In a pungent basement laboratory at the university, graduate student Zhen He works with Largus T. Angenent, an environmental engineer, to develop electricity generators, or fuel cells, fired by bacteria and wastewater. For now, the fuel cells are far less powerful than hydrogen fuel cells used to power some cars - up to a million times less powerful.

"The levels of electricity are still low, but we're working on it," Angenent said. His team hopes to scale the coffee-thermos-size reactor in the lab into a plant that could process millions of gallons of brewery or other food-production wastewater into electricity for up to 900 homes.

The team, which also includes Shelley D. Minteer of St. Louis University, described one of its bacteria-powered generators last week in the online version of the journal Environmental Science and Technology.

The new technology is based on the discovery that some of the bacteria that digest food in the human intestines also can serve as mini-generators. Angenent and He have built a tiny wastewater treatment facility from large test tubes filled with murky water.

Bacteria and methane-making Archaea - a class of single-celled organisms that reesemble bacteria - in the solution settle on carbon electrodes that resemble bricks of steel wool. As the microbes break down the organic material in the wastewater, they give up electrons, which the researchers harvest.

The researchers feed their bacteria a solution of sugar water, but the large-scale reactors would run on wastewater from food processing plants. Sewage also could be used, but it has a lower concentration of organic matter and probably could produce only enough electricity to make a sewage-treatment plant self-sufficient.

"Right now we are putting a lot of electricity into sewage," Angenent said.

Self-powering sewage treatment plants could make more than 1 percent of the nation's electricity production available to heat homes and businesses and keep lights burning, he said.

In the new report, the team describes a stacked reactor that feeds wastewater in through the bottom and shunts electricity out the top. Such reactors could save space and also eliminate the need to stir the waste. That cuts down on the amount of electricity needed to fuel the reactor itself, Angenent said.

The small laboratory reactor generates only 170 milliwatts of electricity per square meter. That's not enough to power a light bulb.

Such cells are inefficient and probably won't ever pack as much power in a small space as hydrogen fuel cells can, Angenent said.

"We're not expecting that bacteria can power a car," he said.

But in large scale - 2 million gallons or more - such wastewater fuel cells could generate enough electricity to power a small town, Angenent said.