Effect of temperature in ethanol fermentation and its thermodynamic analysis

Abstract

In ethanol fermentation, the accumulated ethanol in fermentation broth has an adverse effect on the cell growth and ethanol production. Besides the cell viability is greatly reduced as the ethanol concentration in broth increases. However, the air supplement during fermentation improves significantly the viability. Therefore, the effect of ethanol and air-supplement in ethanol fermentation was studied by means of considering the thermodynamic parameters related to death rate constant of cells using a continuous culture technique. The continuous ethanol fermentation $(S_o=200 g/liter)$ with air-supplement (Air supply rate=0.0 and 5.0 mlair/liter-hr) was performed at various temperature (Temp. = 30,33,35,37℃) using Saccharomyces cerevisiae STV 89. The death rate constant was estimated from the viability which was measured by staining method. It was found that the entropy change related to death rate of cells gradually increased as the ethanol concentration increased but its enthalpy change was nearly constant at various ethanol concentration. In addition, air-supplement in ethanol fermentation caused a decrease in entropy change but did not cause a change in enthalpy change. However, the entropy changes related to growth rate and ethanol production rate was nearly zero at thermal activated zone.