Optimization of substrate concentration of dilute acid hydrolyzate of lignocellulosic biomass in batch hydrogen production

• Three types of lignocellulosic biomass were used as substrate for H2 fermentation.
• Dilute acid pretreatment of biomass was first performed, followed by fermentation.
• Hydrolyzate was diluted to get 5, 10, 15, and 20 g L−1 initial sugar concentration.
• Peak hydrogen production rate was observed at 10 g L−1 initial sugar concentration.

Lignocellulosic biomass is a promising alternative source for biohydrogen production. Its recalcitrant structure requires physicochemical pretreatment methods, such as dilute acid pretreatment, to utilize the carbohydrates in the biomass for fermentation. This study was aimed to investigate the optimum substrate concentration of dilute acid lignocellulosic hydrolyzate for dark hydrogen fermentation processes. Empty palm fruit bunch, rice husk, and pine tree wood were used as the substrates. The lignocellulosic biomass samples were hydrolyzed and fed to batch hydrogen fermentation after adjustment of substrate concentration of the hydrolyzate solutions to 5, 10, 15, and 20 g/L. The maximum hydrogen production rates were 1510 ± 96 mL H2 L−1 day−1, 1860 ± 245 mL H2 L−1 day−1, and 1629 ± 170 mL H2 L−1 day−1 at 10 g L−1 substrate concentration of empty palm fruit bunch, rice husk, and pine tree wood, respectively. These correspond to hydrogen yields of 0.96 ± 0.04 mol H2 mol−1 sugar, 1.25 ± 0.15 mL H2 mol−1 sugar, and 0.99 ± 0.05 mL H2 mol−1 sugar, respectively. The results indicate that dilute acid pretreated lignocellulosic biomass would be a suitable substrate for fermentative hydrogen production.