Kinetics of Chlorine Decay in Water Distribution Systems

A combined first and second-order model, which includes bulk decay and wall decay, was developed to describe chlorine decay in water distribution systems. In the model the bulk decay has complex relationships with total organic carbon (TOC), the initial chlorine concentration and the temperature. Except for the initial stages they can be simplified into a linear increase with TOC, a linear decrease with initial chlorine concentration and an exponential relationship with the temperature. The model also explains why chlorine decays rapidly in the initial stages. The parameters of model are determined by deriving the best fitness with experimental data. And the accuracy of model has been verified by using the experimental data and the monitoring data in a distribution system.

Modeling and verifying chlorine decay and chloroacetic acid formation in drinking water chlorination

This study presents a phenomenological model that can be used by the water professionals to quantify chlorine decay and disinfection byproduct(DBP)formation in water.The kinetic model was developed by introducing the concept of limiting chlorine demand and extending an established reactive species approach.The limiting chlorine demand,which quantifies chlorine reactive natural organic matter(NOM)on an equivalent basis,was mathematically defined by the relation between ultimate chlorine residue and initial chlorine dose.It was found experimentally that NOM in water has limiting chlorine demand that increases with chlorine dose once the ultimate residue is established.These results indicated that the complex NOM has a unique ability to adjust chemically to the change in redox condition caused by the free chlorine.It is attributed mainly to the redundant functional groups that persist in heterogeneous NOM molecules.The results also demonstrated that the effect of chlorine dose on the rate of chlorine decay can be quantitatively interpreted with the limiting chlorine demand.The kinetic model developed was validated for chlorine decay and chloroacetic acid formation in finished drinking water.

Evaluating the effects of granular and membrane filtrations on chlorine demand in drinking water

In this study, chlorine decay experiments were conducted for the raw water from Nakdong River that is treated by Chllseo Water Treatment Plant （CWTP） situated in Haman, Korea as well as the effluents from sand and granular activated carbon （GAC） filters of CWTP and fitted using a chlorine decay model. The model estimated the fast and slow reacting nitrogenous as well as organic/inorganic compounds that were present in the water. It was found that the chlorine demand due to fast and slow reacting （FRA and SRA） organic/inorganic substances was not reduced significantly by sand as well as GAC filters. However, the treated effluents from those filters contained FRA and SRA that are less reactive and had small reaction rate constants. For the effluents from microfiltration, ultrafiltration, and nanofiltration the chlorine demand because FRA and SRA were further reduced but the reaction rate constants were larger compared to those of sand and GAC filter effluents. This has implications in the formation of disinfection by products （DBPs）. If DBPs are assumed to form due to the interactions between chlorine and SRA, then it is possible that the DBP formation potential in the effluents from membrane filtrations could be higher than that in the effluents from granular media filters.