Suitability of Organic Matter Surrogates to Predict Trihalomethane Formation in Drinking Water Sources

Broadly applicable disinfection by-product (DBP) precursor surrogate parameters could be leveraged at drinking water treatment plants (DWTPs) to curb formation of regulated DBPs, such as trihalomethanes (THMs). In this study, dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV₂₅₄), fluorescence excitation/emission wavelength pairs (I_Ex/Em), and the maximum fluorescence intensities (F_MAX) of components from parallel factor (PARAFAC) analysis were evaluated as total THM formation potential (TTHMFP) precursor surrogate parameters. A diverse set of source waters from eleven DWTPs located within watersheds underlain by six different soil orders were coagulated with alum at pH 6, 7, and 8, resulting in 44 sample waters. DOC, UV₂₅₄, I_Ex/Em, and F_MAX values were measured to characterize dissolved organic matter in raw and treated waters and THMs were quantified following formation potential tests with free chlorine. For the 44 sample waters, the linear TTHMFP correlation with UV₂₅₄ was stronger (r²=0.89) than I_240/562 (r²=0.81, the strongest surrogate parameter from excitation/emission matrix pair picking), F_MAX from a humic/fulvic acid-like PARAFAC component (r²=0.78), and DOC (r²=0.75). Results indicate that UV₂₅₄ was the most accurate TTHMFP precursor surrogate parameter assessed for a diverse group of raw and alum-coagulated waters.