Microbial Electrochemical Fuel Cell Setup

Graphite electrodes (65 cm² solid graphite blocks, 1 in. by 0.5 in. by 3 in., grade G10, , Graphite Engineering and Sales, Greenville, MI), poised with a potentiostat (+300 mV versus Ag/AgCl) in ‘H-type cells’ were provided as an electron acceptor as previously described [7] (link), [14] (link). The cells were grown in freshwater medium (2.5 g/L NaHCO₃, 0.25 g/L NH₄Cl, 0.06 g/L, NaHPO₄*H₂O, 0.1 g/L KCl, vitamins and minerals) [30] (link) containing 10 mM acetate and 40 mM fumarate. When the culture reached an A₆₀₀ of 0.2, the anode chamber was swapped to freshwater medium containing 10 mM acetate and no fumarate. Once the current reached approximately 1 mA the system was switched to a continuous flow through mode, in which medium was flowed through the chamber at a dilution rate of 0.15/hr. Current measurements were collected directly from potentiostat outputs every second with a Power Lab 4SP connected to a Macintosh computer, and data was logged with Chart 5.0 software (ADI instruments, Mountain View, CA). Fumarate control fuel cells were grown as described above but with the working, counter and reference electrodes disconnected and with 40 mM fumarate present in the medium.