Assessment of recirculation batch mode operation in bufferless Bio-cathode microbial Fuel Cells (MFCs)

Biocathode microbial fuel cells are cost-effective and environmentally sustainable bio-electrochemical devices. However, the usage of buffer solution will significantly reduce the feasibility of the MFCs (Microbial Fuel Cells) for practical applications in the future. Therefore, in this study the function of PBS (Phosphate Buffer Solution) was substituted by application of recirculation flow mode to enhance the proton transfer. An innovative and novel endeavor of inserting a honey comb structure into an MFC for uniform influent flow was also performed. pH and power performance were investigated in aerobic biocathode MFCs at recirculation flow rates of 0 ml/min, 4 ml/min, 40 ml/min, and 240 ml/min. The results showed that higher recirculation flow rates maintained a steady pH after 1 h of MFC operation and efficiently reduced the time to achieve the favorable pH environment (7.0-7.55) for the growth of electrochemically active bacteria (EAB). Furthermore, the highest power density of 5.71 mW/m2 and lowest charge transfer resistance of 267.7 Ω were obtained at the flow rate of 40 ml/min. But, extremely high flow rate of 240 ml/min was found to be detrimental to the biocathode MFC and reduced the power density and charge transfer resistance. Therefore, these findings would provide useful and progressive insights for pilot and industrial scale studies with bufferless biocathode MFCs in the future.