Mechanisms of AOX removal during biological treatment

It is well known that a portion of the AOX generated during the bleaching o f chemical pulps will degrade to inorganic chloride when alkali and heat ar e added to the waste stream. As reported by others, this hydrolysis can pot entially occur in the mill sewer system as well as within the wastewater tr eatment process. The present study was undertaken to examine the role which alkaline hydrolysis can be expected to play in the removal of AOX during b iological treatment. The results of these experiments indicate that, for the filtrates tested, ( a) biodegradation can account for 75 percent of the total AOX removal acros s secondary treatment, where pretreatment of bleach plant filtrates is not provided, and (b) approximately forty percent of the AOX destroyed under ha rsh thermo-alkaline conditions is biodegradable AOX and approximately one-q uarter of the AOX destroyed would be removed by alkaline hydrolysis in the secondary treatment process itself This suggests that biological and thermo -alkaline treatment processes target many of the same AOX components. (C) 1 999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights res erved.