Formation of trichloronitromethane and dichloroacetonitrile in natural waters: Precursor characterization, kinetics and interpretation

During the chloramination of natural waters, both chloramines and dissolved organic nitrogen (DON) can serve as nitrogen sources for the formation of trichloronitromethane (TCNM) and dichloroacetonitrile (DCAN). The present study investigated the formation kinetics and precursor characteristics of TCNM and DCAN. ¹⁵N-Isotopic monochloramination of the organic fractions produced both ¹⁵N- and ¹⁴N-DCAN and TCNM. Nitrogenous disinfection byproduct (N-DBP) formation, in which the nitrogen precursor originated from DON (¹⁴N-DCAN and ¹⁴N-TCNM), followed a second-order reaction kinetics (k=3.2×10^-5 to 9.4×10^-5μM^-1h^-1). The formation of N-DBP where the nitrogen atoms originated from chloramines (e.g. ¹⁵N-DCAN and ¹⁵N-TCNM) correlated linearly with chloramine exposure. The discrepancy in formation kinetics results in that the ¹⁴N-DCAN concentrations were two to ten times higher than ¹⁵N-DCAN in the beginning of the reaction (<12h). Possible rate equations are proposed in this study. The results of a model compound study support the results of the chloramination of natural waters. In addition, 4-hydroxybenzaldehyde, an oxidative product commonly found during chlorination/chloramination of natural organic matters, gave a 10-fold greater yield of DCAN than that produced from tyrosine; 4-hydroxybenzaldehyde is thus an important precursor in DCAN formation by chloramine incorporation during the chloramination of natural waters.