What is monochloramine and how is it used in water disinfection?

Document ID

Document ID TE183

Published Date

Published Date 06/14/2022
What is monochloramine and how is it used in water disinfection?
Using monochloramine for disinfection
Monochloramine is a disinfectant that is commonly used as an alternative to free chlorine for disinfecting drinking water. This is because monochloramine forms less disinfection by-products (DBP) than free chlorine.

The term "chloramines" as used in the water industry describes the three compounds that can be formed from the reaction of ammonia with chlorine: monochloramine, dichloramine and trichloramine.These compounds are formed in drinking water facilities practicing chloramination, unknowingly in chlorinated ground water systems containing natural ammonia, and in chlorinated wastewater effluents. It is important to note that chloramines refer to a group of compounds and not a single compound. A more technical description for this group would be inorganic chloramines to distinguish them from the organic chloramines. It is generally understood that the chloramines form sequentially; first monochloramine, then dichloramine and finally trichloramine if excess chlorine is continually added to the system.

The goal of chloramination is complete formation of monochloramine, and avoidance of formation of di- and trichloramines. 5:1 Cl 2:N ratio has been found to be an optimal feed ratio, avoiding dichloramine formation (avoiding taste and odor problems), minimizing un-reacted ammonia and controlling biofilm formation and nitrification.

Detailed information about chloramination can be found on the Hach web-site. The document titled, Chlorination, Chloramination And Chlorine Measurement_DOC180.53.20183, is extensive. There is an A Specific and Effective Method for Controlling Chloramination of Waters, by D.L. Harp. This Application Note provides an overview of chloramination, and describes an effective new test method._LIT1755 as well that has good information.

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