Fig. 2
Voltage, current density, and resistance in the MFC. a Voltage (mV, black squares) and current density (A/m2, open circles) from one representative MFC (base case #2 + humic acids). The base case #2 consists of G. sulfurreducens added at the start and sludge, M. acetivorans AA/pES1MAT mcr3 (“M. acetivorans”), and methane (100 mL/min, for 5 min) were added when the voltage became less than 150 mV. 0 on the abscissa indicates the time of adding sludge, M. acetivorans AA/pES1MAT mcr3, and methane. After 8 days, humic acids (conc. 0.5%) were added. After 14 days, the humic acid, concentration was increased to 3.3%. b Resistance from one representative MFC (base case #2 + humic acids) as calculated from the voltage and current (R = V/I) readings each day. Base case #2 consists of G. sulfurreducens added first to the anode followed by the addition of activated sludge, M. acetivorans AA/pES1MAT mcr3 (“M. acetivorans”), and methane (100 mL/min, for 5 min) to the anode once the voltage was reduced to less than 150 mV (0 time point on the abscissa). After 8 days, humic acids (conc. 0.5%) were added, and the concentration was increased to 3.3% at day 14. The external resistance was 1000 Ohm