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Waste Water Treatment Impact On Norovirus

UK - In response to growing concerns over public health from mainly uncooked oysters, Defras Water Quality team has carried out a study to make an initial assessment of whether conventional waste water treatment has any impact on norovirus levels.

The work was carried out at five sewage treatment works (STW) in England during the winter of 2010/11. Seventy samples were taken across the various treatment stages: from the primary influent, after primary and secondary treatment and the final effluent.

The five STW chosen all had different types of treatment systems – advanced activated sludge, percolating filter, high rate activated sludge, biological aerated filter and membrane bio-reactor. Some of the plants also had UV disinfection as a tertiary treatment process.

The results from testing of these samples shows that norovirus was present at all of the STWs and the treatment process removed norovirus to some degree, with membrane bio-reactor treatment being the most efficient and the percolating filter and biological aerated filter systems being less efficient.

However, there was a high level of scatter in the data, due to a small data set, which suggests that further work would be needed to refine these findings.

The project report also highlights the sustainability factors of the different STW, highlighting the operation and capital costs of the various systems covered, and the financial and CO2 costs of upgrading the systems.

Viruses in shellfish, particularly oysters, present a public health concern and the European Food Safety Authority has recently produced an opinion paper which concludes that production of bivalve molluscs in the vicinity of discharges of human faecal pollution is a high risk practice for viral contamination.

The opinion suggests various ways of tackling this, including prohibited zones for shellfish harvesting in the vicinity of sewage discharge points. The results of this research will contribute to the evidence being collated by Defra and the FSA to support policy development on norovirus in shellfish.

Lucy Towers

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