Absorbable Organic Halides (AOX). What is it?
Absorbable organic halides (
AOX) consist of a varied collection of organic compounds to which one or more chlorine atoms have become attached. AOX compounds are formed only when chlorinated compounds are used in the bleaching process to brighten a chemical pulp.
How are they measured?
Environmental regulations require a weekly
effluent sample be taken and analyzed to determine the quantity of AOX compounds in the effluent. A standard test is used to measure the concentration of AOX compounds in pulp mill effluent. In this method an effluent sample is passed through an activated carbon filter. The carbon and the material trapped in it are burned, and the combustion gases are collected in order to determine the chloride content. The concentration of the AOX compounds in the effluent can then be calculated.
Why do they matter?
AOX compounds pose a potential concern because they resist breaking down in the environment. Some of these molecules are
toxic at high concentrations. Because they can accumulate in the food chain, they pose a potential threat to aquatic organisms living in
estuaries near bleached pulp effluents.
How do we control them?
Resolute Forest Products has changed their bleaching processes in order to reduce the generation of AOX compounds. Significant reductions in AOX levels can be achieved by bleaching pulp using alternatives to
chlorine—such as
chlorine dioxide,
ozone, oxygen and peroxide. Resolute Thunder Bay is currently an elemental chlorine free site. In addition to a change in the bleaching process, AOX levels are reduced during secondary effluent treatment. Using these methods, discharges of AOX compounds to the environment have been reduced to levels that cause no adverse effects.