that chloral

hydrate usually occurs in drinking water at concentrations well below those of health concern, they did not set a

formal guideline value (WHO, 2005; 2011).

b: In 2009, WHO reported that cyanogen chloride occurs in drinking-water at concentrations well below those of

health concern. Therefore, WHO did not derive a formal guideline value, but instead they derived a health-based

value based on cyanide, for guidance purposes (WHO, 2011).

c: 100 µg/l at the treatment works.

ADI: Acceptable Daily Intake.

EFSA: European Food Safety Authority.

NOAEL: No Observed Adverse Effect Level.

WHO: World Health Organization.

6.4 Conclusions

A number of in vitro studies have been conducted investigating changes in cytotoxicity and

genotoxicity following treatment with UV at a range of doses. Note that in vitro studies are

frequently used as useful screening tools where there is a lack of data from other sources.

However, as such, effects observed may not necessarily translate to in vivo effects, and

results should be interpreted with caution. In these particular studies, there has also been no

comprehensive identification of the chemicals formed which give rise to the observed effects

with UV, chlorination and/or NOM.

Conflicting results have been reported regarding the effect of UV treatment. In many cases,

no significant increase in genotoxicity or mutagenicity was observed. However, positive

responses have been demonstrated under certain conditions, for example with the use of high

doses (frequently higher than those typically used at treatment works), in the presence of

nitrate, and where UV treatment is used in combination with other treatment processes such

as chlorination. For example, the studies of Plewa et al. (2012) indicate the possibility of an

increase in cytotoxicity and genotoxicity where UV treatment is followed by chlorination, but

also show that reversing the order of these processes, i.e. chlorination followed by UV

treatment, reduces the cytotoxicity and genotoxicity observed with chlorination alone. Several

studies have also reported that post-treatment, for example with GAC, appears to reduce

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genotoxic compounds which may be formed during UV treatment and that no health risks are

expected provided that UV/H2O2 treatment is followed by GAC.

In addition, guidance values have been derived for specific DBPs identified through the

literature review to be formed under conditions relevant for treatment in the UK. UK standards

currently exist for bromate and nitrite, and the World Health Organization have derived health-

based values for chloral hydrate and cyanogen chloride which, whilst not formal guidelines,

give an indication of the concentrations below which adverse health effects are not

anticipated. A guidance value has also been derived for chloropicrin based on an Acceptable

Daily Intake (ADI) derived by the European Food Safety Authority (EFSA).

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7. Future Research

7.1 Public supplies

Existing operating and monitoring data from water treatment works with regard to UV

treatment and DBP formation is limited. In order to collate a more extensive dataset, a series

of laboratory- and/or pilot-scale tests is proposed that will provide a structured approach for

investigating UV-related DBPs formed under typical UK water treatment conditions.

Laboratory-scale tests should be adequate to investigate the formation of DBPs; pilot-scale

tests would provide more realistic results but would be much more expensive.

Three types of water should be investigated:

Upland surface water with moderate-high colour, including both high and low

manganese.

Lowland surface water, both river (with upstream sewage discharges) and reservoir

(high algae) derived.

Low TOC groundwater, with and without high manganese.

The reason for the inclusion of high manganese waters is to investigate the impact of

additional chlorination and pH increase for manganese removal.

For the surface waters, both organic DBPs and bromate should be investigated. For the

groundwaters, only bromate is of interest. Nitrite formation from nitrate by UV is already well

understood, so is not included in the investigations.

The proposed treatment stages and analyses for investigation are illustrated in Figures 7.1,

7.2 and 7.3, and are summarised in Table 7.1. For the lowland surface waters and

groundwater, both AOP UV/peroxide and disinfection UV are included; for the upland surface

water only disinfection UV is included because pesticide removal is rarely a main

consideration for this type of water. For some of the tests coagulation should be carried out at

both an optimal dose (determined from jar tests) and a sub-optimal dose to provide lower

TOC (and DBP precursor) removal. Final chlorination should be carried out with 1-hour and

24-hour contact times to simulate treatment and distribution conditions.

The lowland reservoir water tests include spiking of bromide, to investigate formation of

bromate and brominated THMs/HAAs, and iodide to investigate iodinated THM formation. The

groundwater tests include spiking of bromide to investigate bromate formation.

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Figure 7.1 Upland surface waters and treatment

adjustment (sodium hydroxide)(for manganese removal)

Upland surface water withhigh colour

Coagulation (optimal and

sub-optimal dose),clarification and filtration

Upland surface water withhigh colour and manganese

Coagulation (optimal dose)

and clarification

Chlorination and pH

Filtration UV disinfection

Chlorination with

1 hour and 24 hourscontact time

DBP measurement

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Figure 7.2 Lowland surface waters and treatments

Pre-ozonation

Lowland river water withupstream sewage inputs

Lowland reservoir withhigh algae

Lowland reservoir withhigh algae spiked with

bromide / iodide

GACAOP (UV/peroxide)

(* disinfection dose)

Ozonation

Coagulation (optimal and sub-optimal dose), clarification and filtration

*UV

DBP measurement

Chlorination with1 hour and 24 hours

contact time

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Figure 7.3 Groundwater and treatment

Chlorination /

filtration(for Mn removal)

Bromate measurement

Chlorination with1 hour and 24 hours

contact time

AOP (UV/peroxide)

(* disinfection dose)*UV

Bromide spike

Groundwater withlow TOC

Bromide spike

Groundwater withlow TOC and manganese

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Table 7.1 Summary of proposed small-scale investigations

Water type Water treatment DBPs of interest

Upland surface water with high

colour

Chemical coagulation, clarification, filtration, chlorination THMs, HAAs, bromate

Chemical coagulation, clarification, filtration, UV, chlorination

Upland surface water with high

colour and high manganese

Chemical coagulation, clarification, chlorination/pH increase, filtration,

chlorination

THMs, HAAs, bromate

Chemical coagulation, clarification, chlorination/pH increase, filtration,

UV, chlorination

Lowland river water with upstream

sewage inputs

Coagulation, clarification, filtration, chlorination THMs, HAAs, bromate, N-

containing DBPs Coagulation, clarification, filtration, UV, chlorination

Coagulation, clarification, filtration, ozonation, GAC, chlorination

Coagulation, clarification, filtration, ozonation, GAC, UV, chlorination

Lowland reservoir water with high

algae, with and without spiked

bromide and iodide

Coagulation, clarification, filtration, chlorination THMs, HAAs, bromate, N-

containing DBPs, iodinated DPBs Coagulation, clarification, filtration, UV, chlorination

Coagulation, clarification, filtration, ozonation, GAC, chlorination

Coagulation, clarification, filtration, ozonation, GAC, UV, chlorination

Each of the above preceded by preozonation

Low TOC groundwater with and

without spiked bromide

Chlorination Bromate

UV, chlorination

Low TOC groundwater with high

manganese, with and without

spiked bromide

Chlorination/pH increase, filtration, chlorination Bromate

Chlorination/pH increase, filtration, UV, chlorination

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7.2 Private supplies

The data currently collected by LAs and reported to the DWI has little value in terms of

evaluating risks of formation of DBPs as a result of UV treatment.

The DBPs of most concern would be nitrite (from nitrate for MP UV) and bromate (from

bromide in prechlorinated water), although the risk of formation of both would be small for

well-designed systems.

Risk assessments carried out by LAs should aim to identify private supplies most at risk of

failing to meet water quality standards, including potential formation of DBPs. It is proposed

that the information collected by LAs should identify:

Estuarine or brackish water sources9.

UV lamp type (LP or MP).

Supplies that are chlorinated prior to UV.

Concentrations of nitrate and bromate in drinking water9.

9 Data currently collected.

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8. Conclusions

8.1 Literature review

UV is dosed for disinfection at around 40 mJ/cm2 and in AOPs at an order of magnitude

greater.

Direct formation of nitrite (from nitrate) may occur at wavelengths below 240 nm, particularly

for MP UV, but lamps can be treated to block these wavelengths.

Where chlorination is followed by UV, there is evidence of bromate formation if bromide is

present in the chlorinated water.

Where UV at doses typically used for disinfection is followed by chlorination, there is some

evidence of increased formation of chloropicrin, bromopicrin, cyanogen chloride, chloral

hydrate, and halonitromethanes.

Where UV at doses typically used for AOPs is followed by chlorination, there is some

evidence of increased THMFP but conflicting research also indicates reduced formation of

halogenated organic DBPs.

8.2 Public supplies

A questionnaire survey identified 89 UV plants (existing and proposed) from returns from 16

water companies (including 6 nil returns) with a total UV treatment capacity of 1,492 Ml/d. The

UV treatment capacity represents approximately 23% of the production capacity of the ten

companies utilising UV (between 3-100% of capacity).

UV treatment is used mostly where there is a Cryptosporidium risk and for general

disinfection, with a much smaller usage in AOPs.

UV is used most widely at small groundwater sites, although a greater water volume is treated

by fewer large UV plants at lowland surface water sites. There is little implementation of UV

for upland water sources.

8.2.1 Effects of UV dosage and/or pre-oxidation

Operating and monitoring data from five water treatment works were analysed to evaluate any

effects of UV dosage and/or pre-oxidation. Generally, available data were limited and few

conclusions regarding effect on DBP formation can be made.

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Bromate in excess of the drinking water standard (10 µg/l) had been detected at one works

due to treatment of prechlorinated water containing greater than 100 µg/l bromide with UV at

over 100 mJ/cm2; the high UV dose resulted from operation at less than the design flow rate.

No significant effects on DBP formation were observed as a result of high-dose UV, although

possible enhanced formation of brominated THMs was noted at one works.

8.3 Private supplies

The full extent of UV treatment of private supplies is unclear from LA returns to DWI. In 2013,

private supplies data submitted to DWI did not include details of treatment so it was not

possible to identify supplies using UV treatment.

The LA returns to DWI for 2011 and 2012 gave no indication as to the design or performance

of installed UV treatment. It is unlikely that formation of DBPs is a significant risk for UV

treated private supplies. If UV doses lower than design doses are applied, disinfection could

be compromised which would be of greater concern than the small risk of formation of DBPs.

In 2011 and 2012, boreholes influenced by surface water accounted for the largest

percentage of UV treated water capacity. Boreholes influenced by surface water - and surface

waters - are more susceptible to contamination, particularly from microorganisms, organic

precursors, nitrate and bromide.

UV treated private supplies used for commercial purposes account for substantial

percentages of persons served and water capacity. In 2011 and 2012, UV treated private

supplies for commercial purposes accounted for 90% of persons served and 97-98% of water

capacity.

8.4 Health effects

Conflicting results have been reported regarding the effect of UV in water treatment. In many

cases, no significant increase in genotoxicity or mutagenicity was observed. However,

positive responses have been demonstrated under certain conditions, for example with the

use of high UV doses (frequently higher than those typically used at treatment works), in the

presence of nitrate, and where UV treatment is used in combination with other treatment

processes such as chlorination. Several studies have also reported that post-treatment, for

example with GAC, appears to reduce genotoxic compounds which may be formed during UV

treatment.

Guidance values have been derived for specific DBPs formed under conditions relevant for

water treatment in the UK, giving an indication of the concentrations below which adverse

health effects are not anticipated.

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Glossary of Terms

ADI Acceptable daily intake

AOC Assimilable organic carbon

AOP Advanced oxidation process

AOX Adsorbable organic halide

BDOC Biodegradable dissolved organic carbon

CNCl Cyanogen chloride

DBP Disinfection by-product

DBAA Dibromoacetic acid

DCAA Dichloroacetic acid

DOC Dissolved organic carbon

DOM Dissolved organic matter

DWI Drinking Water Inspectorate

EFSA European Food Safety Authority

GC-NPD Gas chromatograph – nitrogen phosphorus detector

GC-MS Gas chromatograph – mass spectrometer

H2O2 Hydrogen peroxide

HAA Haloacetic acid

HAN Haloacetonitrile

LC-MS Liquid chromatograph – mass spectrometer

LP Low pressure (UV lamp)

MBAA Monobromoacetic acid

MCAA Monochloroacetic acid

MP Medium pressure (UV lamp)

N-DBP Nitrogenous disinfection by-product

NOAEL No observed adverse effect level

NOM Natural organic matter

O3 Ozone

OSEGC On-site electrolytic generation of chlorine

PACl Polyaluminium chloride

SUVA Specific UV absorbance (UV254/DOC)

TBAA Tribromoacetic acid

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TCAA Trichloroacetic acid

TCP Trichlorpropanone

THM Trihalomethane

THMFP THM formation potential

TiO2 Titanium dioxide

TTHMs Total THMs (regulated)

UV Ultraviolet

UV254 UV with a wavelength of 254 nm

VUV Vacuum ultraviolet

WHO World Health Organization

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Appendix A Literature Review

A1 Effect of UV used for disinfection

A1.1 UV lamps

Unless stated otherwise, the literature citations refer to UV reactors with germicidal lamps.

Low pressure (LP) germicidal lamps emit essentially monochromatic UV at 254 nm. Medium

pressure (MP) germicidal lamps normally emit within the range 200–400 nm.

A1.2 Effect of UV on organics

Photolysis of natural organic matter (NOM) can break bonds, resulting in smaller molecules

that are more assimilable for bacteria. The potential therefore exists for UV irradiation to

increase the biodegradability of the NOM, and thus potential for regrowth. UV absorbance is

greater in the 200–230 nm wavelength range than at 254 nm, so this is potentially a greater

issue with MP than LP (Ijpelaar et al., 2007).

Malley et al. (1995) applied LP UV doses of 60–200 mJ/cm2

to a range of groundwaters,

untreated surface waters and treated (clarified or filtered) surface waters. No changes in

dissolved organic carbon (DOC) concentration or UV254 absorbance were observed. Three

techniques were used to assess the potential impact on regrowth potential: assimilable

organic carbon (AOC), biodegradable dissolved organic carbon (BDOC), and the proportion of

hydrophilic DOC – increases in any one of which might indicate increased regrowth potential.

AOC was analysed as two components, P17 and NOX; P17 AOC increased but NOX AOC

was unchanged; total AOC was unchanged because P17 AOC concentrations were much

lower than NOX AOC. BDOC increased in untreated surface waters but remained unchanged

in treated surface waters and groundwaters. The proportion of hydrophilic DOC increased in

treated surface waters and low-colour groundwaters but remained unchanged in high-

coloured waters (whether untreated surface water or groundwater).

Kashinkunti et al. (2004) investigated at bench scale the application of UV followed by

chlorination as a barrier against Cryptosporidium and viruses for a direct river abstraction

water treatment plant and as part of this study evaluated the impact of UV on AOC. At the

proposed point of application of UV at the treatment works the water had been subject to

coagulation, two stages of sedimentation, sand filtration and GAC filtration. LP and MP

collimated beam apparatus were used to apply doses of 40 to 140 mJ/cm2. No well-defined

trend in AOC formation was observed with respect to UV dose, and it was concluded that UV

„does not systematically alter the potential for microbial regrowth following treatment for the

limited conditions investigated‟.

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Ijpelaar et al. (2005) compared LP and MP UV at bench scale applied to a treated surface

water. For the same range of doses, 47–91 mJ/cm2, no significant increase in AOC was

observed for LP whereas for MP the AOC increased approximately in proportion to dose (c.

400% at 91 mJ/cm2). As a control measure for any such increase in AOC they suggested

installing GAC downstream of MP UV.

Ijpelaar et al. (2007) reviewed published data for evidence of AOC formation by UV. They

concluded that AOC formation is lower in LP reactors than MP, and that for MP doses

<100 mJ/cm2 the increase in AOC is unlikely to exceed 10 g/l.

Choi and Choi (2010) investigated the effects of UV on the characteristics of dissolved

organic matter (DOM), chlorine demand and THM formation. Samples were taken from a pilot

plant comprising 4 parallel UV reactors: germicidal MP and LP, each applying a dose of

40 mJ/cm2; dual-wavelength (185/254 nm) LP, applying (at different times) doses of 40 and

150 mJ/cm2; and broader spectrum MP (185–400 nm) applying a dose of 40 mJ/cm

2. The

feed water was filtrate from sand filters at a water treatment plant. Feed water DOC was in the

range 0.96–1.27 mg/l, UV254 1.4–2.2 m-1

, and SUVA (UV254/DOC) 1.45–1.73 l/mg.m. The

duration of the trials included dry and rainy seasons and „normal times‟; the authors noted that

in the rainy season the DOM tended to be of terrestrial origin, higher molecular weight, more

refactory and more hydrophobic; whereas in the dry season it tended to of algal and bacterial

origin, lower molecular weight relatively labile, and more hydrophilic.

DOC, UV254 and SUVA were unchanged after UV. AOC and the proportion of hydrophilic

DOC were also unchanged. Average DOM molecular weight was unaffected during the rainy

season and „normal times‟. However, in the dry season molecular weight was unaffected by

germicidal LP but decreased after the other reactors, in order (largest decrease to smallest):

dual LP (150 mJ/cm2) > broad spectrum MP > germicidal MP > dual LP (40 mJ/cm

2)

Citing other literature, the authors concluded that these observations were consistent with

lower wavelength (<200 nm) and higher wavelength (>280 nm) being able to break organic

bonds, in conjunction with the relatively UV-reactive dry season DOM.

A1.3 Formation of DBPs: Direct formation

A1.3.1 Mutagenicity

Zoeteman et al. (1982) compared alternatives to chlorine for the disinfection of stored River

Rhine water. LP UV was applied at a dose of 120 mJ/cm2. No significant change to

mutagenicity was observed relative to the untreated raw water.


water. For the same range of doses, 47–91 mJ/cm2, no change in mutagenicity was observed

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for LP whereas for MP it increased by c. 600% at the highest dose. However, at pilot scale,

MP UV applied to the same water over a similar dose range increased mutagenicity by c.

100%, a discrepancy which the authors were unable to explain.

A1.3.2 Nitrogenated by-products

Mole et al. (1997) used GC-NPD (nitrogen-phosphorus detector) and GC-MS scans to

investigate if UV can cause formation of nitrogen-containing organics. A LP dose of 6,600

mJ/cm2 was applied to river water samples with and without 50 mg/l NO3

- added nitrate. The

GC-NPD scans suggested some formation of nitrogen-containing compounds, but no specific

compounds were identified by GC-MS. They concluded that, overall, the results provided no

firm evidence of UV generating nitrogen-containing compounds.

Liberti et al. (2002) investigated the potential formation of nitro-phenols and nitroso-amines in

secondary- (clarified) and tertiary- (sand filtered) treated wastewater by UV disinfection. The

secondary effluent received a UV dose of 160 mJ/cm2, and the tertiary effluent a dose of

100 mJ/cm2. Comparisons of GC-MS spectra from samples before and after UV irradiation

showed no evidence of volatile DBP formation. In a further test, comparisons of LC-MS

spectra of a secondary-effluent sample before and after a UV dose of 25,000 mJ/cm2 showed

no evidence of non-volatile DBP formation. It was concluded that UV doses much higher than

the 100-160 mJ/cm2 are necessary to promote formation of the target by-products.

A1.3.3 Aldehydes and carboxylic acids

Malley et al. (1995) applied a LP UV dose of 130 mJ/cm2 to a range of groundwaters,

untreated surface waters and treated surface waters. The formation of up to 10 g/l

formaldehyde was observed in untreated, coloured surface waters and a highly-coloured

groundwater (50 oH). In treated surface waters, formaldehyde formation was in the range 1 - 2

g/l, and was below the detection limit in all other groundwaters. They commented that in

practice UV disinfection would not be appropriate for either untreated surface water or highly-

coloured groundwater.

Liu et al. (2002) applied a wide range of UV doses (0–6,360 mJ/cm2) using LP and MP lamps

to a synthetic drinking water containing c. 3 mg/l TOC. The possible production of two groups

of compounds known to affect biostability, aldehydes and carboxylic acids, was investigated.

No change to background concentration of aldehyde was observed at doses less than 500

mJ/cm2. Aldehyde concentrations were observed to increase at UV doses above 500 mJ/cm

2,

to a greater extent for MP than LP (concentrations approximately double). At the maximum

dose, 6,360 mJ/cm2, average aldehyde formation was 13 g/l for LP and 37 g/l for MP

(primarily formaldehyde and acetaldehyde). Neither LP nor MP UV was observed to increase

carboxylic acid concentration at doses less than 1,000 mJ/cm2. For higher LP doses, an

increase in carboxylic acid concentration was apparent but, because of scatter in the data, not

statistically significant. At the maximum dose, 6,360 mJ/cm2, MP UV generated between 100

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and 240 g/l carboxylic acids (primarily formic, acetic and oxalic). The authors noted that no

reduction in TOC had been observed during the tests.

A1.3.4 Nitrite

Nitrite is a photolysis product of nitrate. Nitrate absorbs UV mainly in the 200–240 nm

wavelength range, so nitrite formation is expected to be very limited in LP reactors but

potentially greater in MP reactors (Ijpelaar et al., 2007).

Malley et al. (1995) applied a LP UV dose of 130 mJ/cm2 to a range of groundwaters with

nitrate concentrations in the range 0.16–8.1 mg/l. They observed no change in nitrate

concentration and did not detect nitrite.

Mole et al. (1997) applied high (1,100–6,600 mJ/cm2) and low (60–120 mJ/cm

2) LP UV doses

to deionised water spiked with 50 mg/l NO3- across a pH range 5–8. At 1,100 mJ/cm

2,

maximum nitrite formation occurred at pH 8.1 (161 g/l NO2-) and was <100 μg/l at lower pH

(5.1 to 7.2), with an apparent minimum at pH 6.1 (59 g/l NO2-). Increasing the dose to 6,600

mJ/cm2 increased nitrite formation approximately in proportion to dose. At the low UV doses,

nitrite formation was below the limit of detection (which was relatively high for the analytical

method used, 33 g/l).


water. For the same range of doses, 47–91 mJ/cm2, and nitrate concentration in the range

13–15 mg/l NO3, no nitrite formation was observed for LP whereas for MP appreciable nitrite

was formed, approximately in proportion to dose (c. 0.8 mg/l at 91 mJ/cm2). However, at pilot

scale, MP UV applied to the same water over the dose range 25–200 mJ/cm2

generated only

about 5% of the nitrite reported at bench scale (c. 0.04 mg/l at 100 mJ/cm2), a discrepancy

which the authors were unable to explain.

Ijpelaar et al. (2007) cited examples of nitrite formation after LP and MP UV exposure. For LP

UV, 2 g/l NO2- after a dose of 25 mJ/cm

2, where nitrate concentration was 50 mg/l NO3

-; and

7 g/l NO2- after a dose of 120 mJ/cm


-. For MP

UV, 40 g/l NO2- after a dose of 70 mJ/cm


-;

and 20 g/l NO2- after a dose of 70 mJ/cm


-.

They noted that nitrite formation from MP UV can be appreciably reduced by providing the

lamps with quartz sleeves to block lower wavelengths. With a water containing 50 mg/l NO3-,

30 g/l NO2- formed after a dose of 50 mJ/cm

2 with lamps sleeved to block wavelengths below

235 nm, whereas 150 g/l NO2- formed with lamps that weren‟t sleeved. They further noted

that, for a given water, nitrite formation is approximately linear with increasing nitrate

concentration and increasing UV dose, and increases with increasing pH (from tests in the

range pH 7–9).

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A1.3.5 Bromate

Malley et al. (1995) applied a LP UV dose of 130 mJ/cm2 to a range of groundwaters with

bromide concentrations in the range 50–250 g/l. They observed no change in bromide

concentration and did not detect bromate.

Ijpelaar et al. (2007) stated that neither UV nor UV/H2O2 are able to convert bromide to

bromate.

Kishimoto and Nakamura (2012) investigated the formation of bromate by LP UV, hydrogen

peroxide and ozone individually and in combination. They observed no bromate formation

after irradiating a 150 g/l Br- solution for 30 minutes (UV dose not specified).

A1.3.6 Other

Zoeteman et al. (1982) compared GC-MS spectra before and after application of LP UV (dose

120 mJ/cm2) to stored River Rhine water and observed some formation of benzene (0.1 g/l

before UV, 1 g/l after) and toluene (not detected before UV, 3 g/l after).

Parkinson et al. (2001) assessed toxicity of water samples from two Australian reservoirs after

treatment by UV and UV/H2O2. UV and UV/H2O2 treated samples were found to be toxic to

Daphnia carinata, which was attributed to the release into solution of copper bound to NOM,

as evidenced by increases in concentrations of copper ions (the origin of the organically-

bound copper likely being the use of copper sulphate to control algae). The concentrations of

copper were well below the applicable water quality standard.

A1.4 Formation of DBPs: Effect of UV upstream of chlorination

Malley et al. (1995) compared DBP formation arising from chlorination and chloramination,

with and without prior exposure to LP UV doses of 60–200 mJ/cm2. The application of UV did

not affect subsequent THM, HAA or cyanogen chloride (CNCl) formation.

Kleiser and Frimmel (2000) reported a decrease of 7% in THM formation potential in filtered

River Ruhr water after exposure to LP UV in a recirculating apparatus after 30 minutes, and a

13% decrease after 240 minutes; no estimate of UV dose was given. Adsorbable organic

halide (AOX) formation potential decreased by 13% and 24%, respectively.

Liu et al. (2002) applied a wide range of UV doses (0–6,360 mJ/cm2) using LP and MP lamps

to a synthetic drinking water containing c. 3 mg/l TOC, and investigated THM and HAA

formation after subsequent chlorination. The synthetic water contained little bromide so

chlorinated species dominated the DBPs formed. No impact on THM formation was observed

at doses below 1,000 mJ/cm2, whether LP or MP. At a LP dose of 5,000 mJ/cm

2, THM

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formation increased by 15%, whereas with MP at the same dose THM formation decreased

by 29%; the authors, however, reported the presence of hydrogen peroxide in the MP test

(without commenting on why), so this decrease was influenced to an unknown extent by an

AOP effect. LP UV did not affect HAA formation at any dose. MP UV did not affect HAA

formation at doses below 1,000 mJ/cm2, but at c. 5,000 mJ/cm

2 reduced formation by

between 15 and 44%.

Kashinkunti et al. (2004) investigated at bench scale the application of UV followed by

chlorination as a barrier against Cryptosporidium and viruses for a direct river abstraction

water treatment plant and as part of this study evaluated the impact of UV on DBPs. At the

proposed point of application of UV at the treatment works the water had been subject to

coagulation, two stages of sedimentation, sand filtration and GAC filtration. LP and MP

collimated beam apparatus were used to apply doses of 40 and 140 mJ/cm2, then 2 mg/l

chlorine was dosed and left for 24 hours before sampling for chlorine residual, THMs, HAAs,

carboxylic acids, aldehydes and TOX. UV was found to have no effect on chlorine demand or

DBP formation, irrespective of UV dose or lamp type.

Chin and Berube (2005) applied UV doses in the range 130–1,600 mJ/cm2 to untreated lake

water (1.8 mg/l TOC; 3.7 mg/l CaCO3 alkalinity; pH 6.6) and observed no reduction in TOC,

and negligible reduction in formation potentials of chloroform and chlorinated HAAs during

subsequent chlorination. They cited other literature reporting results consistent with their own,

but also noted that other studies had observed UV to remove TOC or reduce THM formation

potential; these latter studies, however, had applied UV doses of 13,000 to 288,000 mJ/cm2,

and were, therefore, not at all representative of the typical potable water UV disinfection dose

of 40 mJ/cm2. They concluded that at practical doses UV has very little impact on the organic

constituents in raw water.

Liu et al. (2006) compared the effects of sequential combinations of UV and chlorine on

subsequent DBP formation. UV dose was 60 mJ/cm2, and chlorine was dosed at 7 mg/l free

chlorine. Contact times extended to 7 days to simulate time in distribution. The test matrix

included LP and MP lamps. The impact of UV was determined by comparing against control

tests which dosed only chlorine. Four waters were tested: three were synthetic – buffered

solutions of two commercially available humic acids and one natural organic matter (NOM)

concentrate in ultrapure water, each equivalent to 5 mg/l DOC - and one was a raw river

water (1.8 mg/l DOC). For three out of the four waters, chloroform formation increased when

UV was dosed, with (marginally) greater increases with MP than LP; for the other water,

formation was the same with and without UV. Chloroform formation with chlorine alone was

lowest in the only real water tested (c. 25 g/l after 72 hours) but UV had the greatest impact

in both proportional and absolute terms – the concentration was approximately doubled. In

two waters, UV increased both dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA),

again with greater increases observed with MP than LP; whereas for the other two waters,

DCAA and TCAA were increased by LP but decreased by MP. Chlorine without UV produced

4 to 6 g/l of cyanogen chloride (CNCl) after 7 days contact; in 6 out of 8 tests UV increased

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CNCl concentration, by between 2 and 8 g/l, while in the other 2 tests UV did not change the

concentration.

Choi and Choi (2010) investigated the effects of UV on the characteristics of dissolved

organic matter (DOM), chlorine demand and THM formation. Samples were taken from a pilot

plant comprising 4 parallel UV reactors: germicidal MP and LP, each applying a dose of

40 mJ/cm2; dual-wavelength (185/254 nm) LP, applying (at different times) doses of 40 and

150 mJ/cm2; and broader spectrum MP (185–400 nm) applying a dose of 40 mJ/cm

2. The

feed water was filtrate from sand filters at a water treatment plant. Feed water DOC was in the

range 0.96–1.27 mg/l, UV254 1.4–2.2 m-1

, and SUVA (UV254/DOC) 1.45–1.73 l/mg.m.

Germicidal UV had no effect on chlorine demand or THM formation at 4oC, but at 15

oC it

resulted in an increase in short-term chlorine demand (chlorine decay rate over the first

4 hours contact time increased by a factor of 2.5, but decay rate beyond 4 hours was

unchanged) and increased THM formation (up to 16.5%).

Reckhow et al. (2010) applied LP and MP doses of 40–140 mJ/cm2 to samples of treated and

raw water to determine the impact on DBP formation after subsequent chlorination. Neither

LP nor MP UV affected regulated (US) DBP formation (THM, HAA). Similarly, neither LP nor

MP UV affected formation of haloacetonitriles (HAN), trichlorpropanone (TCP). However,

whereas chloropicrin formation was unaffected by LP UV, it increased with increasing MP

dose; chloral hydrate formation also increased with increasing MP UV dose. Increasing nitrate

concentration was observed to increase formation of chloropicrin when MP UV was applied,

but not LP UV.

Shah et al. (2011) observed that LP UV at doses up to 1,500 mJ/cm2 did not enhance

halonitromethane formation after subsequent chlorination or chloramination, whereas MP UV

doses <300 mJ/cm2 increased chloropicrin formation by as much as an order of magnitude,

formation being greater after chlorination than chloraminaton. The combination MP

UV/chloramination enhanced haloacetonitrile (HAN) formation in a humic acid solution but not

in water samples collected from the field.

Lyon et al. (2012) subjected samples of water collected from a number of water treatment

works to a range of UV doses (LP and MP) followed by chlorination or chloramination. The

impact of the addition of bromide and nitrate was examined. THM and HAA formation were

not affected by disinfection UV doses of 40–186 mJ/cm2, but THM formation increased by 30–

40% at the higher UV dose of 1,000 mJ/cm2. Formation of some non-regulated DBPs

increased at disinfection UV doses. In the presence of nitrate (1–10 mg/l N), 40 mJ/cm2 MP

UV increased chloropicrin formation after chloramination by a factor of 2, and after

chlorination by a factor of 3–6; and in the presence of both bromide and nitrate, bromopicrin

formation after chlorination was increased by c.50 % by 40 mJ/cm2 LP UV and by a factor of

4–10 by 40 mJ/cm2 MP UV. In the presence of nitrate, MP UV doses of 186 and

1,000 mJ/cm2 increased cyanogen chloride formation after chloramination by factors of 2 and

3 respectively, although the concentration never exceeded the World Health Organization

guideline value of 70 g/l.

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Linden et al. (2012) investigated the impact of UV disinfection on the formation of regulated

and non-regulated DBPs. The project included a survey of full-scale UV installations across

North America, and experimental evaluation of DBP formation at bench-, pilot- and full-scale.

Elements of the project were reported by Shah et al. (2011) and Lyon et al. (2012). Overall

conclusions were, that UV doses <186 mJ/cm2:

do not alter chlorine demand (free or combined) to any practical extent;

do not alter THM and HAA formation to any practical extent;

are likely to increase halonitromethane formation, particularly when MP UV is applied,

and chloral hydrate formation (LP or MP), at the single g/l level;

will likely reduce to a small degree nitrosamine formation where chloramination follows

the UV.

and UV doses in the range 186–1,000 mJ/cm2:

increase subsequent chlorine/chloramine demand by up to 1 mg/Cl2/l (higher UV dose

corresponding to greater increase in demand) and correspondingly DBP concentrations

will generally be greater;

are likely to increase halonitromethane and chloral hydrate formation by a few g/l,

particularly when MP UV is applied;

will likely appreciably reduce nitrosamine formation where chloramination follows the

UV.

Chu et al. (2014) investigated the impact of pre-oxidation by LP UV, H2O2 and UV/H2O2 on the

formation of haloacetamides by subsequent chlorination. LP UV at doses in the range 19.5-

585 mJ/cm2 did not change formation relative to no pre-oxidation.

A1.5 Formation of DBPs: Effect of UV downstream of chlorination

Wong (1980) demonstrated that exposure of chlorinated sea water to sunlight increased the

chlorine decay rate and resulted in the formation of bromate. The bromate was formed from

hypobromite, itself the product of the oxidation of bromide ions by hypochlorite. Bromate

formation was not observed in the dark, and increased as light intensity increased.

Huang et al. (2008) investigated bromate formation in chlorinated samples of deionised and

clarified/filtered river water (DOC 1.7 mg/l), in darkness and after exposure to LP UV. The

deionised water was spiked with 88 g/l Br-. The natural bromide concentration in the treated

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river water was 53 g/l Br-, which was increased by spiking to 151 g/l for some experiments.

UV dose was in the range 40–2,000 mJ/cm2. Chlorine doses were in the range 1–5 mg/l, and

bromate concentrations were measured in the sodium hypochlorite stock solutions and

accounted for in the subsequent experiments (typically 0.5–1.0 g/l BrO3-/mg Cl2).

Some bromate formation occurred in darkness, but at low rate. After c. 4 days contact time at

pH 7.4 and chlorine dose 1.2 mg/l, bromate concentrations in treated river water samples

were c. 3 g/l, increasing to c. 4 g/l after a further 20 days; chlorine decay rates and bromate

concentrations were marginally greater in the bromide-spiked samples.

Exposure to UV greatly accelerated chlorine decay; in darkness, 5.1 mg/l Cl2 dosed to

deionised water decayed by 15% in 600 hours but by 25% in 5 minutes when exposed to UV

(cumulative UV dose c. 200 mJ/cm2). Approximately 10 g/l BrO3

- formed in this time,

increasing to c. 15 g/l after 25 minutes (cumulative dose 1,000 mJ/cm2). The authors noted

the capability of UV to reduce bromate but did not attempt to quantify the impact this might

have had on the observed bromate formation. Bromate formation was greater at acidic pH,

particularly at pH <6, than at pH 7.8; raising pH from 7.8 to 11 made little difference to

formation.

Campbell (2011) reported elevated bromate concentrations at two groundwater sites

containing >100 ug/l bromide where UV >100 mJ/cm2 was dosed post chlorination. The UV

dose was substantially greater than the target dose of 48 mJ/cm2 due to the reactor design.

Bromate formation was reduced as a result of a reduction in free chlorine concentration and a

reduction of the UV dose.

Linden et al. (2012) concluded that the point of application of UV doses <186 mJ/cm2,

whether upstream or downstream of secondary disinfection by chlorine or chloramine, does

not alter chlorine or chloramine demand nor regulated DBP formation to any practical extent.

However, they noted the capability of UV to photolyse chlorine and chloramine, for example

hypochlorous acid cleaved into hydroxyl and chloride radicals:

→

and recommended that where possible UV disinfection be installed upstream of secondary

disinfection.

A1.6 Effect of UV on pre-formed DBPs

A1.6.1 Bromate

Siddiqui et al. (1996) compared the effectiveness of LP and MP UV for decomposing bromate

to bromide via the intermediates bromite and hypobromite. Peak UV absorption of bromate is

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195 nm, so LP lamp tailored to transmit mostly in the <200 nm range was found to be the

most efficient of the options tested, achieving 40% destruction of bromate at a dose of

250 mJ/cm2, compared with 550 mJ/cm

2 using a MP lamp and c. 800 mJ/cm

2 using a

standard germicidal LP lamp.

Bensalah et al. (2013) investigated bromate reduction by MP UV (200-600 nm). A dose of

1,000 mJ/cm2 reduced bromate by >90%. Observed reaction rate increased with increasing

UV intensity, and decreased in the presence of DOC, inorganic carbon and nitrate.

A1.6.2 THMs

Mole et al. (1997) applied LP UV doses of 1,100 and 6,600 mJ/cm2 to samples of

groundwater spiked with nominally 50 mg/l of individual regulated THMs and with a mixture of

the four regulated THMs each at nominally 50 mg/l. At 1,100 mJ/cm2, removals of

approximately 80% of bromoform, 50% of chlorodibromoform and 20% bromodichloroform

were observed; at 6,600 mJ/cm2, practically all bromoform and chlorodibromoform was

removed and approximately 50% bromodichloroform. Chloroform was not removed, indicating

that photolysis of the Br-C bond occurs more readily than the Cl-C bond.

Chang (2008), using bench-scale LP UV apparatus, observed removal of THMs to be first

order with respect to UV dose (0–2,200 mJ/cm2). Removal of trichloromethane was low

(c. 20% at 2,000 mJ/cm2) but removal rate increased with increasing bromine content.

A1.6.3 HAAs

Chang (2008), using bench-scale LP UV apparatus, observed removal of chlorinated and

brominated HAAs to be first order with respect to UV dose (0–4,400 mJ/cm2). Removal of

chlorinated HAAs (MCAA, DCAA, TCAA) was negligible, and of MBAA very low, but reaction

rate increased appreciably with increasing bromine content (DBAA, TBAA).

A2 Effect of UV in Advanced Oxidation Processes

When UV is applied as a component of an advanced oxidation process (AOP), in conjunction

with ozone (O3), hydrogen peroxide (H2O2) or titanium dioxide (TiO2), the impact on DBPs

may be different than when UV is applied alone because of the hydroxyl radical reaction

pathway.

A2.1 Effect of UV on organics

Richardson et al. (1996) investigated organic DBPs after ultrafiltration and UV/TiO2

photocatalytic treatment, with and without secondary chlorination. For comparison, raw and

ultrafiltered water were also chlorinated. They observed a 40% reduction in TOC (evidence of

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mineralisation) after UV/TiO2 photocatalytic treatment. Although they were considering

UV/TiO2 in the context of potential use for treating small community supplies, in their

experimental method the water was recirculated through the reactor for 24 hours; whether the

quantitative results from this study, notably the magnitude of reduction in TOC achieved by

UV/TiO2 photocatalytic treatment, are representative is questionable.

Ijpelaar et al. (2007) reported that AOC formation to be much higher after the UV/H2O2 AOP

than UV disinfection, in part because of the greater UV dose but also because of hydroxyl

radical reaction pathways. They reported increases in AOC concentration in the range 27–131

µg/l after an MP UV dose of 540 mJ/cm2 (H2O2 dose in the range 4.0–6.9 mg/l); AOC

formation was inversely related to nitrate concentration, because nitrate strongly absorbs UV

at the wavelengths absorbed by NOM.

A2.2 Formation of DBPs: Direct formation

A2.2.1 Nitrite

Ijpelaar et al. (2007) noted that nitrite formation only occurs through photolysis and is related

to UV dose. Since the UV dose applied for AOPs is typically an order of magnitude greater

than for disinfection, nitrite formation is potentially similarly greater (MP lamps being generally

used for AOP applications). They cited an example of a UV/H2O2 plant for which nitrite

formation was in the range 40–330 g/l NO2- at 540 mJ/cm

2 MP UV dose, where

corresponding nitrate concentration was in the range 4.4–12.5 mg/l NO3- and H2O2 dose was

in the range 3.4–6.9 mg/l.

A2.2.2 Bromate


UV/O3, which included by-product formation. Their batch apparatus incorporated a recycle,

with ozone and UV doses increased by recirculating for longer. The UV dose was in the range

270-1,400 mJ/cm2 and ozone dose 0.3–10 mg/l. Bromate formation was 40–50% lower than

ozone alone provided UV dose was less than 800 mJ/cm2 and/or CT (the product of ozone

dose and contact time) was less than 10 mg.min/l; above these thresholds UV did not reduce

bromate formation.

Hofman et al. (2010) investigated the impact of combining UV with ozone on bromate

formation. At an ozone dose of 2 mg/l they observed that the application of an MP UV dose of

600 mJ/cm2 approximately doubled bromate formation (from 28 g/l with no UV) in one water

(very low DOC 0.24 mg/l; bromide 170 g/l) while using a different water (moderate DOC

1.75 mg/l; bromide 170 g/l) bromate formation increased from c. 85 to c. 125 g/l at

600 mJ/cm2 in one test but was unchanged in a repeat test.

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Kishimoto and Nakamura (2012) investigated the formation of bromate by LP UV, hydrogen

peroxide and ozone individually and in combination. They observed no bromate formation

after irradiating a 150 g/l Br- solution for 30 minutes in the presence of hydrogen peroxide

(UV dose not specified).

A2.3 Formation of DBPs: Effect of UV upstream of chlorination

Richardson et al. (1996) investigated organic DBPs after ultrafiltration and UV/TiO2

photocatalytic treatment, with and without secondary chlorination. For comparison, raw and

ultrafiltered water were also chlorinated. Their results showed that, while many halogenated

DBPs were formed after the combination of UV/TiO2 and chlorination, the number and

concentrations of these DBPs were lower than when chlorine was used alone. They also

observed:

a single DBP formed by UV/TiO2 photocatalytic treatment, tentatively identified as 3-

methyl-2,4-hexanedione;

a single DBP formed only by the combination of UV/TiO2 and chlorination, tentatively

identified as dihydro-4,5-dichloro-2(3H)furanone. It was suggested that this compound

had actually been formed during the analytical process, and hence was initially present

(in the treated water) in a different form, possibly a straight-chain chlorinated hydroxyl

acid.

Kleiser and Frimmel (2000) compared the effect of UV/H2O2 with O3 on DBP formation

potential using filtered River Ruhr water. A transferred O3 dose of 2.3 mg/l reduced THM

formation potential by 24% and AOX formation potential by 26%. Smaller reductions were

observed when LP UV was applied (doses not quantified). UV/H2O2 with 8 mg/l H2O2 dose

initially increased THM formation potential as UV dose was increased, reaching a maximum

of c. 20% greater than the control before declining with further increase in UV dose. There

was a small but statistically significant reduction in DOC, proportional to UV dose. UV254

absorbance also declined with UV dose, initially at a much greater rate than DOC. Both lower

(4 mg/l) and higher (16 mg/l) H2O2 doses reduced the extents to which THM formation

potential increased, and DOC and UV254 absorbance were decreased, relative to the 8 mg/l

dose; this was explained by, on the one hand fewer hydroxyl radicals being formed at the

lower H2O2 dose, and on the other hand more scavenging of hydroxyl radicals by excess

H2O2 at the higher H2O2 dose. They concluded that molecular ozone is more effective than

hydroxyl radicals for decreasing halogenated organic DBP formation and that an ozone-based

AOP is advantageous if wanting to simultaneously remove micropollutants and reduce DBP

formation.


UV/O3, which included by-product formation. Their batch apparatus incorporated a recycle,

with ozone and UV doses increased by recirculating for longer. The UV dose was in the range

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270-1,400 mJ/cm2 and ozone dose 0.3–10 mg/l. THM formation was typically 10–30% lower

than ozone alone but there was considerable scatter in their results, with some samples

showing increased formation.

Chin and Berube (2005) compared the effect of the combination of UV/O3 with UV and O3

individually on precursors of chlorinated DBPs (chloroform, chlorinated HAAs). The UV dose

range (130–1,610 mJ/cm2) was above that which would normally be applied for disinfection

but encompassed the range for an AOP application, while only the lowest O3 consumption in

the experimental range (3–24 mg/l) was representative of what might be expected in water

treatment practice. Their apparatus was operated in a batch recirculation mode for set periods

of time; increasing the time increased both UV and O3 doses. They observed that:

UV alone had no impact on DBP formation.

O3 alone at 3 mg/l oxidised organic material but not to the extent of mineralisation

(UV254 absorption was reduced but not TOC) and reduced chloroform formation by

c. 45% and chlorinated HAA formation by c. 35%. No additional benefit was observed

by increasing O3 dose.

UV/O3 oxidised organic material and mineralised TOC. At 130 mJ/cm2 + 3 mg/l O3, the

reduction in formation of chloroform and chlorinated HAAs was similar to that of O3

alone, but increasing doses resulted in greater reduction. However, there was a point of

diminishing return between 270 mJ/cm2 + 8 mg/l O3 and 810 mJ/cm

2 + 16 mg/l O3.

Dotson et al. (2010) investigated DBP formation following UV/H2O2 treatment. Bench-scale

tests using LP and MP UV, with and without H2O2 addition, were carried out on treated water

sampled from a treatment works (river water source). Mean bromide in the treated water

measured 49 µg/l; mean TOC measured 1.51 mg/l in sand filtered water and 0.86 mg/l in

GAC filtered water. THMFP increased by c. 15% (LP) and c. 30-50% (MP) as a result of UV

dosed at 1,000 mJ/cm2. When the UV dose was supplemented with 10 mg/l H2O2, THMFP

increased by c. 100% for both LP and MP UV. For the main tests with UV/H2O2, sufficient

chlorine was dosed to quench the residual H2O2 and provide a chlorine residual of 1 mg/l after

24 hours. The effect of only partially quenching the H2O2 was also explored, by dosing less

than the stoichiometric amount of chlorine required for quenching. It was observed that some

THM formation still occurred, the amount increasing as the chlorine dose approached the

stoichiometric amount, despite the rapid rate of the quenching reaction.

Chu et al. (2014) investigated the impact of pre-oxidation by LP UV, H2O2 and UV/H2O2 on the

formation of haloacetamides and other N-DBPs by subsequent chlorination. UV/H2O2

(585 mJ/cm2, 10 mg/l H2O2) reduced N-DBP formation relative to no pre-oxidation.

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© WRc plc 2015 84

A2.4 Effect of UV on pre-formed DBPs

A2.4.1 THMs

Chang (2008), using bench-scale LP UV apparatus, compared removal of THMs by UV and

UV/H2O2. Reaction rates were similar with or without 6 mg/l H2O2, and first order with respect

to UV dose (0–2,200 mJ/cm2), resulting in the conclusion that the reactions were primarily by

UV photolysis rather than with hydroxyl radicals. Removal of trichloromethane was low

(c. 20% at 2,000 mJ/cm2) but removal rate increased with increasing bromine content.

A2.4.2 HAAs

Chang (2008), using bench-scale LP UV apparatus, compared removal of chlorinated and

brominated HAAs by UV and UV/H2O2. Reaction rates were similar with or without 6 mg/l

H2O2, and first order with respect to UV dose (0–4,400 mJ/cm2), resulting in the conclusion

that the reactions were primarily by UV photolysis rather than with hydroxyl radicals. Removal

of chlorinated HAAs (MCAA, DCAA, TCAA) was negligible, and of MBAA very low, but

reaction rate increased appreciably with increasing bromine content (DBAA, TBAA).

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© WRc plc 2015 85

Appendix B UV Treatment in Public Supplies: Returned Questionnaires

B1 Introduction

Information on UV treatment in public supplies was collected by a focussed questionnaire

survey of 22 water companies in England and Wales. The questionnaire was designed to

identify the main features of existing and proposed UV treatment plants, including details of

the plant, main function, upstream and downstream treatment, and any related DBP formation

(or degradation). The survey built on a previous survey carried out by WRc in 2007.

Questionnaires were returned by 16 water companies (73% response), including nil returns

from 6 water companies that reported not using UV.

Six water companies failed to respond to the questionnaire and subsequent requests,

although one company confirmed having about 45 UV units (all on groundwater sites).

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© WRc plc 2015 86

B2 Water Company A

B2.1 Site information

Site name

Works design

capacity (Ml/d)

Raw water

1

Water treatment train identifying location of UV treatment (from works

inlet to distribution)

DBPs monitored

2

DBPs detected

3

A1

30 GW / LSW

Inlet - submerged membranes – slow sand filters – UV – marginal chlorination - phosphate-distribution

Bromate Nitrite

Total THM

No No Yes

A2

165 LSW Inlet - pre chlorine - raw water tanks - pre ozone – clarification – RGFs – post ozone – GAC adsorbers – UV – marginal chlorination (OSEC since Feb 2014) – phosphate - distribution

Bromate Chlorate Chlorite Nitrite

Total THM

Yes-due to O3 Yes Yes No Yes

A3

60 LSW Inlet - pre chlorine - raw water tanks - clarification – pre ozone - RGFs (GAC media)– post ozone – UV – marginal chlorination – phosphate – distribution

Bromate Chlorate Chlorite Nitrite

Total THM

Yes-due to O3 Yes Yes No Yes

A4

27 LSW Inlet – microstrainers – pre ozone – RGFs – slow sand filters – UV – superchlorination/dechlorination – phosphate- distribution

Bromate Nitrite

Total THM

Yes-due to O3 No Yes

A5

12 GW Pre-chlorination – RGFs – UV – marginal chlorination – phosphate – distribution

Bromate Nitrite

Total THM

Yes-due to UV No in final

Yes

A6

60 LSW Inlet – microstrainer – slow sand filters – UV (not installed yet) – marginal chlorination (superchlorination/dechlorination at present) – phosphate – distribution

Bromate Nitrite

Total THM

No No Yes

Works A5 can be supplied from two groundwater sources – GW1 and GW2. Both contain soluble iron but GW2 has more (300 µg/l vs 100 µg/l). Pre-chlorine is used to oxidise the soluble iron and is dosed prior to sand RGFs which include a layer of MnO2 coated sand. GW1 contains typically about 0.2 mg/l NH4. The original design was to dose pre-chlorine at 1.5 mg/l which would carry through the process and SO2 dosed at inlet to CWT to bring residual down to 0.50 mg/l. Pre-chlorine oxidised both the iron and the ammonia. We knew that the UV would lead to a reduction in the chlorine residual but this was accepted. GW2 contains about 150 µg/l Br and GW1 220 µg/l Br. A few weeks after commissioning we detected an increased concentration of bromate (26.6 µg/l) in a compliance sample taken in the Works A5 supply area. The UV dose was 200 mJ/cm

2 . The two UV reactors are Xylem LBX1000 and are

sized to provide the minimum required UV dose of 40 mJ/cm2 at a minimum UV transmission of 70%

and at maximum design flow. The works being on the minimum design flow and the raw water quality being excellent with a UVT >95% led to high UV dose. We have now changed the chlorine dosing point so that we have the facility to dose after the UV as well as before the RGFs (a much reduced dose to oxidise Fe). We have installed a chlorine residual analyser at the inlet to the UV reactors so the site shuts down if chlorine is detected. Since the event we have just been running on GW1 with the pre-chlorine turned off and the MnO2 coated sand has been removing the soluble Fe. However, although we have nitrosomonas bugs in the RGF which convert the ammonia to nitrite we don‟t achieve the oxidation to nitrate (probably no nitrobacter present in the RGFs). So we now have nitrite >0.10 mg/l passing through the works and through the UV reactors but the final chlorine breaks this out. Notes:


2. DBPs monitored (regulatory and operational) at the treatment works, within distribution or at customers‟ taps.

3. DBPs detected as a result of regulatory or operational monitoring at the treatment works, within distribution or at customers‟ taps.

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© WRc plc 2015 87

B2.2 UV system information

Site name

Year of installation

of UV system

1

Reason for installation

2

Manufacturer & lamp type

3

Number of units & outline of operation

Design dose

(mJ/cm2)

A1

2007 D&C Wedeco, LPHO

2 units, duty/standby 40 (min)

A2

Jan 2012 D&C Trojan 10L30 Swift

Medium Pressure

3 streams. Duty, Assist and standby

40 (min)

A3

Dec 2012 D&C Trojan 10L30 Swift

Medium Pressure

2 streams. Duty, assist/standby.

40 (min)

A4

Feb 2013 D&C Wedeco LBX 1000

Low Pressure High Output

2 streams. Duty/standby.

40 (min)

A5

Nov 2013 D&C Trojan 10L30 Swift

Medium Pressure

2 streams. Duty/standby

40 (min)

A6

June 2014 D&C Trojan 10L30 Swift

Medium Pressure

2 streams. Duty, assist/standby.

40 (min)

Notes:

1. Installation date or date of proposed installation if not an existing system.

2. D = General disinfection; C = Cryptosporidium risk; M = Micropollutant (e.g. pesticide; UV as part of an AOP).

3. LP = Low Pressure; LPHO = Low Pressure High Output; MP = Medium Pressure.

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© WRc plc 2015 88

B3 Water Company B


Site name

Works design

capacity (Ml/d)

Raw water

1

Water treatment train identifying location of

UV treatment (from works inlet to distribution)

DBPs monitored

2

DBPs detected3

B1

12.2 LSW Until July 2012: Coagulation/flocculation – HBC – pressure filtration – UV – marginal chlorination - distribution From July 2012: Coagulation/flocculation – HBC – pressure filtration – UV/peroxide – GAC – super chlorination /dechlorination – distribution

THMs (extensive)

HAAs, NDMA, & Bromate

(infrequent/limited data),

Audit & operational monitoring:

THMs 2013 Final Water Avg =

43.6 ug/l 2013 SR Outlet Avg = 62.0

ug/l 2013 WIS Zone (customers

taps) Avg = 65.6 ug/l HAAs

All results from Final Water & SR Outlets in 2013 were

<1.0 ug/l NDMA

Average of 73 analyses of Final Water during 2010 &

2011 = 2.7 ng/l, issues identified with ferric coag

not DBP. Bromate

Limited data during 2009 & 2010. All results from Final Water & SR Outlets <0.6

ug/l

B2

13.7 USW Coagulation/flocculation – FBC – RGF – UV – marginal chlorination (gas) – distribution UV will become operational mid-2014

THMs, HAAs THMs = 45.2 ug/l (avg) HAAs = 5.8 ug/l (avg)

B3

0.55 GW Borehole pump – UV – marginal chlorination with sodium hypochlorite – distribution

THMs, Bromate THMs = 5ug/l Bromate = 1 ug/l

HAAs = 1ug/l

B4

2.1 GW Borehole pump – UV – distribution

THMs, Bromate, HAAs

THMs = 0 ug/l Bromate = 1 ug/l

HAAs = 1 ug/l Notes:



3. DBPs detected as a result of regulatory or operational monitoring at the treatment works, within distribution or at customers‟

taps.

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© WRc plc 2015 89


Site name


of UV system

1


2


3


Design dose

(mJ/cm2)

B1

1992

2013- Advanced

oxidation UV system

D

M

Hanovia, LP

Trojan uvPhox, LP

3 units; 3x duty (2x required to maintain minimum UV dose)

Single unit

40

500

B2

2014 D Trojan, LP 2 units; 1x duty (1x required to maintain minimum UV dose)

40

B3

2011 D Trojan, LP 1 unit 40

B4

2012 D Wedeco, LP 1 unit 40

Notes:




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© WRc plc 2015 90

B4 Water Company C


Site name

Works design

capacity (Ml/d)

Raw water

1

Water treatment train identifying location of UV

treatment (from works inlet to distribution)

DBPs monitored

2

DBPs detected3

C1

84 GW (Crypto

risk)

Inlet – part flow aeration – part flow pellet reactor softening-other part flow chlorinated – blending of flows – coagulation – RGF – UV –contact tank disinfection-partial dechlorination-chloramination-phos acid - supply

THMs

Nitrite

TTHM levels <20 µg/l leaving WTWs

TTHM levels <30 µg/l at customer taps

<0.01 mg/l detected

at WTWs <0.2 mg/l detected at

customer taps

C2

50 LSW (Crypto

risk)

Storage -inlet – chlorination-coagulation-clarification –filtration-GAC-phos acid -UV-aeration-contact tank disinfection-chloramination-supply

THMs

Nitrite

TTHM levels <50 µg/l leaving WTWs

TTHM levels <60 µg/l at customer taps

<0.01 mg/l detected

at TWorks. <0.3 mg/l detected at

customer taps Notes:



3. DBPs detected as a result of regulatory or operational monitoring at the treatment works, within distribution or at customers‟ taps.


Site name


of UV system

1


2


3


Design dose (mJ/cm

2)

C1

2005 C Trojan, MP 3 units; 1x duty and 2x assist

60

C2

2010 C ATG, MP 3 units; duty, assist and standby

Minimum 4-log

inactivation of Crypto at 50ML/d with applied dose of 40mJ/cm

2

Notes:




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© WRc plc 2015 91

B5 Water Company D


Site name

Works design

capacity (Ml/d)

Raw water

1

Water treatment train identifying location of UV treatment (from

works inlet to distribution)

DBPs monitored

2

DBPs detected

3

D1

11.0 GW Calgon Aeration (solvent removal) GAC adsorption Nitrate reduction (ion exchange) UV irradiation Plumbosolvency control Chlorination (gas) Ammoniation

Bromate (Treated) Chlorate (Treated)

NDMA (Treated) Nitrite (Treated

& Cust taps) THM (Cust taps)

TOC (Raw & Treated)


NDMA (Treated)

Nitrite (Treated & Cust taps) THM (Cust

taps) TOC (Raw &

Treated)

D2

7.6 GW UV irradiation Filtration (cartridge) – separate source water Nitrate reduction (ion exchange) Plumbosolvency control Chlorination (gas)


Nitrite (Treated & Cust taps)

THM (Cust taps) TOC (Raw &

Treated)

Chlorate (Treated)


taps) TOC (Raw &

Treated)

D3

16.4 SW&GW

Preozonation Clarification Rapid gravity filtration Post-ozonation De-ozonation GAC adsorption UV irradiation Chlorination (gas) Dechlorination Plumbosolvency control


NDMA (Treated) Nitrite (Raw,

Treated & Cust taps)

THM (Treated & Cust taps)

TOC (Raw & Treated)


NDMA (Treated)

Nitrite (Raw, Treated & Cust

taps) THM (Treated & Cust taps) TOC (Raw &

Treated)

D4

Included in above

GW UV irradiation Chlorination (gas) Plumbosolvency control

D5

34.3 GW Nitrate reduction (ion exchange) Filtration (cartridge) UV irradiation Chlorination (gas) Fluoridation Dechlorination Plumbosolvency control




Treated)

Bromate (Treated)


Nitrite (Treated)

THM (Cust taps)

TOC (Raw & Treated)

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© WRc plc 2015 92

Site name

Works design

capacity (Ml/d)

Raw water

1

Water treatment train identifying location of UV treatment (from

works inlet to distribution)

DBPs monitored

2

DBPs detected

3

D6

65.7 SW Microstrainers Preozonation Lime dosing Clarification Calgon Rapid gravity filtration UV irradiation Post-ozonation De-ozonation GAC adsorption Chlorination (gas) Plumbosolvency control Dechlorination

Bromate (Treated & Cust

taps) Chlorate (Treated)

NDMA (Treated) Nitrite (Raw,


THM (Treated & Cust taps) TOC (Raw,


Bromate (Treated & Cust taps) Chlorate (Treated)

NDMA (Treated)

Nitrite (Raw, Treated & Cust

taps) THM (Treated & Cust taps) TOC (Raw,


D7

20 SW Rapid gravity filtration (GAC) Submerged membrane UV peroxide UV irradiation GAC adsorption Chlorination (gas) Plumbosolvency control Fluoridation


Nitrite (Raw & Treated)

THM (Treated) TOC (Raw &

Treated)

Nitrite (Raw) TOC (Raw)

D8

32 GW Plumbosolvency control Chlorination (gas) UV irradiation




Treated)



taps) TOC (Raw &

Treated) Notes:




taps.

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© WRc plc 2015 93


Site name


of UV system

1


2


3


Design dose

(mJ/cm2)

D1

1993 D Hanovia, LP 4 units, 3x duty/assist 1x standby,

changeover every 24 hours

25

D2

2006 M (pesticides - trietazine)

Trojan, LP 2 units, duty/standby, changeover every 6

hours

600

D3

2007 C Trojan, LP (Swift SC DC

30)

3 units duty/duty/standby

Min. of 40

D4 2008 D (drought scheme)

Trojan, LP 2 units, duty/standby 40

D5 2011 C Trojan, LP (Swift SC DC

30)

3 units duty/duty/standby

Min. of 40

D6

2012 C Trojan, LP 4 units plus 2 emergency units

containing two reactors each.

6 duty reactors/2 standby

Min. of 40

D7

Not yet in supply –

planned 2014

M

D

Trojan Torrent

Trojan, LP (Swift SC DC

30)

4 UV reactors in conjunction with peroxide dose –

duty/standby arrangement

dependent on flow and raw water metaldehyde

challenge

2 UV reactors as final stage of disinfection act

as duty/duty or duty/standby

dependent on flow

500

40 - 25

D8

2012 C Trojan, LP 4 reactors 2 or 3 duty (dependent

on plant flow) /1 standby

Min. of 40

Notes:




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© WRc plc 2015 94

B6 Water Company E


Site name

Works design

capacity (Ml/d)

Raw water

1



DBPs monitored

2

DBPs detected

3

E1

3.1 GW E1 mains and E1 borehole sites are abstraction sites, each with two boreholes. E1 Mains pumps groundwater to E1 Treatment works. No water from E1 Mains enters into customer supply it all passes forward to E1 treatment works. At E1 treatment works the only treatment is chlorination and UV treatment.

Total THMs and Bromate

in distribution.

Nitrite at Works.

THMs 6.7-10.1 ug/l (2013)

BrO3 <0.3-0.33 ug/l (2013)

NO2 <1.1-18 ug/l (2013)

E2

7.0 GW Chlorination and phosphate dosing. One borehole/well. 4 pumps with duty standby for maximum 2 pump operation. Installed in pumping main prior to distribution.


in distribution.

Nitrite at Works.

THMs 1.98-56.6 ug/l (2013)

BrO3 <0.3-1.1 ug/l (2013)

(THMs and BrO3 data

from various

supplies)

NO2 <1.1-8.4 ug/l (2013)

E3

7.5 GW At this works there is one borehole with two pumps (duty/duty). The main treatment processes are chlorination and phosphate dosing. Installed in pumping main prior to distribution.


in distribution.

Nitrite at Works.

THMs 1.98-56.6 ug/l (2013)

BrO3 <0.3-1.1 ug/l (2013)

(THMs and BrO3 data

from various

supplies)

NO2 <1.1-8.1 ug/l (2013)

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© WRc plc 2015 95

Site name

Works design

capacity (Ml/d)

Raw water

1



DBPs monitored

2

DBPs detected

3

E4

5.4 GW Chlorination and phosphate dosing. One borehole/well. 2 pumps with duty standby. Installed in pumping main prior to distribution.


in distribution.

Nitrite at Works.

THMs 1.98-56.6 ug/l (2013)

BrO3 <0.3-1.1 ug/l (2013)

(THMs and BrO3 data

from various

supplies)

NO2 <1.1 ug/l (2013)

E5

4.5 GW Chlorination and phosphate dosing. One borehole/well. 2 pumps with duty standby - with one maximum pump in operation. Installed in pumping main prior to distribution.


in distribution.

Nitrite at Works.

THMs 1.98-56.6 ug/l (2013)

BrO3 <0.3-1.1 ug/l (2013)

(THMs and BrO3 data

from various

supplies)

NO2 <1.1-31 ug/l (2013)

E6 (Proposed)

5.0 GW At this works there is one borehole with one pump; treatment consists of chlorination and phosphate dosing.


in distribution.

Nitrite at Works.

THMs 1.98-56.6 ug/l (2013)

BrO3 <0.3-1.1 ug/l (2013)

(THMs and BrO3 data

from various

supplies)

NO2 <1.1-2.8 ug/l (2013)

E7 (Proposed)

8.4 GW Disinfected borehole waters combine at E7 WTW site and the water is pH corrected with caustic soda, phosphate is added for lead control and the supply is disinfected with sodium hypochlorite. There is a contact tank at E7 to provide Ct.


in distribution.

Nitrite at Works.

THMs 1.98-56.6 ug/l (2013)

BrO3 <0.3-1.1 ug/l (2013)

(THMs and BrO3 data

from

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© WRc plc 2015 96

Site name

Works design

capacity (Ml/d)

Raw water

1



DBPs monitored

2

DBPs detected

3

various supplies)

E8 (Proposed)

12.0 GW At this works there are three boreholes with four pumps with variable pump operational combinations possible from one pump to all four. The main treatment processes are chlorination and phosphate dosing.


in distribution.

Nitrite at Works.

THMs 1.98-56.6 ug/l (2013)

BrO3 <0.3-1.1 ug/l (2013)

(THMs and BrO3 data

from various

supplies)

NO2 <1.1-15 ug/l (2013)

Notes:




taps.


Site name


of UV system

1


2


3


Design dose

(mJ/cm2)

E1 2009 D Berson UV MP

A single Inline 1000+ unit installed on

pumping main prior to chemical

dosing in constant operation.

40

E2 2012 D Berson UV MP

A single Inline 5000+ DVGW unit

installed on pumping main

prior to chemical dosing in constant

operation.

40

E3

2013 D Berson UV MP

A single inline 5000 + DVGW unit installed on pumping main


operation.

40

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© WRc plc 2015 97

Site name


of UV system

1


2


3


Design dose

(mJ/cm2)

E4

2012 D Berson UV MP



operation.

40

E5

2012 D Berson UV MP



use.

40

E6 (Proposed)

- D Not yet specified.

E7 (Proposed) - D Not yet specified.

E8 (Proposed) - D Not yet specified.

Notes:




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© WRc plc 2015 98

B7 Water Company F


Site name

Works design

capacity (Ml/d)

Raw water

1



DBPs monitored

2

DBPs detected

3

F1 1.4 GW UV, Chlorination Regulatory THMs at

customers taps

Typically <5ug/l

F2

2.8 GW UV, Chlorination Regulatory THMs at

customers taps

AMP6 project

Notes:




taps.


Site name


of UV system

1


2


3


Design dose

(mJ/cm2)

F1 2004 D ATG MP 2 units operating in duty standby arrangement

25

F2 AMP6 D Unknown, LP 2 units operating in duty standby arrangement

40

F3 (Replacement of F1)

AMP6 D Unknown, LP 2 units operating in duty standby arrangement

40

Notes:


2. D = General disinfection; C = Cryptosporidium risk; M = Micropollutant (e.g. pesticide; UV as part of an advanced AOP).


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© WRc plc 2015 99

B8 Water Company G


Site name

Works design

capacity (Ml/d)

Raw water

1



DBPs monitored

2

DBPs detected

3

G1

10.0 GW BH1 inlet – balance tank – UV – treated water reservoir (mixes with surface water works output) – distribution

Bromate Chlorate

Nitrite THMs

Bromate Chlorate

Nitrite THMs

G2

2.2 GW Inlet – UV – marginal chlorination – distribution

Bromate Chlorate

Nitrite THMs

Bromate Chlorate

Nitrite THMs

G3

3.8 GW Inlet – UV – marginal chlorination – phosphate dosing –distribution

Bromate Nitrite THMs


G4 8.6 GW Inlet – UV – marginal chlorination- phosphate dosing – distribution (incl. blending for pH in DSR)

Bromate Chlorate

Nitrite THMs

Bromate Chlorate

Nitrite THMs

G5 9.1 GW Inlet – UV – marginal chlorination – distribution (incl. blending for arsenic in DSR)

Bromate Chlorate

Nitrite THMs

Bromate Chlorate

Nitrite THMs

G6

15.7 GW Inlet – phosphate dosing – UV – marginal chlorination – distribution

Bromate Chlorate

Nitrite THMs


G7

7.0 GW Inlet – phosphate dosing – UV – marginal chlorination – distribution (incl. blending for nitrate in DSR)



G8

0.87 GW Inlet – UV – marginal chlorination (hypochlorite) – distribution

Bromate Chlorate

Nitrite THMs

Chlorate Nitrite THMs

G9

13.6 GW Inlet – marginal chlorination – phosphate dosing – UV – distribution

Bromate Chlorate

Nitrite THMs

Bromate Chlorate

Nitrite THMs

G10 (Off line)

1.6 GW Inlet – UV – marginal chlorination (hypochlorite) – distribution (incl. blending for pH in DSR)



G11 7.7 GW Inlet – prechlorination (oxidant for manganese removal) – manganese removal filters (incl. blending for nitrate) – UV – dechlorination – emergency chlorination – distribution

Bromate Chlorate

Nitrite THMs

Bromate Chlorate

Nitrite THMs

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© WRc plc 2015 100

Site name

Works design

capacity (Ml/d)

Raw water

1



DBPs monitored

2

DBPs detected

3

G12

10.0 GW - Bromate Chlorate

Nitrite THMs

Bromate Chlorate

Nitrite THMs

G13

2.9 GW BH3 inlet – cartridge filter – UV – nitrate plant – blending tank (for sodium) – phosphate dosing – distribution

Bromate Chlorate

Nitrite THMs

Bromate Chlorate

Nitrite THMs

G14 (Off line)

5.5 GW - Bromate Chlorate

Nitrite THMs

Nitrite THMs

G15

- GW Due to be commissioned - -

G16

- GW Proposed AMP6 scheme - -

G17


G18


G19


G20


G21


G22


G23


G24


G25


G26


G27


G28


G29


G30


G31


G32


G33


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© WRc plc 2015 101

Site name

Works design

capacity (Ml/d)

Raw water

1



DBPs monitored

2

DBPs detected

3

G34


G35


G36


G37


G38


Notes:




taps.


Site name Year of

installation of UV system

1


2


3


Design dose

(mJ/cm2)

G1

2013 C Berson, MP 2 units; duty/standby

40

G2

2006 C, D Hanovia, PMD200D1/6NW

2 units (ARC reactors); duty/duty

-

G3 1990s D Jaybay, MP 2 units; duty/standby

-

G4

2009 C, D Trojan, MP 1 unit; duty only (temporary)

>42

G5

1990s D Jaybay, MP 2 units; duty/standby

-

G6

2012 C, D Berson, MP 2 units; duty/standby

>42

G7

- C, D - - -

G8

1996 D J-Bay 2 units; duty/standby

-

G9

2012 C, D Xylem 1 unit; duty only (temporary)

>42

G10 (Off line)


>42

G11

2012 C, D Trojan, MP 2 units; duty/standby

>42

G12


>42

G13 2005 C, D Xylem 2 units; duty/standby

40 (min)

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© WRc plc 2015 102

Site name Year of

installation of UV system

1


2


3


Design dose

(mJ/cm2)

G14 (Off line)


>42

G15

2014 (Due to

be commissioned)

- - - -

G16

- C - - -

G17

- C - - -

G18

- C - - -

G19

- C - - -

G20

- C - - -

G21

- C - - -

G22

- C - - -

G23

- C - - -

G24

- D - - -

G25

- D - - -

G26

- D - - -

G27

- D - - -

G28

- D - - -

G29

- D - - -

G30

- D - - -

G31

- D - - -

G32

- D - - -

G33

- D - - -

G34

- D - - -

G35

- D - - -

G36

- D - - -

G37

- D - - -

G38

- D - - -

Notes:


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© WRc plc 2015 103



B9 Water Company H


Site name

Works design

capacity (Ml/d)

Raw water

1



DBPs monitored

2

DBPs detected

3

H1

17.5 GW Micro-filtration, UV, aeration, super-de chlorine disinfection

4 regulatory required THMs at

customers taps

All 4

H2

90.0 SW Pressure filtration, slow sand filtration, UV, super-de chlorine disinfection

4 regulatory required THMs at

customers taps

All 4

Notes:




taps.


Site name


of UV system

1


2


3


Design dose

(mJ/cm2)

H1

2012 C MP 2 – duty & standby 45.4

H2

2014 C MP 4 – duty & standby 40.0

Notes:




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© WRc plc 2015 104

B10 Water Company J


Site name

Works design

capacity (Ml/d)

Raw water

1



DBPs monitored

2

DBPs detected

3

J1

25 GW (chalk)

J2

8.4 GW (chalk)

J3

2.88 GW (chalk)

J4

12.70 GW (chalk)

Notes:




taps.


Site name


of UV system

1


2


3


Design dose

(mJ/cm2)

J1

2008 D Berson, MP 3 units; <400 m3/h =

1 unit, 400-600 m3/h

= 2 units, >600 m3/h

= 3 units

40

J2

1998 D Hanovia, MP 2 units; duty/standby, 360 m

3/hr

40

J3

2012 C Xylem, LP 116 m3/hr, 2 units,

duty/standby 40

J4

2014 D Xylem, LP 2 units; duty/duty, 666 m

3/hr

40

Notes:




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© WRc plc 2015 105

B11 Water Company K


Site name

Works design

capacity (Ml/d)

Raw water

1

Water treatment train identifying location of UV treatment (from works inlet to

distribution)

DBPs monitored

2

DBPs detected

3

K1 15 USW Inlet - Coagulation/Flocculation - DAF - RGF1 - RGF2 - UV – Distribution

Nitrites Bromates

No No

K2 18 GW Inlet - Membrane Filtration - Pressure Filtration - UV – Distribution

Nitrites Bromates

No No

K3 27 GW Inlet - Membrane Plant - UV - Chlorine – Distribution

Bromate No

K4 4.5 GW Inlet - Aeration - pH correction - UV - Chlorination – Distribution

Nitrites Bromates

No No

K5 11 GW Inlet - Pressure Filtration - UV – Distribution Bromate Nitrite

1/2 Reg PCV No

K6 45 SW Inlet - Coagulation/Flocculation - Pressure Filters - UV – Distribution

Nitrites Bromates

THMs

No No No

K7 40 SW Inlet - Coagulation/Flocculation - DAF - RGF1 - RGF2 - Chlorination - UV - oPO4 – Distribution

Nitrites Bromates

No No

K8 70 SW Inlet - UV - oPO4 - Chlorination - Distribution Nitrites THMs

No No

K9 11.5 GW Inlet - UV - Chlorination - oPO4 – Distribution No No

K10 25 SW Inlet - UV - oPO4 – Distribution Nitrites Bromates

No No

Notes:




taps.

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© WRc plc 2015 106


Site name


of UV system

1


2


3


Design dose

(mJ/cm2)

K1 2007 D C Wedeco, LP 2 x BX3200; Duty/Duty (each capable of 100% flow)

48

K2 2006 D Wedeco, LP 2 x BX1800; Duty/Assist 48

K3 2007 D Wedeco, LP 3 x BX3200; Duty/Assist/Stand-by

48

K4 2007 D Wedeco, LP 2 x BX1000; Duty/Duty (each capable of 100% flow)

48

K5 2007 D Wedeco, LP 2 x BX3200; Duty/Duty 48

K6 2007 D Wedeco, LP 1 x K series; Duty 48



K9 2006 D Wedeco, LP 1 x BX1800; Duty 48

K10 2007 D Wedeco, LP 2 x BX3200; Duty/Duty 48 Notes:




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© WRc plc 2015 107

Appendix C Site Visit Data

C1 Works A2

C1.1 Works Description

The works treats canal water which is of high alkalinity and moderate colour (typically 30°H),

with occasional high turbidity. The maximum design flow is 165 Ml/d, and the treated flow is

typically in the range 100-110 Ml/d.

Raw water is held in two storage tanks (effective capacity for both tanks combined: 108 Ml/d –

approximately 24 hours storage) prior to treatment. When the water temperature is above

15°C (usually April to September) chlorine is dosed to 1 mg/l prior to the storage tanks to

prevent zebra mussel growth. The storage tanks are fitted with aerators for THM removal.

Feed water to the works is dosed with sulphuric acid (to give a coagulation pH of 6.8) prior to

preozonation at a dose of 1 mg/l (capacity of each tank is 0.306 Ml; two streams are always in

service – total capacity of 0.612 Ml). The water is coagulated with polyaluminium chloride and

split between a bank of 12 hopper bottomed clarifiers and 2 superpulsators after dosing with

Magnafloc LT27 polyelectrolyte separately to each of the two streams. The clarified water is

filtered with a bank of 7 rapid gravity sand filters.

The filtered water is repumped to main ozonation, typically with a dose of 0.3-0.4 mg/l to give

a residual of 0.15 mg/l after the contactors. During normal operation, 2 ozone streams are in

service – the capacity of one ozone stream is 0.797 Ml, the capacity of two ozone streams is

1.593 Ml. At a flow of 100 Ml/d, the contact time in one stream is 11.5 minutes, the contact

time in two streams is 22.9 minutes. Sulphuric acid can be dosed upstream of ozonation to

reduce bromate formation.

The water is treated on 8 GAC contactors for pesticide, taste and odour removal prior to UV

disinfection. There are three Trojan units with a minimum design dose of 42 mJ/cm2 at 70%

UVT, but the dose is usually in the range 60-120 mJ/cm2. The MP lamps are sleeved to

prevent nitrite formation. The UV was installed in early 2012.

The water is dosed with NaOH to pH 7.2 and phosphate prior to final chlorination with a dose

typically around 1.2 mg/l to give a residual of 1 mg/l after the clear water tanks (capacity:

27 Ml). On-site electrolytic chlorine generation with low-bromide salt is used for final

chlorination and prechlorination when used, with the hypochlorite product stored for up to 4

days.

DWI


© WRc plc 2015 108

Backwash water and clarifier sludge are treated on-site using Magnafloc LT22, with recycling

of supernatants to the works inlet. (Supernatant is pumped to Canal Pump Sump A where it

mixes with the raw water and is then pumped over to the raw water storage tanks).

DWI


© WRc plc 2015 109

Figure C.1 Works A2: Schematic

Canal

Canal (optional by-pass)Sulphuric acid

Polyaluminium chloridePolyelectrolyte (LT27)

Sulphuric acid(seasonal for bromate control)

PhosphateSodium hydroxide (to pH 7.2)

Chlorine residual Chlorine 1.0 mg/l afterfinal tanks

Chlorine(seasonal)

Final watertanks

UV

GAC

Ozonation

Pre-ozonation

Raw waterstorage

Clarification Clarification

Rapid gravityfiltration

DWI


© WRc plc 2015 110

C1.2 DBP Formation

Figure C.2 shows THM concentrations in the final water. A seasonal influence is evident, with

higher levels in the summer. This will be partly a temperature effect, but may also result from

prechlorination used in the summer for zebra mussel control, and changes in the nature of

raw water DOC between summer and winter (although there is no clear indication of these

seasonal changes based on UV absorbance in the water after preozonation, Figure C.3, and

after GAC, Figure C.4).

Figure C.2 Works A2: Final water THMs

Generally, THM levels have been lower since installation of the UV in early 2012 (this may

reflect reduced chlorine use or possibly when THM removal in the raw water tanks with the

aerators was started).

Elevated bromate occurs in the final water, Figure C.5, but this is likely to be from ozonation

rather than any influence from the UV.

Nitrite levels in the water immediately after UV treatment are always very low or non-

detectable.

0

10

20

30

40

50

60

70

80

90

06

/07

/20

09

22

/01

/20

10

10

/08

/20

10

26

/02

/20

11

14

/09

/20

11

01

/04

/20

12

18

/10

/20

12

06

/05

/20

13

22

/11

/20

13

10

/06

/20

14

27

/12

/20

14

tothaloforms (ug/l)

tribromomethane (ug/l)

trichloromethane (ug/l)

dibromochloromethane (ug/l)

dichlorobromomethane (ug/l)

DWI


© WRc plc 2015 111

Figure C.3 Works A2: UV254 absorbance after preozonation

Figure C.4 Works A2: UV254 absorbance after GAC

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.450

6/0

7/2

00

9

22

/01

/20

10

10

/08

/20

10

26

/02

/20

11

14

/09

/20

11

01

/04

/20

12

18

/10

/20

12

06

/05

/20

13

22

/11

/20

13

10

/06

/20

14

27

/12

/20

14

uv254 Abs/cm

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

14/09/2011 01/04/2012 18/10/2012 06/05/2013 22/11/2013 10/06/2014 27/12/2014 15/07/2015

uv254 Abs/cm

DWI


© WRc plc 2015 112

Figure C.5 Works A2: Final water bromate and bromide

C2 Works A5


The works is fed from groundwater boreholes (GW1) high in iron. There is also a local

groundwater source with wells on site but this is no longer used. The maximum design flow is

12 Ml/d, but the normal flow is around 4 Ml/d. The water is high alkalinity with pH typically

between 7.5 and 8, and the water temperature is usually around 10°C. Turbidity is low and

microbiological quality high.

Up to 2013, chlorine was dosed to the water at 2-3 mg/l for iron precipitation, but this is no

longer used because of concerns over bromate formation. The water then flows through two

contact tanks in parallel to a bank of 5 rapid gravity sand filters for iron removal. The filtered

water then splits between two Wedeco LP UV units, via a common feed tank. The UV dose at

the maximum design flow is 48 mJ/cm2, but the dose is usually over 100 mJ/cm

2.

The water is chlorinated (chlorine gas) to 1 mg/l dose to give a residual of 0.8 mg/l after the

final water tanks. Phosphate dosing is carried out immediately before distribution.

0

2

4

6

8

10

12

14

16

18

200

2/0

3/2

01

4

21

/04

/20

14

10

/06

/20

14

30

/07

/20

14

18

/09

/20

14

07

/11

/20

14

27

/12

/20

14

ug/l Br

ug/l BrO3

DWI


© WRc plc 2015 113

Backwash water is settled after polyelectrolyte dosing, and the supernatant is returned to the

works inlet.

Figure C.6 Works A5: Schematic

C2.2 DBP Formation

The raw water at the works has low TOC. Over 2013 and 2014, the mean TOC was 0.5 mg/l

(standard deviation 0.2 mg/l). As a result, THM formation is very low, Figure C.7.

Chlorine(no longer used)

Chlorine

GW1 boreholes

Final water

Contact tank

Filters

UV

tank

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© WRc plc 2015 114

Figure C.7 Works A5: Final water THMs

One concern identified at the works has been bromate formation when prechlorination was

used before the filters for iron removal. The results of tests carried out to address the problem

are shown in Table C.1. The water was running to waste at the time of the tests (works flow

2.8 Ml/d).

Table C.1 Works A5: Effect of prechlorination on bromate formation

Date Prechlorine

dose (mg/l)

Raw water (µg/l) Filtered water

1

(µg/l)

Post-UV water

(µg/l)

Bromide Bromate Bromide Bromate Bromide Bromate

30/04/13 0 210 <0.1 213 0.1-0.8 213 0.2

30/04/13 1 135 <0.1 33 3.3-3.8 95 11

01/05/13 2 154 <0.1 36 7.5-21.6 33/32 26.1/24.2

Note:

1. Including samples taken from supernatant water above the filters.

Bromate was seen in the filtered water with prechlorination, and it is believed that this was

being formed from UV in sunlight on the supernatant water. The bromate then increases

further after UV treatment. For this reason prechlorination is no longer used at the works.

To further investigate bromate formation from sunlight, tests were carried out using GW1

water chlorinated and left in buckets exposed to sunlight or in the dark. The results shown in

Figure C.8 indicate the potential for bromate formation from chlorination and sunlight.

DWI


© WRc plc 2015 115

Figure C.8 Works A5: Bromate formation due to sunlight

C3 Works B1


The works treats lowland water with generally low colour (20°H). The catchment is

agricultural, so nutrient levels in the reservoir water are high enough to cause high algal levels

during summer. The maximum design flow is 12 Ml/d, but usually the flow is around 8 Ml/d.

Reservoir water is dosed with lime and ferric sulphate to a coagulation pH of between 4.9 and

5.3. Polyelectrolyte (LT22S) is then dosed prior to 7 hopper bottomed clarifiers. Lime is then

dosed to the clarified water to pH 7.2, followed by chlorination for manganese removal on two

banks of 4 pressure filters. The chlorine (gas) dose is controlled automatically to a set point

before the filters; the set point is adjusted manually to give a residual of 0.1-0.2 mg/l after

around 20 minutes retention time in the filters.

Hydrogen peroxide is dosed to the filtered water to 5.3 mg/l (5 mg/l for Advanced Oxidation

plus 0.3 mg/l to remove remaining chlorine), prior to UV treatment with a dose of 400 mJ/cm2

using a Low Pressure Trojan system. GAC is then used to remove any remaining pesticides,

geosmin/MIB and peroxide. There are 4 GAC beds giving 20 minutes EBCT at 142 l/s

0

5

10

15

20

25

30

0 1 2

Bro

mat

e a

s B

rO3

µg/

l

Hours exposed to strong sunlight (UV index 6)

Cl2 dose 0.5mg/l

Cl2 dose 1.0mg/l

Cl2 dose 2.0mg/l

WQ standard

DWI


© WRc plc 2015 116

(12 Ml/d). Regeneration is planned every 4 years (one per year), and a staggered

regeneration cycle is being developed.

Chlorine (gas) is dosed to the water leaving the GAC to give a residual of 0.9 mg/l after the

first 5 minutes in the contact tank. The minimum contact time (T10) is 35 minutes at maximum

design flow. Sulphur dioxide is dosed for dechlorination to a chlorine residual of 0.5 mg/l. The

residual after the contact tank prior to dechlorination is not monitored, and the CT10

calculation assumes a chlorine concentration of 0.5 mg/l to give a conservative measure.

Lime is dosed to pH 8 immediately before dechlorination, and the water is stored in two Final

Water Tanks before distribution. Routine THM monitoring includes in-works samples as well

as at 5 Service Reservoirs in the distribution system.

DWI


© WRc plc 2015 117

Figure C.9 Works B1: Schematic

Ferric sulphateCalcium hydroxide (to pH 4.9)Polyelectrolyte (LT22)

Calcium hydroxide (to pH 7.2)Chlorine residual Chlorine0.1-0.2 mg/l afterfiltration

Hydrogen peroxide

Chlorine residual Chlorine 0.9 mg/l after5 minutes incontact tank

Calcium hydroxide (to pH 8.0)Chlorine residual Sulphur dioxidereduced to 0.5 mg/l

Clarification

Filtration

GAC

Contact tank

Final watertanks

UV

DWI


© WRc plc 2015 118

C3.2 DBP formation

Figure C.10 shows THMs in the water leaving the works, and Figures C.11 and C.12 show

THMs at the two Service Reservoirs (SR1 and SR2) furthest from the works. The seasonal

changes in THMs may result from the influence of water temperature on THM formation, but

may also be linked to seasonal changes in algae (Figure C.13) or raw water TOC (Figure

C.14). However, the treated water TOC is relatively consistent throughout the year, and the

large difference in algal levels between 2013 and 2014 is not reflected in the THM differences,

suggesting the THM variations are primarily related to water temperature.

A significant feature of the THM data is the very high proportion of brominated THMs. This

may result largely from the relatively high bromide in the raw water. Six raw water samples for

bromide in 2013/14 showed a range of 45-192 µg/l, with a mean of 149 µg/l. For the final

water and Service Reservoir samples, trichloromethane represents around 10% of the total

THMs. However, for filtered water, trichloromethane is a higher proportion of the total THMs,

Figure C.15, and is in similar proportions to the brominated species. This may suggest that

UV/peroxide is enhancing the formation of brominated THMs, but is it difficult to draw any firm

conclusions because of the differences in chlorination and contact times between the sample

types. THMs for SR1 in 2010-12, prior to UV implementation, are shown in Figure C.16.

During the period the mean bromide concentration in the raw water was 126 µg/l. The

trichloromethane was a higher proportion of the total THMs, but, again, not enough to allow

firm conclusions to be drawn.

Sampling for bromate mainly in 2014 showed between 1–3.1 µg/l at the GAC inlet (11

samples) falling to 1 µg/l in the final water (7 samples).

Single samples for total HAAs in September 2014 shows levels of 13 µg/l leaving the works

and 19 µg/l at SR1.

DWI


© WRc plc 2015 119

Figure C.10 Works B1: Final water THMs

Figure C.11 Works B1: SR1 THMs

0

10

20

30

40

50

60

18/10/2012 26/01/2013 06/05/2013 14/08/2013 22/11/2013 02/03/2014 10/06/2014 18/09/2014 27/12/2014

Tribromomethane (ug/l)

Dibromochloromethane (ug/l)

Bromodichloromethane (ug/l)

Trichloromethane (ug/l)

Total THM (ug/l)

0

10

20

30

40

50

60

70

80

90

18/10/2012 26/01/2013 06/05/2013 14/08/2013 22/11/2013 02/03/2014 10/06/2014 18/09/2014 27/12/2014





THM Total (ug/l)

DWI


© WRc plc 2015 120

Figure C.12 Works B1:SR2 THMs

Figure C.13 Works B1: Filtered water THMs

0

10

20

30

40

50

60

70

80

90

18/10/2012 26/01/2013 06/05/2013 14/08/2013 22/11/2013 02/03/2014 10/06/2014 18/09/2014 27/12/2014





THM Total (ug/l)

0

5

10

15

20

25

30

35

18/10/2012 26/01/2013 06/05/2013 14/08/2013 22/11/2013 02/03/2014 10/06/2014 18/09/2014 27/12/2014

Tribromomethane Total ug/l

Dibromochloromethane Total ug/l

Bromodichloromethane Total ug/l

Trichloromethane Total ug/l

THM Total ug/l

DWI


© WRc plc 2015 121

Figure C.14 Works B1: Raw water algal counts

Figure C.15 Works B1: Raw and final water TOC

0

100000

200000

300000

400000

500000

600000

700000

18/10/2012 26/01/2013 06/05/2013 14/08/2013 22/11/2013 02/03/2014 10/06/2014 18/09/2014 27/12/2014

Total Blue Green

Total Algal Count

0

1

2

3

4

5

6

7

8

9

10

18/10/2012 26/01/2013 06/05/2013 14/08/2013 22/11/2013 02/03/2014 10/06/2014 18/09/2014 27/12/2014

Final Water TOC (mg/l)

Raw water TOC (mg/l)

DWI


© WRc plc 2015 122

Figure C.16 Works B1: SR1 THMs (2010-12)

C4 Works B2


The raw water from the reservoir is low alkalinity, and often highly coloured (up to 100°H),

from a catchment with little or no agricultural or human activity. The water is therefore of low

risk in terms of pesticides, pathogens and algal growth. The flow through treatment is around

13 M/ld.

Turbines are installed in the raw water feed pipeline to generate electricity. The water is then

dosed with NaOH and PACl before a flash mixer and flocculators for coagulation at pH 6-7.

The flow then splits between older precipitator clarifiers (4 units) and a new flat bottomed

clarifier, with separate polyelectrolyte (LT22S) dosing to each stream. The clarified water is

dosed with chlorine (gas) to 0.7 mg/l, with NaOH to pH 7, for manganese removal across four

rapid gravity sand filters. The chlorine residual in the filtered water after around 20 minutes in

the filters is 0.3 mg/l.

Further chlorine (gas) is added to 1.1 mg/l before a contact channel giving a few minutes

contact time. The water is then treated with UV to a dose of 40 mJ/cm2 (based on a minimum

UVT of 93% at maximum flow) using two Trojan MP units in parallel, with sleeving of the

lamps to prevent nitrite formation.

Further NaOH is added to the UV treated water to pH 9, before two final water tanks giving

around 6 hours storage. The chlorine residual leaving these tanks is typically around 0.8 mg/l,

for distribution.

Sludge thickening is carried out on site, with return of supernatant to the flash mixer.

0

20

40

60

80

100

120

03/12/2009 21/06/2010 07/01/2011 26/07/2011 11/02/2012 29/08/2012





Total THM (ug/l)

DWI


© WRc plc 2015 123

There are plans to relocate the second chlorine dose to a point after the UV disinfection stage

and reduce the free chlorine residual to about 0.5 mg/l in the distributed water.

Figure C.17 Works B2: Schematic

Polyaluminium chlorideSodium hydroxide (to pH 6-7)

Polyelectrolyte

Chlorine (0.7 mg/l dose)Sodium hydroxide (to pH 7.0)

Chlorine residual Chlorine (1.1 mg/l dose)c. 0.3 mg/l

Sodium hydroxide (to pH 9.0)

Chlorine residualc. 0.8 mg/l

Clarification Clarification

Final watertanks

Flocculation

DWI


© WRc plc 2015 124

C4.2 DBP formation

UV was installed in April 2014. A comparison of DBP formation in April–October 2013 with the

same period in 2014 has been used to identify any influence of the UV treatment.

Figures C.18 and C.19 show final water THMs for 2013 and 2014 respectively, and Figures

C.20 and C.21 show the data for the Service Reservoir (SR1) furthest from the works. The

THMs in the works final water samples are predominantly trichloromethane, whereas the

longer contact time at the SR shows an increased proportion of bromodichloromethane.

Raw and treated water TOC were generally similar between 2013 and 2014 (Figures C.22

and C.23), as were raw water colour levels (Figure C.24 and C.25).

Final water HAA sampling on 2 occasions in 2013 showed low levels (<10 µg/l). Sampling on

a single occasion in 2014 showed higher levels of around 55 µg/l. However, there are

insufficient data to draw any firm conclusions from this.

Bromate was measured in 7 samples in 2014, showing a range of 1.9 to 3.3 and an average

of 2.4.

No nitrite was found in any final water samples taken in 2013 or 2014. Raw water nitrate

levels are generally low.

The results suggest that implementation of the UV has not increase the DBPs measured.

THMs were higher in 2013 before the UV installation, which may result partly from slightly

higher chlorine dose in 2013 than 2014 (1 mg/l in the treated water compared with 0.8 mg/l).

DWI


© WRc plc 2015 125

Figure C.18 Works B2: Final water THMs (April-September 2013)

Figure C.19 Works B2: Final water THMs (April-September 2014)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

17/03/2013 06/05/2013 25/06/2013 14/08/2013 03/10/2013 22/11/2013

Total THMs (ug/l)


0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

02/03/2014 21/04/2014 10/06/2014 30/07/2014 18/09/2014 07/11/2014

Total THM (ug/l)


DWI


© WRc plc 2015 126

Figure C.20 Works B2: SR1 THMs (2013)

Figure C.21 Works B2: SR1 THMs (2014)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

17/03/2013 06/05/2013 25/06/2013 14/08/2013 03/10/2013 22/11/2013

Total THM (ug/l)


Bromodichloromethane ug/l

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

02/03/2014 21/04/2014 10/06/2014 30/07/2014 18/09/2014 07/11/2014

Total THM (ug/l)



DWI


© WRc plc 2015 127

Figure C.22 Works B2: TOC (2013)

Figure C.23 Works B2: TOC (2014)

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

17/03/2013 06/05/2013 25/06/2013 14/08/2013 03/10/2013 22/11/2013

Raw TOC (mg/l)

Final TOC (mg/l)

0.00

2.00

4.00

6.00

8.00

10.00

12.00

02/03/2014 21/04/2014 10/06/2014 30/07/2014 18/09/2014 07/11/2014

Raw TOC (mg/l)

Final TOC (mg/l)

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© WRc plc 2015 128

Figure C.24 Works B2: Raw water colour (2013)

Figure C.25 Works B2: Raw water colour (2014)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

17/03/2013 06/05/2013 25/06/2013 14/08/2013 03/10/2013

Raw water colour (mg/l)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

02/03/2014 21/04/2014 10/06/2014 30/07/2014 18/09/2014 07/11/2014

Raw water colour (mg/l)

DWI


© WRc plc 2015 129

C5 Works D2


The works is fed by three borehole sources, the number used at any time depending on

demand. Borehole 3 (maximum flow 35 l/s) has high pesticides (trietazine and bentazone),

and is treated with high dose UV (design dose based on power consumption of 0.24 kWh/m3).

There are three Trojan LP units, one as standby. UV treated water is then blended with water

from Boreholes 4 and 5 (maximum flows 45 and 27 l/s, respectively), and a required

proportion of the blended water is treated by ion exchange nitrate removal before being

blended back prior to chlorination. Chlorine (gas) is dosed to typically 0.6 mg/l prior to a

contact tank giving around 1-hour storage. There is very little reduction in chlorine

concentration across the contact tank, and the residual leaving the tank is monitored. The

water is than held in a balance tank for around 30 minutes before distribution. The maximum

design flow is 86 l/s, but actual flows are between 27 and 80 l/s.

Figure C.26 Works D2: Schematic

Borehole 4Borehole 5

Chlorine (0.6 mg/l dose)

Balance tank

Borehole 3

UV (x3)

Ion exchange

Contact tank

DWI


© WRc plc 2015 130

C5.2 DBP formation

THM samples taken in distribution since implementation of UV (12 samples over the past 5

years) show very low levels (<20 µg/l total THMs), reflecting the low chlorine demand of the

water. Nitrite concentrations in the final water have been non-detectable over the past three

years, although any nitrite formed by UV would be removed by chlorine. The low chlorine

demand suggests that nitrite formation would not be an issue, consistent with the use of LP

lamps rather than MP. Initial pilot plant trials at the site raised potential problems with nitrite

from MP systems, because of the high nitrate. No bromate data are available, but bromide in

the raw water is very low, so any potential for bromate production would be expected to be

negligible.

Documents

Effect of UV on the Chemical Composition of Water including DBP …dwi.defra.gov.uk/research/completed-research/reports/DWI... · 2015-06-03 · Version Control Table Version number