Comparison between constant and variable chlorine decay models applied to urban water supply network

Abstract. Monitoring of chlorine residual in water distribution systems is necessary not only for ensuring potable water quality but also prevent emergence of disinfection by-products due to excess chlorination. Modelling work for chlorine residual was carried out for water supply distribution network of a town using both second order and first order reaction rate models. For the development of the model, the bulk reaction decay rate was determined in the laboratory using bottle testing while the wall decay rate was determined by calibration of the water quality model using field residual chlorine concentration measurements. The model results show that there is no significant difference in the residual chlorine between the two models or the cost saving that result in terms chlorine usage for the range of initial chlorine dosages anticipated. Constant rate chlorine model is more conservative and offers additional safety in terms of chlorine residual present. Significant differences only occur at excess chlorine residual concentration within the distribution system above the intended maximum residual to be attained. Further research that relates the chlorine dose with the water quality characteristics is necessary to make a more general evaluation.