During which part of chlorination does breakpoint chlorination occur?

Breakpoint chlorination occurs during the third part of the chlorination process. This stage is significant as it represents the point at which all forms of chlorine demand have been satisfied, including the chlorine used to oxidize organic and inorganic compounds, as well as to disinfect the water.

At this stage, any additional chlorine added to the water begins to produce free available chlorine, which is effective for disinfection. This is critical as it ensures that there is enough chlorine remaining in the water to eliminate pathogens effectively. By reaching breakpoint chlorination, the water treatment process maximizes the disinfection efficiency, reducing the risk of waterborne illnesses.

The other parts of the chlorination process focus on meeting the chlorine demand and then reaching a state where residual chlorine begins to form. However, it is specifically in the third stage that the treatment exceeds the total chlorine demand, allowing free chlorine to be available for effective disinfection.