Solving the stink from sewers

The rotten egg gas leaking from sewer pipes and costing billions of dollars worldwide in odour control may soon be far less of a problem, thanks to new research discussed at the 2012 International Water Association (IWA) conference last week.

Trials with a mix of chemicals called Cloevis, on sewers in the Gold Coast, stopped 99% of the rotten egg gas, or hydrogen sulfide, emitted from these pipes.

Lead researcher Professor Zhiguo Yuan, from the University of Queensland, told IWA delegates that one week after dosing for a few hours, in most cases the gas level increased to less than one fifth of its emissions prior to the treatment, and this has been repeatedly observed over a period of five months.

“We are currently looking to commercialise Cloevis and are doing a further four trials ... in the US and Canada,” Professor Yuan said. “Our partners over there are very excited by Cloevis’s potential.”

The gases causing the bad smells in sewers also play a role in corroding sewer pipes, which is another costly problem, especially in warm climates.

Professor Yuan’s team, involving active participation from key members of Australia’s water industry, is also working on corrosion issues and has another study into chemical-free methods for managing hydrogen sulfide gas.

“We have done some trials with oxygenation of sewage using an electrochemical method which has reduced hydrogen sulfide enormously,” Professor Yuan said. “We probably won’t stop all bad smells from sewers forever but we’re well on the way to reducing their extent.”

Other speakers at the IWA conference spoke about managing bad smells from sewers and wastewater drains once they had escaped.

Dr Valentina Lazarova from France reported on trials on the strong smells coming from the Oued El Harrach River in Algiers. Her team used jasmine-smelling microsprays on the highway crossing the river and gels on pedestrian bridges nearby to mask the smells.

“We used 1000 questionnaires and face-to-face interviews with local people and found out that 70% of the population were satisfied or very satisfied with what we did and 96% wanted the project to continue,” she said.

Zdaravka Doquang from France talked about how to determine how bad a sewage-based smell is for people, with regards to both its type and intensity of smell. Her team has developed an ‘odour wheel’ for sewage smells that “helps to classify odours and ensure a common language to communicate about the odours”.

“People are most sensitive to hydrogen sulfide or rotten egg gas compounds both qualitatively and quantitatively compared to any other compounds,” she said.