Modelization of Trihalomethanes Formation in Drinking Water Distribution Systems in France

Abstract

In France, trihoalomethanes (THM) are regulated and regularly monitored at the water treatment plant and more recently in the drinking water system. THM concentrations at tap water depend on many factors like chlorine level, organic precursor’s concentrations, water temperature, residence time in the network, and presence of rechlorination stations. To predict concentrations in the water distribution system using data collected from treated water at the plant (i.e., the entrance of the distribution system), a first mathematical model was developed in 2009, from three sites supplied by surface water. Predicted concentrations produced with this model for five new sites didn’t match with observed concentrations. New efforts were then made in order to adapt this mathematical model to cover more types of water. Two formulations have been developed: a first model based on a minimum of variables and those easily available (from the French national SISE-Eaux database collecting all data from drinking water regulations) and a second model that includes more information about the reactivity of the organic matter with chlorine. The choice of variables and the general shape of the models were made by dividing the database into two random editions of the couples of data (75% of the data to build the models/25% to validate them). The validation of both models (simplified and complete model) was satisfactory, explaining respectively 87% and 88% of the variance, with a good capacity of generalization. The models developed herein can be used to assess THM concentrations at different points between the treated water at the plant and the consumer’s tap in a large range of French water systems supplied by surface waters.