Chlorine demand-based predictive modeling of THM formation in water distribution networks

The potential carcinogenicity of trihalomethanes (THMs) has led to increasingly stricter regulation of drinking water supplies. This has led to the need to manage better the chemical and microbiological risk balance in chlorinated supplies. The use of empirical equations to predict THM concentrations in water quality models is challenging and expensive due to the numerous temporally and spatially dependent uncertainties involved. In this paper, the benefits of a simple predictive method using a THM productivity parameter based on chlorine consumed by bulk free chlorine reactions are explored using extensive field data from a water distribution system in the Midlands region of the UK. It is concluded that the productivity parameter provides an appropriate, relatively robust, yet straightforward alternative to the use of an empirical equation based on regression analyses to predict THM concentrations in distribution, and that the method has the potential to help distribution system water quality model calibration.