Monday, August 13, 2012
Columbia Hall, Terrace Level (Washington Hilton)
Non-renewable energy sources are being consumed such that it is estimated that almost 90% of these resources will be depleted in the next 25 years. Thus, there is a great need for research to generate to generate economical alternative and renewable energy source. One of the widely researched alternatives is fuels ethanol. Currently, a majority of ethanol is produced from corn starch, which competes with food industry for its feedstock. Bioethanol from lignocellulosic biomass, which includes plant wastes, forestry residues, paper waste etc, would not compete for food feedstocks. However, bioethanol from lignocellulosic biomass is not an economical process yet. The poor economics are primarily due to the inability of Saccharomyces strains to consume xylose – one of the major sugars present in lignocellulosic hydrolysates in addition to glucose. In order to improve utilization of xylose in lignocellulosic hydrolysates, a novel two-stage fermentation process was developed to improve the bioethanol productivity. In the first stage, glucose is consumed by Saccharomyces pastorianus to produce ethanol. Then, the mixture of ethanol and unconverted xylose is separated. In the second stage, Escherichia coli is allowed to grow on xylose. The E. coli cells obtained are then heat-killed and fed to first stage yeast fermentation. This novel cyclic process has resulted in improved ethanol productivity by S. pastorianus in the presence of E. coli extract.