Author's personal copy Comparison of microbial electrolysis cells operated with added voltage or by setting the anode potential

Hydrogen production in a microbial electrolysis cell (MEC) can be achieved by either setting the anode potential with a potentiostat, or by adding voltage to the circuit with a power source. In batch tests the largest total gas production (46 3 mL), lowest energy input (2.3 0.3 kWh/m of H2 generated), and best overall energy recovery (sEþS 1⁄4 58 6%) was achieved at a set anode potential of EAn 1⁄4 0.2 V (vs Ag/AgCl), compared to set potentials of 0.4 V, 0 V and 0.2 V, or an added voltage of Eap 1⁄4 0.6 V. Gas production was 1.4 times higher with EAn 1⁄4 0.2 V than with Eap 1⁄4 0.6 V. Methane production was also reduced at set anode potentials of 0.2 V and higher than the other operating conditions. Continuous flow operation of the MECs at the optimum condition of EAn 1⁄4 0.2 V initially maintained stable hydrogen gas production, with 68% H2 and 21% CH4, but after 39 days the gas composition shifted to 55% H2 and 34% CH4. Methane production was not primarily anode-associated, as methane was reduced to low levels by placing the anode into a new MEC housing. These results suggest that MEC performance can be optimized in terms of hydrogen production rates and gas composition by setting an anode potential of 0.2 V, but that methanogen proliferation must be better controlled on non-anodic surfaces. Copyright a 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights