Improvement of dry simultaneous saccharification and fermentation of rice straw to high concentration ethanol by sodium carbonate pretreatment

Ethanol at high concentration was produced from rice straw pretreated with sodium carbonate through dry simultaneous saccharification and fermentation (DSSF). A high concentration of ethanol was obtained without mechanical mixing, an increase in fermentation time, and pre-hydrolysis. The most important influencing factors, including pretreatment time (3–10 h), enzyme loading (5–40 FPU/g substrate), solid loading (15–30 wt %), and DSSF reaction time (48–120 h), were investigated on dry hydrolysis and DSSF. An increase in pretreatment time from 3 to 10 h improved ethanol concentration from 55.1 to 67.7 g/L, obtained through DSSF at 20% solid loading and 10 FPU/g substrate. A glucose concentration as high as 124.6 g/L was obtained from the hydrolysis of the straw treated for 5 h. The highest total sugar and ethanol concentration were 137.3 g/L and 83.1 g/L for the treated straw, while they were 65.2 g/L and 38.6 g/L for the untreated ones, respectively, obtained by hydrolysis and DSSF at 30% solid loading. Changes associated with pretreatment, i.e., composition, crystallinity, and microscopic structure of untreated and treated straws, were investigated to find the reason for the improved hydrolysis and DSSF.