Sodium carbonate–sodium sulfite pretreatment for improving the enzymatic hydrolysis of rice straw

Abstract The performance of sodium carbonate–sodium sulfite (Na 2 CO 3 –Na 2 SO 3 ) pretreatment on improving the enzymatic hydrolysis of rice straw was investigated. The results indicated that both Na 2 CO 3 and Na 2 SO 3 pretreatments are effective in improving the enzymatic digestibility of rice straw. A higher ratio of Na 2 SO 3 in pretreatment liquor performed better at softening the rice straw through degradation of hemicellulose, delignification, and lignin sulfonation, while it was conserving more polysaccharides during the pretreatment than Na 2 CO 3 . The highest sugar recovery of pretreated rice straw, 74.5%, 82.7%, and 59.5% for total sugar, glucan, and xylan, respectively, was obtained at cellulase loading of 20 FPU/g-cellulose after the pretreatment at 140 °C, chemical charge of 12%, Na 2 CO 3 –Na 2 SO 3 ratio of 0:1 (i.e., only Na 2 SO 3 pretreatment). The corresponding delignification ratio of pretreated solid was 53.4%, and 91.4% of the polysaccharides were conserved. The sugar recovery of only Na 2 CO 3 pretreatment at the ratio of 1:0 was 67.1%, 74.4%, and 53.7% for total sugar, glucan, and xylan, respectively, at 140 °C, chemical charge of 12%, and enzyme loading of 20 FPU/g-cellulose. Its corresponding delignification ratio was 40.3%, and polysaccharides conservation ratio was 88.9%.