Sewage sludge-derived biocarbons as catalysts of bioanodes in a dual-chamber microbial fuel cell using nejayote as substrate

In this work, nejayote (wastewater from tortilla industry) was evaluated as substrate of a dual-chamber microbial fuel cell (MFC). For this purpose, novel bioanodes were built using Bacillus subtilis (B. subtilis) as the electrochemically active microorganism (EAM), and sewage sludge-derived biocarbon (SSB) and methanolfunctionalized SSB (FSSB) as catalysts. The relationship between the physicochemical properties of SSB and FSSB, biocompatibility, electrochemical performance and the percentage of COD removed was analyzed. Up to 70% of chemical oxygen demand (COD) from nejayote was successfully removed using the SSB + B. subtilis bioanode, with the advantage of energy generation by the MFC (Pcell= 1.44 mW m-2 and jcell= 41 mA m-2). An adverse effect was observed when functionalizing SSB to produce FSSB. Despite a fair biocompatibility, the FSSB + B. subtilis bioanode promoted fermentation reactions that increased the COD and charge transfer resistance. The improved performance of SSB + B. subtilis was ascribed to a reasonable biocompatibility, low charge transfer resistance and less limitation to the diffusion of proton species between the biofilm and the substrate. Therefore, the treatment of nejayote in a MFC with the SSB + B. subtilis bioanode was identified as a promising alternative for decreasing COD and generating small amounts of energy, instead of using energy for its remedy.