percent pulp contains considerably less liquid which is to be displaced whereby the invention has the great advantage that the displaced liquid quantity 19 will be considerably smaller since dirty water or back water from the chlorination stage is considered one of the major sources of pollution from such facilities and must be treated in various manners in the factories such treatment is considerably facilitated if the quantity of back water is considerably less as it is according to the present invention if the same reaction time is provided for the pulp after the addition of the chlorine as when bleaching conventionally it is possible with bleaching of 10 percent pulp to reduce the volume of the reaction container 15 correspondingly another advantage according to the present invention is that a bleach tower of smaller size may be used than at conventional chlorine bleaching facilities which means reduced buying installation and maintenance costs the necessary chemical quantity needed for the treatment of pulp is dependent upon the type of pulp and in order to illustrate the charges which can come into question the below figures can serve as an example the chlorine is given in kilograms per ton of pulp and the chlorine dioxide is expressed as active chlorine in kilograms per tone of pulp ______________________________________ clo sub 2 cl sub 2unbleached.