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Updated: Jul 10, 2026

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
Published on: October 7, 2020
Enhanced nitrogenous disinfection byproduct formation near the breakpoint: implications for nitrification control
I Marie Schreiber1, William A Mitch
1Department of Chemical Engineering, Yale University, Mason Lab 313b, 9 Hillhouse Avenue, New Haven, Connecticut 06520, USA.
Abstract:
Increasing the chlorine to ammonia molar ratio and breakpoint chlorination are two control strategies practiced by drinking water treatment utilities experiencing nitrification during chloramination. The first strategy will increase dichloramine formation, which increases nitrosamine formation. Moreover, our results indicate that dichloramine is also an important factor for nitrile formation. Near the breakpoint, nitrosamine formation is over an order of magnitude higher than that observed during chloramination. We propose that there are two nitrosamine formation pathways active in the breakpoint chlorination region: (i) a relatively slow reaction of dichloramine with amine precursors in the presence of dissolved oxygen and (ii) a fast reaction involving reactive breakpoint chlorination intermediates. Lastly, in the presence of nitrite, if breakpoint chlorination is conducted to achieve a significant free chlorine residual, nitrosamines and nitramines will form through a reaction with nitrite and hypochlorite. However, nitrosamine formation will be much lower than when breakpoint chlorination is conducted with no significant free chlorine residual.
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