Modelling THMs in water treatment and distribution systems

The formation of potentially harmful trihalomethanes (THM) when using chlorine as a disinfectant in potable water supplies has led to tighter regulatory controls and hence a need for better models for THM management. The prediction of THM concentration is difficult due to the complex and changing hydrodynamic and chemical regimes found in water treatment works and distribution systems. A simple and cost-effective model is described to model chlorine decay and total THM concentration through water treatment works and within distribution systems. With knowledge of the bulk chlorine decay characteristics and the THM productivity of the water, this model offers a simple and straightforward tool which can be readily applied to water treatment works and distribution systems alike to provide an initial assessment of the risks of total THM formation at different sites, and to identify sites and systems at risk of compliance failure.