V. Baratharaj
August 5, 2016

Halogenated organic compounds are the by-products, formed when chlorine is used as disinfectant in water and waste water.

What is it?

Adsorbable organically bound halogens (AOX) are a group of chemicals which can be adsorbed from water into activated carbon. Most AOXs are the compounds containing chlorine, but some also contain the similar elements of bromine or iodine. The properties of AOXs vary: some evaporate easily (such as trichloromethane or chloroform), some are complex molecules such as dioxins and furans. THMs are part of AOX. AOX once formed cannot be destroyed by any chemical means or process. They have to be removed from water or waste water.

Industry Water Guzzlers

Both the power plants as well as paper and pulp plant use more than 60 percent of the total water used in the country. Therefore they also discharge large quantities of water as waste water. Both the power plants as well as the paper and pulp plants use lots of chlorine in their water treatment/process etc.

Where Does it Come From?

The main sources of AOX are from the chlorine chemicals used for treating cooling water in power plants and chlorine used to bleach fibers in the paper and pulp industry. AOX are also formed during the routine chlorination (disinfection) of drinking water, swimming pools and industrial effluents.

How Might it Affect the Environment?

Some AOXs are toxic to fish and aquatic organisms - Even at low concentrations. Many are persistent and have a tendency to accumulate in the environment which causes concern at global level. AOX once formed remains, either in the ground, polluting water source or in humans when they are consumed with water.

How Might Exposure to it Affect Human Health?

Exposure of AOXs to humans can occur through eating contaminated food, drinking contaminated water and the fact that AOXs can concentrate up the food chain means that humans could be exposed to dangerous levels. The type and severity of adverse effects depend on the AOX in question. Some (such as dioxins) are known to be very toxic. Many AOX/THMs are cancerous to humans and known to be precursors to rectum and colon cancer.

In the UK (including Scotland) releases of AOX are controlled through the Pollution Prevention and Control (PPC) regulations. Chlorinated AOXs have been on the European Commission's "black list" of toxic substances since 1976. In India pollution control board provide levels of AOX that industries must control in their waste water discharge.

For example ,according the German classification system regarding AOX levels in river water, a concentration below 5 mgCl/l is slightly polluted, 5-20 mgCl/l is moderately polluted, 20-40 mgCl/l is strongly polluted, and over 40 mg Cl/l is very strongly polluted. This classification is relatively severe. It is Normal to choose the maximum AOX data in river water as the nonpolluting level.

In India paper and pulp plants have already taken conscious efforts to reduce AOX levels by replacing part of chlorine in their process with Ozone (ITC is the first plant). The main by-product of ozone chemistry is oxygen, it is an ideal choice to limit the formation of chlorinated by-products (AOX), formed during conventional bleaching processes. Similarly power plants have already taken conscious efforts to replace chlorine with ozone in cooling water treatment and in waste water treatment.

V. Baratharaj V. Baratharaj is Head, Ozone Technologies & Systems India Pvt Ltd. He can be reached at, and +91 44 4211 8266.

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