Sulfate and organic carbon removal by microbial fuel cell with sulfate-reducing bacteria and sulfide-oxidising bacteria anodic biofilm

Biological sulfur removal can be achieved by reducing sulfate to sulfide with sulfate-reducing bacteria (SRB) and then oxidising sulfide to elemental sulfur (S0) with sulfide oxidising bacteria (SOB) for recovery. In sulfate–carbon wastewaters lacking electron acceptor for sulfide, excess sulfide will be produced and accumulated in the reactor. This study applied the microbial fuel cell (MFC) cultivated with the SRB + SOB anodic biofilm for treating the sulfate + organic carbon wastewaters. Excess sulfate ions were efficiently converted to sulfide by SRB cells in the biofilm, while the formed sulfide was diffused to the neighboring SOB cells to be irreversibly converted to S0 with produced electrons being transferred to the anode. The cell–cell sulfide transport principally determined the electron flux of the MFC. Short diffusional distance of sulfide ions between cells significantly reduced the polarization resistances, hence enhancing performance of the MFC.