Types of chlorination

Types of Chlorination – Water Treatment and Purification

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Chlorination is used to disinfect the drinking water. There are different types of chlorination.

Pre chlorination

This is practiced by adding chlorine before filtration or rather sedimentation. In pre chlorination the 5mg to 10mg of chlorine per liter is added to the water. After treatment of water the chlorine will be present as 0.5 to 1 mg as residual.

Post chlorination

This is done after water treatment. In this type of chlorination also residual chlorine is available as 0.5 to 2 mg per liter.

Plain chlorination

It simply means that no other treatment applied to the water except chlorination. Usually, chlorination done such that 0.5 mg to 1 mg per liter chlorine being available residue.

Double chlorination

It simply indicates that the both pre chlorination and post chlorination are applied to the water.

Super Chlorination

Super chlorination means adding excess amount of chlorine say 5mg to 15mg per liter is applied. This is done during pandemics.

Break Point chlorination

The concept behind break point chlorination is that some part of the chlorine is consumed in killing the bacteria. The additional amount of chlorine will remain as residual.


It simply means removing chlorin from the water. This could be done by aerating the water. Dechloration can also be done by dechlorinating agents.
Some dechlorinating agents are

  1. Sulphur Dioxide Gas (SO2)
  2. Activated Carbon
  3. Sodium thiosulphate (Na2S2O3)
  4. Sodium Metabisulphate (Na2S2O5)
  5. Sodium sulphite (Na2SO3)
  6. Sodium bisulphite (NaHSO3)
  7. Ammonia as (NH4OH)

Desirable Properties Of Potable Water

  • Potable water should be colorless and odorless.
  • Drinking water should be free from harmful microorganisms.
  • It should have some minerals and salts for body requirements and some gases to add taste.
  • It is desirable that drinking water is free from suspended particles.


How to test the residual chlorine?

There are four ways to determine residual chlorine. Orthotolidine test, D.P.D. Test, Chlorotex test, Starch Iodine Test.

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