Sequential pretreatment of lignocellulosic biomass employing hydrothermal treatment and ball milling to improve the efficiency of enzymatic hydrolysis

In this study, biomass (oak, miscanthus, and sweet sorghum bagasse) are subjected to pretreatments involving either hydrothermal treatment followed by ball milling (HT/BM) or ball milling followed by hydrothermal treatment (BM/HT) in order to increase the enzymatic hydrolysis efficiency. The chemical composition and structure, and especially the crystallinity, of the treated biomass are found to depend on the order of pretreatment. The biomass obtained via hydrothermal treatment followed by 60 min of ball milling (HT/BM60) has a relatively low crystallinity (0-17.68 %) for all biomass, with the lowest value being obtained for miscanthus. Moreover, the particle size distribution span of the HT/BM60 miscanthus is low (0.79) compared to those of the other biomass due to an increased proportion of fine particles in the miscanthus. Meanwhile, the enzymatic hydrolysis efficiency of the HT/BM60 biomass is high, and the glucose conversion rate differs depending on the biomass, with the lowest in oak (55.91 %) and the highest in miscanthus (90.47 %). The enzyme adsorption isotherms and kinetics are suitable described by the Langmuir isotherm and pseudo-second-order model, thus implying chemical adsorption of the enzyme as a monolayer on the substrate surface. The principle component analysis shows the particle size and crystallinity of the biomass significantly affect the enzymatic hydrolysis.