Delignification and bleaching of kraft pulp using oxidative enzymes

Prebleaching of kraft pulp with xylanase enzyme is now in use at several mills. The chemical savings achieved in subsequent bleaching stages is limited to a ceiling of around 20%. Fungal delignification prior to chemical bleaching can produce larger savings, but the process is slow. Two oxidative enzymes, laccase and manganese peroxidase, are produced during pulp bleaching by the fungus Trametes versicolor. Laccase, in the presence of oxygen and a mediator, and manganese peroxidase, with hydrogen peroxide and manganese (II), delignify kraft pulp effectively within a relatively short time. A subsequent treatment with alkaline hydrogen peroxide resulted in pulps up to 10 points brighter than those obtained without enzyme.