When ammonia or organic amines are present (as they usually are in wastewater effluents), chlorination produces a class of compound called chloramines. They have the
Cl2 + H2O « HOCl prefix mono, di, or tri depending on their final form as follows:
Chloramines are often present with hypochlorites, and together they comprise combined available chlorine. Chloramines are sometimes beneficial because a combined-available-chlorine residual lasts longer than a free-chlorine residual. However, the killing power of the free chlorine is much greater.
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