Wastewater Treatment for Water Recycling Using Microbial Fuel Cells

Microbial fuel cells (MFCs) have long been researched for their use as energy recovery devices during wastewater treatment. However, commercial applications of MFC systems have been challenged by high material costs and low energy recovery efficiencies. While energy densities remain low for these systems, recent work has demonstrated a reduction in capital costs, low biomass production, odor reduction, and accelerated treatment rates relative to conventional anaerobic systems.  Here we describe a small pilot scale (100 gallon) anaerobic MFC system that is able to remove 88% of biological oxygen demand (BOD) and 80% of volatile suspended solids (VSS) from primary sludge in a 7 day residence time.  A duplicate system was operated in parallel and held at open-circuit to determine what portion of BOD removal was associated with electrogenic activity as opposed to physical trapping or other mechanisms. The open-circuit system was only able to remove 45% of BOD and 38% of VSS in the same operational time frame.  Under closed circuit conditions, operating with a 10 Ohm resistor, a maximum BOD removal rate of 1.09 kg-BOD/m³/day was achieved for primary sludge samples at ambient temperatures, while the open circuit condition showed a maximum BOD removal rate of 0.47 kg-BOD/m³/day. A coulombic efficiency of 13% was measured from the closed circuit system during maximum BOD removal. While system improvements are still required, these results represent significant progress toward the practical development of MFCs for municipal wastewater treatment and suggest that MFC technology may contribute toward realizing energy efficient water recycling.   Acknowledgements: Funding for this project was provided by the California State PIER EISG program, NSF BBBE award 0933145, the Roddenberry Foundation, and the San Diego Foundation Blasker Science and Technology Award.