No subject

Devices in which bacteria burn organic fuel and convert it to electricity=
 have been made before. They are called microbial fuel cells, and many re=
searchers are now exploring them as potential sources of cheap power - so=
metimes in unusual places.

Electrodes stuck into the sea bed, for example, can harvest the energy re=
leased by bacteria that live in mud at the bottom of the ocean. Although =
the amount of power that can be generated this way is typically small, it=
 should be enough to drive underwater environmental monitoring equipment.=


Logan's device is just one such fuel cell. It consists of a plastic tube =
6.5 cm wide and 15 cm long. Eight graphite rods running lengthwise throug=
h the tube act as negative electrodes. The positive electrode is a centra=
l rod made out of plastic, carbon and platinum. When wastewater is pumped=
 through the chamber, bacteria stick to the graphite rods and channel ele=
ctrons into them as they eat organic material. The electrons travel throu=
gh wires to the platinum rod, completing the circuit. =


The larger the surface area of the graphite rods, the greater the power g=
enerated. The Penn State team has so far managed to extract 150 milliwatt=
s per square metre of graphite surface from their fuel cell. "We believe =
we can increase power generation to levels of about 1000 mW per square me=
tre," Logan says. A reasonably-sized device would generate enough electri=
city to power small devices like light bulbs, but not enough to run a who=
le house. "We are continuing to improve power generation levels," Logan s=
ays.

The device encourages bugs to eat hefty meals of organic waste by providi=
ng a convenient place for them to dump the electrons stripped from their =
food. The team says that bugs in their device remove up to 80 % of organi=
c waste in the water.

If the lab prototype can be scaled up to a household version, the team sa=
ys it could save energy and treat waste for every home. And that could sa=
ve money: the annual bill for treatment of domestic wastewater in the US =
is currently about $25 billion. =

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References
Liu, H., Ramnarayanan, R. & Logan, B. E. Production of electricity during=
 wastewater treatment using a single chamber microbial fuel cell. Environ=
mental Science and Technology, published online, doi:10.1021/es034923g (2=
004). |Article| =

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=A9 Nature News Service / Macmillan Magazines Ltd 2004