Effects of anolyte recirculation rates and catholytes on electricity generation in a litre-scale upflow microbial fuel cell

Microbial fuel cells (MFCs) are an attractive technology for simultaneous bioenergy recovery and organic removal; however, the lack of studies conducted with large-scale MFCs, especially those larger than 1 L, obstructs further development of this technology. In this paper, we built and operated a 4.9 L upflow microbial fuel cell (UMFC) with a liquid volume of 2.4 L. Its electricity generation and organic removal performance were examined under different operating conditions. The UMFC produced an open-circuit potential of 1.00 V with an acidified catholyte. Changing the recirculation of the anolyte did not significantly affect the power output in a short period, but a long-term test demonstrated improved electricity production at higher recirculation rates. The water produced via oxygen reduction or diffused from the anode was not sufficient for the cathode reaction; thus, an external supply of water is necessary. Lowering the pH of the catholyte benefited the cathode reaction and increased power production; however, pH is not the only factor affecting the cathode reaction and if organic matters were contained in the catholyte, for instance using the anode effluent as a catholyte, electricity generation decreased. The results and experiences gained from this study will help to further develop pilot-scale MFCs for practical applications.