Performance of microbial fuel cells with dairy manure as the substrate and combined with anaerobic digestion

Microbial fuel cells (MFCs) may offer an opportunity to gain value from dairy manures through direct electrical generation. The MFCs in this study (internal resistance = 1090 ± 84 Ω) were operated at 20°C with raw manure concentrations of 0 to 100,000 mg COD (chemical oxygen demand) L -1, generating a maximum power density of 138 ± 19 mW m-2 (at 100 g COD L-1). Total coulombs (C) captured over four days increased from 18.8 ± 1.3 C to 40.5 ± 2.4 C (coulombic efficiencies of 3.4% ?1.2% and 5.8% ± 1.4%, respectively) when the incubation temperature was raised from 20°C to 37°C but fell to less than 1.42 C at 55°C, indicating that the electrochemically active bacteria established at 20°C were inhibited or killed at thermophilic temperatures. Operating an MFC before anaerobic digestion (AD) had a statistically insignificant impact on the total volume of biogas produced after 45 days (37°C). Although prior MFC operation decreased the maximum rate of biogas production by 55% (from 0.145 ± 0.0256 to 0.062 ± 0.0018 mL biogas mL-1 reactor d-1), the timing of biogas production was actually earlier following MFC pretreatment, suggesting that electricity harvesting with MFCs may have an additional benefit of decreased AD reactor retention time required for biogas production. Reversing the order of the unit operations, prior AD decreased MFC performance, with a 65% decrease in the total coulombs captured (from 18.1 ± 8.84 to 5.62 ± 1.44). © 2011 ASABE ISSN 1934-2799.