Penn State environmental engineers have shown that a microbial fuel cell (MFC) can generate electricity while simultaneously cleaning the wastewater that is flushed down the drain or toilet. Between 10 and 50 milli Watts of power per square meter of electrode surface can be produced, while removing up to 78 percent of organic matter as measured by biochemical oxygen demand (BOD). Thus MFCs represents a completely new approach to wastewater treatment in addition to power generation. The MFC technology can provide a new method to offset operating costs of wastewater treatment plant, making advanced wastewater treatment more affordable for both developing and industrialized nations as claimed by the researchers.
Other researchers have shown that MFCs can be used to produce electricity from water containing pure chemicals including glucose, acetate or lactate.
Principle
Microbial fuel cells work by the action of bacteria which can pass electrons to an anode, the negative electrode of a fuel cell. The electrons flow from the anode through a wire, producing a current, to a cathode, the positive electrode of a fuel cell, where they combine with hydrogen ions (protons) and oxygen to form water in accordance with the conventional fuel cell principles. The naturally occurring bacteria in wastewater drive power production via a reaction that allows them to transport electrons from the cell surface to the anode. In addition, a reaction (oxidation) that occurs in the interior of the bacterial cell lowers the biochemical oxygen demand thus cleaning the water. MFC used has an overall dimension of about six inches in length and 2.5 inches in diameter and contains eight anodes, composed of graphite. The cathode is a carbon/platinum catalyst/proton exchange membrane fused to a plastic support tube. The unit has about 36 square inches of surface area to which the bacteria can adhere and pass electrons.
See for photos at: http://live.psu.edu/still_life/2004_02_23_research/index.html and for animation : http://www.nsf.gov/od/lpa/newsroom/pr.cfm?ni
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