Study On Pretreatment And Enzymatic Hydrolysis Of Bamboo Residues Powder

Bamboo can be used to produce fuel ethanol as a cheap and abundantly available lignocellulosic resource instead of limited grain feedstocks. Bioconversion of bamboo to fuel ethanol is very meaningful in the aspects of new energy development and environmental protection. The important issue to produce ethanol from lignocellulosic material lies in that lignocellulosic material must be pretreated and then hydrolyzed with cellulose. Therefore, the most essential thing is to clarify pretreatment fundamentals and explore the optimal pretreatment method. In this thesis, the production of reducing sugar for the research direction. Discussed the effect of the particle size, pretreatment time, temperature, pH on the cellulose, hemicellulose, lignin and residues weight of bamboo powder. Studied the conditions of enzymatic hydrolysis include enzymatic hydrolysis pH, substrate composition and concentrationBamboo powder was pretreated by mechanical grinding and chemical method, respectively, for enhancing the enzymatic susceptibility of substrate. The results show that, after mechanical grinding pretreatment, the cellulose, hemicellulose and lignin content was change. Although the combination of layer is not damage, but the reducing sugar yield of enzymatic hydrolysis is increased. When the particle size of bamboo powder is 106μm-180μm, the reducing sugar yield is 27.85mg/g, about 3 times of the particle size of >380μm. This shows that the pretreatment of mechanical grinding changes the bamboo fiber surface area, increasing the enzyme accessibility, thus contributing to increasing the reducing sugar yield. After 80℃, 100℃, 120℃, 180℃pretreatment, the content of cellulose was raised with pretreatment temperature increased. When the temperature rose from 20℃to 120℃, the cellulose content increased from 40.27% to 48.8%, but the hemicellulose and lignin content was dropped from 26.10%, 23.33% to 20.46% and 20.42%, respectively. The removal is not very clear. When the pretreatment temperature increased to 180℃, cellulose, hemicellulose and lignin content reached 59.36%, 10.88% and 16.92%, respectively. After the sample soaked by buffer, cellulose content decreased with the soaking solution pH increased, but the hemicellulose and lignin content in reverse relations. The buffer soaking is good for the removal of hemicellulose. After soaking with pH4.0 buffer, the lignin removal rate is get to 15.71%; Soaking with pH4.0 buffer, and then 120℃hot water pretreatment can remove 32.53% of hemicellulose.Observed the samples by the scanning electron microscope (SEM) pretreated with 120℃, 180℃, buffer soaking, buffer soaking and 120℃conditions. It can see the surface structure of bamboo becomes loose, the layers is stripped, pore size increased large; samples treated at 180℃, the surface pore size is almost completely broken, and the broken pieces can be found around the present rules of the arc-shaped, the original holes have been broken.The experimental results indicated that the optimum pH is 4.8, the optimum temperature is 50℃for reducing sugar yield. Study hydrolysis conditions of the cellulase in 0.1mL-1.0 mL, the results showed that with the increase of cellulase content, reducing sugar yield tended to increase initially, but because of its high reducing sugar content of cellulose, the reducing sugar yield is not further increase but decrease. In the experimental conditions, the highest reducing sugar yield was reached when the addition of 0.5mL cellulase enzyme. Investigate the effect of substrate concentration within the 0.2g/10mL-1.5g/10mL on the reducing sugar yield, the results showed that reducing sugar content was raised with the substrate concentration increases, but the rate of reducing sugar was reduced. When the substrate concentration was 1.0g/10mL, the speed of enzymatic hydrolysis was significantly reduced. So the optimum substrate concentration was 1.0g/10mL. Study the enzymatic hydrolysis time from 0h to 96h. The results show that in the initial, hydrolysis reaction can to a high speed, and the reducing sugar is raised with the reaction time increased. However, when the reaction time reached 48h and the enzyme reaction rate was gradually decreased, leveling off. Used fed-batch enzymatic hydrolysis, after 96h hydrolysis, the reducing sugar yield reached 69.38mg in the final substrate concentration 1.5g/10mL. It showed that the fed-batch hydrolysis was greatly improve the reducing sugar yield.