Electric bacteria for sewers could save millions

When not working with sludge from Melbourne’s sewers, La Trobe University scientist Elizabeth Mathews is busy thinking about it. In partnership with Western Water, her research is designed to further the understanding of the processes that lead to sewer corrosion in order to ultimately further progress towards a solution.

The corrosion of concrete sewer infrastructure is an expensive and widespread environmental problem that affects water utilities worldwide. The corrosion results from microbial sulfur cycling occurring within the sewer. Oxidation of hydrogen sulfide produces sulfuric acid, which erodes the concrete pipes.

Mathews’ doctoral research study is one that few would envy – trying to change the respiratory or ‘breathing’ chemistry of bacteria in our waste stream.

Why? “A healthy society is built on good sanitation,” she said. “And many of our sewers are ageing and breaking down as a result of pipe corrosion, a by-product of bacterial respiration.

“Replacing just a single metre of corroded pipe can cost a staggering $40,000,” she said.

Mathews is a member of La Trobe’s Environmental Microbiology Laboratory, which studies a wide range of bacteria that ‘breathe and eat electricity’ to power their biological processes.

Our lungs and respiratory system work by taking in air, removing oxygen and exhaling carbon dioxide. However, anaerobic bacteria in sewers thrive on sulfur, which they expel as hydrogen sulfide — more commonly known as ‘rotten egg gas’.

“The gas forms sulfuric acid,” said Mathews. “And the acid attacks concrete, which causes corrosion, weakens sewer pipes and eventually leads to their collapse.”

So her aim is to disrupt the respiratory cycle of two of the most common types of sewer bacteria, replacing their sulfur diet with one of electrodes.

“The bacteria can then use the electrodes to complete their respiratory reactions — but without producing hydrogen sulfide and sulfuric acid in the process.”

Mathews said these electrodes were economical and long lasting, and could be added to the existing sewer system.

Her project, being carried out with the help of Western Water, is studying a wide range of bacteria in residential and industrial sewer streams. Some of these sewers show signs of corrosion and some don’t.

“By analysing them we will get data to help design the most effective electrodes to convert the bacteria’s diet from sulfur to the electrodes,” she said.

Western Water Customer and Community Relations Manager Graham Holt said without the hydrogen sulfide being converted into sulfuric acid in sewers there would be much less corrosion and no need for expensive chemicals.

He said the project has great potential for use across the whole Victorian water industry.

“If we come up with a workable solution for this problem, it could save Western Water more than $100,000 a year — and millions of dollars a year across Victoria,” he said.

The Electric Bacteria program in La Trobe’s Environmental Microbiology Laboratory is led by Dr Ashley Franks.

“The aim,” said Dr Franks, “is to manipulate these processes to help clean up waste and pollution, produce energy more efficiently — and maybe even as an alternative to petroleum.”

Image caption: PhD student Elizabeth Mathews, right, with Associate Professor Ashley Franks, left, and  Dean Barnett, Manager, Field Services and Network Operations Western Water, sampling bacteria from a sewer in Melton. Picture: Western Water.