Impact of Wastewater Treatments on Removal of Noroviruses ...randd.defra.gov.uk/Document.aspx?Document=Impactof... · included activated sludge treatment processes, biomass support

Impact of Waste Water Treatments on Removal of Noroviruses from Sewage

R&D Technical Report WT0924/TR Produced: November 2011

www.defra.gov.uk

Defra Water Availability and Quality R&D Programme

Impact of Waste Water Treatments on Removal of Noroviruses from Sewage

R&D Technical Report WT0924/TR

Produced: November 2011 Author(s): Roderick Palfrey, Mark Harman,

Robert Moore WRc

Statement of use This report presents the results of preliminary study which aims to assess the efficacy of waste water treatments in reducing norovirus levels in treated sewage effluent and the utility of faecal indicator organisms in monitoring noroviruses. The study has been undertaken by WRc. Dissemination status Internal: Released Internally External: Released to Public Domain

Keywords: water quality, sewage treatment, norovirus removal Research contractor: WRc

WRc Ref: UC8471 Defra project officer: Elaine Connelly

Publishing organisation Department for Environment, Food and Rural Affairs Water Availability and Quality Division, Ergon House, Horseferry Road London SW1P 2AL

Tel: 020 7238 5524

www.defra.gov.uk/environ/quality/water

© Crown copyright (Defra);2010 Copyright in the typographical arrangement and design rests with the Crown. This publication (excluding the logo) may be reproduced free of charge in any format or medium provided that it is reproduced accurately and not used in a misleading context. The material must be acknowledged as Crown copyright with the title and source of the publication specified. The views expressed in this document are not necessarily those of Defra. Its officers, servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance on views contained herein.

Contents Summary .................................................................................................................................. 1

Acknowledgement .................................................................................................................... 5

1. Introduction .................................................................................................................. 7

1.1 Background ................................................................................................................. 7

1.2 Project overview .......................................................................................................... 7

1.3 Objectives .................................................................................................................... 8

2. Method ........................................................................................................................ 9

2.1 General approach........................................................................................................ 9

2.2 Site selection ............................................................................................................. 10

2.3 Sampling ................................................................................................................... 12

2.4 Sampling procedure .................................................................................................. 16

2.5 Analytical methods .................................................................................................... 16

3. Results ...................................................................................................................... 17

3.1 Results from measurement of samples..................................................................... 17

3.2 Characteristics of the treatment works at the sample times ..................................... 25

3.3 Measurements of faecal determinands and norovirus .............................................. 29

3.4 Removal of microbial determinands .......................................................................... 38

4. Discussion ................................................................................................................. 43

4.1 Presence of norovirus in sewage samples ............................................................... 43

4.2 Impact of treatment processes on microbial removal rates ...................................... 44

4.3 Surrogates for assessing efficiency of norovirus removal......................................... 45

4.4 Analytical methods for norovirus ............................................................................... 45

4.5 Sustainability factors for different works types .......................................................... 45

4.6 Sampling programme costs ...................................................................................... 46

4.7 Options for reducing pathogens discharged from sewage ....................................... 47

5. Conclusions ............................................................................................................... 49

5.1 Conclusions ............................................................................................................... 49

5.2 Potential opportunities for future work....................................................................... 50

References ............................................................................................................................. 51

List of Tables

Table 2.1 Effluent discharge consents for selected works – main parameters .............................................................................................. 11

Table 2.2 Sampling locations and numbers ........................................................... 13

Table 2.3 Dates and times of sampling .................................................................. 15

Table 3.1 Results of chemical and microbiological analysis for works AdvASP ................................................................................................... 18

Table 3.2 Results of chemical and microbiological analysis for works PercFilt .................................................................................................... 20

Table 3.3 Results of chemical and microbiological analysis for works ASP ......................................................................................................... 21

Table 3.4 Results of chemical and microbiological analysis for works BAF .......................................................................................................... 22

Table 3.5 Results of chemical and microbiological analysis for works MBR ......................................................................................................... 24

Table 3.6 Average process stage flows and concentrations ................................... 26

Table 3.7 Geometric mean values for microbial determinands ............................... 30

Table 3.8 Ranges of norovirus concentrations ........................................................ 30

Table 3.9 Relative standard deviations (%) to geometric mean values of microbial determinands ....................................................................... 32

Table 3.10 Microbial determinand removal rates between influent or primary and secondary effluent ............................................................... 38

Table 4.1 Sustainability factors for works types sampled; effect of changing from percolating filter works to ASP or MBR ........................... 46

Table 4.2 Costs of sampling and analyses .............................................................. 47

List of Figures

Figure 2.1 Probability of no detection of norovirus in samples ................................. 10

Figure 2.2 Works processes pictograms with sample locations and numbers ................................................................................................... 13

Figure 3.1 Comparison of influent samples BOD and SS concentrations with average values (including ASP works values) ................................. 27

Figure 3.2 Comparison of final effluent samples BOD and SS concentrations with average values ........................................................ 28

Figure 3.3 Geometric mean values of microbial determinands from each sample location ............................................................................... 31

Figure 3.4 F+ phage concentrations in samples ...................................................... 33

Figure 3.5 E.coli concentrations in samples ............................................................. 34

Figure 3.6 Norovirus concentrations in samples ...................................................... 35

Figure 3.7 Selected norovirus influent and effluent concentrations.......................... 36

Figure 3.8 Selected F+ phage influent and effluent concentrations ......................... 36

Figure 3.9 Selected E.coli influent and effluent concentrations ................................ 37

Figure 3.10 Microbial determinand removal rates between influent or primary and secondary effluent ............................................................... 39

Figure 3.11 Removal rates between influent (influent or primary) and secondary effluent for each sampling occasion ...................................... 40

Figure 3.12 Correlation of E.coli, F+ and somatic phage with total coliforms in all samples ........................................................................... 41

Figure 3.13 Correlation of norovirus genome copies with F+ phage in all samples ................................................................................................... 42

Defra

WRc Ref: UC8471/15541-0 November 2011

© Defra 2011 1

Summary

i Reasons

Noroviruses are a group of highly infectious viruses that are the most common cause of viral

gastroenteritis in adults; they infect all ages, and any immunity developed by contact is short

lived enabling repeated infections. There is a distinctly seasonal pattern, with the majority of

cases developing in winter. The sources are commonly contaminated food and water, with a

particularly high risk from contaminated shellfish. Very large numbers of norovirus are passed

in faeces of infected individuals and enter sewage collection systems. Where sewage

treatment works (STWs) discharge to coastal waters, these viruses may accumulate in

shellfish and subsequently pose a risk to public health.

No reliable information is available in the UK to determine the extent of norovirus removal that

can be achieved during sewage treatment, making it difficult to work out the scale of the risk.

Therefore, the objective of this project is to provide data on the numbers of norovirus that are

eliminated during treatment, and to recommend improvements in the operation of STWs to

ensure effective removal of noroviruses.

An investigation was conducted at several STWs to monitor the numbers of noroviruses

present at various stages during treatment. The work was conducted during the winter months

which corresponds to the peak level of infection in the community. At the same time other

measurements were carried out on site to assess the performance of each STW and to

indicate if any alternative measurements can provide a more straightforward means of

indicating how well noroviruses are removed. A range of STWs were investigated that

included activated sludge treatment processes, biomass support treatment processes and

membrane treatment.

The outcome from this preliminary study will be used to inform Defra of the potential risks to

shellfish waters, and determine how best these can be mitigated during sewage treatment.

Where uncertainties still exist, recommendations are made for further research to ensure any

implications arising from this work are underpinned by sound and robust scientific evidence.

ii Objectives

The overall objective for this project was to recommend an optimum treatment strategy to

minimise discharge of noroviruses from sewage treatment works (STW), based on a

preliminary assessment of their removal efficiency through different treatment processes.

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The specific objectives were:

a) Measurement of the norovirus template in crude sewage, storm sewage and treated

sewage following treatment by a range of different processes, to determine the relative

significance of treated effluents on the total load discharged.

b) Determination of reductions in norovirus concentrations across treatment (crude

sewage to final effluent) for a representative group of STWs.

c) Investigation of correlations between removal of faecal indicator organisms (FIOs), and

the potential surrogate F+ coliphage, and attenuation of norovirus across the various

types of treatment process.

iii Benefits

Norovirus, potentially present in sewage at large loads, is highly infectious to humans, and

may be transmitted to the human food supply as a result of sewage discharges into shellfish

waters. The importance of different types of sewage treatment on risk reduction has not been

established for norovirus although some similarity with other viral indicators may be expected.

This project will measure variability in load to some works and the effects of treatment stages

on risk reduction, either in storm sewage or in final effluent.

The study will enable Defra to have a better understanding of the requirements for treatment

of sewage that is to be discharged into sensitive areas, including possible differences

between treatment works types. Risk assessments on potential harm to human health will be

improved, with improved ability to assess reliability of treatment works, or consequences of

storm discharges. It may identify that some types of treatment process trains provide

improved overall security. The relative benefits of this against costs may then be assessed.

iv Conclusions

Sewage treatment reduces norovirus load in all sewage works effluents by between

one to two log reductions across the five sites investigated; although the norovirus

concentration data are scattered, more of the secondary or final effluent samples had

non-detectable levels of norovirus than the influent or primary effluent samples;

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Summary Figure 1 - Concentrations of Norovirus at different stages in sewage works samples showing average, standard deviations and maximum and minimum values

The scale of norovirus removal is low compared to the level of removal of bacteria

which the treatment sites are designed to do. Norovirus was still present in 63% of

samples following secondary treatment and 36% of samples following tertiary

treatment. There was a poor correlation between F+ coliphage and norovirus,

suggesting that F+ coliphage may not be a suitable indicator organism to use to test for

the presence of norovirus;

Treatment process types may affect removal efficiencies of norovirus; there is some

indication that processes that use biomass support systems, are less effective at

removing viruses (as phage) than suspended biomass processes, but no process was

found that completely removes norovirus;

Norovirus analysis is complex; results may be confused by:

Measurement problems in the sample matrix;

Inability to distinguish between active and inactive norovirus;

True variations in presence and efficiencies of process removal.

Further development of norovirus analysis is necessary including full agreement on

appropriate and economic analytical procedures between providers;

Loads of potential pathogens into catchments during storm events may not be

significantly increased by treatment works discharges of treated effluent; however,

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discharges from storm tanks, which tend to perform in a similar manner to primary

tanks, are likely to contain pathogens at concentrations only slightly reduced from the

influent sewage concentrations, similar to primary treatment removal; other storm

discharges will have concentrations of pathogens reduced inversely in proportion to the

increased flow.

v Further research options

This work has shown some differences between treatment works which should be

further studied;

Validation and agreement on economic and effective norovirus analysis for water

samples is required;

The extent and amount of storm overflows into shellfish waters should be evaluated.

vi Résumé of Contents

Sampling has been conducted at several STWs to monitor the numbers of noroviruses

present at various stages during treatment. This work was conducted during the winter

months (November to February). Approximately 70 samples were collected for analysis during

the study period. Other measurements were also carried out to assess the performance of

each STW and to indicate if any alternative measurements can provide a more

straightforward means of indicating how well noroviruses are removed.

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Acknowledgement

This study was made possible by the co-operation of Thames Water, Wessex Water, Southern Water

and South-West Water. The authors and sponsors of this study are grateful for this co-operation, and

for individual operating staff who provided information and assistance before, during and following the

sampling programme. These include Peter Pierce, Stewart Burnley, Steven Tomlin, Neil Whittington,

Mike Robinson, and Julian Dennis.

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1. Introduction

1.1 Background

Noroviruses (NV) are a group of highly infectious viruses that are the most common cause of

viral gastroenteritis in adults; they infect all ages, and any immunity developed by contact is

short lived enabling repeated infections. There is a distinctly seasonal pattern, with the

majority of cases developing in winter. The sources are commonly contaminated food and

water, with a particularly high risk from contaminated shellfish. Very large numbers of

norovirus are passed in faeces of infected individuals and enter sewage collection systems.

Where sewage treatment works (STW) discharge to coastal waters, these viruses may

accumulate in shellfish and subsequently pose a risk to public health.

No reliable information has been available in the UK to determine the extent of norovirus

removal that can be achieved during different types of sewage treatment, making it difficult to

work out the scale of the risk. Therefore, the objective of this project is to provide data on the

numbers of norovirus eliminated during treatment and to identify features of treatment

processes that affect attenuation of NV, including differences between treatment processes.

1.2 Project overview

WRc carried out the programme of research and conducted the fieldwork at the STWs during

November 2010 to January 2011. Samples of raw and treated sewage were collected from

five sewage treatment works (WwTW) in which different types of processes were used for

treatment. Samples were collected on four to six occasions from each treatment works, from

the influent sewage, after primary settlement, secondary and tertiary treatments from the

works for which these were present.

The concentrations of norovirus present were measured as the genome copy number, by

VeroMara, based at the European Centre for Marine Biotechnology in Oban. Measurements

of faecal indicator organisms (E.coli, total coliforms, F+ and somatic coliphage) together with

sanitary determinands BOD and suspended solids were carried out by National Laboratory

Service (NLS). This work was conducted during the winter months of 2010 - 2011 to

correspond with peak levels of infection in the community.

Other measurements were also made to assess the performance of each STW and to

indicate if any alternative measurements can provide a more straightforward means of

indicating how well noroviruses are removed from sewage.

The outcome from this preliminary study will be used to inform Defra of the potential risks to

shellfish waters, and determine how best these can be mitigated during sewage treatment. As

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© Defra 2011 8

a result of this work, opportunities for further research have been proposed to ensure any

implications arising from this work are underpinned by sound and robust scientific evidence.

1.3 Objectives

The overall objective for this project was to be able to recommend optimum treatment

strategies to minimise discharge of noroviruses from sewage treatment works (STW), based

on a preliminary assessment of their removal efficiency through different processes.

The specific objectives were:

a) Measurement of the norovirus template in crude sewage, storm sewage, and treated

sewage following treatment by a range of different processes, to determine the relative

significance of treated effluents on the total load discharged;

b) Determination of reductions in norovirus concentrations across treatment (crude

sewage to final effluent) for a representative group of STWs;

c) Investigation of correlations between removal of faecal indicator organisms (FIOs), and

the potential surrogate F+ coliphage, and attenuation of norovirus across the various

types of treatment process.

An early description of results from this work was presented at the annual meeting of the

Shellfish Association of Great Britain, in London, 17th- 18

th May 2011.

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2. Method

2.1 General approach

The objective was to obtain a general survey of presence and concentrations of norovirus in

sewage and sewage effluents at several locations and find effects of different sewage

treatment process stages on removal of norovirus. Measurement of other biochemical and

microbial determinands from the same samples were required to place measurements of

norovirus in relation to treatment efficiencies.

2.1.1 Site and sample numbers determination

The number of norovirus analyses from separate samples was limited to 70 samples. There

was no previous information on the likelihood of finding high or low concentrations of

norovirus at any sites, although the period between November and February was expected to

raise the likelihood of high concentrations present in raw sewage.

Others have reported norovirus present in sewage influent samples at detectable levels with

frequencies of 50% or more (for example, Lodder & Husman, 2005; da Silva et al., 2007).

HPA data1 shows that in the UK (2002-2009) the detection rate of norovirus in human

infections approximately doubled each fortnight from week 47 (3rd

to 4th week in November) to

the end of December, and remained at that level, in 2009-2010 to the end of February 2010.

A chart showing the likelihood of obtaining no detectable norovirus in a series of samples at

different rates of presence, is shown in Figure 2.1. If detectable norovirus is present in 50% of

samples taken frequently over a period then if four samples are taken from a works influent

there is less than 10% chance that all samples taken would have no detectable norovirus

present (binomial probability assessment).

This led to the sampling schedule shown in Table 2.2 for which at least four separate samples

were taken from each works, with four separate visits separated by at least one week to four

of the five works selected for the programme.

A further check on the likelihood of obtaining detectable norovirus was made at the start of the

sampling programme. A single sample of influent from works 1 (AdvASP – see section 2.2.2)

was supplied for preliminary analysis. This first sample contained detectable norovirus, so

giving confidence in the adequacy of the limited numbers of samples to be taken from each

works.

1 www.hpa.org.uk

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Figure 2.1 Probability of no detection of norovirus in samples

2.2 Site selection

2.2.1 Selection basis

Choices of treatment works for the sampling programme were made as follows:

to represent a range of secondary treatment process types and a wide spread of

population equivalents;

to include some works that discharge to bathing waters and have a requirement to

disinfect the effluent;

to have a predominantly domestic catchment, of sufficient size to enhance the chance

of frequently having norovirus present;

to minimise time delays between sample collection and delivery to the analytical

laboratories.

2.2.2 Works selected

Two works were selected for an initial series of samples, to check adequacy of the sampling

and measurements. Three further works were chosen to extend the range of works types,

provided that the initial set of samples and measurements were consistent with expectations.

The two initial works were:

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1 2 3 4 5 6

likelih

ood o

f no h

igh v

alu

es

sample number

probability not finding detectable norovirus load in samples

20 % time present

30 % time present

50 % time present

70 % time present

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An advanced activated sludge works (AdvASP) – primary settlement, low rate activated

sludge with biological nutrient removal and chemical dosing, secondary settlement; this

works has been upgraded over the last ten years to produce very high quality effluents;

A percolating filter works (PercFilt) – primary settlement with ferric chloride dosing,

percolating filters, secondary settlement humus tanks; this works represents a

widespread traditional design for smaller sewage treatment works.

The three additional works were:

A high rate activate sludge works (ASP) – primary settlement, non-nitrifying activated

sludge, and secondary settlement with UV disinfection;

A biological aerated filter works (BAF) – chemically aided primary settlement, and two

stage aerated flooded filter, with UV disinfection;

A membrane bio-reactor (MBR) – fine screens, activated sludge process at high mixed

liquor concentration, membrane separation to nominal 0.1 µm (operated for 10 years).

The discharge consent standards for the main effluent quality parameters are shown in Table

2.1 below.

Table 2.1 Effluent discharge consents for selected works – main parameters

Site pe,

000’s Suspended solids (mg/l)

BOD (mg/l)

COD (mg/l)

NH4-N (mg/l)

PO4-P (mg/l)

Advanced

activated sludge,

AdvASP

193 17 11 125 1 1

High rate activated

sludge, ASP 142 25 12 125 5 na

Percolating filter,

Percfilt 25 40 30 125 5 2

Biological aerated

filter, BAF 89 30 20 125 10 na

Membrane Bio-

Reactor, MBR 21 60 40 125 na na

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2.3 Sampling

2.3.1 Process sample locations and frequency

The sampling programme was agreed by the Project Steering Group and modified to reduce

the number of samples of primary effluent and increase other secondary and tertiary samples.

The programme is shown in the Table 2.2. A pictogram for each works is shown in Figure 2.2

which summarises sewage treatment layouts for each works, and also shows the sample

numbers taken from each location during the whole programme.

Samples were taken from the following main locations within each STW:

crude sewage influent downstream of screening and grit removal;

settled sewage downstream of the primary settlement tanks;

secondary treated effluent pre-disinfection; and

effluent downstream of disinfection.

On each visit at least one sample of influent sewage was taken, and at least one sample of a

secondary or tertiary effluent. For four of the five works (not the MBR works), additional

samples were taken after a delay of at least 2 hours, or after an overnight delay, to give an

opportunity to identify any short term variations. Dates for each visit to each works, with the

times for each sample taken for as the influent sample for that visit, are shown in Table 2.3.

Settled sewage following primary settlement was considered to be a best option, for the

limited scope of this project, to represent storm sewage. Many storm tanks at sewage

treatment works have similar structures to primary tanks. Sewer overflows are more difficult to

model, but after any first flush, which should reach a sewage works, the overflow sewage is

likely to be more dilute than treatment works influent sewage during non-storm periods.

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Table 2.2 Sampling locations and numbers

Works type

Visit no.

Influent

Primary

effluent

Secondary effluent Tertiary effluent

ASP PF BAF ASP high rate

MBR Filters UV

Stage 1

AdvASP works 1 1 1 1

1

AdvASP works 1 2 1 1

1

AdvASP works 1 3 3 3 3

Percfilt works 2 1 1 1

Percfilt works 2 2 2 2 2

Percfilt works 2 3 1 1

Stage 2

AdvASP works 1 4 1 1 1

Percfilt works 2 4 1 1 1

BAF works 3 1 1 1

1

1

BAF works 3 2 1

1

1

BAF works 3 3 2

2

2

BAF works 3 4 1 1

1

1

ASP works 4 1 2 1

2

2

ASP works 4 2 1

1

1

ASP works 4 3 1 1

1

1

MBR works 5 1 1

1

MBR works 5 2 1

1

MBR works 5 3 1

1

MBR works 5 4 1 1

Samples from each process 24 11 6 5 5 4 4 2 9

Total samples 70

Figure 2.2 Works processes pictograms with sample locations and numbers

AdvASP works - primary settlement, low rate activated sludge with biological nutrient removal

and chemical dosing, secondary settlement; this works has been upgraded over the last ten

years to produce very high quality effluents.

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ASP – primary settlement, non-nitrifying activated sludge, and secondary settlement, with UV

disinfection.

PercFilt – primary settlement with ferric chloride dosing, percolating filters, secondary

settlement humus tanks; this works represents a widespread traditional design for smaller

sewage treatment works.

BAF works - Primary settlement uses a chemically aided settlement tank that is integrated into

the biological aerated flooded filter. Clarified effluent from the process is discharged through a

denitrifying filter, and disinfected using UV.

MBR – Fine screens, activated sludge process at high mixed liquor concentration, membrane

separation to nominal 0.1µm (operated for 10 years).

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Table 2.3 Dates and times of sampling

Works Date Time

Percfilt 23-Nov-10 00:00



Percfilt 07-Dec-10 11:30

Percfilt 17-Jan-11 13:30

AdvASP 23-Nov-10 00:00

AdvASP 30-Nov-10 11:30

AdvASP 06-Dec-10 14:58



AdvASP 17-Jan-11 11:00

ASP 17-Jan-11 08:54

ASP 17-Jan-11 14:10

ASP 25-Jan-11 10:00

ASP 01-Feb-11 13:05

BAF 17-Jan-11 10:00

BAF 25-Jan-11 11:32

BAF 01-Feb-11 10:05

BAF 01-Feb-11 14:20

BAF 08-Feb-11 10:55

MBR 17-Jan-11 12:09

MBR 25-Jan-11 13:15

MBR 01-Feb-11 11:10

MBR 8-Feb-11 11:55

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2.4 Sampling procedure

Sampling and transport of samples to the analytical laboratories was carried out, so far as

possible, to comply with best practice recommendations (for example, Environment Agency

(2002))2. This states that it is best practice to measure determinands within 24 hours from

sampling, with samples chilled before measurement, transferred to dark storage conditions,

and kept at temperatures 2°C – 8°C, in insulated containers.

All samples were collected from each location using a bucket or purpose-built weighted

sample device (Casella) and plastic funnel. The sampler and funnel were thoroughly rinsed

between each location to reduce carry over between samples. The samples were transported

in cooled containers and transferred to the laboratory and stored in a cold room overnight

before despatch for analysis.

Samples were transported to the National Laboratory Service (NLS) for E.coli, total coliforms,

and the F+ and somatic coliphage examination, and for BOD, ammonia and suspended solids

analyses. Most samples were received within 24 hours of sampling.

Samples were also transported to VeroMara (Oban) for norovirus examination. These

samples were also chilled and despatched in a coolbox with ice, and a thermometer. On

receipt the temperature of the samples was noted. The time between sampling and receipt of

samples at Oban was less than 48 hours. The samples were then frozen to -80°C before

analysis. A single set of samples, 25 January 2011, had a temperature of 18°C on arrival. The

rest of the samples were below 8°C.

2.5 Analytical methods

Standard well-characterised methods were used by the NLS laboratory to carry out microbial

and biochemical measurements. These were all carried out using UKAS accredited methods.

The norovirus (NV) measurements were developed by VeroMara for this project, based on

their existing UKAS accredited method for quality testing of shellfish. The NV analysis

measures the number of copies of a unique section of the NV genome present in the sample.

It does not measure infectivity of the NV. A NV particle may have been disrupted so that it is

biologically inactive, but it could still register as a genome copy. No distinction is made

between partial and complete NV genome. The two genotypes of norovirus assessed were GI

and GII, of which GI was identified in only 4 samples. Therefore all references in this report to

norovirus refer to the GII type.

2 Environment Agency (2002). The Microbiology of Drinking Water – Part 2 – Practices and Procedures

for Sampling. Methods for Examination of Waters and Associated Materials. Standing Committee of

Analysts.

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3. Results

3.1 Results from measurement of samples

Measurement results for biochemical and microbial determinands from the samples of

sewage taken during the visits made to the STWs are shown in the following tables:

AdvASP Table 3.1

PercFilt Table 3.2

ASP Table 3.3

BAF Table 3.4

MBR Table 3.5

Values for the concentrations of the microbial determinands are shown as the log10

concentration values. Subsequent sections show these data arranged in different ways, which

include finding the geometric mean values for microbial concentrations.

For Norovirus, when samples analysis found non-detectable concentrations, these are shown

in the tables as the log10 concentration of the detection limit, which is -1.30 log10 units gene

copies/ml.

The performance of the STWs and measured determinands are within expected ranges for

the different sewage sources.

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Table 3.1 Results of chemical and microbiological analysis for works AdvASP

Date (time)

Treatment stage

BOD (mg/l)

SS (mg/l)

Coliforms confirmed

(cfu/100ml)

Coliforms presumptive (cfu/100ml)

E.coli

presumptive (cfu/100ml)

F+ (pfu/ml)

Somatic phage

(pfu/ml)

Coliforms confirmed (log10 cfu/ 100 ml)

E.coli

presumptive (log10/

100 ml)

log10 F+ (pfu/ml)

Somatic phage

(log10 pfu/ ml)

Norovirus (log10 gc/ml)

23-NOV-10 Influent 351 452 3.840E+07 4.800E+07 1.727E+07 7670 29000 7.58 7.24 3.88 4.46 2.82

not sampled Primary settlement

nd nd nd nd nd nd nd nd nd nd nd

23-NOV-10 Secondary nd nd 5.622E+06 9.369E+06 2.300E+06 44 7800 6.75 6.36 1.64 3.89 -1.30

23-NOV-10 Tertiary 2.9 3 2.240E+04 2.800E+04 4.600E+03 0.9 9 4.35 3.66 -0.05 0.95 -1.30

30-NOV-10 11:30

Influent 443 344 3.150E+07 3.500E+07 1.455E+07 3050 11818 7.50 7.16 3.48 4.07 3.82

not sampled Primary settlement

nd nd nd nd nd nd nd nd nd nd nd

30-NOV-10 11:45

Secondary 4.4 9.9 1.440E+05 2.400E+05 3.100E+04 10 56 5.16 4.49 1.00 1.75 1.00

30-NOV-10 11:55

Tertiary 2.9 3 3.600E+04 1.200E+05 2.800E+04 4 38 4.56 4.45 0.60 1.58 -1.30

06-DEC-10 14:58

Influent 341 262 2.400E+07 2.400E+07 6.200E+06 5018 10600 7.38 6.79 3.70 4.03 1.49

06-DEC-10 14:47

Primary settlement

231 132 2.970E+07 3.300E+07 5.500E+06 2946 8000 7.47 6.74 3.47 3.90 3.51

06-DEC-10 14:40

Secondary 3.2 9.25 4.410E+04 4.900E+04 7.600E+03 5 30 4.64 3.88 0.70 1.48 3.34

not sampled Tertiary nd nd nd nd nd nd nd nd nd nd nd nd

07-DEC-10 10:00

Influent 344 324 2.000E+07 2.000E+07 7.500E+06 4064 10600 7.30 6.88 3.61 4.03 1.89

07-DEC-10 10:10

Primary settlement

249 118 2.790E+07 3.100E+07 6.300E+06 3262 7300 7.45 6.80 3.51 3.86 3.46

07-DEC-10 10:20

Secondary 2.9 8.2 3.600E+04 4.500E+04 5.200E+03 10 30 4.56 3.72 1.00 1.48 2.63


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© Defra 2011 19

Date (time)

Treatment stage

BOD (mg/l)

SS (mg/l)

Coliforms confirmed

(cfu/100ml)


E.coli


F+ (pfu/ml)

Somatic phage

(pfu/ml)


E.coli

presumptive (log10/

100 ml)

log10 F+ (pfu/ml)

Somatic phage

(log10 pfu/ ml)

Norovirus (log10 gc/ml)

07-DEC-10 14:25

Influent 371 258 1.455E+07 1.455E+07 7.600E+06 5580 9000 7.16 6.88 3.75 3.95 0.81

07-DEC-10 14:35

Primary settlement

239 145 2.520E+07 2.800E+07 7.000E+06 5618 6800 7.40 6.85 3.75 3.83 3.71

07-DEC-10 14:45

Secondary 3.5 10.5 2.610E+04 2.900E+04 7.000E+03 0.9 46 4.42 3.85 -0.05 1.66 1.66


17-JAN-11 11:00

Influent 116 158 6.240E+06 7.800E+06 4.500E+06 1070 2400 6.80 6.65 3.03 3.38 1.21

17-JAN-11 11:10

Primary settlement

104 90.1 9.000E+06 1.000E+07 5.000E+06 915 2700 6.95 6.70 2.96 3.43 -1.30

17-JAN-11 11:20

Secondary 2.8 4.27 2.320E+04 2.900E+04 9.091E+03 0.9 18 4.37 3.96 -0.05 1.26 2.61


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© Defra 2011 20

Table 3.2 Results of chemical and microbiological analysis for works PercFilt

Date (time)

Treatment stage

BOD (mg/l)

SS (mg/l)

Coliforms confirmed

(cfu/100ml)


E.coli


F+ (pfu/ml)

Somatic phage

(pfu/ml)


E.coli

presumptive (log10/

100 ml)

log10 F+ (pfu/ml)

Somatic phage

log10 pfu/ ml

Norovirus (log10 gc/

ml)

23-NOV-10 Influent 255 284 2.970E+07 3.300E+07 7.600E+06 2660 6500 7.47 6.88 3.42 3.81 -1.30

not sampled Primary settling

nd nd nd nd nd nd nd nd nd nd nd nd

23-NOV-10 Secondary 8.2 25.9 1.800E+05 3.000E+05 7.800E+04 152 1818 5.26 4.89 2.18 3.26 -1.30

30-NOV-10 09:45

Influent 242 235 3.040E+07 3.800E+07 1.545E+07 2867 3800 7.48 7.19 3.46 3.58 3.58

30-NOV-10 10:15

Primary settling

84.1 41.6 6.400E+06 3.200E+07 4.000E+06 1376 1909 6.81 6.60 3.14 3.28 1.77

30-NOV-10 10:00

Secondary 10.5 27.7 4.410E+05 4.900E+05 2.200E+05 540 1909 5.64 5.34 2.73 3.28 2.37

30-NOV-10 13:45

Influent 254 268 2.080E+07 2.600E+07 1.036E+07 3130 7000 7.32 7.02 3.50 3.85 1.61

30-NOV-10 14:15

Primary settling

134 78.4 2.790E+07 3.100E+07 6.200E+06 1277 4300 7.45 6.79 3.11 3.63 2.53

30-NOV-10 14:00

Secondary 12.5 28 3.220E+05 4.600E+05 1.892E+05 442 2000 5.51 5.28 2.65 3.30 2.58

07-DEC-10 11:30

Influent 230 280 5.000E+06 1.000E+07 5.400E+06 3840 5700 6.70 6.73 3.58 3.76 1.05

not sampled Primary settling


07-DEC-10 11:40

Secondary 10.5 25.2 1.727E+05 1.727E+05 6.000E+04 681 1480 5.24 4.78 2.83 3.17 1.38

17-JAN-11 13:30

Influent 166 224 7.000E+06 1.400E+07 3.200E+06 457 4200 6.85 6.51 2.66 3.62 2.55

17-JAN-11 13:40

Primary settling

82.3 136 1.470E+07 2.100E+07 3.000E+06 706 4100 7.17 6.48 2.85 3.61 3.16

17-JAN-11 13:35

Secondary 24.9 57.7 8.500E+05 1.700E+06 6.200E+05 145 4400 5.93 5.79 2.16 3.64 0.46

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© Defra 2011 21

Table 3.3 Results of chemical and microbiological analysis for works ASP

Date (time) Treatment

stage BOD (mg/l)

SS (mg/l)

Coliforms confirmed

(cfu/100ml)


E.coli


F+ (pfu/ml)

Somatic phage

(pfu/ml)


E.coli

presumptive (log10/

100 ml)

log10 F+ (pfu/ml)

Somatic phage

log10 pfu/ ml


ml)

17-JAN-11 08:54

Influent 1560 3290 5.700E+07 5.700E+07 3.100E+07 273 11600 7.76 7.49 2.44 4.06 -0.85

17-JAN-11 08:55

Primary Settlement

204 139 3.040E+07 3.800E+07 1.364E+07 1020 3200 7.48 7.13 3.01 3.51 2.31

17-JAN-11 08:59

ASP 4 13 4.909E+04 1.636E+05 4.500E+04 5 106 4.69 4.65 0.70 2.03 -1.18

17-JAN-11 09:03

Final 25 66 2.050E+03 4.100E+03 1.260E+03 11 9 3.31 3.10 1.04 0.95 2.55

17-JAN-11 14:10

Influent 570 980 2.150E+07 4.300E+07 1.636E+07 704 5700 7.33 7.21 2.85 3.76 2.53

not sampled Primary Settlement


17-JAN-11 14:30

ASP 3 9 1.680E+05 2.400E+05 3.000E+04 7 64 5.23 4.48 0.85 1.81 -1.30

17-JAN-11 14:25

Final 5 14 4.480E+02 5.600E+02 4.500E+01 1 3 2.65 1.65 -0.05 0.48 -1.30

25-JAN-11 10:00

Influent 811 2010 7.200E+07 7.200E+07 1.909E+07 1140 9000 7.86 7.28 3.06 3.95 1.76

not sampled Primary Settlement


25-JAN-11 09:48

ASP 7 12 2.880E+04 3.200E+04 1.802E+04 34 220 4.46 4.26 1.53 2.34 -1.30

25-JAN-11 09:38

Final 9 11 4.950E+03 5.500E+03 2.300E+03 10 11 3.69 3.36 1.00 1.04 -1.30

01-FEB-11 13:05

Influent 1640 2500 4.500E+07 5.000E+07 1.600E+07 1130 34000 7.65 7.20 3.05 4.53 -1.3

01-FEB-11 12:50

Primary Settlement

221 144 9.000E+06 9.000E+06 6.100E+06 1785 7200 6.95 6.79 3.25 3.86 2.53

01-FEB-11 12:40

ASP 10 21 3.120E+05 3.900E+05 9.273E+04 26 17 5.49 4.97 1.41 1.23 2.63

01-FEB-11 12:30

Final 4 22 1.800E+04 4.500E+04 1.455E+04 9 310 4.26 4.16 0.95 2.49 -1.30

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© Defra 2011 22

Table 3.4 Results of chemical and microbiological analysis for works BAF


stage BOD (mg/l)

SS (mg/l)

Coliforms confirmed

(cfu/100ml)


E.coli


F+ (pfu/ml)

Somatic phage

(pfu/ml)


E.coli

presumptive (log10/

100 ml)

log10 F+ (pfu/ml)

Somatic phage

log10 pfu/ ml


ml)

17-JAN-11 10:00

Influent 151 221 2.320E+08 2.900E+08 4.700E+06 501 3600 8.37 6.67 2.70 3.56 -1.30

17-JAN-11 10:05

CAS 86.8 132 1.920E+07 2.400E+07 5.500E+06 140 1364 7.28 6.74 2.15 3.13 1.93

17-JAN-11 10:11

BAF 5 14.3 3.400E+04 3.400E+04 2.500E+04 41 500 4.53 4.40 1.61 2.70 2.61

17-JAN-11 10:15

Final 5.5 7.47 7.800E+03 7.800E+03 3.200E+03 0.9 8 3.89 3.51 -0.05 0.90 -1.30

25-JAN-11 11:32

Influent 173 293 2.000E+07 2.000E+07 4.600E+06 1760 9200 7.30 6.66 3.25 3.96 -1.30

not sampled CAS nd nd nd nd nd nd nd nd nd nd nd nd

25-JAN-11 11:11

BAF 8 14.6 2.480E+04 3.100E+04 2.100E+04 31 470 4.39 4.32 1.49 2.67 -1.30

25-JAN-11 11:19

Final 4.2 4.98 4.300E+03 4.300E+03 2.100E+03 1 3 3.63 3.32 0.00 0.48 -1.30

01-FEB-11 10:05

Influent 307 322 2.580E+07 4.300E+07 7.000E+06 2100 8100 7.41 6.85 3.32 3.91 -1.30


01-FEB-11 09:50

BAF 4.3 15.2 1.273E+04 1.818E+04 3.800E+03 34 360 4.10 3.58 1.53 2.56 -1.30

01-FEB-11 09:35

Final 4.8 7.42 1.980E+03 2.200E+03 3.200E+02 0.9 2 3.30 2.51 -0.05 0.30 2.58

01-FEB-11 14:20

Influent 245 383 6.200E+07 6.200E+07 2.100E+07 1294 7100 7.79 7.32 3.11 3.85 2.53


01-FEB-11 14:10

BAF 3.8 14.5 1.164E+04 1.455E+04 2.400E+03 8 209 4.07 3.38 0.90 2.32 -1.3

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© Defra 2011 23


stage BOD (mg/l)

SS (mg/l)

Coliforms confirmed

(cfu/100ml)


E.coli


F+ (pfu/ml)

Somatic phage

(pfu/ml)


E.coli

presumptive (log10/

100 ml)

log10 F+ (pfu/ml)

Somatic phage

log10 pfu/ ml


ml)

01-FEB-11 14:05

Final 15.8 13.4 1.273E+04 1.273E+04 3.900E+03 6 6 4.10 3.59 0.78 0.78 2.55

08-FEB-11 10:55

Influent 310 368 4.900E+07 7.000E+07 1.600E+07 2100 6900 7.69 7.20 3.32 3.84 1.47

08-FEB-11 10:45

CAS 155 147 1.800E+07 2.000E+07 9.636E+06 970 4000 7.26 6.98 2.99 3.60 3.23

08-FEB-11 10:25

BAF 9.3 28.2 2.880E+04 3.600E+04 7.000E+03 96 470 4.46 3.85 1.98 2.67 2.15

08-FEB-11 10:15

Final 6.1 10.2 3.360E+03 4.200E+03 2.000E+03 20 2 3.53 3.30 1.30 0.30 1.68

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© Defra 2011 24

Table 3.5 Results of chemical and microbiological analysis for works MBR

Date (time)

Treatment stage

BOD (mg/l)

SS (mg/l)

Coliforms confirmed

(cfu/100ml)


E.coli


F+ (pfu/ml)

Somatic phage

(pfu/ml)

Coliforms confirmed (log10 cfu/

100ml)

E.coli

presumptive (log10/100ml)

log10 F+ (pfu/ml)

Somatic phage

(log10 pfu/ ml)


ml)

17-JAN-11 12:09

Influent 67 89.9 4.000E+06 5.000E+06 3.100E+06 370 1130 6.60 6.49 2.57 3.05 2.98

17-JAN-11 12:14

Membrane 2.8 2.9 8.100E+01 8.100E+01 3.600E+01 0.9 0.9 1.91 1.56 -0.05 -0.05 2.85

25-JAN-11 13:15

Influent 174 419 2.160E+06 2.700E+06 1.545E+06 688 4900 6.33 6.19 2.84 3.69 0.60

25-JAN-11 13:00

Membrane 2.8 2.9 9.000E+00 9.000E+00 9.000E+00 0.9 0.9 0.95 0.95 -0.05 -0.05 -1.30

01-FEB-11 11:10

Influent 291 350 2.880E+07 3.200E+07 2.000E+07 2860 21000 7.46 7.30 3.46 4.32 3.28

01-FEB-11 11:00

Membrane 2.8 10.1 7.636E+03 1.273E+04 2.600E+03 0.9 6 3.88 3.41 -0.05 0.78 2.59

08/02/11 Influent 336 348 2.240E+07 2.800E+07 1.000E+07 2700 8100 7.35 7.00 3.43 3.91 3.33

08/02/11 Membrane 2.8 5.67 4.230E+03 4.700E+03 1.982E+03 0.9 10 3.63 3.30 -0.05 1.00 -1.30

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© Defra 2011 25

3.2 Characteristics of the treatment works at the sample times

At each visit the works operators were asked to confirm that the works was operating in a

typical manner for that works, and that there were no unusual activities or events known to the

operators. All samples were taken during periods of normal plant operation, and no unusual

events at the works were brought to our attention.

The BOD and suspended solids concentrations were measured in each sample taken. The

operators of the works were also asked for additional summary operating data for the period

of sampling – at least to include influent flow rates, BOD and suspended solids

concentrations, and any other data that would increase understanding of the operating

characteristics of the works during the sample period.

Some of these additional data were supplied for some of the works. The most complete set of

data were the influent flow rates, and final effluent BOD, SS and ammonium or nitrate

concentrations for three of the works (ASP, BAF and MBR works). There were substantially

fewer intermediate stage operating data made available.

Average values for concentrations and flows at the works from measurements taken during

the sampling period are shown in the Table 3.6. Where data in addition to the sample

analyses were available the standard deviation values are shown.

Observations from these are:

All STWs operated within their discharge consent values (see Table 2.1);

Nitrification and denitrification is shown in the data from three works; whilst no

measurements were made on the other two works they both normally achieve complete

nitrification;

The high rate activated sludge works (ASP) had unusually high concentrations of

suspended solids and ammonia in the influent samples taken for this study, and in

samples taken by the operators from the same influent sewage location at other times;

these are not reflected in high concentrations in subsequent stages, indicating highly

settleable fractions in the samples taken as influent sewage;

The values found for the individual treatment stages are within normally expected

values for the stages – about 40% removal of BOD, and 60% removal of SS in primary

settlement; and 90-99% removal of BOD through the whole process.

Figure 3.1 and Figure 3.2 show BOD and SS concentrations of each sample compared to the

average value for each works for influent and effluent samples respectively.

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© Defra 2011 26

Table 3.6 Average process stage flows and concentrations

Works Average Flow

(m3/d) BOD (mg/l)

SS (mg/l)

NH4-N (mg/l)

NO3-N (mg/l)

PercFilt, influent 229 258

Primary 100 85

Final effluent 13 33

AdvASP influent 328 300

AdvASP primary 206 121

AdvASP

secondary 3.4 8.4

AdvASP final 2.9 3.0

ASP influent 45,370 (10,259) 938 (466) 1,801

(893) 59

ASP primary 213 (12) 138 (7) 55

ASP secondary 11 28 1.6 26.3

ASP final 16 (21) 34 (41) 1.7 22

BAF influent 39,370 (6,777) 237 (74) 317 (65)

BAF primary

(CAS) 125 (29) 121 (18) 38

BAF secondary 6 (2) 17 (6)

BAF final 7 (2) 11 (6) 2 7

MBR influent 4,094 (1,844) 180 (112) 363 (317) 13

MBR final 3.6 (2.6) 5.0 (3.7) 0.7 20.3

Notes: Standard deviations are shown as ( ) for sets with more than 4 sample values.

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© Defra 2011 27

Figure 3.1 Comparison of influent samples BOD and SS concentrations with average values (including ASP works values)

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© Defra 2011 28

Figure 3.2 Comparison of final effluent samples BOD and SS concentrations with average values

The charts compare the data for each sample with average values, which include values for

samples taken by the operators in addition to samples taken for this study.

A comparison between the average value and the standard deviation values show that most

sample time values were less than 1 x standard deviation, and all were less than 2 x standard

deviation from the average. Therefore, all samples were within a normally expected range of

variation for treatment works operations.

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© Defra 2011 29

All influent samples taken from all the works on the 17th January 2011 were more dilute, and

at the three works for which flow data were available, the influent flows were about double the

average flow. Heavy rain fell throughout the South of England from late on the 16th January,

which resulted in the high flows, and probably also resulted in some storm overflows. There

were poorer effluent qualities (BOD and SS) at two of the works shown in the samples taken

on that day – from the filter works (PercFilt) and the high rate activated sludge plant (ASP).

3.3 Measurements of faecal determinands and norovirus

3.3.1 Mean concentrations

Mean values for the microbial determinands are shown in Table 3.7, as geometric mean

values for samples taken from influent and after individual treatment stages. Between one and

six samples were taken from each individual location, as shown in the sampling programme

(Section 2.3.1) and the full measurements results in Section 3.1.

Many of the concentrations of coliforms, E.coli, F+phage and somatic phage measured in

samples from each location were similar to concentrations in samples taken at other times

from the same location. 78% of relative standard deviation values for these determinands

were less than 20% of the average value for the determinand (Table 3.9). Just 4% of the

norovirus measurements met the same criteria.

The data shown in Table 3.7 are also shown in Figure 3.3. This shows close linkages in

values between the two bacterial determinands (coliforms and E.coli), and close linkages

between the two bacteriophage determinands (F+ phage and somatic phage).

The norovirus geometric mean values also show reductions in concentrations through each

STW, but the primary effluent mean concentration measurements were greater than the

influent concentrations for the four works with primary treatment. This conflicts with the other

determinand measurements, and with normal expectations.

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© Defra 2011 30

Table 3.7 Geometric mean values for microbial determinands

Works Coliforms

(log10 cfu/ dl)

E.coli (log10

cfu/ dl)

F+ phage (log10

pfu/ ml)

Somatic phage (log10

pfu/ ml)

Norovirus GII

(log10 gc/ ml)

PercFilt, influent 7.16 6.86 3.32 3.72 1.50

PercFilt primary 7.14 6.62 3.03 3.51 2.48

PercFilt final 5.51 5.22 2.51 3.33 0.92

AdvASP influent 7.29 6.93 3.58 3.99 2.01

AdvASP primary 7.32 6.77 3.42 3.76 2.34

AdvASP secondary 4.63 3.98 0.54 1.52 1.70

AdvASP final 4.45 4.05 0.30 1.27 -1.30

ASP influent 7.65 7.30 2.85 4.08 0.54

ASP primary 7.22 6.96 3.13 3.68 2.42

ASP secondary 4.97 4.59 1.12 1.85 -0.29

ASP final 3.48 3.07 0.74 1.24 -0.34

BAF influent 7.71 6.94 3.14 3.82 0.02

BAF primary (CAS) 7.27 6.86 2.57 3.37 2.58

BAF secondary 4.31 3.91 1.50 2.58 0.17

BAF final 3.69 3.24 0.40 0.55 0.84

MBR influent 6.94 6.75 3.07 3.74 2.55

MBR final 2.59 2.31 -0.05 0.42 0.71

Table 3.8 Ranges of norovirus concentrations

Influent sewage Secondary

effluent Final effluent

ASP – advanced 6.4 – 6545 ND – 2170 ND

ASP – high rate ND – 341 ND – 431 ND – 354

Percolating filter ND – 3818 ND – 382

ND – 382 ND – 340 ND – 407 NC – 384

Membrane bioreactor 4 – 2147 ND – 708

Measurements all as genome copies / ml;

ND = not detected in 10 mls;

Sensitivity of 0.05 gc/ml reported

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© Defra 2011 31

Figure 3.3 Geometric mean values of microbial determinands from each sample location

Note to Figure 3.3 – 1e refers to primary treatment; 2e refers to secondary treatment

(activated sludge, percolating filters, biological aerated filters, and membrane bioreactors; 3e

refers to tertiary filters (carbon filters at one works only) and to ultra-violet (UV) disinfection

treatment at 2 works.

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© Defra 2011 32

Table 3.9 Relative standard deviations (%) to geometric mean values of microbial determinands

Works Coliforms E.coli F+ phage Somatic phage

Norovirus GII

PercFilt, influent 5 4 11 3 123

PercFilt primary 4 2 5 6 28

PercFilt final 5 8 13 5 188

AdvASP influent 4 3 8 9 56

AdvASP primary 3 1 10 6 104

AdvASP secondary 7 8 94 13 98

AdvASP final 3 14 141 35 0

ASP influent 3 2 10 8 354

ASP primary 5 4 5 7 6

ASP secondary 10 7 37 25 679

ASP final 19 34 71 70 569

BAF influent 5 4 8 4 9133

BAF primary (CAS) 0 3 23 10 35

BAF secondary 5 11 26 6 1178

BAF final 9 13 155 50 236

MBR influent 8 7 14 14 51

MBR final 54 54 0 130 327

3.3.2 Microbial determinands influent and effluent concentrations at individual sample times

Using all concentration values

Mean values of microbial determinands, reported in section 3.3.1 above, show that, for the

bacterial and phage determinands, most individual samples from each location had similar

values. The individual concentrations values for F+phage, E.coli and norovirus are shown in

Figure 3.4, Figure 3.5, and Figure 3.6 respectively.

The concentration values for F+phage and E.coli show distinct differences between the

influent (inf), primary effluent (1e), secondary effluent (2e) and final effluent (3e) for most of

the sample times. The equivalent distinction between treatment stages for the individual

sample times, is not demonstrated for the norovirus measurements (Figure 3.6), with some of

the influent sample concentrations less than the primary effluent concentrations.

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© Defra 2011 33

There were two sets of samples for which all sample locations reported non-detectable

norovirus: these were:

PercFilt 23 Nov Influent and secondary effluent;

BAF 25 Jan Influent, secondary and final effluent.

At all other sample times at least one of the samples was reported to contain detectable

norovirus.

Figure 3.4 F+ phage concentrations in samples





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© Defra 2011 34

Figure 3.5 E.coli concentrations in samples





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© Defra 2011 35

Figure 3.6 Norovirus concentrations in samples





Using selected values

In this section the data are rearranged to show whole works influent and effluent

concentrations. For this assessment of overall works performance the larger of either the

influent sample or the primary effluent sample are shown as the influent, and the smaller of

either the secondary effluent or the final effluent are used as the works effluent values.

Data values for influent and effluent to each works at each sample time are shown for

norovirus, F+ phage and E.coli in Figure 3.7, Figure 3.8 and Figure 3.9.

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© Defra 2011 36

Figure 3.7 Selected norovirus influent and effluent concentrations

Figure 3.8 Selected F+ phage influent and effluent concentrations

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© Defra 2011 37

Figure 3.9 Selected E.coli influent and effluent concentrations

Short period variation

Four sets of samples were taken at closely related times:

PercFilt 30 Nov, 9:45 & 13:45, influent, primary and final effluent;

AdvASP 6 Dec, 14:58 & 7 Dec, 10:00 and 14:25, influent, primary and

secondary effluent;

ASP 17 Jan, 08:54 & 14:10, influent, secondary and final effluent;

BAF 1 Feb, 10:05, & 14:20, influent, secondary and final effluent.

There are differences between the determinands at the different times. E.coli changes by

log10 0.3 (doubling or halving); F+ phage concentrations were slightly less variable (log10 =

0.2).

These short term variations are small compared to the longer term (several week) differences

between equivalent samples. The norovirus concentration changes that might be present

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© Defra 2011 38

cannot be distinguished from the overall variations between measurements. Many more

frequent samples would be required to identify clear diurnal variations.

3.4 Removal of microbial determinands

3.4.1 Average values

Average values for the removal rates of microbial determinands are shown in Figure 3.10 and

Table 3.10.

Figure 3.4 to Figure 3.6 show that E.coli and F+ phage influent concentrations were, in nearly

all samples, the same as or greater than the primary effluent concentrations. The

measurements reported for norovirus in the same samples were much less consistent, with

many influent sample measurements less than the primary effluent, and in some cases, less

than the secondary effluent measured concentrations.

If the lower measured influent concentrations of norovirus are not accurate, then a

combination of data between the influent measurements and the primary effluent

measurements would provide a better representation of norovirus entering the works.

Therefore, for these removal rate calculations, the greater of either influent or primary effluent

concentration was used to represent the influent load (see also Figure 3.7 to Figure 3.9).

The results show that the two processes that involve retention of significant amounts of

biomass on support media, the percolating filter process (PercFilt) and the biological aerated

filter (BAF) had lower removal rates of viruses, that is, F+ phage, and norovirus, than the

three activated sludge processes.

Table 3.10 Microbial determinand removal rates between influent or primary and secondary effluent

Works Removal rate, log10

E.coli F+ phage Norovirus

PercFilt 1.65 0.85 0.89

AdvASP 2.57 2.87 1.38

ASP 2.71 1.92 2.57

BAF 3.05 1.64 0.85

MBR 4.44 3.12 1.84

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© Defra 2011 39

Figure 3.10 Microbial determinand removal rates between influent or primary and secondary effluent

3.4.2 Individual samples removal rates

The distribution of the data values used to prepare the average values for removal are shown

in Figure 3.11. Negative values show that the reported effluent concentration was greater than

the influent during the same sampling visit. Zero values mean that the influent and effluent

concentrations were the same – in each case, no norovirus was detected in either the influent

or the secondary effluent.

These values do not include the effect of UV disinfection for the high rate ASP, and the BAF

works, or the final tertiary filtration at the AdvASP works.

The chart shows that removal rates of the bacterial determinand, E.coli, were greater than for

the F+ phage for most samples.

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Figure 3.11 Removal rates between influent (influent or primary) and secondary effluent for each sampling occasion

3.4.3 Correlations between microbial determinands

Correlations between the total coliforms concentrations, and E.coli, F+ and somatic coliphage,

are shown in the Figure 3.12. The measurements are from all the samples, influent, primary

effluent, secondary and tertiary effluents, and from all the works. It was expected that, since

E.coli are a large proportion of the total coliform population, that there should be a close

correlation, and this is confirmed by the data.

In the same way, the phage populations are dependent on E.coli, and the data also show this

close relationship.

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Figure 3.12 Correlation of E.coli, F+ and somatic phage with total coliforms in all samples

A similar comparison between the norovirus genome copy concentrations and the F+phage

concentrations is shown in the Figure 3.13. No correlation is apparent between these

measurements.

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Figure 3.13 Correlation of norovirus genome copies with F+ phage in all samples

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4. Discussion

4.1 Presence of norovirus in sewage samples

4.1.1 Normal treatment conditions

Out of the 24 sample groups taken from the five works, only 2 groups had no detectable

norovirus GII in any of the samples. Therefore, for all the works, it can be concluded that

measurable norovirus was present in the influent sewage for most of the time during the

period of sampling.

4.1.2 Storm sewage

No samples were taken at any storm overflows. Storm conditions dilute the concentrations in

sewage but increase flows, including wash down of settled solids in sewers, towards

treatment works. Under high flow conditions some of the raw sewage may discharge via

overflows into the catchment, by-passing the treatment works.

During sampling there was one day (17th January 2011) on which overflows may have been

discharging. On this day concentrations of the biochemical and microbial determinands

reaching the treatment works were reduced in proportion to the increased flows. Flows

measured at the works on this day were double the average flow rate for the period.

These conditions did not significantly adversely affect operating performance of the treatment

works. This happened to be the one day on which samples were taken from all the treatment

works. The percolating filter works (PercFilt) showed an increase in the effluent

concentrations (BOD and SS) to greater than the average values, and one of the two ASP

samples taken on the same day also showed effluent concentrations greater than the average

for the works. Effluent qualities in the other three works were lower than the average

concentrations for the period. However, because the flows were greater, the overall discharge

load was probably similar or may have been slightly greater from the treatment works, apart

from the filter works. The filter works discharge may have been up to four times greater than

the average discharge (double the flow and double the concentrations).

Of the microbial determinands, the phage concentrations were lower in the influents on 17th

January than the average concentrations; approximately inversely proportional to the increase

in the flow. Reductions in the E.coli concentrations were less than those for the phage

concentration. For the three plants with traditional primary settlement, removal of phage and

E.coli was less than the average, tending to minimal or no removal across primary treatment;

although overall plant removal rates were similar to the non-storm sampling days. The

chemically aided settlement primary treatment at the BAF plant may have retained its

settlement efficiency. All these observations are based on very few sample numbers across

the primary treatments.

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Although there are few measurements of primary treatment performance, they suggest that

storm tanks alone may give rather poor microbial removal performance during storm events.

There is nothing to suggest that norovirus removal during these conditions would differ in any

way to the removal of the other microbial determinands, and in particular, the phage

determinands.

Assessment of the consequences of these observations on overall storm loading into

catchments would require good understanding of flows from storm overflows into sensitive

catchments. This has not been carried out for this project.

4.2 Impact of treatment processes on microbial removal rates

4.2.1 Treatment process features

There were two significant differences in the treatment processes: the use in two works of

biomass support media (PercFilt and BAF), compared to suspended biomass; and in one

works, the use of a membrane to provide a physical barrier between the biological treatment

process and the final effluent. A further difference in two works was the use of UV treatment

on the secondary effluent to provide additional disinfection.

Traditional primary settlement processes provide initial separation of settleable particulate

solids in raw sewage. Solids removal rates that are aimed for in design are in the region of

60% removal of solids. Soluble, and very fine particulate materials are not removed, although

some filtering of fine solids and trapping in the settling particulate material does occur.

Primary settlement is not expected to reduce microbial load to any greater extent than

suspended solids removal. Bacteria and phage are initially linked to solids in sewage, but

turbulence provides some re-suspension and disintegration. Dependent on sludge

management and influent sewage components, there can be release of ammonia and

sulphides both of which can slightly enhance any physical removal of particulates, which

together with the normal decay due to retention time is expected to aid removal. However,

degradation of sludge in the tanks can also result in additional release of micro-organisms into

suspension. Hence primary tanks or storm tanks are not significant disinfectant processes.

Secondary treatment processes all provide large removals of bacteria and viruses, by

attachment, engulfment and degradation by biomass that is growing rapidly in the sewage.

The results found here are consistent with expected removal rates, providing 10-1000 fold

removal of E.coli and phage. The lowest removal rates were for the percolating filter and the

BAF stages, for both E.coli and for phage.

The most effective disinfection process was the MBR process which achieved (from the

geometric mean values) over 10,000 fold removal of E.coli, and 1,000 fold removal of phage.

The effectiveness of this process is due to the combination of a high suspended biomass

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concentration (at three to four times the concentration in standard activated sludge

processes), as well as the membrane acting as a very fine filter.

The tertiary UV treatment at the ASP and BAF plants produces an additional 4 to 30 fold

removal of E.coli, and 2 to 12 fold removal of phage.

The tertiary filtration at the AdvASP process did not provide significant additional disinfection

probably because the remaining microbial content, having passed through the final settlement

stage were fully suspended in the liquor and unlikely to be trapped by media designed to trap

particulates.

4.3 Surrogates for assessing efficiency of norovirus removal

The relationships between the faecal determinands of coliforms, E.coli and the two phage

measurements, show clear positive linkages.

The variation in the norovirus results, and the lack of clarity in understanding whether the

norovirus measured represents potentially infective norovirus, means that a detailed

distinction between operation of individual stages of treatment is unrealistic. However, the

geometric mean results for each works provide good reasons to suppose that the removal

efficiencies would be similar between norovirus and phage for the different works.

4.4 Analytical methods for norovirus

The analysis provided a measurement of the concentration of a unique section of norovirus

GII genome present in the sample. This may have been either a complete and infective

norovirus particle or an incomplete disintegrated section of nucleic acid. Therefore

measurements may underestimate the extent of removal of active norovirus from sewage.

In addition, the analysis itself is complex. Adjustments were made to an existing method, by

VeroMara for this project. Small volume samples (25 ml volumes) were used, and

concentrated by freeze drying before extraction. The efficiency of the procedure was

monitored by addition of a known spike of Mengovirus, and the average efficiency of the

procedure was reported to be 71%. However, there are severe inconsistencies in the

measurement results in the expected relationships between succeeding stages; it seems

unreasonable to suppose that concentrations after primary treatment should be greater than

in the influent. These inconsistencies indicate that the extraction and concentration methods

require further validation.

4.5 Sustainability factors for different works types

There is a small indication in the data that treatment processes that use biofilms on support

media (percolating filters and BAF plants) may have poorer virus removal characteristics.

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These types of plants tend to be present at smaller works, and usually have lower energy,

emissions and other operational costs.

An outline estimate of costs of operation and sustainability factors was carried out using the

UKWIR (2008) Sustainability Tool. This was prepared by WRc, and is used in conjunction with

the water industry carbon accounting workbook. The tool includes estimates operating and

capital costs for a variety of process changes.

Results from the estimations are shown in Table 4.1. This shows operational and

sustainability costs for three works types, percolating filter, membrane bioreactor and

activated sludge works, for a population size of 20,000 pe.

The effect on costs, energy and emissions have been calculated for changing percolating filter

works to either of the two suspended biomass type of works, for populations totalling 1 million.

The total population size has been used only as an indicator of possible costs, and has not

been based on any proper assessment of sensitive locations or works.

The estimation demonstrates the substantial capital and new ongoing operating and other

sustainability factor costs involved in moving from biomass support processes to suspended

solids treatment processes. These would have to be balanced against the possible

improvements in treated sewage qualities when discharged into suitable locations.

Table 4.1 Sustainability factors for works types sampled; effect of changing from percolating filter works to ASP or MBR

Sustainability factor

Costs for works of 20,000pe Cost for works change,

for total 1million pe

PercFilt MBR ASP PercFilt to

MBR PercFilt to

ASP

Energy, MWh/a 46 466 211 21,000 8,250

Sludge, tonne/a 441 520 572 3,950 6,550

CAPEX, £m 2.7 4.8 1.4 240 70

OPEX, £k/a 39 73 53 2,200 700

Greenhouse gases,

tCO2eq, 25years 9,852 18,942 14,733 450,000 240,000

4.6 Sampling programme costs

Visits were made to 5 separate treatment works, with a total of 24 visits (see Table 2.3). An

outline of the analysis and other direct visit costs is shown in Table 4.2. This may be used to

provide guidance for any future programme of sampling and analysis. No costs for other

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interactions with the management group, management of the project, collection of results,

analysis of results and reporting are included in this summary.

Table 4.2 Costs of sampling and analyses

Activity Cost

Norovirus analyses, at £100/sample £7000

Other biochemical and microbial determinands £4447

Associated equipment for sampling and transport to analytical labs £295

Transport costs for sampling and delivery to analytical labs £723

24 visits made to 5 works sampling approx. 18 days

Preparation, including health & safety plans and agreements with

site operators, transport of samples, analytical arrangements approx. 7 days

4.7 Options for reducing pathogens discharged from sewage

Sewage treatment works provide a high degree of protection to the environment from

substances present in raw sewage. Storm discharges by-pass this protection, whilst

protecting the treatment works from excessive flows.

New designs of surface water discharge systems do not include discharge into sewers, so

that the sewer flow is less affected by storms. Elimination of all existing discharges into

sewers would be a huge cost. Treatment works could be expanded to accept intermittent

discharges, or store larger volumes of waters for return into the treatment works after a storm

event. This option would also be of considerable cost, even if limited to works that discharge

into the most sensitive areas.

General discharge concentrations of potential pathogens may be reduced by replacing less

efficient works – indications in this study are that percolating filters are less efficient at

removing viruses from sewage, but this too would have high costs, including carbon and

energy costs, in both capital and operating areas.

There may be some benefit in considering a combination of approaches, to include better

management of some surface water flows (identifying major infiltration locations for example),

including managed areas for storm discharge ponds upstream of treatment works, to

subsequently return to sewers, and including flow balancing at treatment works to a greater

extent than currently available.

Disinfection of storm discharge overflows may also be considered, although UV disinfection of

raw sewage has a low efficiency due to opacity of the sewage.

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5. Conclusions

5.1 Conclusions

Sewage treatment reduces norovirus load in all sewage works effluents by between

one to two log reductions across the five sites investigated; although the norovirus

concentration data are scattered, more of the secondary or final effluent samples had

non-detectable levels of norovirus than the influent or primary effluent samples;

Summary Figure 1 - Concentrations of Norovirus at different stages in sewage works samples showing average, standard deviations and maximum and minimum values

The scale of norovirus removal is low compared to the level of removal of bacteria

which the treatment sites are designed to do. Norovirus was still present in 63% of

samples following secondary treatment and 36% of samples following tertiary

treatment. There was a poor correlation between F+ coliphage and norovirus,

suggesting that F+ coliphage may not be a suitable indicator organism to use to test for

the presence of norovirus;

Treatment process types may affect removal efficiencies of norovirus; there is some

indication that processes that use biomass support systems, are less effective at

removing viruses (as phage) than suspended biomass processes, but no process was

found that completely removes norovirus;

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Norovirus analysis is complex; results may be confused by:

Measurement problems in the sample matrix;

Inability to distinguish between active and inactive norovirus;

True variations in presence and efficiencies of process removal.

Further development of norovirus analysis is necessary including full agreement on

appropriate and economic analytical procedures between providers;

Loads of potential pathogens into catchments during storm events may not be

significantly increased by treatment works discharges of treated effluent; however,

discharges from storm tanks, which tend to perform in a similar manner to primary

tanks, are likely to contain pathogens at concentrations only slightly reduced from the

influent sewage concentrations, similar to primary treatment removal; other storm

discharges will have concentrations of pathogens reduced inversely in proportion to the

increased flow.

5.2 Options for future work

This work has shown some differences between treatment works which should be

further studied;

Validation and agreement on economic and effective norovirus analysis for water

samples is required;

The extent and amount of storm overflows into shellfish waters should be evaluated.

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References

Lodder, W.J. and de Roda Husman, A.M. (2005). Presence of noroviruses and other enteric viruses in

sewage and surface waters in the Netherlands. Applied and Environmental Microbiology Vol 71

pp1453-1461

da Silva, K.A., Le Saux, J.C., Parnaudeau, S., Pommepuy, M., Elimelech, M. and Le Guyader, F.S

(2007). Evaluation of Removal of Noroviruses during Wastewater Treatment, Using Real-Time Reverse

Transcription-PCR: Different Behaviors of Genogroups I and II. Applied and Environmental

Microbiology, December 2007, p. 7891-7897, Vol. 73, No. 24

UKWIR (2008). Water Framework Directive: Sustainable Treatment solutions for achieving good

ecological status (08/WW/20/3).ISBN: 1 84057 501 8. www.ukwir.org/ukwirlibrary/92397

http://www.ukwir.org/ukwirlibrary/92397

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