Xylanase production and its impact on bleaching of hardwood kraft pulp

Traditionally, wood pulp used for paper making process is bleached using chlorine or its derivatives such as calcium hypochlorite and sodium hypochlorite to remove residual lignin present in the pulp. The main cause for brown colour of the pulp is the presence of residual lignin. Chlorinated organic compounds produced during conventional pulp bleaching are detrimental to environment and highly resistant to microbial degradation. Chlorinated organic compounds are mainly responsible for the discharge of AOX (adsorbable organic halogens) in the receiving waters. Modern techniques such as prolonged kraft cooking, bleaching with hydrogen peroxide, oxygen, enzyme (xylanase) and ozone have been introduced recently to reduce the production of chlorinated organics during bleaching. Among the new techniques, enzyme bleaching is becoming important in the recent past due to its environmentally friendly nature.