Recycled gas purge system was developed to alleviate the ethanol inhibition in ethanol fermentation and to increase ethanol productivity. This system has many advantages such as the alleviation of ethanol inhibition, removal of $CO_2$, preservation of cell viability etc.
In this study, $\underline{Saccharomyces cerevisiae (ATCC24858)}$ immobilized in Ca-alginate gel was used.
The kinetic paterns of the fermentation of glucose to ethanol by Saccharomyces cerevisiae was a growth-associated fashion that the products are synthesized during the cell growth. In batch fermentation performed in the absence of recycled gas purge system, using 250g/l glucose medium, glucose was not utilized completely and the production of ethanol was stopped owing to ethanol inhibition. This phenomenon was more serious in immobilized cell than in free cell. The product yield in immobilized cell was higher nearly 3% than in free cell. In batch fermentation, as baed volume fraction was increased, the rate of glucose uptake and ethanol production increased, but the final concentration of ethanol decreased.
In recycled gas purge system, glucose was utilized completely but the concentration of ethanol in the fermentor was maintained below 90g/l. Thus, ethanol inhibition was alleviated.
In continuous fermentation using recycled gas purge system and immobilized cell, the optimum temperature was 33-35℃. When recycled gas purging rate was increased from O vvm(L/min) to 35 vvm(L/min), the ethanol productivity increased by 1.4 times. As dilution rate was increased, the concentration of glucose and the ethanol productivity increased, but the concentration of ethanol in fermentor decreased. So, when bead volume fraction was 1/5, the ethanol productivity of 24 g/l/hr was obtained at dilution rate of 0.35hr-1. When the bead volume fraction was 1/2, the ethanol productivity of 59g/l/hr was obtained at dilution rate of $3.6hr^{-1}$.
