The suitability of molasses, Napier grass (Pennisetum purpureum), empty fruit bunches (EFB), palm oil mill effluent (POME), and glycerol waste as a co-substrate with Chlorella sp. TISTR 8411 biomass for biohythane production was investigated. Mono-digestion of Chlorella biomass had hydrogen and methane yield of 23-35 and 164-177 mL gVS(-1), respectively. Co-digestion of Chlorella biomass with 2-6% TS of organic wastes was optimized for biohythane production with hydrogen and methane yield of 17-75 and 214-577 mL gVS(-1), respectively. The hydrogen and methane yield from co-digestion of Chlorella biomass with molasses, POME, and glycerol waste was increased by 8-100% and 80-264%, respectively. The biohythane production of co digestion of Chlorella was 6-11 L L-mixed waste 1 with an optimal C/N ratio range of 19-41 and H-2/CH4 ratio range of 0.06-0.3. Co-digestion of Chlorella biomass was significantly improved biohythane production in term of yield, production rate, and kinetics. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.