Biological bleaching of hardwood kraft pulp using Trametes (Coriolus) versicolor immobilized in polyurethane foam

Summary Incubation of hardwood kraft pulp (HWKP) in agitated aerated cultures of the white-rot fungus Trametes versicolor increases pulp brightness and decreases its residual lignin content. A consequence of this biobleaching with whole cultures is that the resulting pulp also contains fungal biomass (up to ca. 10% (w/w)). In this report culture conditions for the immobilization of T. versicolor on polyurethane foam and bleaching of HWKP with the immobilized fungus are described. The major advantage of using immobilized fungus to bleach HWKP is that the fungal biomass can be separated from the pulp after treatment, resulting in a biologically bleached pulp free of fungal mycelium. From an analysis of pulp samples bleached with free and foam-immobilized mycelium, we conclude that fungal biomass in pulp treated with free mycelium accounts for up to 25% of the reduction in pulp viscosity (indication of cellulose chain length) whereas the zero span breaking length (indication of fibre strength) is not significantly affected by the presence of the fungus. Immobilization of the fungus on polyurethane foam also allows the repeated use of the same fungal biomass to bleach successive batches of pulp, either immediately or after storage at 4°C. Offprint requests to: I. D. ReidIssued as NRCC no. 30975