Optimal immobilization of Trichoderma asperellum laccase on polymer coated Fe3O4@SiO2 nanoparticles for enhanced biohydrogen production from delignified lignocellulosic biomass

Recalcitrant lignin in the lignocellulosic biomass (LCB) is a major barrier in biofuel production. Thus, its removal from LCB is imperative before conversion into biofuels. Enzyme-mediated degradation of lignin is considered to be a green approach as it does not generate any toxic intermediates. Further, enzyme activity may be enhanced by its immobilization onto polymer-coated magnetic nanoparticle support, that enhances anchorage and enables easy recovery for reuse. Hence, in the present study Trichoderma asperellum laccase was immobilized onto Fe3O4@SiO2-chitosan nanosupport for delignification of LCB and subsequently utilized for biohydrogen production. The optimum immobilization conditions determined statistically via response surface methodology were Fe3O4@SiO2-chitosan (58.37 mg), enzyme concentration (24.11 mu g), pH (5.95), time (5.3 h) and N-ethyl-N'-(3-dimethyl aminopropyl) carbodiimide (EDAC) (1.41%) for maximum immobilization efficiency (92.41%) and yield (91.23%). The immobilized laccase was found to have higher delignification potential than the free enzyme (84.46%), with sweet sorghum stover as substrate, and could be efficiently reused up to 8 cycles. Biohydrogen yield and production rates were 2.8 mol H-2/mol reducing sugar and 25 L H-2/L-d, respectively, in a continuous stirred tank reactor. Developed Fe3O4@SiO2-chitosan particles have a high potential for use in biohydrogen production.