Correlation between ph loss and chlorine loss?

[rmp0012002]

I am working at a new plant and have come across an issue related to a poor design of a lime pump system. Aside from the pump issue we are having an issue that when we lose lime to the clarifier and the ph drops out we also lose our chlorine residual. What is the cause of this as we are running almost 4ppm of chlorine into the clarifier but it’s not making it out? Once the lime is restored the chlorine is restored. Is it a ph issue or an alkalinity issue?

 

[ashtree]

Without knowing anything about the quality of your water it is impossible to know for sure however these would be a couple of things to look at.

1) Is the performance of the coagulant used in the clarifier better at the higher pH and more organics are being removed?
2) At a higher pH the rate of oxidation of iron and managanese is faster. If you had an aerator ahead of the clarifier maybe the iron is already fully oxidised before the chlorine is added. (Probably unlikely).
3) At the higher pH you have changed the threshold for the reaction or settling of something that is chewing up the chlorine.
4) The lime is acting as a disinfection agent.

I would suggest that you move your chlorine dose point to a spot after the clarifier, as this reduces the formation potential for disinfection by products.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

The disinfectant power of Free Chlorine is relative to the pH of the water. As pH increases, the chlorine becomes less effective. As pH decreases, the chlorine becomes more effective.

Free available chlorine is the part of the total chlorine measurement that has not yet reacted with contaminants. Therefore, it is called available or free. The total chlorine in this case is the sum of combined available chlorine and free available chlorine, also called total residual chlorine.

With a pH level of 6.0 your chlorine will be highly effective with 97% of your chlorine available to kill bacteria and algae. However, at 6.0 your pool water would be extremely acidic and unsafe to swim in. On the flip side, if you pH is at 8.5 only 9% of your chlorine will be available to kill bacteria and algae.

 

[ashtree]

The OP does not mention what pH range is being used nor the chlorine measurement method.
However the DPD method is pH sensitive at certain ranges and tends to under read even to the point of reading nothing as the pH goes below pH6.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[QualityTime]

What are you trying to accomplish by using the lime?