Inhibition of methane production in microbial fuel cells: operating strategies which select electrogens over methanogens.

Methanogenesis may diminish coulombic efficiency of microbial fuel cells (MFCs), although its importance is application dependent; e.g., suppression of methanogenesis may improve MFC sensing accuracy, but may be tolerable in COD removal from wastewaters. Suppression of methanogenesis was investigated in three H-type MFCs, enriched and acclimated with acetate, propionate and butyrate substrates and subsequently operated under open and closed circuit (OC/CC) regimes. Altering the polarisation state of the electrode displaces microorganisms from the anodic biofilm and leads to observable methane inhibition. The planktonic archeal community was compared to the electrode biofilm whilst under the OC/CC regimes. Semi-quantitative DNA analyses indicate a shift in some dominant species, from the electrode to the solution, during OC operation. The effect of prolonged starvation on anodic species was also studied. The results indicate progressive inhibition of methanogenesis from OC/CC operations; and virtual cessation of methanogenesis when an MFC was starved for a significant period.