Contribution of a Storm Event to Disinfection Byproduct Formation: Natural Organic Matter Sources, Characteristics, and Mobilization

This study investigates the relationship between storm-driven changes in natural organic matter (NOM) and disinfection byproduct (DBP) formation. The novel framework presented correlates specific differential absorbance at 254 nm (Sp-ΔUV₂₅₄), which measures the change in UV₂₅₄ due to chlorination normalized by initial dissolved organic carbon (DOC) concentration, with critical water quality parameters such as chlorine demand, DBP formation, size-fractionated NOM, and lignin to enhance mechanistic understandings of DBP precursor dynamics. To evaluate the impact of a storm on the DBP precursor dynamics, samples were collected from the Neversink River (NY) during a high-flow event. The formation of total trihalomethanes (THMs), or specific trihalomethanes (Sp-THM) when normalized by initial DOC, strongly correlated to Sp-ΔUV₂₅₄. The pre- and postchlorinated samples' quotients of absorbances at 250 and 365 nm (<i>E</i>₂/<i>E</i>₃) yielded a strong correlation despite a decreased ΔUV₂₅₄ due to chlorination, suggesting dissolved organic matter transformation to less aromatic structures, in agreement with size exclusion chromatography (SEC) data. A novel SEC-DOC technique showed THM precursors increased during the rising limb of the storm with a predominant molecular weight range of 2000-10,000 Da. Stable water isotope (δ¹⁸O) measurements suggest quick mobilization of stored NOM accumulated in the watershed, which was also supported by quantified lignin concentrations.