© WRc plc 2012

IMPACT OF WASTE WATER TREATMENTS ON

REMOVAL OF NOROVIRUSES FROM SEWAGE

1 March 2012

• defra project reference WT0924

• Elaine Connolly, project manager, defra

• Roderick Palfrey, WRc plc, Swindon,

Wiltshire (rod.palfrey@wrcplc.co.uk)

• Project period October 2010 – May 2011

Impact of wastewater treatments on

removal of noroviruses from sewage

Background to the research

• Increasing industry and food safety

concerns about norovirus

• Little known about norovirus in the

natural environment

• Initial research to look into the scale

of the problem

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• NV – single stranded RNA virus

• Source – human type, commonly cycles

through shellfish, then by human cross-

infection, returning to sewage (and other

wastes)

• Major risk to elderly and other immuno-

compromised populations

• Commonly known as the “winter vomiting

bug”

Norovirus in the Environment

© CDC National Center for immunisation and respiratory disease

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• Measurement of Norovirus gene template in crude, storm and treated sewages

• Determine significance of treated effluents on total load discharged

• Determine reductions in Norovirus by different treatment process trains

• Investigate correlations between removal of faecal indicators, in particular coliphage, and attenuation of Norovirus by treatment processes

Note: There are estimated to be 1 million cases of Norovirus infection in UK each year. Theinfective dose is 1-10 particles. Shellfish, being filter feeders, concentrate NV out of seawater if it is present. Shellfish are a source of human NV infection, hence the importance of wastewater discharges into shellfish waters. Settled sewage was sampled as a surrogate for storm overflow. NV cannot be enumerated by cultural methods so reverse transcription PCR was used, however this really only shows whether NV is or has been present; it does not distinguish infective from non-infective, just the presence/absence of NV DNA. [TE]

Objectives

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Sampling from sewage treatment

Final / tertiary effluent sample

Secondary effluent sample

Primary effluent / storm sewage

surrogate sample

Crude / influent sample

Storm tanks

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• 5 works (3 coastal)

• Advanced activated sludge

• High rate activated sludge

• Biological (percolating) filter

• Chemically aided settlement (CAS) + biological

aerated flooded filter (BAFF)

• Membrane bio-reactor

• 70 samples between November 2010 and

February 2011

Sampling

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Sample locations and

numbers (1)

6 4 6

3

Influent Primary

Filter Advanced activated sludge Effluent

Influent High rate activated sludge

UV

2 4

4

4

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Sample locations and

numbers (2)

5

Primary Biological filter

3

5

Membrane bio-reactor

4 4

Biological aerated flooded filter (BAFF)

CAS

5

5 2 5

UV

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Measurements

• Norovirus

• RNA genome using threshold cycle count

• VeroMara at Scottish Marine Institute, Dunstaffnage

• Faecal indicators

• E.coli, total coliforms

• F+ & somatic coliphage

• Samples to NLS (National Lab Service)

• Works operation indicators

• BOD, suspended solids

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Hypotheses and principles

• Primary settlement can model storm tank

performance

• Norovirus behaves as bacteriophage (F+ and

somatic) in terms of physical removal

• Norovirus activity cannot be measured

• Membrane bioreactor (MBR) treatment likely

to reduce concentrations of norovirus

significantly

• UV treatment is not expected to affect

norovirus measurement

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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

Biological

aerated filter,

BAF

ND – 340 ND – 407 ND – 384

Membrane

bioreactor 4 – 2147 ND – 708

Measurements all as genome copies / ml; ND = not detected in 10 mls;

sensitivity

Range of norovirus

concentrations

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Microbial determinand concentrations

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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F+ phage concentrations

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Norovirus concentrations

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Removal rates across works

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Norovirus concentrations by individual stages

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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Correlation between faecal

indicators

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Correlation between F+ and

norovirus

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• Sewage treatment reduces Norovirus load

• Treatment process types may significantly affect

removal of norovirus

• Activated sludge processes and Membrane

Bioreactors most effective

• Filter processes may have differential effects between

bacterial and viral indicators

• Norovirus analysis is complex – individual values in

this study were inconsistent with related samples

• Some indication that F+ phage could be a surrogate

for treatment effectiveness

• Within this study difficult to identify effectiveness of

individual treatment stages

Findings

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Summary of Norovirus data

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

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• Replace percolating filters with activated

sludge plants or membrane bioreactors?

• Build new works to accept all sewer flows?

• Costs for new works (10 million population)

• Energy costs increase 5 – 10 fold

• New build – £1 – 3 billion

• Operating costs increase

• Greenhouse gas emissions double

Final thoughts…..

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Sustainability

factor

Costs for works of 20,000pe

Cost for works

change, for total

1 million 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

Costs of changing works

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Related work

• Other work has been carried out by CEFAS

for the FSA at a single site over a two year

period.

• Findings include seasonal effects, and

persistence of Norovirus at long distances

from discharges

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• Report now on the Defra web-site:

• With thanks to the staff and management of

the host sampling sites (Thames, Wessex,

Southern, South-West Water)

• Questions?

Thank-you

Comment from meeting: Since CSO discharge is inevitable, the wastewater collection and treatment system can never be a Critical Control Point (in a HACCP, Hazard Analysis and Critical Control Point protocol) for controlling norovirus in seafood because by-pass is inevitable. In addition apparently 2% of properties have misconnection of foul wastewater to surface water drainage (as high as 10% in some areas) which is another by-pass. Irrespective of investment, the wastewater system can never be a CCP for norovirus in seafood. [Tim Evans]