Review pubs.acs.org/journal/estlcu
Recovery of Electrical Energy in Microbial Fuel Cells Brief Review Zheng Ge,† Jian Li,† Li Xiao,‡ Yiran Tong,‡ and Zhen He*,† †
Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States ‡ Department of Civil Engineering and Mechanics, University of WisconsinMilwaukee, Milwaukee, Wisconsin 53211, United States S Supporting Information *
ABSTRACT: 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 ( 0.05). The average NER with acetate is 0.25 kWh/m3 or 0.40 kWh/kg of COD, and that with glucose is 0.18 kWh/m3 or 0.12 kWh/kg of COD; the average NER with domestic wastewater is 0.04 kWh/ m3 or 0.17 kWh/kg of COD, and industrial wastewater results in a value of 0.10 kWh/m3 or 0.04 kWh/kg of COD (Figure 2A). Large variations associated with those values indicate the existence of some exceptional performances (either extremely high or low) in a few studies. Domestic wastewater generally has a low energy output based on the treated volume because of its low concentration, which, however, may also lead to an NER based on COD removal comparable to that of the pure organics, likely because of a better conversion of organics into electrical energy with low-concentration organics compared to that of a high-concentration organic stream. To further examine the effect of substrate concentration on energy recovery, we plot NER versus acetate in two different concentration ranges (expressed in COD), 500 mg/ L (Figure 3). Acetate was chosen because of the availability of a large sample size for statistical analysis, and 500 mg/L was arbitrarily used as a boundary value for the concentration of soluble organic compounds in domestic wastewater. The MFCs fed with 500 mg/L acetate, but the NER expressed in kilowatt hours per kilogram of COD from
