Some critical aspects of the enzymatic hydrolysis at high dry-matter content: a review

Enzymatic hydrolysis represents the crucial phase in bioethanol production. Its aim is to convert pretreated lignocellulosic polymers in hexose sugars for fermentation into bioethanol. To be economically advantageous, the enzymatic hydrolysis should operate with a high concentration of dry matter. The drawback of this is the increase in the reaction medium’s viscosity and consequently bad mixing within the bioreactor due to the complexity of the lignocellulosic polymers. Another critical aspect of the enzymatic hydrolysis is enzyme deactivation, which is mainly due to two factors: the presence of lignin by-products, originating from the pretreatment of lignocellulosic biomass, and the accumulation of glucose in the reaction medium by cellulose hydrolysis. This review details these two critical aspects of enzymatic hydrolysis conducted with high dry-matter content. The most relevant milestones and technological solutions to improve rheological performance and to reduce enzyme deactivation have been investigated.