Improved performance of microbial fuel cells enriched with natural microbial inocula and treated by electrical current

• Voltage stimulation (+2 V) during inoculation reduced MFC internal resistance and improved biofilm resilience.
• Voltage stimulation increased biofilm electrical capacitance by 5-fold.
• Negative voltage stimulation (−3 V) enhanced the maximum power output by 37%.
• River sediment MFC obtained higher power due to better anodic biofilm coverage.
• Anaerobic sludge quickly developed anodic biofilm for MFC and quickly utilized volatile fatty acids.

Microbial fuel cells (MFCs) are increasingly attracting attention as a sustainable technology as they convert chemical energy in organic wastes to electricity. In this study, the effects of different inoculum sources (river sediment, activated sludge and anaerobic sludge) and electrical current stimulation were evaluated using single-chamber air-cathode MFCs as model reactors based on performance in enrichment process and electrochemical characteristics of the reactors. The result revealed the rapid anodic biofilm development and substrate utilization of the anaerobic sludge-inoculated MFC. It was also found that the river sediment-inoculated MFC achieved the highest power output of 195 μW, or 98 mW m−2, due to better developed anodic biofilm confirmed by scanning electron microscopy. The current stimulation enhanced the anodic biofilm attachment over time, and therefore reduced the MFC internal resistance by 27%, increased the electrical capacitance by four folds, and improved the anodic biofilm resilience against substrate deprivation. For mature MFCs, a transient application of a negative voltage (−3 V) improved the cathode activity and maximum power output by 37%. This improvement was due to the bactericidal effect of the electrode potential higher than +1.5 V vs. SHE, demonstrating a substantial benefit of treating MFC cathode after long-term operation using suitable direct electrical current.