Estimation of water utility compliance with trihalomethane regulations using a modelling approach

Over the last few years, the presence of chlorination by-products (CBP) in drinking water has become an issue of particular concern for utility managers. As regulations about CBP (in particular trihalomethanes – THM), are becoming more strict, water utilities will have to adjust their operation strategies to comply with new standards while maintaining a residual chlorine which ensures an acceptable microbiological quality. Complying with stricter THM standards is particularly difficult for utilities which use surface raw water and practice chlorination as the unique treatment process. In this paper, the authors explore the usefulness of predictive models as decision-making tools for drinking water managers in dealing with the THM issue. In the first part of the paper, the process of developing models of THM formation in chlorinated surface waters using two different sources of data (from bench-scale and from field-scale studies) is described. The second part of the paper focuses on the application of such models to the analysis of the feasibility of updating THM regulations in the province of Quebec (Canada). Simulations allow the estimation of the percentage of utilities, currently using chlorination as the unique treatment, which would have to upgrade treatment to comply with a new THM standard.