Ethanol Production from Sugar Beet Pulp using Escherichia coli KO11 and Saccharomyces cerevisiae

Abstract

The effectiveness of sugar beet pulp as a feedstock for ethanol production was tested in three different hydrolysis and fermentation systems using Escherichia coli KO11 alone or in combination with Saccharomyces cerevisiae. Two microorganisms were used to improve ethanol yields from the galacturonic acid, arabinose, and glucose in sugar beet pulp hydrolyzates. The baseline system used E. coli KO11 as the only fermenting organism in a simultaneous saccharification and fermentation (SSF) with pectinase, hemicellulase, and cellulase enzymes. Ethanol was produced with a yield of 0.30 g ethanol g-1 sugar. S. cerevisiae could not be used to ferment glucose successfully following a fermentation with E. coli KO11 because of the inhibitory levels (>10 g L-1) of acetic acid produced during galacturonic acid utilization. Use of E. coli KO11 for fermentation of a sequential hydrolysis of pectin and hemicellulose followed by cellulose resulted in 27% lower ethanol yields than the baseline system. When starting with an SSF with S. cerevisiae using pectinases, cellulases, cellobiases, and following with a second fermentation with E. coli KO11, total ethanol yield increased to 0.34 g ethanol g-1 sugar. Despite the lower ethanol yields in the baseline system (using only E. coli KO11), that fermentation finished 48 to 72 h earlier and had the highest volumetric ethanol productivity (0.22 g L-1 h-1).