Dark fermentative hydrogen production following the sequential dilute acid pretreatment and enzymatic saccharification of rice husk

This study examined the effect of sequential dilute acid hydrolysis and enzyme saccharification conditions of rice husk on hydrogen (H₂) fermentation. The rice husk was hydrolyzed using dilute H₂SO₄ and then further enzymatically hydrolyzed with various concentrations (0.1, 0.25, 0.5, 0.75, and 1.0 mg protein mL⁻¹) of Celluclast 1.5 L^®. The sequential pretreatment significantly enhanced sugar recovery, up to 174% for 1.0 mg mL⁻¹ concentration of the enzyme. Increasing the concentration of enzyme slightly increases sugar recovery. While the production of furfural and 5-hydroxymethylfurfural occurred during dilute acid hydrolysis, it was not observed during enzymatic saccharification. At the following H₂ fermentation of the hydrolyzates, H₂ yield was improved up to 150% by using the dilute acid and enzymatic hydrolyzate as substrate, as compared when only dilute acid hydrolyzate was used. The highest H₂ yield of 473.1 mL H₂ g⁻¹ rice husk was achieved with enzyme concentration of 0.75 mg protein mL⁻¹.