Bug-Powered Fuel Cells Could Run on Waste

Oct. 09, 2008 -- The race is on to make commercial amounts of ethanol or other biofuels out of plant waste containing cellulose -- a fibrous component of plants that gives them structure. But some researchers are looking at a different option -- using cellulose to power microbial fuel cells, in which bacteria digest plant waste matter to create electricity directly.

These fuel cells could be used to charge batteries or power electrical devices.

Others are considering drawing power from microbes digesting human waste at wastewater treatment plants or manure from feedlot lagoons.

"Basically, we're converting cellulose into a different energy source than ethanol," said John Regan of Pennsylvania State University in University Park.

"It's not more efficient right now, but if you look at what's been done over the last decade, there has been about a five to six order-of-magnitude (100,000-1,000,000-fold) increase in power density."

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Microorganisms generate electrons as they break down food sources for energy, but in most species the electrons are transferred to molecules inside the cell. Microbial fuel cells rely on the ability of certain bacteria to transport electrons to the outside of the cell. If provided with electrodes in the right arrangement, the bacteria can dump their exterior electrons through a circuit, providing power.

But these "exoelectrogenic" microbes, as Regan calls them, cannot digest cellulose. So the system relies on another type of bacteria to break the cellulose down into simple molecules that the electron dumpers can then use.

Regan found that wastewater, which contains a diverse community of microorganisms, could generate electricity from cellulose, too, though not as much. Adding extra cellulose-degraders to the wastewater sped up the process. He is presenting his results this week at a meeting of the Geological Society of America in Houston, Texas.