Simultaneous Saccharification and Fermentation of Rice Straw Pretreated by a Sequence of Dilute Acid and Dilute Alkali at High Dry Matter Content

In lignocellulosic materials, the presence of lignin and hemicellulose makes the access of enzymes to cellulose difficult, thus reducing the efficiency of the hydrolysis. To improve the substrate hydrolysis for ethanol production, and to decrease the ethanol cost, rice straw was pretreated by a sequence of dilute acid and dilute alkali to remove lignin and hemicellulose, and then the production of bio-ethanol from the pretreated rice straw using simultaneous saccharification and fermentation at high dry content was investigated. After the complex pretreatment, the cellulose content in rice straw increased from 41.5 to 88.5%. Complex method and dilute acid pretreatment of rice straw result in glucose concentrations of 101.7 and 50.2 g/L, respectively. As a result, ethanol concentration of 58.7 g/L was obtained by simultaneous saccharification and fermentation of rice straw pretreated using a sequence of dilute acid and dilute alkali at a substrate concentration of 160 g/L; the ethanol yield was 73.4% based on the glucose content in the raw material. A biorefinery combining a sequence of dilute acid and dilute alkali pretreatment with commercial ethanol instant active dry yeast (S. cerevisiae) in SSF could achieve 175 g EtOH/kg untreated rice straw.