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Chlorine is a heavier liquid than water, which is highly soluble in water and decays as the temperature increases.

Chlorination: This method is commonly used and chlorine is highly toxic to microorganisms. Chlorine depends on its effect on microorganisms. The principle of oxidation is to inhibit the enzymatic synthesis of germs. Chlorine or its compounds are usually added to the water to purify them. Adding chlorine to water or adding sodium hypochlorite occurs following reactions:

Cl2 + H2O → HOCl + HCl

NaOCl + H2O → HOCL + Na + OH

HOCL → H + OCL

The three forms of chlorine overlap and bind together (CL2-HOCL-OCL)

The effectiveness of chlorine to exterminate germs and their impact on temperature and degree of pH is entirely on many factors, including:

- Temperature: The amount of chlorine added at high temperature due to the rapid decomposition of chlorine compounds and the effect of chlorine at high temperature.

- Light: Light disables these materials while exposed to light.

Acid factor: pH The dose of chlorine increases as the value of pH increases.

- Application range: Chlorine is more effective with increased contact time (disinfectant + water). In practice, it should be 30 minutes after chlorine is added before water is used.

- Census of germs and their types: Each type of bacteria with certain resistance to the effect of chlorine

The turbidity of the chlorine is increased with the increase of wastewater turbidity because the substances that cause the dirt cause protection or provide the germs with places of protection from environmental factors.

- Availability of Nitrogen compounds; Nitrogen compounds lead to reduced chlorine effect.

- High concentration of chlorine in sterilization should not be allowed, but dose should be minimal.

Basically, Chlorine decay depends on, water quality (if more pollutants in treated water, chlorine decays quickly), temperature, residual chlorine concentration, pH, hydraulics, etc.

Once you decided the desired residual chlorine at the end of pipeline, then you can do a back calculation to find out the required amount at the beginning.

There are free available software for chlorine calculation.

http://epanet.de

following my be useful

http://shodhganga.inflibnet.ac.in/bitstream/10603/149847/9/file8_chapter%205.pdf

https://pdfs.semanticscholar.org/aa3c/c4c5fb9a1cf944eaa8489c7ae793ae1f1f13.pdf

https://www.mikepoweredbydhi.com/upload/publications/mikenet/Nagatani_Residual_Chlorine.pdf

Chapter COMPUTER MODELING OF CHLORINE CONCENTRATIONS IN WATER DISTRI...

https://www.sciencedirect.com/search?qs=chlorine%20decay%20in%20the%20water%20transmission%20lines&show=25&sortBy=relevance&offset=25

dC/dt = k0C where C is the concentration of chlorine, t refers to time, and k0 stands for the chlorine decay coefficient Regards