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Now we will discuss Break Point Chlorination.
Now when chlorine is added to water, a number of different reactions occur.
One of the things is that two acids are formed - Hydrochloric Acid, Hypochlorous Acid.
It is the Hypchlorous Acid that is the active disinfection. A number of other things will also take when chlorine is added to water
and we will realize this in the break point chlorination curve.
First of all on your horizontal line it will represent the chlorine dosage.
That's the amount of chlorine that is added continuously to water
On the vertical axis, or the Y axis, we see the residual. The residual is what remains after the demand has been taken care of.
So in Stage 1 as you add chlorine to water, there is no residual.
The reason there is no residual is because we have the destruction of chlorine by all the inorganics and chloro-organics that are being
reducing agents there.
In Stage 2 we see the formation of a residual. It is a weak residual at this point because now chlorine is binding with your chloramines
such as your monochloramines, your dichloramines, your trichloramines. This is a very weak disinfectant but still effective.
In Stage 3 we see the destruction of these compounds, the monochloromines, the dichloromines, and so the residual will go down.
At this point we reach breakpoint chlorination. There's nothing else in that water that chlorine can bind with
and so if you continue to add the dosage now we have what we refer to as a free residual.
Very potent, very fast acting. That is break point and then free residual.
So in Stage 1 chlorine is destroyed by all of your chloro-organics and reducing compounds.
We have the combined residual in Stage 2- chloromines, monochloromines, dichloromines and trichloromines.
The destruction of those compounds as you continue to add chlorine. And then breakpoint chlorination and free residual.
That is break point chlorination.