Managing THM and Brominated Fractions in Treatment Adaptation to Source Water Changes under Hydroclimatic Impacts

Hydroclimatic impacts on surface water can significantly change the level and reactivity of natural organic matter (NOM), the precursor to disinfection byproducts (DBPs), including regulated trihalomethanes (THM), thereby affecting competitive reactions of chlorine with THM-forming NOM and other reactants. These effects at a given water plant may not be fully represented by widely used empirical statistical THM models. To address the shortfall, we propose a model-monitoring approach for plant-spefic operational and planning adaptations. The newly developed mechanistic THM model is used to account for the competitive reactions. It relates the THM formation potential (FP) and bromine incorporation factor (BIF) of treated waters to the kinetic constants of THM formation relative to those of overall chlorine decay, the chlorine dosage in chlorine disinfection, and the removal of NOM reactivity that can be indexed by surrogate parameters. We further examine the model-monitoring approach and its utilities at a full-scale drinking water plant in Cincinnati, USA, during two episodes of flash floods in the nearby Ohio River. The results show fine model representations of the competitive NOM–Cl-Br reactions and THM FP and BIF variations through treatment units, based on which general adaptation options to climate-related source water changes are discussed.