Optimizing Semisimultaneous Saccharification and Fermentation for Ethanol Production from Chinese Distiller's Spent Grains

Spent grains are a main byproduct for Chinese liquor production. In this study, the semisimultaneous saccharification and fermentation (S-SSF) for ethanol production based on multi-enzyme degradation of the spent grains was investigated. After optimization with orthogonal design experiments, an enzyme combination composed of cellulase NS22086 at 0.30 mL/g, β-glucosidase NS22118 at 0.20 mL/g, xylanase NS22083 at 0.08 mL/g, complex enzyme NS22119 at 0.08 mL/g, complex enzyme NS22002 at 0.02 mL/g, and glucoamylase NS22035 at 0.01 mL/g was obtained. With 14% of the substrate concentration and the optimal enzyme combination, reducing sugar, glucose, and xylose at 109.97, 60.02, and 16.05 g./L, respectively, were attained in the saccharified solution, which are approximately fourfold of those obtained before optimizing and are among the highest values reported for different lignocellulosic materials. Experiments of batch and fed-batch S-SSF for ethanol production from the spent grains were then performed, and higher efficiency of saccharification and ethanol formation was observed in the fed-batch S-SSF, where an ethanol concentration of over 30 g/L was attained. Kinetic models satisfactorily describing the processes of S-SSF were developed and analyzed. This study contributes to the utilization of Chinese distiller's spent grains and other similar materials.