Potable Water Chloramination Process Description

Chloramination process can be applied to both water treatment and wastewater treatment (1,29). In the field of potable water treatment, chloramine is recommended as a secondary disinfectant because it is ineffective as a virucide, and is only marginally effective against Giardia cysts. It is formed from the combination of ammonia and chlorine (hypochlorite or hypochlorous acid). The chemical is generated on site, usually by injecting ammonia gas or adding an ammonium sulfate solution to chlorinated water. 

This section describes the chloramination process, chloramine residual establishment, system design considerations, and chloramination systems case histories. 

When water, chlorine, and ammonia are combined, three different species of chloramine compounds can be generated  

The mix of species produced depends on the ratio of chlorine to ammonia and the pH of the water. In the pH range of 7-8 with a chlorine-to-ammonia ratio (by weight) of 3 to 1, monochloramine is the principal product. At higher chlorine-to-ammonia ratios or at lower pH values (5-7), some dichloramine will be formed. If the pH drops below 5, some nitrogen trichloride (often erroneously called trichloramine ) may be formed. Nitrogen trichloride formation should be avoided because it imparts undesirable taste and odor to the water. To compare the disinfection efficiencies of secondary chlorination with secondary chloramination, a design engineer should also consider the effect of each process on corrosion control (see Appendix A). 

Care should be taken not to exceed chlorine-to-ammonia ratios of 5 to 1. This is the breakpoint curve above which aU ammonia is removed, chloramines are absent, and free residual chlorine is present. 

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