Relationships between specific ultraviolet absorbance and trihalomethane precursors of different carbon sources

A rapid and effective detection method is essential for water utilities to monitor variability of dissolved organic carbon (DOC) in source waters in order to apply strategies to minimize formation of disinfection by-products in treated waters. Ultraviolet absorbance at 254 nm (UVA₂₅₄) and specific UVA₂₅₄ (SUVA₂₅₄) have been widely used as surrogates of concentration and reactivity of DOC, respectively. However, poor correlations between SUVA₂₅₄ and specific trihalomethane formation potential (STHMFP) have been occasionally reported and the reliability of using SUVA₂₅₄ to predict trihalomethane (THM) formation has been questioned. In this study, the correlations of SUVA₂₅₄ and THM reactivity of three different DOC sources commonly found in water treatment facilities (aquatic carbon, soil carbon, and fecal matter) were evaluated. A 0.22 μm filter, instead of 0.45 μm filter, was used for water filtration to minimize the effects of colloidal materials on UVA₂₅₄. UVA₂₅₄ and DOC after chlorination were also examined and differential UVA₂₅₄ and SUVA₂₅₄ (ΔSUVA₂₅₄) were compared to THM reactivity. Results showed correlations between UVA₂₅₄ and DOC were source dependent suggesting natural humification and degradation processes did not alter DOC characteristics from its original sources. The STHMFP of river and soil DOC samples were comparable, whereas their UVA₂₅₄ normalized THMFP were different (p<0.05), suggesting that UVA₂₅₄ is a better indicator in predicting THM formation potential than DOC concentrations. ΔSUVA₂₅₄ showed a stronger correlation with STHMFP than the conventional surrogate—SUVA₂₅₄.