A METHOD FOR TREATING ACID AND ALKALINE WASTE STREAMS FROM A BLEACH PLANT SEPARATELY

摘要

Acid and alkaline waste water from a bleach plant comprise different amounts of inorganic and organic materials and have varying salts contents. If the acid and the alkaline waste water are mixed, it becomes more difficult to separate the different substances from the process flow in a subsequent treatment and it also results in larger amounts of waste water, which is disadvantageous in methods where aiming at closing up the bleach plant. Also, problems arise due to the formation of incrustations on heat-transfer surfaces. This invention relates to an improved method for treating the process waste water from a bleach plant, where the acid and the alkaline process flow being separately concentrated in evaporators, whereupon the salt content of the acid process flow is reduced by electrodialysis and the alkaline process flow is combusted. This method enables the recirculated amount of water to be reduced and the problems regarding the processing equipment to be avoided, and also contributes to a higher degree of closing, even if the bleaching involves clorine dioxide (ECF).