8-25: Minimizing enzyme dosage and maximizing sugar yields from corn stover pretreated with alkaline peroxide

Pretreatment is a critical step in the conversion of lignocellulose to fermentable sugars. An ideal pretreatment would be effective (high sugar yields, short time, low enzyme loading), simple (avoidance of multiple handling steps), and inexpensive (for capital equipment, energy input, and chemicals). The process should also be compatible with high biomass loadings, minimize water consumption, and not generate inhibitors of downstream processes. Alkaline peroxide (AP) pretreatment (i.e., hydrogen peroxide at pH 11.5) satisfies many of these criteria. In order to determine if the AP process as previously developed (JM Gould, 1984, Biotechnol Bioengineer 26:46-52) could be improved further, we examined the effects of biomass loading, hydrogen peroxide concentration, residence time, and pH adjustment on subsequent enzymatic release of Glc and Xyl from corn stover. Enzymatic digestions were performed with Accellerase 1000 alone, an optimized mixture of four commercial enzymes (Accellerase 1000, Multifect Xylanase, Multifect Pectinase, and Novozyme 188), or an optimized mixture of 16 pure hydrolytic enzymes. At 0.5 g H₂O₂ /g biomass, >90% Glc yield with an enzyme loading of 8 mg protein/g glucan (~4–8 FPU/g glucan) was achieved in 48 h. The efficiency of AP pretreatment was improved by increasing the biomass loading (from 2% to 15%), decreasing the H₂O₂ loading (from 0.5 to 0.125 g/g biomass), extending the residence time (24 to 48 h), and readjusting the pH to 11.5 during the course of the pretreatment. Alteration of additional factors could likely contribute to a further reduction in the cost of AP.