Haloacetonitrile (HAN) Precursors in the Colorado River Watershed: Sources and Mitigation

Abstract Submission: Haloacetonitriles (HANs) are a type of nitrogenous disinfection byproduct (DBP) that is frequently formed in chlorinated or chloraminated water. Compared to regulated DBPs such as trihalomethanes and haloacetic acids, unregulated HANs have been found to be more cytotoxic and genotoxic. Previous studies have identified amino acids and wastewater-derived nitrogenous compounds as major sources of HAN precursors, but information is lacking regarding HAN precursors in different source waters such as pristine surface waters and wastewater-impacted surface waters, agricultural runoff, urban runoff, and stormwater. The aim of this research was to understand the relative sources of precursors in varying water sources across the Colorado River watershed. A newly developed and optimized formation potential (FP) test was used across all locations, and it incorporated three disinfection schemes commonly used in water treatment plants: free chlorination, chloramination, and in-situ chloramination with 30 minutes prechlorination. For all the water sources, free chlorine resulted in maximum HANs (0.52-26.22 𝜇g/L) with lower net formation for in-situ chloramination with prechlorination (0.46- 15.08 𝜇g/L) or preformed monochloramination (0.46-7.32 𝜇g/L). Brominated HANs were observed in stormwater and wastewater-influenced samples while they formed at lower levels in other samples. Dihalogenated HANs (DHANs) had the highest concentration, while trihalogenated, monohalogenated and iodinated HANs were formed at low levels (0.03-0.5 𝜇g/L) for all source water types. This can be attributed to the lack of precursors and/or higher hydrolysis of trihalogenated HANs. The research also investigated the precursor removal due to treatment processes in different drinking water or wastewater treatment plants. In conclusion, this study provides insights into the sources and reactivity of HAN precursors in different water sources. These findings could be used by drinking water operators to minimize HANs in their distribution systems for improved water quality and to ensure safe drinking water.

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