Evaluation of chlorine decay kinetics expressions for drinking water distribution systems modelling

The decay of chlorine in drinking water involves a complex set of reactions that is usually simplified to first order kinetics in models of water qual ity in distribution systems. However, to be useful in optimising chlorine d osing regimes, the kinetics expression should accurately describe the shape of the chlorine decay curve for different chlorine doses and be able to si mulate re-chlorination. After considering the nature of the reactions invol ved in chlorine decay, five simplified reaction schemes were evaluated for their suitability to describe chlorine concentration in bulk water. Each sc heme was fitted to a sample of experimental data of chlorine decay in raw w ater obtained from Warragamba Dam (the major source of water supplied to Sy dney, Australia). A scheme involving two parallel reactions of organic carb on compounds with chlorine is both necessary and sufficient to satisfy the requirements of modelling chlorine decay accurately.