Patent ID: 8632657

Claim:
A method of treating and utilizing liquid flows at a chemical pulp mill comprising: producing brown stock pulp in an alkaline cooking process; bleaching the brown stock pulp in a pulp bleaching plant using elemental chlorine free (ECF) bleaching, wherein chloride-containing bleaching effluents are formed by the bleaching; in a first effluent treatment line, purifying the bleaching effluents with a biological treatment to remove lignin from the effluents, and returning at least a portion of the purified bleach effluents for use as water at a first location in the chemical pulp mill; in a second effluent treatment line, purifying other effluents produced in bleaching of the pulp, wherein the concentration of chlorides in the other effluents is lower than the concentration of chlorides in the bleaching effluents; whereby a second effluent treatment line returns the purified other effluents to a second location in the pulp mill separated from the first location.