Domestic Greywater Reuse: Overseas Practice and its Applicability to Australia

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Domestic Greywater Reuse: Overseas Practice and its Applicability to Australia

Report no. UWRAA 73

March 1994

Synopsis

This report is the second on a research project to determine the potential for domestic greywater re-use in Australia.

The first report, “Domestic Greywater Re-use: Preliminary Evaluation (UWRAA Research Report No 60)”, was based on overseas correspondence, a literature search, and chemical and micro-biolanalysis of some sullage systems. That report concluded that the western states of the USA and Japan are the world leaders in this type of onsite re-use and that greywater re-use poses environmental and health concerns but, with adequate guidelines, could achieve substantial water savings. This second report investigates overseas practices in greywater re-use and how these practises could apply to Australia.

Domestic wastewater can be segregated into two separate flows, namely:

· Blackwater – comprising water closet, bidet and bidette waste and having gross faecal contamination

· Greywater (also referred to as sullage) – comprising all remaining household wastewater; for example, bath, laundry.

Although toilet wastes are excluded from greywater, greywater still contains human faecal indicator bacteria in concentrations high enough to indicate a health risk from the potential presence of pathogenic micro organisms. Overseas authorities have confirmed this conclusion.

For safe re-use, either of the following must occur:

· greywater must be treated to remove or destroy these micro organisms

· human contact with greywater must be prevented.

Treatment of greywater to make it safe for human contact is expensive to achieve on an individual household basis. It is also difficult to ensure that treatment systems are maintained. Surveys in the USA, Australia and Brisbane have found that 60% to 80% of “onsite domestic wastewater treatment plants” are not maintained adequately. These treatment plants consistently do not produce an acceptable quality effluent.

Limited evidence from trials and existing greywater systems suggests that there are no adverse effects on lawns and ornamental gardens from chemicals occurring in greywater. However concerns are raised that chemicals in greywater could cause damage to clay soils and some native plants and increase the levels or nutrients in groundwater and waterways.

The twenty-two Western States of the USA allow the direct re-use of untreated domestic greywater by sub-surface watering of ornamental gardens and lawns. To prevent human contact with untreated greywater, sub-surface techniques, such as sub-surface drip emitters and leach fields, are specified.

Toilet flushing with greywater is not allowed because of the risk of human contact(from splashing and aerosols) and the unreliability of household treatment. The preliminary evaluation given in the first report wrongly concluded that greywater re-use for toilet flushing did not require treatment other than disinfection and coarse screening.

Japan does not re-use greywater, except for hand washing water (without soap) being re-used to flush toilets. However, the Japanese carry out wastewater reclamation for toilet flushing, irrigation, and ornamental ponds/fountains, using expensive and sophisticated treatment processes. This happens in high rise buildings and at regional treatment plants and, because of Japan’s severe water shortage, is economical.

The third and final part of the research will include testing and evaluation of existing sullage systems to determine guidelines for the application of domestic greywater re-use for Australia. Trials will also be carried out on hand basin cisterns which re-use hand washing water for toilet flushing.

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