Abstract
BackgroundAlthough various pre-treatment methods have been developed to disrupt the structure of lignocellulosic biomass, high dosage of cellulases is still required to hydrolyze lignocellulose to fermentable sugars. Enzyme recycling via recycling unhydrolyzed solids after enzymatic hydrolysis is a promising strategy to reduce enzyme loading for production of cellulosic ethanol.ResultsTo develop effective enzyme recycling method via recycling unhydrolyzed solids, this work investigated both enzymatic hydrolysis kinetics and enzyme adsorption kinetics on dilute acid and dilute alkali pre-treated corn stover (CS). It was found that most of the hydrolysable biomass was hydrolyzed in the first 24 h and about 40% and 55% of the enzymes were adsorbed on unhydrolyzed solids for dilute alkali-CS and dilute acid-CS, respectively, at 24 h of enzymatic hydrolysis. Lignin played a significant role in such adsorption and lignin materials derived from dilute acid-CS and dilute alkali-CS possessed different enzyme adsorption properties. Enzyme recycling was performed by recycling unhydrolyzed solids after 24 h enzymatic hydrolysis for five successive rounds, and successfully reduced 40% and 50% of the enzyme loadings for hydrolysis of dilute alkali-CS and for hydrolysis of dilute acid-CS, respectively.ConclusionsThis study presents that the enzymes adsorbed on the unhydrolyzed solids after short-time hydrolysis could be recycled effectively for efficient enzymatic hydrolysis. Lignin derived from dilute acid-CS has higher enzyme adsorption capacity than the lignin derived from dilute alkali-CS, which led to more enzymes recycled. By applying the enzyme recycling strategy developed in this study, the enzyme dosage needed for effective cellulose hydrolysis can be significantly reduced.
Highlights
Various pre-treatment methods have been developed to disrupt the structure of lignocellulosic biomass, high dosage of cellulases is still required to hydrolyze lignocellulose to fermentable sugars
Various pre-treatment methods have been developed to disrupt the structure of lignocellulosic biomass and to change physical and chemical properties of lignocellulosic biomass, high dosage of cellulases is still required to hydrolyze lignocellulose to fermentable sugars [8, 9]
Biomass composition comparison of acid and alkali pre‐treated corn stover To study the effect of pre-treatment on enzyme adsorption, dilute acid and alkali pre-treatments were carried out under optimized conditions to achieve efficient cellulose hydrolysis
Summary
Various pre-treatment methods have been developed to disrupt the structure of lignocellulosic biomass, high dosage of cellulases is still required to hydrolyze lignocellulose to fermentable sugars. Recycling cellulases from the liquid phase of hydrolysate has been studied extensively, it was reported that the enzymes adsorbed on the solid substrates are the key enzymes that are necessary for effective cellulose hydrolysis [19,20,21]. This is because the enzymes adsorbed on the solid substrates included the major cellulase degrading enzymes that have been reported to have high binding affinity towards cellulose [15] and have been considered as the rate-limiting enzyme component for the overall cellulose hydrolysis [16]. Acid catalyzed pre-treatments eliminated mainly hemicellulose from biomass [25, 26] while alkali pre-treatments can remove lignin [27], which may greatly affect their enzyme adsorption properties and affect the effectiveness of enzyme recycling via recycling unhydrolyzed solids
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