Recovery of Electrical Energy in Microbial Fuel Cells

Recovery of electrical energy is a key parameter for evaluating the performance of microbial fuel cells (MFCs). In this brief review, we analyze energy data in the sampled publications on continuously operated MFCs from the past 12 years and present a rough picture of energy recovery in MFCs. We observe that most MFCs produce a normalized energy recovery (NER) lower than 1.5 kWh/m3 or 1.0 kWh/kg of chemical oxygen demand (COD). The small MFCs (<100 mL) that produce high power densities do not exhibit any obvious advantage in NER compared with the larger MFCs. Pure substrates lead to better performance in both power and energy recovery. MFCs seem to be able to extract more energy (kilowatt hour per kilogram of COD) from low-strength substrates. The separator/membrane does not significantly affect NER. To establish an energy balance in MFCs and gain a better understanding of the MFC application niche, NER should be properly presented in future studies.