Monday, May 4, 2009
9-54
Continuous saccharification and fermentation of dilute acid pretreated corn stover and Avicel
Simone Brethauer, Michael H Studer, and Charles E. Wyman. Center for Environmental Research and Technology and Chemical and Environmental Engineering Department, University of California, Riverside, 1084 Columbia Avenue, Riverside, CA 92521
In contrast to batch operations, continuous fermentations are recognized for such advantages as higher volumetric productivity, reduced labor costs, and reduced vessel down time for emptying, cleaning, and filling. Lignocellulosic conversion processes can especially benefit from continuous process designs due to the presence of fermentation inhibitors generated or released during biomass pretreatment. High cell densities and adaptation abilities of the fermenting organism in a continuous setup enable higher productivities and yields than in batch systems and additional detoxification steps can be omitted or at least reduced. However, continuous processing of lignocellulosic materials faces some important challenges such as the handling of insoluble substrate and concerns about organism washout and contamination. Furthermore, although many economic studies assume that continuous saccharification or continuous saccharification and fermentation (cSSF) would be employed commercially, available experience and literature data are extremely limited. Thus, we set up a small scale, multi stage reaction system for continuous saccharification and cSSF of lignocellulosic materials to evaluate the effects of dilution rate, substrate concentration, and enzyme loadings on performance and to determine the potential to reduce enzyme loadings. In addition, data were sought on critical dilution rates for maintaining cell growth without washout. Results for cSSF of Avicel and dilute sulfuric acid pretreated corn stover are compared with kinetic modelling data to predict an optimal process design.