The present invention relates to a method for treating pulp at a chemical pulping plant comprising at least a pulp bleaching plant using elementary chlorine free bleaching and having at least one chlorine dioxide stage, and wherein chloride-containing effluents are formed, a chemical recovery plant comprising a black liquor evaporation plant and a chemical recovery boiler plant, and effluent purification. An object of the present invention is to offer a method for utilizing liquid flows generated at a chemical pulp mill in an advantageous objet and for efficiently circulating them and minimizing the emissions from the mill. A characteristic feature of the method is that chloride-containing bleaching plant effluents are led to effluent purification, where they are treated in order to decrease the organic matter content thereof, that purified effluent is led back to a chemical pulp mill process, so that at least 20 % of the liquid used for brown stock washing is purified effluent and that condensates originating from the evaporation plant are used in the amount of at least 1 m 3 /adt pulp as washing or dilution water of the bleaching for reducing the total amount of effluent, and that a separation process for chlorides is arranged at the chemical recovery boiler plant for decreasing the chloride level of the chemical cycle.