Determination of optimum electrical connection mode for multi-electrode-embedded microbial fuel cells coupled with anaerobic digester for enhancement of swine wastewater treatment efficiency and energy recovery

In this work, three multi-electrode-embedded microbial fuel cells (MFCs) were connected sequentially and operated in series and parallel modes, fed by effluent of an anaerobic digester continuously operated using swine wastewater. The anaerobic digester achieved ~0.75 CH4 L d−1 while removing 71.2% of COD and 0.8% of ammonia, which was comparable to the literatures reported. The MFCs removed additional COD from the anaerobic digester effluent, achieving the lowest concentration in the last unit, leading to a voltage reversal in the serially-connected unit. The MFCs connected and operated in parallel mode showed the highest power density of ~25 W m−3, which is 18% higher compared to the one operated in series mode. These results definitively show that differences in substrate concentrations among MFC units are inevitable with sequential flow. Further, a parallel connection mode of operation is necessary to achieve stable, long-term power generation from MFC units, without any electrical malfunction.