Effects Of Sodium Sulfite Pretreatment On Enzymatichydrolysis Of Cellulose Of Wheat Straw

Wheat straw was pretreated by sodium sulfite with a charge of 4% to 14% at a temperature of 155 ℃ for 1.2 to 1.4 h. The effects of sodium sulfite pretreatment on the chemical composition, enzymatic saccharification and ethanol fermentation of the wheat straw were examined.Under the pretreatment conditions, when the charge of sodium sulfite increased, the recovery of solid material decreased, together with the increasing of lignin removal. Glucan and xylan were both degraded; the degradation of xylan was larger than that of glucan.Enzymatic hydrolysis was conducted at 50 ℃ with a rotation speed of 150 r/min to investigate the hydrolysis efficiency of pretreated wheat straw. The substrate was wheat straw pretreated at 155 ℃ for 1.2 to 1.4 h with a sodium sulfite charge of 4% to 14%. The concentration of substrate was 5%. When cellulase loading increased from 15 FPU/g cellulose to 20 FPU/g cellulose, the yield of enzymatic hydrolysis increased as well, although the increase was less effective than that when the charge of sodium sulfite increased. After enzymatic hydrolysis, the yields of glucan, xylan and total sugars were 45.7%,37.4% and 44.3%, respectively.The SEM spectra of samples showed that pretreated wheat straw was looser and more flexible than that of untreated samples. The FT-IR spectra of samples showed that the hydrogen bonds in the pretreated wheat straw were weaker than those of untreated ones with the decreasing of crystalline region. Lignin removal increased with the increasing of the charge of sodium sulfite.The cellulase enzyme system was improved by the addition of β-glu cosidase and xylanase. At an enzyme loading of cellulase 15 FPU/g cellulose,β-glucosidase 12 IU/g cellulose and xylanase 30 IU/g cellulose, the highest yields of glucan, xylan and total sugars were obtained at 74.7%,85.2% and 73.9%, respectively.Fermentation of the enzymatic hydrolysate was conducted with the yeast P. stipitis at cell concentrations of 15g/L, 10g/L,7g/L and 5g/L, respectively. Fermentation was run at 30℃, pH 5 and at a rotate speed of 150 r/min. The time to achieve the highest ethanol concentration reduced with the increasing of yeast concentrations. When cell concentration of P. stipitis was 15g/L, highest ethanol concentration,7.14 g/L, was obtained at 16 h, with a sugar utilization rate of 73.9% and an ethanol yield of 63.4%. The contents of fermentation inhibitors were formic acid 0.28 g/L, acetic acid 0.30g/L, furfural 1.06g/L, xylitol 0.47 g/L and glycerol 0.03g/L.