Haloacetonitriles (HANs) are nitrogenous disinfection byproducts (DBPs) that are formed during free chlorine (Cl2) or chloramine (CLM) disinfection of water. Despite being detected frequently in different water sources and showing a higher order of cytotoxicity and genotoxicity as compared to their regulated counterparts, only a few studies have been conducted to determine relative sources of HAN precursors in source waters. DBP precursors are often assessed through formation potential (FP) testing, although the conditions (pH, Cl2/CLM dose, time) vary among DBP and type of test (e.g., uniform formation condition). HANs are known to undergo hydrolysis, with increasing hydrolysis rate as pH and number of halogen atoms increases. In addition, HAN stability is affected by chlorine residual, with increasing residual leading to a shorter half-life. Therefore, it is important to tailor formation potential conditions for HANs.  Formation potential tests with free chlorine and preformed monochloramine were conducted with non-disinfected wastewater effluent at two pHs (7 and 8), three Cl2/CLM doses, and five reaction times (<i>i.e.,</i> 0.5, 1, 2, 3 and 5 days). After the designated reaction time, samples were extracted and analyzed by gas chromatography mass spectrometry for 10 HANs. As expected, HAN FP concentrations were higher at pH 7 compared to pH 8, and chlorination produced higher HAN FP as compared to chloramination. Concentrations of dichloroacetonitrile and bromochloroacetonitrile were greatest, indicating greater stability and/or preferred formation from precursors. It was observed that trihalogenated, monochlorinated, and iodinated HANs (trichloroacetonitrile, monochloroacetonitrile, and monoiodoacetonitrile) had low yields under all experimental conditions. This can be attributed to the lack of precursors and/or greater hydrolysis in the case of trihalogenated HANs. In general a higher disinfection dose at pH 7 resulted in maximum formation for most compounds; however, reaction time had varying effects on final concentration with some HANs continually increasing while other HANs peaked and decreased with time.

Establishing formation potential test conditions for assessing haloacetonitrile precursors in source waters

ACS Fall 2021

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