Economic feasibility is important for the development of microalgae bioenergy industry. Dark fermentation of microalgal residue in a biorefinery context can improve the energy conversion efficiency of biomass and reduce the cost of microalgae industry. The present study proposes a promising dark fermentation model that combines thermophilic hydrogen-producing bacteria with algal residue substrates. Lipid-extracted Dunaliella residue can greatly improve hydrogen production by Thermococcus eurythermalis A501, the yields of which are more than four times higher than with algal cells as substrates. Under the optimal conditions of 2.5 g/L algal residue concentration and a 2:1 initial volume ratio of gas to liquid, the highest hydrogen yields of 192.35 and 183.02 mL/g volatile solid (VS) with algal residue of Dunaliella primolecta and D. tertiolecta are obtained, respectively, in less than 19 h without any pretreatment. This work may provide a biorefinery approach for comprehensive utilization of microalgae resources. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.