What does breakpoint chlorination refer to?

• A. The chlorine dose at which combined chlorine demand is satisfied and free chlorine remains to disinfect.
• B. The dose to remove taste.
• C. The dose that kills all organisms instantly.
• D. The dose at which chlorine is detected by odor.

Answer: (A)

Breakpoint chlorination is the point where enough chlorine has been added to neutralize the combined chlorine formed from ammonia and other nitrogen compounds, so that free chlorine remains to disinfect. As chlorine is added to water containing ammonia and organic nitrogen, it first reacts to form combined chlorine (chloramines) and uses up chlorine demand. Once that demand is satisfied and you pass the breakpoint, free chlorine appears and continues to disinfect. This ensures effective disinfection and lowers chloramines that can cause taste and odor issues. The other options describe aspects that aren’t about crossing from combined to free chlorine or the persistence of disinfection, not the breakpoint concept.