Evaluation of impact of pretreatment strategies on structural deconstruction, biodegradability, and solubility of agricultural biomass for enhanced biohydrogen production via high-solids anaerobic fermentation (HSAF)

Rising global energy demands and environmental concerns underscore the importance of biohydrogen production from lignocellulosic agricultural residues as a clean and renewable energy alternative. This study evaluates the effects of acid, alkali, hydrogen peroxide, ultrasonic, and thermal pretreatments on rice husk to enhance biohydrogen production under high-solids anaerobic fermentation (HSAF). Despite extensive research on pretreatment strategies, pretreatment-induced structural deconstruction is rarely quantified in an integrated manner and directly linked to biohydrogen yield and kinetics in existing studies, particularly under high-solids conditions. Structural changes were assessed using FTIR, XRD, SEM, BET, proximate, and CHNS analysis, revealing key changes that enhanced biodegradability and hydrogen production efficiency. Alkali pretreatment (2% NaOH) achieved the highest hydrogen yield (248 ± 2.69 mL/g VS), driven by effective delignification, cellulose enrichment (60.18%), increased crystallinity (46.70%), surface area (3.29 m2/g), and mesoporosity (55.53%). Kinetic modeling using the Modified Gompertz equation indicated the shortest lag phase (1.56 days) and peak production rate (811.3 mL/day). Strong correlations (r = −0.973 to +0.972) between structural attributes and hydrogen yield highlight the significance of targeted pretreatment. These findings demonstrate that linking structural deconstruction with fermentability enables scalable strategies for efficient biohydrogen production from lignocellulosic biomass.