Fig. 5. Dominant methane production pathways in the various digesters. Solid grey arrows indicate a pathway through syntrophic acetogenesis and acetoclastic methanogenesis which dominated in MD and MD þ R. Dashed arows indicate a pathway through syntrophic acetogenesis, acetate oxidation and hydrogenotrophic methanogenesis which dominated in TD and TD þ R. SAB: syntrophic acetogenic bacteria; SAOB: syntrophic acetate oxidizing bacteria; AM: acetoclastic methanogens; HM: hydrogenotrophic methanogens.