Enhancement in hydrogen production by thermophilic anaerobic co-digestion of organic fraction of municipal solid waste and sewage sludge – Optimization of treatment conditions

•H2 was produced from thermophilic anaerobic co-digestion of OFMSW and sewage sludge.•Enhanced H2 production was achieved for OFMSW+sewage sludge co-fermentation.•Mixed sludge was the best co-substrate (with OFMSW) among the sludge types studied.•Best hydrogen yield was achieved at 20% TS concentration.•Highest H2 yield was achieved at OFMSW to mixed sludge ratio of 5:1. Batch dry-thermophilic anaerobic co-digestion (55°C) of organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) for hydrogen production was studied under several sludge combinations (primary sludge, PS; waste activated sludge, WAS; and mixed sludge, MS), TS concentrations (10–25%) and mixing ratios of OFMSW and SS (1:1, 2.5:1, 5:1, 10:1). The co-digestion of OFMSW and SS showed a 70% improvement in hydrogen production rate over the OFMSW fermentation only. The co-digestion of OFMSW with MS showed 47% and 115% higher hydrogen production potential as compared with OFMSW+PS and OFMSW+WAS, respectively. The maximum hydrogen yield of 51mLH2/gVSconsumed was observed at TS concentration of 20% and OFMSW to MS mixing ratio of 5:1, respectively. The acetic and butyric acids were the main acids in VFAs evolution; however, the higher butyric acid evolution indicated that the H2 fermentation was butyrate type fermentation.