Biosynthesis And Application Of Xylanase For Pretreatment Of Wheat Straw Pulp

Conventional pulping and bleaching are chloridized processes, the effluents with high load of toxic and mutagenic substance are produced during these courses and make serious pollution environmentally.Many nations in the world set down rules to control organic and chloridized drainage strictly.With the development of biotechnology in recent ten years, the use of enzymes in biobleaching industry has grown rapidly. The processes use microbe and microbial enzymes to replace some and even all chlorine in pulp and paper, and many breakthrough have been made. While many applications of enzymes in the pulp and paper industry are still in the research and development stage, several applications have found their way into the mills in an unprecedented short period of time. This thesis studied the biosynthesis of xylanase by Trichoderma reesei Rut C-30 with Xylo-oligosaccharides carbon source,the basic characteristics of xylanase and CMCase, the conditions of pretreating wheat straw pulps with xylanase and the applicacation of xylanase in wheat straw are also optimized. The main results are as follows : Using the Xylo-oligosaccharides as carbon source, C/N ratio was 5, xylanase with poor-cellulase increased, the xylanase activity was 150IU/ml at the third day, the relative activity increased to 1052.17. The speed of biosynthesis of xylanase was faster than CMCase during the production of xylanase with xylan as substrate, and the higher X/C ratio xylanase was obtained with longer fermentation. The optimal temperature for xylanase CMCase and were 50 ℃and 55℃,CMCase was stable in first three hours. Repectively, the optimal pH for xylanase and CMCase were both 5.6, xylanase was stable in a pH range from 4.0 to 6.0, while CMCase was stable in a pH range from 4.0 to 5.6. When xylanase was used in biobleaching of pulp, higher brightness values of pulp and reduced chlorine consumption could be resulted. The optimum coditins for xylanase pretreatment in the bleaching of wheat straw pulp were 45 ℃, pH 6.0, 1.5 hours,pulp concentration 5%, and xylanase loading 5IU/g. Compared with control test,the blightness of bleached pulp increased by 2.4～3.9 percentages when pretreated with xylanase,the intensity of bleached pulp also a little increased. It was found that xylanase contained a small amount of cellulase contributed to the improvement of pulp brightness and intensity. When the xylanase and CMCase activity ratio between 403.87 and 1052.17,and that means the structure of coarse enzymes produced from 2.5 to 3 day can meet the demand of pretreated wheat straw pulp. Decrease the temperature and increase the xylanase loading both can′t improve the pH of pretreating wheat straw pulp with xylanase. Compared with test without xylanase ,however the xylanase treating before or after wheat straw pulp bleaching, which all identified xylanase treaing contribute to the improvmnt of blightness and intensity.