| Summary: | 碩士 === 國立中正大學 === 化學工程所 === 98 === In the research, we adopt continuous culture with cell recycling as an ethanol fermentation process. It could increase the ethanol productivity and continuous operation in the industry. Flocculating yeast strains used in this study were Saccharomyces diastaticus LORRE-316 and Saccharomyces cerevisiae WY1335, respectively. We used 80 g/L sucrose solution as cultivation medium in place of sugar cane juice and performed the fermentation in a 5-L continuous fermenter with cell recycling. Because of S. diastaticus LORRE-316 and S. cerevisiae WY1335 in the batch fermentation, with an ethanol yield of over 80%. They also could be industrial strains for ethanol production.
First of all, the utilization of the response surface methodology for the optimization conditions in the ethanol fermentation of the yeast strain S. cerevisiae WY1335. The optimization conditions were found to be the temperature of 34.7 °C and the pH of 5.2. By experimental result, the predicted value of the ethanol yield was very close to experimental value. In following experiment, we observed from the settling rate and flocculation for flocculating yeast strains that could compare their flocculation ability, the S. diastaticus LORRE-316 was better than the S. cerevisiae WY1335. After, we carried out the experiment of continuous fermentation with cell recycling, to find out the effect for the ethanol productivity. In the process of fermentation, we considered the major operating conditions of dilution rate, reflux ratio and cell settling rate. They were important factors for the ethanol productivity. We used the settler as the cell separator by flocculating yeasts in order to the high cell mass in the fermenter was maintained and increased substrate concentration to obtain high ethanol productivity. In experimental result, the yeast S. diastaticus LORRE-316 at a dilution rate of 0.24 h-1 and a reflux ratio of 0.8 resulted in an ethanol productivity of 9.14 g/L h, compared with batch fermentation process more then 96%. Because of the yeast S. cerevisiae WY1335 has low settling rate, leading to washout occurred. Therefore, a hollow-fiber microfiltration module offered an alternative of the settler. The result show that using the way could avoid cell washout and at a dilution rate of 0.24 h-1 and a reflux ratio of 0.8 resulted in a ethanol productivity of 7.10 g/L h, compared with batch fermentation process more then 83%.
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