Chlorine decay modelling in water treatment

Chlorine reacts with both organic and inorganic substances in water as well as functioning as an antimicrobial agent. Generally, in natural waters, the species that are most reactive with chlorine are inorganic (e.g. iron, manganese, sulphide, bromide and ammonia). These reactions are relatively quick, often occurring within seconds. Chlorine will also react with organic substances in the water, although these reactions usually proceed at a slower rate, dependent on the nature of the species present. As both organic and inorganic particles are present in varying concentrations and have different degrees of reactivity, the loss of chlorine over time is a gradual process and the half-life of chlorine in treated water can vary from several hours to several days.
Understanding the reaction rates between chlorine and water is important so that the residual chlorine concentration in water, and thus its likely efficacy as a disinfectant, can be assessed at any particular point in time. Thus, many researchers have attempted to assess the manner in which chlorine decays in water with time. However, most workers often fall back on a simple first order decay expression.
This project will take the results of various chlorine decay rate experiments, conducted on different types of water over 10 years and reassess the most appropriate means of modeling chlorine decay. Whilst the model assessment will be based on analysis of existing decay, all new model approaches developed as part of this project will be tested via new chlorine decay tests undertaken in the lab, delivering a revised methodology for modelling chlorine decay in water.