Effects of stirring on residual chlorine during chlorination of seawater containing ammonia nitrogen

Abstract

Stirring affected the concentration and proportions of residual chlorine during the chlorination of seawater containing ammonia nitrogen. At high stirring speed, the residual chlorine level rose in direct proportion to the dose of chlorine, then decreased to a minimum. At low stirring speed, the residual chlorine level began to decline before the peak of the break-point curve, which was flatter than the one obtained with high stirring speed. Regardless of the speed of stirring, monochloramine was the predominant species in the residual chlorine that remained after 1 h and the break-point was at the same chlorine dose. The amount of monobromamine produced was inversely related to the speed of stirring. Residual chlorine loss occurred primarily via the disproportionation of monobromamine to form dibromamine and ammonia nitrogen. Later, dibromamine and bromochloramine disappeared on reacting with monochloramine, and only stable monochloramine remained. The degree of mixing of chlorine and seawater with ammonia nitrogen is of importance in evaluating the residual chlorine concentrations.