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This article published in the online magazine WaterWorld describes PhD student Nyoman Marleni's dissertation research in engineering at Victoria University in Australia:
But if everyone shifted to greywater reuse this would give the "worst scenario", says Marleni.
The reuse of waste water from the bathroom and laundry to water the garden and flush toilets would reduce potable water consumption by 70 per cent, resulting in a much greater impact on odour and corrosion.
If everyone in the study area recycled their greywater, Marleni's model found hydrogen sulfide would shoot up to 46 parts per million. Not only would it result in an unpleasant odour, but it would also cause eye, nose and throat irritation, as well as headaches and nausea.
The extra gas would also cause a major corrosion problem, reducing the pipe life by 77 years. Marleni's model found the use of water-saving devices and sewer mining, in which wastewater is recycled, had an intermediate affect on odour and corrosion.
"If we want to use water conservation then rainwater harvesting would be the best option," says Marleni.
But, she says, climate change might make greywater reuse a preferred option in which case authorities would need to use chemicals in the sewers to protect pipes and stop odour.
But wait, there is more to the debate...
Professor Stuart White from the Institute for Sustainable Futures at the University of Technology, Sydney welcomes the study. "This work is important in highlighting the difficulties that sewer systems have in coping with different operating conditions," he says. But, White says the problem is not water conservation but the design of our "antiquated sewer networks", which are gravity fed and need too much water to push waste through.
"The solution is not to slow down the improvement in water efficiency, but to design smarter sewers, and to smarten the sewers as they are replaced," he says.