Pilot scale pretreatment of wheat straw and comparative evaluation of commercial enzyme preparations for biomass saccharification and fermentation

Abstract

Conversion of pretreated lignocellulosic biomass (LCB) into sugars is one of the critical steps for bioethanol production. High LCB hydrolysis could be achieved by employing robust enzymes having high inhibitor tolerance, low irreversible lignin binding, and low end-product inhibition. In this study, acid pretreatment of wheat straw was carried out at pilot scale (250kg/day) and three commercial cellulase preparations from Advanced Enzyme (AD), Novozyme (CL), and Genencor (AC) were evaluated for inhibitor (lignin, furfural, hydroxyl methyl furfural, vanillin) tolerance. Pretreated wheat straw (PWS) hydrolysis was carried out at different enzyme concentrations (1–30mg protein/g of PWS) under optimum pH and temperature in rolling bottle reactor. Simultaneous saccharification and fermentation was performed employing in-house thermotolerant Saccharomyces cerevisiae. Results indicated that, maximum saccharification (more than 85%) was achieved at low protein loadings (10–15mg protein/g PWS) of CL and this enzyme was also found to be more robust in presence of inhibitors. Maximum ethanol yield (78%) was found at 20mg protein/g of PWS using CL. This study suggests that inhibitors have significant detrimental effect on enzymes and better understanding of enzyme-inhibitor correlation with its critical moderation would help in further enhancing the LCB hydrolysis at low enzyme dosage.