Monochloramine and total haloamine decay after a short prechlorination time in the presence of bromide

The Chlorine-Ammonia Process was developed recently as a preoxidation process to minimize the formation of bromate during ozonation of the waters containing a significant bromide concentration. Chlorine is added first followed by ammonia 5–10 minutes later, with the goal of sequestering bromide in monobromamine during the subsequent ozonation step. The goal of this research was to improve the Chlorine-Ammonia Process by introducing a very short prechlorination step (i.e. 30 seconds before addition of ammonia) to minimize overall disinfection by-product formation. Also, in this strategy, formation of a powerful halogenating agent, HOBr, is minimized and bromochloramine (NHClBr) is used predominantly instead of monobromamine to sequester bromide during ozonation. To support this improved approach to bromide sequestration, this study examined the formation and decay of bromochloramine as a function of operating conditions, such as pH and Cl₂:N ratio, and refined a chemical kinetic model to predict haloamine concentrations over time.