Electron carriers increase electricity production in methane microbial fuel cells that reverse methanogenesis

Table 2 MFC voltage (mV), current density (A/m²) and power density (mW/m²) after adding humic acids as additional electron carriers with a MFC with a small cathode (surface area is 50 × 10⁻⁶ m²)

MFC reactor	Voltage (mV)	Current density (A/m²)	Fold change	Power density (mW/m²)	Fold change
Base case #1	670 ± 60	0.10 ± 0.01	1	68 ± 6	1
Base case #2	721.5 ± 0.7	0.6 ± 0.1	6	450 ± 90	7
Base case #2 + humic acids (total 0.5%)	712 ± 4	2.1 ± 0.4	21	1400 ± 200	21
Base case #2 + humic acids (total 3.3%)	750 ± 60	6 ± 1	60	4700 ± 800	69
Base case #2 + cytochrome C from S. cerevisiae (20 µM)	732 ± 2	0.97 ± 0.07	10	710 ± 40	10

The base case #1 is M. acetivorans AA/pES1MAT mcr3 (“M. acetivorans”) and G. sulfurreducens was added first followed by sludge once the voltage was below 150 mV and using 38-mm-diameter cathode electrode (surface area is 0.00227 m²). The base case #2 consists of G. sulfurreducens added at the start followed by the addition of sludge + M. acetivorans AA/pES1MAT mcr3 once the voltage was reduced below 150 mV and using a small cathode electrode (surface area is 50 × 10⁻⁶ m²). The additional electron carriers (humic acids) were added after obtaining the first maximum voltage; 0.5% humic acids were added after 7–8 days and 3.3% humic acids were added after 13–14 days of adding sludge and M. acetivorans. Cytochrome C from S. cerevisiae (20 µM) was added as an additional electron carrier after obtaining the first maximum in voltage after adding sludge and M. acetivorans AA/pES1MAT mcr3. The external resistance was 1000 Ohm

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