Sulfite-formaldehyde pretreatment on rice straw for the improvement of enzymatic saccharification.

Rice straw is one of the most abundant agricultural residues in China. It is considered as a promising raw material for bioethanol production. In this work, rice straw was pretreated by sodium sulfite-formaldehyde (SF) for improving enzymatic saccharification. The SF pretreatment, using proven technology and industrialized equipment, showed efficient delignification selectivity and high carbohydrates retention in pretreated solid. The highest sugar yields of 79.0%, 88.8% and 71.1% for total sugar, glucan and xylan, respectively were obtained at an enzyme loading of 40 FPU/g-substrate after the raw material pretreated with 12% sodium sulfite at 160°C. About 75% of lignin was dissolved in pretreatment spent liquor and 78% of silica was retained in the residue of enzymatic hydrolysis. The results proved sulfite-formaldehyde as a promising pretreatment for the production of bioethanol as well as potential high value added by-products of silica nanoparticles and lignosulfonate.