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

Co-digestion of pig manure (PM(1)) with fish (FW(2)) and biodiesel waste (BW(3)) was evaluated and compared with sole PM digestion. Results indicated that co-digestion of PM with FW and/or BW is possible as long as ammonium and volatile fatty acids remained under inhibitory levels by adjusting the operating conditions, such as feed composition, organic loading rate (OLR) and hydraulic retention time (HRT). PM and FW co-digestion (90:10 and 95:5, w/w(4)) was possible at OLR of 1-1.5g COD/Ld, resulting in biogas production rates of 0.4-0.6 L/Ld and COD removal efficiencies of 65-70%. Regarding BW, good results (biogas production of 0.9 L/Ld and COD elimination of 85%) were achieved with less than 5% feeding rate. Overall, operating at the same OLR, the biogas production and methane content in the co-digester was higher than in the only PM digester.