Development of a steam or microwave-assisted sequential salt-alkali pretreatment for lignocellulosic waste: Effect on delignification and enzymatic hydrolysis

This study compares two different sequential pretreatments for sugarcane leaf waste (SLW): steam salt alkali (SSA) and microwave salt-alkali (MSA). The two pretreatment types were modelled, optimized and validated with R-2 > 0.97. Reducing sugar yields of 1.21 g/g were obtained with optimized SSA pretreatment using 1.73 M ZnCl2, 1.36 M NaOH and 9.69% solid loading, and 1.17 g/g with optimized MSA pretreatment using 1.67 M ZnCl2, 1.52 M NaOH at 400 W for 10 min. A lower pretreatment time (10 min) was required for the MSA model (83% lower). The structure of pretreated SLW was assessed using scanning electron microscopy (SEM) and Fourier Transform Infrared analysis (FTIR). The optimized SSA and MSA models showed lignin removal of 80.5 and 73% respectively. The MSA pretreatment was further examined on sorghum leaves and Napier grass and showed yield improvements of 1.9- and 2.8-fold compared to recent reports. The developed pretreatment methods demonstrated high efficiency at enhancing enzymatic hydrolysis on various lignocellulosic substrates. (C) 2017 Elsevier Ltd. All rights reserved.