Reduction of organically bound chlorine formed in chlorine dioxide bleaching

摘要

A reduction in AOX levels is obtained when the process conditions in the chlorine dioxide stage are elevated to above 91° C. and extended to more than 90 minutes. A major reduction of AOX up to 50% has been shown without a corresponding increase in OCl. The chlorinated substances is degraded by the process conditions to harmless chloride ions, instead of being liberated into the effluent as AOX or bound to pulp as OCl. No oxygen gas or nitrogen gas are added during the first or any subsequent chlorine dioxide bleaching stage.