Abstract

The invention relates to a method for updating plants for treating effluents from pulp and paper production processes, wherein salts are removed from the effluent in order to reuse the water and recover chemicals. The process comprises: a first dialysis system for removing salts; a second treatment system for recovery or re-concentration; and, optionally, post-treatment of the re-concentrate, thereby preventing liquid from being released into the environment. The first system carries out a step of reversible or pulsed reversible electrodialysis, separating the salts of the effluent, which are sent to the second treatment system to concentrate the salts (re-concentrating) or to convert them into chemicals useful for the same process (recovery). The chemicals are recovered by means of electrodialysis using bipolar membranes or using metathesis to reduce the re-concentrate stream, which cannot be reused in the same plant. Lastly, said stream can be treated with spray drying, crystallisation or evaporation.