Device Uses Sewage Bacteria to Produce Electricity

Brian Handwerk
for National Geographic News
March 1, 2004

Researchers at Pennsylvania State University are working to tap the power of a renewable energy source that flows from our own homes—Earth's enormous volume of domestic wastewater.

"Everybody has to eat," said Penn State environmental engineering professor Bruce Logan. "And you know the implications of eating." Logan is talking about human waste, of course.

Household wastewater from bathrooms and kitchens contains both organic materials and bacteria. Logan and his colleagues have designed a new "reactor" that not only treats the waterwater, but uses bacteria and sewage raw materials to produce power.

The double benefit might someday reap enormous financial savings while providing a clean energy source and improved wastewater treatment, particularly in the developing world.

However, much work remains. To date, the team has only produced enough electricity to meet five percent of the power drawn by a single Christmas tree light bulb.

Bacteria Power

Wastewater bacteria feed on everything from solid human waste matter to last night's leftovers. As the bacteria eat, they convert organic matter to carbon dioxide, releasing electrons, the basic element of electrical current.

Logan and his team have discovered how to tap into this unorthodox energy source using a fairly simple contraption.

Their reactor is comprised of a plastic tube measuring just 6 inches (15 centimeters) long and 2.5 inches (6.5 centimeters) in diameter through which wastewater is circulated. Graphite rods inside the tube function as negative electrodes and host bacteria that stick to the rods' surfaces. As the bacteria feed, electrons are released and move as electrical current through the graphite rods into wires outside the liquid container to a cathode, or positive electrode, constructed of plastic, carbon and platinum.

"When we eat, we oxidize material and we get rid of electrons using oxygen through the lungs and blood," Logan said. "Bacteria have to put the electrons somewhere, or they can't continue to eat. So those electrons can be transferred to the electrode and through the complete electric circuit we've created."

The result keeps the bacteria hungry and the juice flowing.

Logan and Penn State colleagues Hong Liu and Ramanathan Ramnarayanan recently published their findings in the online edition of the science journal Environmental Science & Technology.

Continued on Next Page >>




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