Bromamines are found in drinking water when bromide-containing waters are disinfected in presence of ammonia. Dissolved copper can be detected in drinking water distribution system either because of its use as a biocide or corrosion from copper pipes. This study demonstrates that Cu(II) can significantly enhance the decomposition rate of bromamines. Apparent second order rate constants of 2.31 M-1s-1 and 0.36 M-1s-1 at pH 7.5 were determined for the reaction of Cu(II) with bromamines and the self-decomposition of bromamines, respectively. With increasing pH from 6.0 to 8.5, the rate of bromamine self-decomposition decreased while the rate of Cu(II)-catalysed decomposition of bromamines increased. The species specific rate constant were determined to be kCuOH+/NH2Br = 1.69 × 10-4 M-1s-1, kCu(OH)2/NH2Br = 6.46 × 10-5 M-1s-1, kCu2+/NHBr2 = 1.71 × 10-5 M-1s-1, kCuOH+/NHBr2 = 2.28 × 10-4 M-1s-1, and kCu(OH)2/NHBr2 = 2.85 ×10-5 M-1s-1 while kCu2+/NH2Br was found negligible. Membrane Introduction Mass Spectrometry (MIMS) was applied to differentiate the different bromamines species i.e., monobromamine and dibromamine. Experiments were carried out with 15N to analyze the nitrogenous degradation products of bromamines in the presence and absence of Cu(II). N2 was quantified by GC-MS, NO2- and NO3- by ionic chromatography and N2O by MIMS. The main bromamines self-decomposition product was found to be N2 (75% in our experimental conditions) and low concentration of N2O, NO2- and NO3- were detected. When Cu(II) was present at 1.0 mg/L, the product speciation changed and nitrification occurred with NO2- representing 50% of the total nitrogen while N2O became significant (30%) and N2 was only 10%. Increasing the Cu(II) concentration to 5.0 mg/L led to an increase of N2O production to 50% while NO2- decreased to 25% and N2 to 6%. It has to be noticed that NO3- was always found at low concentration (~5%) indicating that bromamines slowly reacts with NO2-. Based on these results a mechanism for Cu-catalysed bromamines decomposition is proposed. These novel findings have important implications to control the stability of chloramine in drinking water distribution system. In real chloraminated distribution system, the presence of nitrite might not only occur from ammonia oxidising bacteria but could result from the decomposition of bromamines in the presence of corrosion product i.e., Cu(II).

Mechanistic investigation of bromamines decomposition in the presence of Cu(II)

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.