Ferric ion improves power generation in microbial fuel cells under optimized conductivity and external resistance

Microbial fuel cells are sustainable power generation devices that suffer from low power output. Iron ion enhances the biocompatibility of anode electrode and changes the community structure of biofilm in favor of power production. However, the conditions where iron ion demonstrates its maximum potential in boosting power output is unclear. In this study it is hypothesized that effectiveness of iron ion increases when Fe3+ concentration is coordinated with conductivity of anolyte and control of electric current through external resistance. Using a two-level factorial design, a series of experiments are conducted to determine the optimized values of Fe3+ concentration, NaCl concentration and external resistance, to achieve maximum attainable power. The statistical analysis revealed that in flow rate of 4.5 mL h−1 and substrate concentration of 50 mM, under Fe3+ concentration of 12 mM, NaCl concentration of 12 g L−1 and external resistivity of 100 Ω, the maximum power density of 26.11 ± 0.26 mW m−2 (249 mV, 0.57 mA) is the highest power output with the lowest internal resistance of 402 ± 4 Ω. Without optimization, the maximum power density reduces to 11.31 ± 0.12 mW m−2, indicating the importance of optimizing conductivity and external resistance at a specified Fe3+ concentration. This improvement expands the application of MFCs in cases where high power energy sources are required.