Water and the Circular Economy
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Alternative Sewage Systems: Investigation of Composting Toilets in a High-Density Residential Setting

The Challenge

The waterless or dry composting toilet (DCT) is most often used in rural or remote areas of Australia, where there is no established sewerage system. However, the use of this technology has yet to be embraced in urban and highly populated areas and there is little research or evidence to prove whether this type of sanitation technology is a viable option in cities and metropolitan areas.

GHD is an international professional services company committed to minimising the ecological footprint of water and sanitation services. GHD, in association with Bensons Property Group, Demaine Partnerships and Environment Equipment, conducted research into the feasibility of using DCT sanitation systems, also incorporating urine separation, in an urban environment.

The Project

A Smart Water Fund grant was awarded to the group to undertake a study into the technical and economic feasibility of introducing DCTs into inner urban apartment buildings. The study examined regulatory constraints around the technology and its possible environmental advantages, such as the potential to decrease sewage discharge as well as the potential use of compost collected from apartment blocks as agricultural fertilizer. The study also surveyed potential apartment buyers in the inner Melbourne area on their attitude to, and acceptance of, DCT systems. GHD proposed to use the feasibility study to support the installation of a demonstration model in an inner city apartment block. The proposed demonstration would equip 12 new apartments with DCTs as well as an agricultural compost and urine separation recycling trial.

Lessons Learnt

The study identified that, whilst there is an Australian Standard and approvals processes for individual installations, there is no established approvals process for large-scale application, particularly within urban areas.

The study also confirmed transport of collected compost and separated urine would not require special approvals, though general provisions of the Health and Environment Protections Acts would apply, and works approval would be needed for any storage facilities.

Health risks involved with the use of DCTs were found to be no higher than using a conventional toilet, provided that insect breeding was controlled and the system was properly maintained. When researching health risks involved in the use of compost material and urine from waterless toilets as an agricultural fertilizer, the study took its direction from European studies, which indicated that risks were minimal if bio-solids were properly composted, urine was stored before use, and use was confined to dry land crops.

The study recommended investigating how beneficial use of compost and urine residues would be regulated under the Environment Protection Act.

All regulators consulted, including EPA Victoria, Department of Human Services, Moonee Valley Council and City West Water, indicated their support for a demonstration project. Market research indicated more than half of survey participants said they would buy an apartment with this type of sanitation system, while 98 per cent of all respondents indicated that they would consider paying extra for a water-efficient apartment.

The Benefits

The study revealed that DCTs would provide savings of up to 19 per cent in domestic water use and reduce the volume of household sewage discharge by 28 per cent. More than 50 per cent of the nitrogen and phosphorus in domestic sewage can be captured by DCTs and beneficially reused with consequent savings in sewage treatment. The total household cost of dry sanitation plus grey water sewerage is likely to be similar to or less than existing water flushing toilets and likely to be more economical in the future if the price of water rises.

Benefits to the environment and ecological systems included the potential for this sanitation system to be more energy efficient and reduce the release pollutants such as bio-solids, salts and nutrients associated with domestic sewage systems, into the environment. In turn, these nutrients can be used for agricultural purposes.

The demonstration project considered in this feasibility study did not proceed but there remains an opportunity for an interested developer to undertake the demonstration phase.

Supporting documents