Effect of copper oxide on monochloramine decomposition in bromide-containing waters

Copper oxide (CuO), a common corrosion product found in copper pipes, has been shown to catalyse the decay of different oxidants in drinking water, including chlorine, bromine, iodine, and chlorine dioxide. However, its impact on monochloramine (NH₂Cl), a disinfectant commonly used in long distribution system worldwide is still unknown. In this study, the effect of CuO on NH₂Cl decay in the absence or presence of bromide was investigated. Results showed that in the presence of CuO and the absence of bromide, NH₂Cl slightly decayed under acidic conditions. When bromide was present in NH₂Cl solutions, the total oxidant concentration (sum of the different bromo-chloro-amines) was significantly decreased by CuO. This was primarily due to the degradation of bromochloramine (NHBrCl) by CuO which was evidenced by membrane inlet mass spectrometry. The decomposition rate of the total oxidant was similar for different CuO dosages (0.02-0.2 g/L) but increased with increasing bromide concentration (0-80 μM) and decreasing pH (6.5-8). An apparent second-order rate constant of 0.73 M^-1 s^-1 was determined with respect to NH₂Cl and bromide concentrations for a CuO concentration of 0.05 g/L. Our findings suggest that, during water transportation in copper pipes or in distribution systems where copper oxide is present, special attention should be given to the stability of chloramines when bromide-containing waters are chloraminated.