Abstract: 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.

Abstract: The invention relates to an improvement in bleaching of kraft pulp. In ECF bleaching chlorine dioxide is most often a prefered bleaching chemical in certain process positions. The disadvantage is that residual amounts of organically bound chlorine in form of AOX, i.e organically bound chlorine in effluents, and/or OCl, i.e. chlorine organically bound in the produced pulp, is obtained. A normal approach has been to reduce charges of chlorine dioxide.

Abstract: A process for chlorine-free bleaching of chemical pulp in association with the production thereof, where a suspension of the pulp preferably has a concentration exceeding 8% of cellulose-containing fiber material and where the pulp entering into a bleaching line is preferably fed continuously through at least one bleaching vessel in the bleaching line, is treated with at least one acid for adjusting the pH to a value below 7, and with a chelating agent, and is subsequently bleached in at least one stage to a brightness exceeding 75% ISO, preferably exceeding 80%, with hydrogen peroxide or the corresponding quantity of another peroxide, employed in a quantity exceeding 5 kg/BDMT, where the peroxide bleaching takes place at elevated temperature and at a pressure in the bleaching vessel which exceeds 2 bar and where the cross-sectional area of the bleaching vessel exceeds 3 m.sup.2 and the area of the metal surface exposed towards the interior of the bleaching vessel is less than 4V m.sup.