Effect of oxygen supplement on ethanol productivity and yeast viability in continuous alchol fermentation process

Abstract

For the purpose of improving ethanol productivity the effect of air supplement on the performance of continuous ethanol fermentation system was studied. The effect of oxygen supplement on yeast concentration, cell yield, cell viability, extracellular ethanol concentration, ethanol yield, maintenance coefficient, specific rates of glucose assimilation and ethanol production, and ethanol productivity have been evaluated, using a high alcohol tolerant $\mbox{\underline{Saccharomyces}}$ $\mbox{\underline{cerevisiae}}$ STV89 strain and employing a continuous fermentor equipped with an accurate air metering system in the flow rate range of 0-11. ml air/liter/hr. It was found that, when a small amount of oxygen up to about 80 μmoles of oxygen/liter/hr was supplied, the ethanol productivity was significantly enhanced as compared to the productivity of the culture without any air supplement. It was also found that the oxygen supplement improved cell viability considerably as well as the ethanol tolerance level of yeast. As the air supply rate was increased, from 0 to 11 ml air/liter/hr while maintaining a constant dilution rate t about 0.06 $hr^{-1}$, the cell concentration increased from 2.3 to 8.2 g/liter and the ethanol productivity increased from 1.7 to 4.1 g ethanol/liter/hr, although the specific ethanol production rate decreased slightly from 0.75 to 0.5 g ethanol/g cell/hr. The ethanol yield was slightly improved also with an increase in air supply rate, from about 0.37 to 0.45 g ethanol/g glucose. The maintenance coefficient decreased with the increase of the air supplement. Some attempts were made to elucidate the relationship between the changes in extracellular ethanol concentration and viability pattern. The experimental model equation could be formulated and confirmed to be valid for other different fermentation systems. In order to further out understanding on alcohol fermentation system, the inhibition effect of substrate and product have been studie...