BIOT 122 |
| High processing costs present an important barrier to commercialization of biomass-to-ethanol processes, and the biological steps of enzymatic hydrolysis and fermentation account for the major fraction of these costs. Combining both hydrolysis and fermentation in one vessel via the simultaneous saccharification and fermentation (SSF) process can significantly reduce capital investment and operating costs, and realize high ethanol yields and concentrations at lower enzyme loadings. Continuous fermentation can further reduce ethanol costs for the increased biomass conversion, ethanol concentrations, ethanol productivity, and enzyme effectiveness. In this study, an automatically-controlled two-stage continuous fermentation system was applied to evaluate the effects of flow rates and enzyme loadings on performances of yeast and enzymes in continuous ethanol process with pure cellulose as the substrate. An important finding is that ethanol concentration and yield for both stages decreased with dilution rate. When the dilution rate was increased from 0.02 to 0.08 h-1 for continuous SSF of 8wt% Avicel at 15 FPU/g glucan (FPU/Beta-g = 1:1), the ethanol concentration decreased from 24.3 to 14.7 g/L for the first tank, and 32.6 to 19.8 g/L for the second at steady state, respectively. A similar trend was observed for continuous operation at a lower enzyme loading of 10 FPU/g glucan. When the dilution rate was increased to 0.12 h-1, yeast was washed out from the first tank after 6 days of continuous operation, resulting in accumulation of glucose in the first tank and an increase in ethanol concentration in the second. In addition, glucose concentrations oscillated in the first tank, particularly for runs at high enzyme loadings and high dilution rates, though cellobiose accumulation was not observed in any of the runs. These results suggest that more fundamental issues should be addressed to develop a continuous process for production of cellulosic ethanol. |
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Emerging Technologies: Bioenergy
8:00 AM-11:00 AM, Tuesday, August 21, 2007 BCEC -- 109A, Oral
Division of Biochemical Technology |