Improvement of batch and continuous ethanol fermentations from sweet sorghum stem juice in a packed bed bioreactor by immobilized yeast cells under microaeration

Microaeration during ethanol fermentation from sweet sorghum stem juice (SSJ) by immobilized Saccharomyces cerevisiae NP01 was investigated in a tubular packed bed bioreactor to improve ethanol production. In batch fermentation from SSJ containing 230 g/L of total sugars, aeration time and its rate were optimized using a factorial design. The highest ethanol concentration (PE) and productivity (QP) was 106.9 g/L and 1.78 g/L & sdot;h, respectively, with sugar consumption (SC) of 89.9% under an aeration rate of 0.35 vvm for 12 h. In continuous ethanol fermentation under an aeration rate of 0.05 vvm, the initial sugar concentration and dilution rate were optimized for high values of SC, PE and QP using response surface methodology. The optimal conditions for continuous fermentation were an initial sugar concentration of 160 g/L and a dilution rate of 0.05 h-1, yielding satisfactory experimental values of SC, PE and QP values at 90.8%, 75.4 g/L and 3.72 g/L & sdot;h, respectively.