The Penicillium Zcf57 Xylanase In The Biobleaching Of Wheat Straw Chemical Pulp In Applied Research, And

With the development of economy and improvement of people' s life, the requirement of paper has been increasing rapidly, stimulating the development of pulp and paper-making industry, but bringing severe pollution to our environment. To seek for a pollution-free and economical bleaching method has aroused worldwide interest of many scientists in order to protect our environment. The biobleaching method emerged as the times required. Many researches have indicated that pretreating pulp with xylanase before bleaching could decrease the dosage of bleaching reagents, improve the brightness and some intensity capabilities of the pulp, and decrease the effluent pollution load of paper-making industry.A strain, Penicillium sp.ZCF57, excreting high-level xylanases has been isolated by our laboratory. And some basic enzymatic properties of these xylanases have been evaluated. In this paper, the enzymatic properties, the bleaching efficiency and the influence on the effluent pollution load of these xylanases were further investigated. Firstly, the crude enzyme was purified by ammonium sulfate fractionation, ultrafiltration, Sephadex G-100 and DEAE-Sephadex A-50 chromatographies, and two pure enzymes, X I and XII were obtained. The kinetic parameters of crude enzyme, X I and XII were evaluaed. The Km and Vmax of crude enzyme, X I and X II were 0.056, 0.175, 0.128mg/mL; 1111.11, 2500.00, 256.41 μ mol/min.mL, respectively. Biobleaching effectiveness of the crude enzyme, the pure enzymes X I and XII were researched by pretreating wheat straw chemical pulp and poplar chemical pulp. Some technical parameters, such as the pretreating time and the enzyme charge were optimized. The reducing sugars, the lignin-derived compounds and chromophoric materials released in filtrates after the crude enzyme and two pure enzymes pretreating wheat straw and the brightness of the pulp after hydrogen peroxide bleaching chemical pulp and poplar chemical pulp were monitored with different treating time and enzyme charges. According to the results, the optimum enzyme charge was 10IU/g oven-dried pulp and the optimum treating time of xylanases was 60min. And we also found that the brightness of the bleached pulp after xylanase pretreatment and hydrogen peroxide bleaching showed a similar trend with the reducing sugars, the lignin-derived compounds and chromophoric materials released in filtrates after xylanases pretreatment with different enzyme charge and pretreating time. Monitoring the amount of reducing sugars and change of lignin-derived compounds and chromophoric materials in filtrate after enzyme pretreatment, is a handy and quick method for optimization of enzyme treating conditions when there are not enough enzymes (e.g only pure enzyme) for some traditional methods, such as monitoring the brightness of the pulp, for verifying the biobleaching efficiency of xylanases. In addition, when pulps were pretreated with the same amount of xylanases, the pulp pretreated with crude enzyme released more reducing sugars that the sum of that pretreated with two pure enzymes. And when wheat straw pulp were pretreated with different proportion of X I and XII, it released more reducing sugars that that pretreated with X I or XII separately, indicating there must be some cooperative mechanism between X I and XII. The pulp pretreated with XII released more reducing sugars, the lignin-derived compounds and chromophoric materials than that pretreated with the same amount of X I. The xylanase produced by Penicillium sp.ZCF57 is more effective on wheat straw chemical pulp than on polar chemical pulp according to the comparison of the amount of reducing sugars, the lignin-derived compounds and chromophoric materials released by these xylanases-pretreated pulps.After xylanase treatment, the fiber surface of wheat straw pulp was very rough observed by scanning electron microscope (SEM). The fiber surface was peeled and many cracks, holes and fossae were found on the fiber surface. The emergence of cracks, holes and fossae could improve the penetration ability of bleaching reagents. It could make bleaching reagents move into the inside of fiber more rapidly and improve the bleaching effect of bleaching reagents.There are many kinds of poisonous materials in traditional bleaching sequence with chlorine, bringing severe pollution to our environment and ecology. Effect of xylanase produced by Penicillium sp. ZCF57 pretreatment on the effluent pollution load after each bleaching stage was investigated. The wheat straw chemical pulp was pretreated by xylanase, following hydrogen peroxide bleaching and conventional CEH bleaching. According to our results, xylanases pretreatment could improve the brightness of bleached pulp and decrease the effluent pollution load and the toxicity of the effluent. The brightness of pulp pretreated by xyalnase was significantly higher than the control with the same amount of hydrogen peroxide. Compared to the control, the amount of hydrogen peroxide after xylanase pretreatment was reduced from 5% to 3%, with a similar brightness. And after xylanase pretreatment, the total BOD and COD of hydrogen peroxide bleaching effluent decreased by 13.2% and 17%, respectively, and the total COD and AOX of CEH bleaching effluent decreased by 50% plus and 20% plus, respectively.