Course: BFM 203 Water Treatment and Control

Lecture

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Breakpoint Chlorination

Breakpoint chlorination is required in systems that do not add ammonia for chloramination. This ensures a free available chlorine residual at the entry point to the distribution system as required by Primary Drinking Water Regulations. Breakpoint chlorination refers to the process wherein we add chlorine to water until the chlorine demand has been satisfied. At this point, further addition of chlorine will result in a free available chlorine residual that is directly proportional to the amount of chlorine added.

Free available chlorine residual is that portion of the total available residual chlorine composed of dissolved chlorine gas, hypochlorous acid, and/or hypochlorite ion remaining in the water after chlorination. This does not include chlorine that has combined with ammonia, nitrogen, or other compounds.

The following diagram represents the chlorine breakpoint curve. After the breakpoint, the free and total residuals will increase at the same rate.

http://mostwatertraining.com/blog/the-chlorine-breakpoint-curve

Chlorine Residual

It is important to maintain a chlorine residual in the distribution system because it is effective in eliminating bacteria (coliform) that reaches the distribution system through cross-connections or leaks in the system. It also helps control any microorganisms that could produce slimes, tastes, or odors in the distribution system. Maintaining an adequate chlorine residual in the distribution system is the most effective way to make sure that treated water reaches the customer in a safe condition.