Kinetic and mechanistic investigations of the decomposition of bromamines in the presence of Cu(II)

Abstract

This study demonstrates that Cu(II) can significantly enhance the decomposition rate of bromamines. Apparent second order rate constants of 2.31 ± 0.01 M−1s−1 and 0.36 ± 0.01 M−1s−1 at pH 7.5 were determined for the reaction of Cu(II) with bromamines and the self-decomposition of bromamines, respectively. Increasing the pH from 6.0 to 8.5, the rate of bromamines self-decomposition decreased while the rate of Cu(II)-catalysed decomposition of bromamines increased. Species-specific rate constants indicated that Cu(OH)2 was the most reactive copper species towards NH2Br and NHBr2. Experiments were carried out with 15N-labelled bromamines to analyse the nitrogenous degradation products of bromamines in the presence and absence of Cu(II). Nitrogen gas (N2) was found to be the major product from the self-decomposition of bromamines, with N2O, NO2−, and NO3− as additional minor products. When Cu(II) was present, the product distribution changed and NO2− and N2O became significant, while N2 and NO3− were produced at low levels. Increasing the Cu(II) concentration from 1.0 to 5.0 mg/L increased the N2O production while decreased the NO2− formation. Based on these results, a mechanism for Cu(II)-catalysed decomposition of bromamines is proposed. This work provides new insights related to the chemistry of bromamines in chloraminated drinking water distribution systems where copper is present.