[Kinetics of monochloramine decay in disinfection of drinking water]

The model of second-order reaction kinetics has been used to fit the monochloramine decay in water samples by nonlinear imitation. Several factors were investigated, including pH, temperature, carbonate, bromide, iodide concentrations and natural organic matters in this system. The results showed that pH value was an important factor on the monochloramine decay rate, especially when pH was below 7.0. Temperature and carbonate levels also had obvious effect on the monochloramine decay. Co-existence of bromide anions had different impact under different pH values. At pH 6.60, monochloramine decay rate tended to decrease dramatically with the increment of bromide levels. However, when pH was above 7.60, 0.1 mg/L of bromide hardly affected the decay rate of mononchloramine. Co-existence of iodide showed stronger effect on the decline rate of monochloramine than that of bromide. It was demonstrated that the second-order kinetic model could fit well the experimental results of monochloramine decay reaction under the conditions of bromide or iodide co-existence. The results of this study will be of benefit to the theory and technology of drinking water disinfection, especially for the reduction of DBPs and the control of disinfectant dosages in the area of coastland and estuary.