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March 21, 2007

Microbial fuel cells generate power from waste water

Generating electricity from renewable sources will soon become as easy as putting a brush and a tube in a tub of wastewater. A carbon fiber, bottle-brush anode developed by Penn State researchers will provide more than enough surface for bacteria to colonize, for the first time making it possible to use microbial fuel cells for large scale electricity production. In addition, a membrane-tube air cathode, adapted from existing wastewater treatment equipment, will complete the circuit.

Microbial fuel cells work through the action of bacteria, which can pass electrons to an anode of a fuel cell. The electrons flow from the anode through a wire to the cathode, producing an electric current. In the process, the bacteria consume organic matter in the wastewater and clean the water. The Penn State approach uses the bacteria that naturally occur in wastewater, requiring no special bacterial strains or unusual environmental demands.

In the best test case, the researchers used a carbon fiber brush anode and two tubular cathodes of about .6 inches in diameter doped with a cobalt catalyst on the inside, the fuel cell produced 18 watts per 260 gallons of water and achieved a charge efficiency of more than 70 percent. An additional benefit to the microbial fuel cell is that while it generates electricity, it cleans up the wastewater, something that usually requires the consumption of energy.

Lesser developed countries discharge approximately (the equivalent of) 100 trillion gallons (380×109 m³) of untreated sewage per annum This could potentially generate 7 Terawatts of power for them and clean up their waste water.

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