Bioconversion of Plant Biomass to Ethanol. Final Report, December 1, 1979-December 31, 1980

摘要

This final report describes research performed on a process for the direct fermentation of pretreated hardwood and corn stover to ethanol. Experimental investigations were conducted on the technical problem areas that limit the utilization of lignocellulose for ethanol production, i.e., wood pretreatment, culture development, and fermentation. Considerable technical progress has been demonstrated in each area. The experimental findings have led to process design improvements that can reduce the capital cost for ethanol production. Studies on wood pretreatment to enhance carbohydrate recovery and susceptibility to enzymatic hydrolysis continued to show progress. Rapid decompression of treated fibers to atmospheric pressure was found to make little or no contribution to enhancing the rate of enzymatic hydrolysis. Acid extraction of the hemicellulose component prior to sulfur dioxide augmented wood steaming increased the overall fermentable carbohydrate recovery and, therefore, the attainable yield of ethanol. Only modest improvements in fiber digestibility are now required to meet the pretreatment goals. A new and highly cellulolytic strain of C. thermocellum, designated as strain YS, was isolated from hot springs soil samples and tested. A previously unreported effect of stirring and hydrogen on the fermentation product pattern of several strains of C. thermocellum was discovered. Mono- and co-culture fermentations were performed to understand the factors that affect the yield of ethanol. Co-culturing C. thermocellum strain YS with efficient ethanol-producing non-cellulolytic strains resulted in higher ethanol yields than that observed in strain YS mono-culture cellulose fermentation. The feasibility of ethanol production at high substrate concentrations was investigated in serum bottle experiments. The amount of ethanol produced declined as the substrate concentration increased. (ERA citation 07:010405)