Tuesday, May 3, 2011
Higher ethanol concentrations from bioprocesses are needed to make ethanol production from biomass fermentation more cost effective. We utilized dewatering to increase sugar concentrations in the feedstock to enable higher ethanol concentrations by fermentation. Feedstock consisted of switchgrass that was delignified through ammonia pretreatment and saccharified to produce soluble sugars. Sugar concentrations in this study were within the range that could be easily utilized by the two fermenting yeasts Saccharomyces cereviciae D5A and S. bayanus. Since S. bayanus demonstrated superior growth and ethanol production at elevated sugar concentrations, it was used throughout the rest of this study. Increased growth rates were demonstrated at elevated switchgrass-sugar concentrations by S. bayanus. The addition of yeast extract and peptone as sources of micronutrients further increased yeast growth rates. The addition of sorghum molasses without yeast extract and peptone also increased growth rates, likely due to the presence of required nutrients. In addition to growth stimulation, sorghum molasses also directly increased sugar concentrations further boosting the final concentration of ethanol product. In summary, dewatering of ammonia-treated, saccharified switchgrass resulted in higher sugar concentrations and overall ethanol production. Co-fermentation of saccharified switchgrass and sorghum molasses offers a potential strategy for high gravity fermentation to achieve elevated ethanol concentrations. The increased osmotic pressure of these increased sugar concentrations may also provide a potential means of biomass storage as a concentrated feedstock.