Directly convert lignocellulosic biomass to H₂ without pretreatment and added cellulase by two-stage fermentation in semi-continuous modes

Cost-competitive production of lignocellulosic H₂ using biological methods is limited by energy-intensive pretreatments and expensive cellulase hydrolysis. Here we report stable two-stage fermentation to convert unpretreated energy sorghum without added cellulase to H₂, where Clostridium thermocellum was fed semi-continuously with 20 g/L sorghum in the first stage and then Rhodobacter sphaeroides consumed the effluent wastes in the second stage to achieve residence times (RTs) of 60, 48, and 24 h. Glutamic acid was the preferred nitrogen source for coordinating the two-stage, two-organism fermentation. 25.0 ± 1.1 mL-H₂/day in consolidated bioprocessing stage and 133.0 ± 1.5 mL-H₂/day in photofermentation stage were obtained for 200 mL cultures at RT 48 h. Propionate is the main product accumulated, with cellobiose, xylose, arabinose, formate, acetate and ethanol also observed in the effluent wastes, which were degraded effectively by Rhodobacter sphaeroides with COD removal of 72.6%. These results provide references for developing low-cost H₂ production from lignocellulose.