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Water Science & Technology: Water Supply Vol 1 No 4 pp 103–110 © IWA Publishing 2001

Using a comprehensive model to identify the major mechanisms of chloramine decay in distribution systems

J. Woolschlager*, B. Rittmann**, P. Piriou***, L. Kiene**** and B. Schwartz*****

*Department of Civil Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA
**Department of Civil Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA
***Distribution System Department, Suez-Lyonnaise des Eaux/CIRSEE, 38 rue du President Wilson, Le Pecq 78230, France
****Distribution System Department, Suez-Lyonnaise des Eaux/CIRSEE, 38 rue du President Wilson, Le Pecq 78230, France
*****Director of Water Quality, United Water, 200 Old Hook Road, Harrington Park, New Jersey 07640, USA


ABSTRACT
The principle mechanisms of chloramine residual decay in drinking water distribution systems is examined using a comprehensive model of chloramine reactions calibrated to distribution system data. The results reveal that four principle chloramine decay mechanisms must be considered, including: reactions with hypochlorous acid/ion (HOCl/OCl-); an auto- catalytic reaction in which chloramines spontaneously decay in the absence of other reactants; oxidation reactions with reduced forms of organics and iron; and biologically-catalyzed reactions, such as the reactions with nitrite produced by nitrifiers as well as the direct cometabolism of chloramines by nitrifiers. The chloramine reaction model fits the distribution system data best when all of these reactions, including cometabolism of chloramines by nitrifiers, are included in the model.

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