Effects of operating parameters on hydrogen production from raw wet steam-exploded cornstalk and two-stage fermentation potential for biohythane production

• Wet steam-exploded cornstalk was first used for hydrogen fermentation.
• Two-stage biohythane led to more energy recovery than one-stage biomethane.
• The hydrogen and methane yields of 12 and 195 L kg−1 TS−1 were obtained.
• Heat treatment was unnecessary for seeding sludge for hydrogen production.

Biohythane (biohydrogen + biomethane) production from agricultural residue is a win–win solution for the supply of renewable energy and valorization of waste biomass. This study reported the first investigation on hydrogen fermentation directly using raw wet steam-exploded cornstalk (SC) without any further processing for drying or detoxification. The effects of key operating parameters (feedstock concentration, initial pH and heat treatment of seed sludge) were systematically studied. The suitable conditions for hydrogen fermentation from the wet SC were the feedstock concentration at 200 g L−1 (TS, 6–8%), pH at 6.5 and seed sludge without heat treatment. In addition, compared to one-stage biomethane fermentation, the two-stage biohythane fermentation by integrating hydrogen fermentation with biomethane production from SC led to the hydrogen and methane yields of 12 and 195 L kg−1 TS−1, respectively, corresponding to an increased energy recovery of 26%, reduced fermentation time and facilitated conversion of volatile fatty acids. These results demonstrated the feasible energy-efficient biohydrogen or biohythane production from the wet steam-exploded cornstalk, implying the promising potential of this method for harvesting clean hythane vehicle fuel from agricultural biomass.