Enhanced methane production from pig manure anaerobic digestion using fish and biodiesel wastes as co-substrates

► Fish and biodiesel waste were used as co-substrates in pig manure anaerobic digestion. ► Both co-substrates improved methane yield but caused VFA and ammonium accumulation. ► Shorter HRT and FW < 10% in the feeding allow to control ammonium inhibition. ► Biodiesel waste co-digestion requires feeding shares < 6% and/or fed-batch operation. ► The poorer the co-digester operation, the higher the Methanosarcina/Methanosaeta ratio.