Enrichment of microbial biocathodes to replace platinum catalyst in microbial fuel cells

Microbial biocathodes are gaining interest due to their low cost, environmentally friendliness and sustainable nature. In this study, activated sludge from a textile treatment plant was enriched by chronoamperometry over 70 days to select for electroactive bacteria for use as a cathode catalyst in microbial fuel cells (MFC) designed for azo dye degradation in the anode chamber. The resultant biofilm produced an average peak current of 0.7 mA during the enrichment and produced a maximum power density of 64.6±3.5 mW m-2 compared to platinum (72.7±1.2 mW m-2) in a MFC. The acclimated biocathode eliminated start-up lag and decreased the activation overpotential at the cathode. The rate of dye decolourisation at the anode was similar in both platinum and biocathode MFCs. Activation losses were lower for the biocathode than with platinum suggesting that the bacteria act as true cathode catalysts. The microbial community analysis of the initial sludge sample and enriched samples revealed the selection of electrolithoautotrophs. The most dominant orders were Flavobacteriales (Bacteriodetes) and Rhizhobiales (Alphaproteobacteria) in the enriched samples. A nitrogen cycle micro-environment was proposed with the presence of Nitrosomonas and Nitratireductor species. Metabolic interactions between CO2 fixers and nitrate reducers may contribute to biofilm formation and current production.