Bioethanol Production from Alkali-Pretreated Rice Straw by Simultaneous Saccharification and Fermentation

The process of simultaneous saccharification and fermentation (SSF) combines the enzymatic hydrolysis of cellulosic matters and ethanol fermentation of hydrolysate within a single stage. This paper describes the SSF for the production of ethanol from sticks of rice straw pretreated with 10% NaOH at room temperature. Each SSF of alkali-pretreated rice straw was carried out with 10% (or another specific percentage) of water-insoluble-solids (WIS) at pH 5.0 using the commercial cellulase Accellerase 1000 and Ethanol Red dry yeast. The influence of various factors-including temperature (37, 40 and 42 degrees C), amount of dry yeast inoculum (0.5, 1 and 5 g/L), and enzyme loading (13.2, 17.5, 21.9 and 26.3 FPU/g-glucan)-on the efficiency of SSF was studied. SSF was found to be very effective at converting the cellulose in rice straw into ethanol, even at low enzyme doses. With 13.2 FPU/g-glucan, 10% WIS and 1 g/L dry yeast, SSF of alkali-pretreated rice straw at 40 degrees C produced an ethanol concentration of 29 g/L and an ethanol yield of 86% (based on the glucose content in the pretreated raw material) in a 72-h reaction. Also, the SSF in a rotary drum reactor for 96 h under the same WIS, enzyme and yeast loading resulted in an ethanol yield of 84.4%.