Is AOX Removal by Biological Effluent Treatment Consistent with Environmental Protection Objectives?, 1992 Environmental Conference Proceedings

The requirements for AOX removal are discussed in relation to different effluent regulation philosophies. The concept of the "Assimilative Capacity" of the environment was formulated at the United Nations Conference on the Human Environment in Stockholm, 1972. Its use implies a clear distinction between processes resulting in "contamination" and processes resulting in "pollution". "Contamination" means increased (harmless) occurrence of substances in the environment, while "pollution" implies harm to ecosystems and living resources as well as reduction of amenities. Concepts such as "critical loads" or "critical levels" need to be developed. When the "Best Available Technology" (BAT) policy is uncritically combined with the "Principle of Precautionary Action", the result may be sub-optimizations of available resources for environmental protection, and occasionally even in counter-protective action. The determination, expressed in international conventions and by national regulators, to eliminate AOX from pulp mill effluents is based on such a questionable argument: "Some chlorinated organics are known to be hazardous. Therefore, all chlorinated organics are potentially hazardous and should be regulated". As an effluent control parameter AOX lacks the correlation between discharge and effects on ecosystems. A modern kraft pulp mill, where the chlorine multiple in the first C/D-stage in the bleach plant has been reduced to less than about 0.15, corresponding to an AOX formation of 1.5-2 kg/Adt, normally produces an effluent with relatively harmless chlorinated organics, which furthermore seem to be fairly similar to naturally formed chloroorganics. Therefore, a continued strong emphasis on further reductions of AOX below levels of, say 1.5 kg/ADt, seems to be a dissipation of resources without obtaining optimum environmental protection. The fraction of AOX which may be harmful to the environment, the polychlorinated organics, can be targeted by regulating the contents in effluents of polychlorinated phenolics (PoCPs). These compounds resist biological degradation and have a potential for being widely distributed in the environment.