Ethanol Production from Solid-State Fermentation of Sweet Sorghum by Thermotolerant Yeast

摘要

Of the many crops currently being investigated for energy and industry in China, sweet sorghum is one of the most promising, particularly for ethanol production. It is also considered as a potential alternative crop for energy and industry in the EU, mainly because it can yield biomass and fermentable sugars. Solid-state fermentation of chopped sweet sorghum particles to ethanol was studied statically using thermotolerant yeast. The influence of various process parameters, such as yeast cell concentration, particle size, moisture content, on the ethanol yield was investigated. The initial particle size 、moisture and reducing agent significantly affected the ethanol yield. More ethanol was produced with smaller particle sizes (0.5~1.5mm) due to closer packing densities of substrate and reduction of void space between particles. But too small particle size is also disadvantageous for heat transfer and exchange of carbon dioxide between the air and the solid surface. The moisture level of 75% was the optimal moisture level with the ethanol yield of 7.5 g ethanol per 100 fresh stalks. The optimal cell concentration 、range of pH were 5×106 cells/g raw sorghum 、3.5~6.5 respectively. Addition of reducing agent H2SO3 into the fermentation medium provided anaerobic conditions, and resulted a high ethanol yield of 7.9 g ethanol per 100 fresh stalks which is 5.3% higher than the one without reducing agent.