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The ATI Model A15/79 Total Chlorine Monitor uses the standard iodometric method for the determination of total chlorine in highly contaminated samples.  A unique sensing technique is used to determine total chlorine concentration, while minimizing system maintenance requirements.  The system takes the reacted sample containing iodine and uses a membraned gas sensor rather than exposed electrodes. The gas permeable membrane allows only iodine to permeate into the sensor. Sample contaminants are eliminated from coming in contact with measuring electrodes, providing better stability and reducing sensor maintenance.  This method is ideal for very low range measurement of dechlorinated wastewater, where biological growth from sulfur reducing bacteria can cause severe fouling problems in contact systems.

This system brings a sample of water to the chemistry module where pH 4 buffer and potassium iodide solutions are added.  All of the various chlorine compounds in the sample water react with the iodide to form an equivalent amount of molecular iodine.  The reacted sample then enters an air-stripping chamber where the released iodine is stripped from the sample, with the resulting air stream directed to the iodine gas sensor located in a separate chamber.  A membrane across the face of the sensor allows iodine to diffuse to the active electrode surface.  Iodine is reduced to iodide, generating a current proportional to total chlorine concentration.

Chlorination of potable water, wastewater effluent, and cooling water is widely used throughout the world to control biological activity in the water. Disinfection of potable water with chlorine ensures that tap water is safe to drink once it has passed through the distribution system. Wastewater disinfection helps to ensure that receiving streams are safe for recreational use, and cooling water chlorination reduces biofouling that can degrade heat transfer efficiency. In addition to these common uses, there are many other applications where chlorine addition helps to reduce biological contamination.