Secondary disinfection chloramines

Chloramines Mildly effective for bacteria. Long-lasting residual. Generally does not produce THMs. Some harmful by-products. Toxic effects for kidney dialysis patients. Only recommended as a secondary disinfectant. Ineffective against virases and cysts. 

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. 

Because ozone is employed only for primary disinfection, a chlorinated compound (chlorine or chloramine) must be added for secondary disinfection following ozonation, i.e., to provide a residual for the distribution system. Consequently, the secondary byproducts, those formed by the reaction of chlorine or chloramine with the primary byproducts of ozonation, become a concern to water treatment specialists. Although some studies have examined by-products produced by two-step oxidation sequences of this type, no compounds have yet been reported that are not produced by one of the two oxidation processes acting alone. 

At a typical water treatment plant, the dominant chloramine species will be monochloramines. Chloramine generating reactions are 99% complete within a few minutes. Chloramines are a weak disinfectant that are less effective against virases or protozoa than free chlorine but produce fewer disinfection by-products. The use of chloramines as a DBF control strategy is well estabhshed in the United States. Chloramines ate generated onsite at the treatment plant. Anhydrous ammonia and ammonia sulfate ate examples of armnonia containing chemicals used by water systems to form chloramines. In most situations in the Urrited States, chloramines are used as a secondary disinfectant to maintain a residual in the distribution system. 

Chlorine, when combined with ammonia, forms chloramines. This form of chlorine is a common secondary disinfectant used in... 

The primary use of anhydrous ammonia (ammonia gas) in water treatment is to combine with chlorine to form chloramines. Chloramines are used both as primary and secondary disinfectants. Use as a secondary disinfectant (residual in the distribution system) is more common. A typical treatment strategy is to use free chlorine to satisfy the USE PA regulatory CT requirements as a primary disinfectant. Ammonia is then added to combine with the free chlorine residual to form chloramines for use as the secondary distribution system disinfectant. The ammonia added is carefully controlled to ensure that all the free chlorine is combined and little free ammonia remains. This control is necessary because the presence of free chlorine can form regulated by-products. Free ammonia can increase the growth of nitrifying bacteria, thus causing residual demand that could lead to conditions that could violate the Total Coliform Rule. 

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). 

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