Microbial Health Hazards Associated with Effluent Reuse
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report no. UWRAA 144
The reuse of effluent for irrigation purposes has occurred for centuries and, with increasing pressure on potable water supplies, such reuse is increasing. Today, effluent reuse managers are aware of the potential environmental problems posed by such reuse and the management practices required to reduce this. Similarly, knowledge of the pathogens which may be present in effluent is increasing, and managers and the public question the potential health hazards posed by such pathogens.
This report details the pathogens found in effluent and those pathogens which pose the greatest health risk in the developed world i.e. viruses and protozoa. The relevance of current Guidelines and indicators of the microbial quality of effluent, e.g. faecal coliforms is discussed. The standard indicators do not directly reflect the microbial quality of effluent, although many can be used as treatment process indicators. A survey of the pathogen content in effluent in Queensland demonstrates the lack of correlation between the indicators of microbial quality and the levels of viruses and protozoa. This survey also demonstrates the large variation in treatment plant efficacy, both between and within sewage treatment plants. It is suggested that, until an indicator which correlates with viruses and protozoa can be found, guidelines and regulations should emphasise the use of process indicators and treatment and a greater emphasis should also be placed on the reliable production of effluent with low variability.
A survey of effluent reuse practices also demonstrates the lack of adherence to the current Guidelines by effluent re users. Using Quantitative Microbial Risk Assessment, the level of risk of infection to the public from effluent reuse is calculated. These results demonstrate that the current poor quality effluent, together with the disregard for the current guidelines for reuse, cumulates in an unacceptably high level of risk. This risk may be reduced by either the reduction of pathogens in the effluent and/or by the reduction of the dose ingested by the public – through detailed education of the public and effluent reuse managers and staff.
In conclusion, effluent reuse is important as it removes the pressure on potable water. However, one should never lose sight of the fact that effluent contains pathogens and, as such, should be treated with caution if potential health risks are to be minimised.