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Water Additive Eyed in Corroded Sewers

Thursday, August 21, 2014

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A surprising connection between water treatment and wastewater management could be causing the sewers in Australia to quickly corrode.

Researchers from the University of Queensland say an additive used to treat drinking water could be to blame.

In some instances, the concrete pipes have had their lifetime reduced by up to 90 percent, reported.

Professor Zhiguo Yuan, research team leader and deputy director of the University of Queensland's Advanced Water Management Centre, said sewer systems are one of the most critical infrastructure assets for urban societies.

sewer collapse
Images, video: University of Queensland

Sulfate levels in sewage are greatly made up of sulfates from the drinking water treatment process and are causing rapid corrosion in concrete sewer systems, researchers said.

"Maintenance costs for these concrete sewers run into the billions of dollars a year across the world," said Yuan.

Rapid Sewer Corrosion

Over the course of several years, the research team performed a sampling in South East Queensland, did an extensive survey across Australia, provided a global literature review, and made a comprehensive model-based scenario analysis of the various sources of sulfate.

The research team said adding aluminum sulfate to water may be a key contributor to sulfate levels in sewage. The aluminum binds to the particles in the water and is removed in the process, but the sulfate is soluble and remains in the treated water.

"This, in turn, is the primary source of hydrogen sulfide, which creates rapid concrete degradation and is the main cause of global sewer corrosion," Yuan explained.

Microbes oxidize the hydrogen sulfide to form sulfuric acid, which is extremely powerful in corroding concrete. The concrete deteriorates at a rate of up to 10mm per year, or more in extreme cases, reported.

This video explains the researchers' discoveries.

According to the researchers, their study showed that in systems with low sulfate levels in raw water, the sulfate added in the drinking water treatment could cause significant additional sulfide formation.

Switching from Sulfates

Yuan said the cost to switch to sulfate-free coagulants in water treatment would be nothing compared to the large potential savings in sewer maintenance and corrosion costs.

Switching would reduce concrete corrosion by 35 percent after just 10 hours and by 60 percent over a longer time frame, the researchers said.

The reason this was never known before, the researchers said, is probably because the water system is separated into water and wastewater sections that are often run by different organizations.

"Therefore, a more fully integrated urban water management approach is necessary to identify such interactions and determine the most optimal long-term solution for the overall system, rather than primarily minimising costs locally," the researchers said. 

Research Partners

The research, "Reducing sewer corrosion through integrated urban water management," was published in Science.

Professor Zhiguo Yuan

"Maintenance costs for these concrete sewers run into the billions of dollars a year across the world," said Professor Zhiguo Yuan.

"What Zhiguo and his team have achieved is a perfect example of a successful industry collaboration that has added the 'plus factor' to excellent research and delivered an innovative, cost-effective solution to a global problem," commented Professor Peter Høj, University of Queensland's vice-chancellor and president.

The University of Queensland partnered with the University of New South Wales, the University of Newcastle, the University of Sydney, Curtin University of Technology, Barwon Water Corporation, CH2MHILL, City of Gold Coast, Hunter Water Corporation, Melbourne Water Corporation, South Australian Water Corporation, South East Water Limited, Sydney Water Coporation, Veolia Water, Water Research Australia Limited, and Water Corporation of Western Australia.


Tagged categories: Colleges and Universities; Concrete; Corrosion; Research; Sulfates; Wastewater Plants

Comment from Tom Schwerdt, (8/21/2014, 12:00 PM)

While this is quite interesting, I find it odd the research doesn’t mention sulfate attack. Sulfates are known to directly degrade concrete, without the need for the interim steps forming sulfides, etc.

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