Assessing UV- and fluorescence-based metrics as disinfection byproduct precursor surrogate parameters in a water body influenced by a heavy rainfall event

Although disinfection byproducts (DBPs) were discovered decades ago and surrogate parameters have been developed to track their precursors, the accuracy of these metrics in waters impacted by heavy rainfall events is largely unknown. We measured DBPs and their precursor surrogate parameters in a water body impacted by 28 cm of rain between 4/24/11 and 4/26/11. Raw waters collected from four locations within the water body from April to August 2011 were treated by coagulation and anion exchange. Ultraviolet absorbance at 254 nm (UV₂₅₄) and fluorescence excitation-emission pairs (I_Ex/Em) were measured. Excitation-emission matrices (EEMs) were processed with parallel factor (PARAFAC) analysis, which resulted in six component fluorophore groups (C1-C6), each with a maximum intensity (F_MAX). DBP formation potential (DBPFP) with free chlorine was used to assess the precursor concentrations. Chloroform (TCM) was the predominant DBP formed, and 37–63% of its precursors were removed by treatment. The trichloromethane formation potential (TCMFP)-UV₂₅₄ correlation was poor (r² = 0.25) and adversely impacted by the influx of dissolved iron from the heavy rainfall event; in contrast, correlations with fluorescence-based metrics were strong – TCMFP-I_278/506 (r² = 0.88) and TCMFP-C1 F_MAX (r² = 0.87) – illustrating the accuracy of these precursor surrogate parameters in waters impacted by a heavy rainfall event.