A breakpoint chlorination yields which residual?

A breakpoint chlorination yields which residual?

• A. Free
• B. Combined
• C. Total
• D. Chloramine

Answer: (A)

Breakpoint chlorination means dosing chlorine until all ammonia and other substances that consume chlorine are oxidized. During the buildup, chlorine is tied up forming chloramines, so the measurable residual is primarily combined chlorine. Once you pass that point, the remaining chlorine no longer reacts with ammonia or chloramines and appears as free chlorine (the HOCl/OCl− form), providing a free chlorine residual. So the residual produced after breakpoint is free chlorine. In contrast, combined chlorine is what you’d see before breakpoint, and chloramine is the type of species that represents the combined form; total chlorine would be the sum of both free and combined.

Breakpoint chlorination means dosing chlorine until all ammonia and other substances that consume chlorine are oxidized. During the buildup, chlorine is tied up forming chloramines, so the measurable residual is primarily combined chlorine. Once you pass that point, the remaining chlorine no longer reacts with ammonia or chloramines and appears as free chlorine (the HOCl/OCl− form), providing a free chlorine residual. So the residual produced after breakpoint is free chlorine. In contrast, combined chlorine is what you’d see before breakpoint, and chloramine is the type of species that represents the combined form; total chlorine would be the sum of both free and combined.