Free chlorine consumption in distribution systems is due both to chemical reactions occurring in the bulk phase and at the pipe walls. Knowledge of the relative importance of these various reactions is needed in order to improve chlorine decay modeling. Experimental results carried out in this study make it possible to propose a hierarchical classification of the main parameters involved in the free chlorine decay observed in distribution systems. Corrosion of metallic pipe appears to be a major parameter, while synthetic materials are of little influence. The rate of chlorine decay in bulk phase can be estimated according to the TOC and the temperature. Influence of biofilms depends on the BDOC content of water, and on the pipe diameter. Chlorine decay due to corrosion phenomena must be modeled according to a zero order kinetics, while chlorine decay due to other parameters can be modeled according to a first order kinetics with respect to chlorine.

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