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

This study demonstrates that Cu(II) can significantly enhance the decomposition rate of bromamines. Apparent second order rate constants of 2.31 ± 0.01 Ms and 0.36 ± 0.01 Ms 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) was the most reactive copper species towards NHBr and NHBr. Experiments were carried out with N-labelled bromamines to analyse the nitrogenous degradation products of bromamines in the presence and absence of Cu(II). Nitrogen gas (N) was found to be the major product from the self-decomposition of bromamines, with NO, NO, and NO as additional minor products. When Cu(II) was present, the product distribution changed and NO and NO became significant, while N and NO were produced at low levels. Increasing the Cu(II) concentration from 1.0 to 5.0 mg/L increased the NO production while decreased the NO 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.