Understanding the distinguishing features of a microbial fuel cell as a biomass-based renewable energy technology

Biomass-based renewable energy, which utilizes biomass derived from photosynthesis, could sustainably provide 67-450 EJ of energy annually. Biomass in organic wastes, for example, can annually provide 7.5 EJ of energy, and utilization of organic wastes locally as an energy source can prevent environmental pollution and reduce the energy losses associated with transportation. The technological challenge is to sustainably capture this biomass energy without creating serious environmental or social damage. A microbial fuel cell (MFC) is a novel biomass-based technology that marries microbiological catalysis to electrochemistry. In an MFC, bacteria present at the fuel-cell anode catalyze the oxidation of diverse organic fuel sources, including domestic wastewater, animal manures, and plant residues. As an electrochemical process, an MFC converts the energy value stored in the organic fuel directly to electrical energy, avoiding combustion and combustion- associated contaminants. The main product at the anode is CO₂ that is carbon neutral. When oxygen is the oxidant at the fuel-cell cathode, an MFC produces only H₂O. An MFC is an attractive renewable energy technology, because it produces electricity at the same time it treats wastes, and it does so without producing harmful byproducts. We introduce MFCs in the context of the general cycle for biomass-based renewable energy technology. Tracking of carbon oxidation state highlights the distinctly different approach that an MFC takes with respect to biofuels. Then, we review some of recent progress in MFC research, with an emphasis on mathematical modeling. At last, we conclude with our perspectives on biomass-based renewable energy by comparing the MFC with two more mature technologies for generating biofuels: bioethanol and anaerobic digestion to methane.