“Microbial battery” could turn wastewater into electricity

Flickr user: Paul Everett

Most of the material we consider to be waste, from sewage to discarded food, actually contains significant amounts of potential energy in the form of carbon-rich chemicals. The problem is that it's generally diffuse and often present in water-saturated materials, making it impossible to combust without extensive processing.

And, if we ever tried, we'd end up competing with microbes that make a living off extracting energy from those same carbon sources. So in recent years, researchers have been experimenting with microbial fuel cells, where bacteria clustered at an electrode extract carbon from waste metabolize it in a way that releases electrons into the device. Researchers have now developed a new device design that merges features of a battery and a fuel cell to extract more electricity from the bacteria.

Most microbial fuel cells have a design where bacteria grow at the anode, which is separated from the cathode by a membrane. Typically, the cathode transfers electrons to reduce oxygen. However, some of that oxygen typically diffuses across to the bacteria, which can use it directly instead of transferring their electrons to the fuel cell itself.