A substantial effort is now underway around the world to develop affordable hydrogen based fuel cells, both to reduce emissions of greenhouse gases such as carbon dioxide, and the reliance of a country on oil.  Sustainable energy production is only possible if it is based on renewable resources, such as biomass, solar, wind, and other technologies.  There are substantial biomass resources already available to use for hydrogen production, but the technologies to make hydrogen from biomass are not well developed.  Research at Penn State has shown that hydrogen can readily be made from organic matter in industrial wastewaters that have a high content of carbohydrates. Bacteria make hydrogen via fermentation reactions that produce a gas stream that is 60% hydrogen gas (40% CO2). Theoretically, 12 moles of H2 can be made per mole of glucose.  However, a maximum of only 4 moles of H2 can be achieved by known biochemical routes used by bacteria, and typically only half of this (2 to 3 moles of hydrogen) is recovered during fermentation.  In order to make hydrogen production economical, energy must be recovered from the remaining organic matter. Microbial fuel cells (MFCs) offer great promise as a new method to recover the remaining energy directly as electricity.  In a MFC, bacteria transfer electrons obtained from the oxidation of organic matter to an electrode under anaerobic conditions.  The electrons flow to a cathode where they combine with oxygen and protons (from the anaerobic chamber) to form water. In MFCs developed at Penn State, we have shown it is possible to generate power at 10 to 150 mW/m2 using domestic wastewater, and from 250 to 500 mW/m2 using glucose.  We estimate that there may be an upper limit in achievable power density, on the order of 1000 mW/m2, when the bacteria must be in contact with the anode surface area.  Although such power densities appear low, comparable surface areas are already used for treating domestic wastewater in treatment plants using trickling filters. Hydrogen production and MFCs may therefore represent a whole new approach to bioenergy production and wastewater treatment.
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