Effect of xylanases from Aspergillus niger NKUC3-0.2 mutant strain on prebleaching of wheat straw and mixed hardwood pulps

Abstract

Effects of Aspergillus niger NKUC3-0.2 pretreatment on total chlorine demand during conventional bleaching sequence of pulp and its impact on pulp brightness, viscosity, effluent characteristics and mechanical strength of wheat straw and mixed hardwood were studied. The xylanase production by A. niger NKUC3-0.2 was found optimum after the 3rd day of incubation under solid-state fermentation conditions using cotton hull as the solid matrix. Optimal temperature and pH were found to be 34°C and 7.0, respectively. An enzyme addition of 40 IU g-1 of pulp at 65°C, pH 7.0, reaction time 2 hours and consistency 10% was found optimum to reduce kappa number of pulp to the maximum extent. BOD5 days, COD, and AOX of effluents generated by XCEHH bleaching sequence of wheat straw are reduced by 7.3, 8.8 and 22.22%, respectively. On the other hand, brightness and viscosity of wheat straw pulps improved by 0.8% (ISO) and 7.69%, respectively. BOD 5 days, COD, and AOX of effluent generated by XCEHH bleaching sequence of mixed hardwood pulp were reduced by 50.3, 33.8 and 31.6%, respectively, while brightness and viscosity improved by 1.2 and 25%, respectively.