Optimization of Fermentation Conditions for the Production of Ethanol from Stalk Juice of Sweet Sorghum by Immobilized Yeast Using Response Surface Methodology

Optimization of three parameters, including initial total sugar concentration, supplement rate of (NH4)(2)SO4, and particles stuffing rate, was attempted using response surface methodology based on a Box-Behnken design for the optimal production of ethanol by immobilized yeast fermentation of stalk juice of Liaotian number 1 sweet sorghum cultivar in shaking flasks. The correlation analysis of the mathematical regression model indicated that the quadratic polynomial model could be employed to optimize ethanol production. The optimum conditions were found to be an initial total sugar concentration of 22.88%, supplement rate of (NH4)(2)SO4 of 0.244%, and particles stuffing rate of 25.15%. At the optimum conditions, the maximum predicted ethanol yield of 93.83% was obtained. The ethanol yield and fermentation time of verification experiments in the shaking flask were 92.37% and 14 h at the corresponding parameters, respectively, while they were 93.23% and 13 h, respectively, in a 5 1, bioreactor, in which the predicted value of ethanol yield was very close to experimental values. In addition, the fermentation time of the stalk juice of sweet sorghum was about 3-4 times shorter with immobilized yeast than that of conventional fermentation technology. Thus, by immobilized yeast fermentation of the stalk juice of sweet sorghum, the Box-Behnken design was found to be the favorable strategy investigated with respect to the optimization of fermentation conditions for ethanol production.