(285c) Improving Simultaneous Saccharification and Co-Fermentation (SSCF) Performance by Optimizing Biomass and Enzyme Feeding Strategies

Low enzyme usage and high ethanol yields and concentrations are the keys to cost effective cellulosic ethanol production. The simultaneous saccharification and co-fermentation (SSCF) configuration is often favored due to its lower end product inhibition and better performance than separate hydrolysis and fermentation. However, further improvement has slowed primarily because enzymatic hydrolysis is rate limiting, especially at low enzyme loadings. An important challenge is to better match enzyme properties and enhance performance of ethanol fermentation. In this study, we focused on testing biomass and enzyme feeding strategies to improve SSCF performance by using stream exploded corn stover and recombinant C5-C6 co-fermenting Zymomonas mobilis. Fed batch operation was evaluated to process high solids and yield high ethanol concentrations and compared to hybrid operations based on hydrolysis with just enzyme at higher optimal temperatures in the initial stage followed by cooling to allow introduction of a fermentative organism for the SSCF approach in later stages. We also looked at enzyme feeding strategies such as supplementation with xylanase and beta-xylosidase and staged addition of enzymes in conjunction with SSCF to enhance performance. The effect of pretreatment severity on enzyme usage and fermentation inhibition was also evaluated and used to suggest integration strategies for these essential operations.