| Enzymatic treatment of softwood kraft pulp using immobilized xylanase was studied. More than 85% of free xylanase was immobilized using a covalent crosslinking method. The immobilized xylanase was tested on pure xylan. The hydrolysis rate was only 10--20% lower compared to soluble xylanase. The immobilized enzyme could be recovered and reused in up to eight subsequent xylan-hydrolysis batches.; When the immobilized xylanase was used on pulp, the xylan hydrolysis rate was 15% lower compared to soluble xylanase. More than 80% of the immobilized enzyme was recovered from the treated-pulp and was reused in up to three pulp-hydrolysis reactions. After a one step DE bleaching sequence on the enzyme-treated pulp, the brightness was improved up to 4%ISO compared to the untreated pulp. The results of this study confirm that the application of immobilized xylanase on pulp is technically feasible, and ultimately improves the pulp brightness and lowers the toxicity of the bleaching effluent. |
