Enzymatic hydrolysis of lignocellulosic biomass at high solids loading

Abstract

The conversion of lignocellulosic materials into reducing sugar needs an enzymatic hydrolysis step known as saccharification and is a key rate-limiting step in lignocellulose biomass-based biorefinery. The saccharification with high solids loading (above 15% solids w/w) results in high concentrations of sugar syrups that can have a positive impact on operational and capital costs making the overall biorefinery process economically viable. However, increasing the solid load results in negatively decreasing the glucan conversion efficiency known as the "high-solid effect." The probable explanations for this effect are associated with structural properties of biomass and physicochemical parameters such as degree of polymerization, rheological factors, water constraints during saccharification, and increase in viscosity resulting in improper mixing, thus poor heat and mass transfer. Other critical factors causing the HSE are nonproductive binding of the enzyme with lignin, product inhibition, and an increase in inhibitor concentration arising from the pretreatment of lignocellulosic biomass. The chapter presents a comprehensive outlook on factors impacting the performance of the high solids loading during saccharification. Some of the recent developments for overcoming hindrances caused by HSE are the development of efficient enzyme cocktails, enzyme feeding, and biomass loading strategies (e.g., fed-batch system), feeding the hydrolysis system with nonhydrolytic proteins and other enzymes, application of additives and surfactants, posttreatment washing of biomass, and improvement of bioreactor designs. Thus, the chapter also reviews the technological and economical assessment of contemporary technologies for high solids loading bioreactors which will provide insight into identifying the areas that need immediate scientific and technological efforts for overcoming the limitations of HSE and further enhancing the efficiency of lignocellulosic biorefinery at the commercial scale. © Springer Nature B.V. 2024. All rights reserved.