Optimization of simultaneous saccharification and fermentation for the production of ethanol from sweet sorghum (Sorghum bicolor) bagasse using response surface methodology

The response surface method was used to investigate the effects of process parameters, including temperature from 35 to 45 °C, enzyme loading from 10 to 30 filter paper units (FPU)/g-glucan, yeast concentration from 0.5 to 1.5 g/L, and bagasse solid concentration from 4 to 10% on ethanol yield, concentration and production rate during simultaneous saccharification and fermentation (SSF) of sweet sorghum bagasse. The results showed that the maximum ethanol yield, concentration and production rate were obtained at different SSF conditions. Under the recommended SSF condition of the temperature at 37 °C, yeast concentration at 1.4 g/L, enzyme loading at 25 FPU/g-glucan and bagasse solid concentration at 10%, the ethanol yield, concentration and production rate were 89.4%, 38 g/L and 1.28 g/L/h, respectively. The bagasse solid concentration had significant effects on the ethanol concentration and ethanol production rate. The optimum bagasse solid concentration for the ethanol yield was 7%. The increase of the bagasse solid concentration significantly increased the final ethanol concentration but decreased the ethanol production rate. Fed batch operation could be used to maintain the bagasse solid concentration at a low value (e.g., 7%) to achieve high ethanol yield and production rate while increasing the final ethanol concentration.

► The response surface is effective to optimize SSF of sweet sorghum bagasse.
► Maximum ethanol yield, concentration and rate were obtained at different conditions.
► 25 FPU cellulase/g-glucan, 1.4 g yeast/L and 10% bagasse at 37 °C were recommended.
► Ethanol at 89.4% yield, 38 g/L concentration and 1.28 g/L/h production rate obtained.