'Living Battery' Uses Exoelectrogenic Microbes To Turn Sewage Into Energy [STUDY]

By Josh Lieberman on September 17, 2013 4:24 PM EDT

microbe stamford
Stanford University scientists have created a "living battery" that converts wastewater into energy using microbes one hundred times narrower than human hair. (Photo: Stanford University)

Stanford University scientists have developed a "living battery" that takes sewage and turns it into energy. The battery system prototype is only the size of a D-cell battery, but the Stanford team hopes to scale the system up for practical uses, including potentially powering sewage treatment plants themselves.

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The living battery prototype uses two electrodes, one positive and one negative, and places the electrodes into a bottle of wastewater. In the bottle, bacteria feed on organic waste in the water, creating an electricity that is captured by the positive electrode of the battery. The power-creating bacteria are exoelectrogenic microbes, organisms which live in airless environments and react with oxide minerals to create biological fuel (as opposed to breathing oxygen like animals or humans). So after ingesting waste, the exoelectrogenic microbes give off electrons that flow to the positive electrode, which is made up of electron-attracting silver oxide.  

"We call it fishing for electrons," said Craig Criddle, a Stanford environmental engineer and co-author of a study about the living battery.

The result of this electron fishing is an efficiency that is equivalent to solar cells. The living battery scoops up roughly 30 percent of the potential energy of the wastewater, about the same the solar panels harness from the sun. The researchers admit that the sun has far greater energy potential than sewage, and that wastewater alone couldn't become a large-scale energy source. Rather, they believe that a bigger living battery could help offset the energy that goes into treating wastewater; developed nations currently use about three percent of their energy on wastewater treatment.

The Stanford team says that a big challenge in scaling up the living battery will be finding a cheaper material for the positive electrode.

"We demonstrated the principle using silver oxide, but silver is too expensive for use at large scale," said Yi Cui, a materials scientist and co-author on the study. "Though the search is underway for a more practical material, finding a substitute will take time."

The study, "Microbial battery for efficient energy recovery," was published in Proceedings of the National Academy of Sciences. 

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