ABSTRACT
Chlorine has a long and successful history as a water disinfectant and its use is often cited as one of the greatest public health stories of all time. Regardless of the chlorine source, free chlorine is used as a primary disinfectant and combined chlorines (chloramines) are used as a secondary disinfectant. Small system equipment costs are lowest for the hypochlorites while chemical cost, service and manpower are lowest for chlorine gas. Chlorine participates in three reactions in the water treatment process - oxidation, substitution and the action of disinfection. There are three forms of chlorine utilized by the drinking water industry for the disinfection of water. Reactions of chlorine with some organics will produce disinfection byproducts, including the trihalomethanes. Oxidation of soluble iron, manganese and sulfides in water is a common use of chlorine in water treatment. Chlorine has long been recognized as a very effective disinfection agent.
