Wastewater fuel cells help turn raw sewage into raw power

Scientists at Pennsylvania State University are developing a microbial fuel cell that can provide energy while treating wastewater, the American Chemical Society has reported.

The power output is still relatively low, researchers say, but the technology is improving rapidly and could soon be used to run a small wastewater treatment plant. It could also be used to treat waste from animal farms, food processing plants and even manned space missions.

Similar in design to a hydrogen fuel cell, the microbial fuel cell captures electrons that are naturally released by bacteria as they digest organic matter and then converts the electrons into electrical current.

Bruce Logan Ph.D, an environmental engineer and co-author of the published study, said the technology was developing so rapidly he had tweaked microbial fuel cells to produce up to 350 watts per square meter.

“Two years ago we had 0.1&.and now we’re in the 100s,” he said. “We’d like to get in the range of 500-1,000. We’re looking for another order of magnitude increase.”

Logan envisions using his cells in places where there is a high concentration of organic matter, rather than developing them for the same applications as hydrogen fuel cells.

The most obvious application would be in wastewater treatment plants, which essentially could power themselves as they treat water. Such technology would be particularly useful in developing countries, Logan suggests, because it would produce a net amount of electricity, offering a reason to keep a treatment plant running besides just treating wastewater.

David Bagley, a scientist at the University of Toronto has calculated that the energy potential in wastewater is almost ten times the cost to treat it.

“In our system, the two electrodes are separated by a proton exchange membrane, just like in a conventional hydrogen fuel cell,” says Logan. “It opens the door to using existing hydrogen-gas based stack technologies with bacteria in water.”

The design principles of the microbial cells are very similar to those of hydrogen based ones – wastewater flows on one side of the cell and air flows on the other, continuously generating electricity while also removing organic matter from the water.

The device could also be used to treat waste from the food processing industry and farms – especially pig farms, which have tremendous problems with costs and odours. NASA scientists are said to be developing a similar technology to be treat astronauts waste and turn it into extra power.

A full report of the research is published in Environmental Science and Technology, the peer reviewed journal of the American Chemical Society.

By David Hopkins

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