Enhanced enzymatic hydrolysis of sisal waste by sequential pretreatment with UV-catalyzed alkaline hydrogen peroxide and ionic liquid

Abstract

Combinatorial pretreatment is widely recognized as a promising strategy for bioconversion of lignocellulosic feedstock. In this study, a two-step sequential approach with UV-catalyzed alkaline hydrogen peroxide (UHP) process and ionic liquid (IL) treatment was performed on sisal waste in order to achieve a higher saccharification. The integrated UHP-IL pretreatment removed lignin by 79.2%, increased cellulose content to 73.5% and reduced the crystallinity index to 16.2%. The maximum reducing sugar yield of 69.2 g/100 g dry sisal waste and sugar conversion of 89.4% were attained by UHP pretreatment with 0.1 g/g hydrogen peroxide for 6 h followed by IL pretreatment with 20 mL/g tetrabutylammonium hydroxide at 60 °C for 40 min and enzymatic hydrolysis for 36 h with enzyme loading of 10 FPU/g. Kinetic modeling analysis revealed that UHP-IL process promoted the adsorption and binding of the substrate to enzymes via its combination effect of delignification and decrystallization, which increased the initial rate of enzymatic hydrolysis and the yield of reducing sugar.