Hydrogen production from acid and enzymatic oat straw hydrolysates in an anaerobic sequencing batch reactor: Performance and microbial population analysis

•H2 production from acid/enzymatic oat straw hydrolysate was demonstrated in an ASBR.•Granules and high H2 production were obtained when ASBR was fed with glucose/xylose.•Selective pressures over biomass were successful to prevent methane production.•Clostridium pasteurianum predominated during high H2 production stages.•Low bacterial diversity was correlated to high H2 production stages and vice versa.

Feasibility of hydrogen production from acid and enzymatic oat straw hydrolysates was evaluated in an anaerobic sequencing batch reactor at 35 °C and constant substrate concentration (5 g chemical oxygen demand/L). In a first experiment, hydrogen production was replaced by methane production. Selective pressures applied in a second experiment successfully prevented methane production. During this experiment, initial feeding with glucose/xylose, as model substrates, promoted biomass granulation. Also, the highest hydrogen molar yield (HMY, 2 mol H2/mol sugar consumed) and hydrogen production rate (HPR, 278 mL H2/L-h) were obtained with these model substrates. Gradual substitution of glucose/xylose by acid hydrolysate led to disaggregation of granules and lower HPR and HMY. When the model substrates were completely substituted by enzymatic hydrolysate, the HMY and HPR were 0.81 mol H2/mol sugar consumed and 29.6 mL H2/L-h, respectively. Molecular analysis revealed a low bacterial diversity in the stages with high hydrogen production and vice versa. Furthermore, Clostridium pasteurianum was identified as the most abundant species in stages with a high hydrogen production. Despite that feasibility of hydrogen production from hydrolysates was demonstrated, lower performance from hydrolysates than from model substrates was obtained.