Simulation of THM species in water distribution systems

The Safe Drinking Water Act and its Amendments (SDWAA) may potentially limit each individual species of THM compounds in water distribution systems since the health risks associated with these species are not alike. A new approach to characterize and model the kinetics of THM species using nonlinear optimization was introduced in an earlier study. The approach combines site-specific water quality trends with stoichiometric expressions based on an average representative bromine content factor of the source. This paper incorporates the proposed kinetic approach in a full-dynamic water quality transport model. The model is capable of modeling chlorine, total THM, and the four THM species in water distribution systems subjected to different varying loading conditions. The model has been tested and verified by application to a portion of the Abu-Dhabi distribution system in the United Arab Emirates. High levels of bromoform and bromine incorporation factors were reported throughout the system. The quality trends of the bromide-rich desalinated water at the source were transmitted to different locations in the network using the proposed modeling approach. Overall agreement between the modeled and measured concentrations was reported. However, deviations at distant locations from the source indicate the degradation in the bromine incorporation factor under dynamic conditions and an increased tendency of the brominated THM compounds to hydrolyze. The model represents a useful and robust numerical tool to water utilities attempting to verify the SDWAA potential regulations regarding the THM species.