It is well known that a portion of the AOX generated during the bleaching of chemical pulps will degrade to inorganic chloride when alkali and heat are added to the waste stream. As reported by others, this hydrolysis can potentially occur in the mill sewer system as well as within the wastewater treatment process. The present study was undertaken to examine the role which alkaline hydrolysis can be expected to play in the removal of AOX during biological treatment.
The results of these experiments indicate that, for the filtrates tested, (a) biodegradation can account for 75 percent of the total AOX removal across secondary treatment, where pretreatment of bleach plant filtrates is not provided, and (b) approximately forty percent of the AOX destroyed under harsh thermo-alkaline conditions is biodegradable AOX and approximately one-quarter of the AOX destroyed would be removed by alkaline hydrolysis in the secondary treatment process itself. This suggests that biological and thermoalkaline treatment processes target many of the same AOX components.