MicrobialHealth Hazards Associated with Effluent Reuse

ReportNo WSAA 144

August 1998

SYNOPSIS

The reuse ofeffluent for irrigation purposes has occurred for centuries and, withincreasing pressure on potable water supplies, such reuse is increasing. Today,effluent reuse managers are aware of the potential environmental problems posedby such reuse and the management practices required to reduce this. Similarly,knowledge of the pathogens which may be present in effluent is increasing, andmanagers and the public question the potential health hazards posed by suchpathogens.

This reportdetails the pathogens found in effluent and those pathogens which pose thegreatest health risk in the developed world i.e. viruses and protozoa. Therelevance of current Guidelines and indicators of the microbial quality ofeffluent, e.g. faecal coliforms is discussed. The standard indicators do notdirectly reflect the microbial quality of effluent, although many can be usedas treatment process indicators. A survey of the pathogen content in effluentin Queensland demonstrates the lack of correlation between the indicators ofmicrobial quality and the levels of viruses and protozoa. This survey alsodemonstrates the large variation in treatment plant efficacy, both between andwithin sewage treatment plants. It is suggested that, until an indicator whichcorrelates with viruses and protozoa can be found, guidelines and regulationsshould emphasise the use of process indicators and treatment and a greateremphasis should also be placed on the reliable production of effluent with lowvariability.

A survey ofeffluent reuse practices also demonstrates the lack of adherence to the currentGuidelines by effluent reusers. 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 withthe disregard for the current guidelines for reuse, cumulates in anunacceptably high level of risk. This risk may be reduced by either thereduction of pathogens in the effluent and/or by the reduction of the doseingested by the public – through detailed education of the public and effluentreuse 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 containspathogens and, as such, should be treated with caution if potential healthrisks are to be minimised.

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