This study investigated the formation and speciation of dihaloacetonitrile (DHAN) species that included dichloro-, bromochloro- and dibromoacetonitriles (DCAN, BCAN and DBAN, respectively) generated by the chlorination of two water sources, varying concentrations and characters of Natural Organic Matter (NOM), bromide concentrations, reaction times, chlorine doses, temperatures and pHs.  DHAN formation and NOM transformations in these reactions were examined based on the kinetic analysis of DHAN data and also via differential spectroscopy that quantifies the extent of NOM halogenation. DHAN speciation was interpreted based on the previously published approach to model mixed chlorination/bromination pathways via apparent dimensionless ratios of bromination/chlorination reaction rates at each halogen incorporation node. The model assumed the presence of three kinetically distinct sites (S1, S2 and S3) that upon halogenations yield DCAN, BCAN and DBAN. The contribution of sites S1, S2 and S3 to the DHAN formation changed with the different water qualities with a prominent contribution of the slowest reactive site in NOM whose reactivity in DHAN formation increased in treated or fractionated waters. Absorbance values were intrinsically related to the formation and speciation of DHAN. Indeed, a good relationship was found between the contributions of site S1, S2 and S3 to TDHAN formation and absorbance values at 254 nm. Furthermore, differential absorbance (?A) values were correlated with both DHAN yields and speciation at varying chloriantion conditions. The interpretation of ?A data also showed the existence of correlations between the speciation coefficients and the slope of DHAN vs. ?A correlation.  The developed model can ultimately help ascertain the kinetics of DHAN generation in conditions pertinent to water treatment and distribution as well as to assess toxicological and epidemiological effects of these important DBPs. Further research is needed to expand the modeling of HAN formation in chloraminated waters also containing iodine other than bromide.

Formation and speciation of dihaloacetonitriles in chlorinated water: Kinetic and spectroscopic modeling

248th National Meeting (2014)

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