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.
Two 4 L tubular microbial fuel cells (MFCs) were installed in a municipal wastewater treatment facility and operated for more than 400 days on primary effluents. Both MFCs removed 65-70% chemical oxygen demand (COD) at a hydraulic retention time (HRT) of 11 h and reduced about 50% suspended solids. The COD removal rates were about 0.4 (total) or 0.2 (soluble) kg m(-3) day(-1). They could handle fluctuation, such as emptying the anode for 1-3 days or different HRTs. The preliminary analysis of energy production and consumption indicated that the two MFCs could theoretically achieve a positive energy balance and energy consumption could be reduced using larger tubing connectors. Through linkage to a denitrifying MFC, the MFC system improved the removal of total nitrogen from 27.1 to 76.2%; however, the energy production substantially decreased because of organic consumption in the denitrifying MFC. Establishing a carbon (electron) balance revealed that sulfate reduction was a major electron scavenger (37-64%) and methane production played a very minor role (1.3-3.3%) in electron distribution. These results demonstrate the technical viability of MFC technology outside the laboratory and its potential advantages in low energy consumption, low sludge production, and energy recovery from wastes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.