During the purification of water, if chlorine is applied beyond the stage of break-point

Question

A. Super chlorinated

B. Pre-chlorinated

C. Post chlorinated

D. Double chlorinated

Answer: Option A – Super chlorinated

Explanation:

• 1. Plain chlorination:
  
  • This term is used to indicate that only the chlorine treatment and no other treatment has been given to the raw water
  
  • It is used for clean water, i.e turbidity between 20 – 30 mg/l
  
  • Dose is 0.5 mg/l
  
  2. Pre-chlorination:
  
  • It is the process of applying chlorine to the water before filtration or rather before sedimentation and coagulation.
  
  • Normal dose is 5 to 10 mg/l and pre- chlorination is always followed by post chlorination
  
  3. Post chlorination:
  
  • It is the normal standard process of applying chlorine in the end, when all other treatments have been completed.
• 4. Double chlorination:
  
  • It simply means that the water has b chlorinated twice
  
  5. Break-point chlorination:
  
  • It means an extent of chlorine is ado water.
  
  • It represents that much dose of chlorination, beyond which any further additional chlorine will appear as free residual chlorine.
• 6. Super-chlorination:
  
  • When excess chlorine (5 to 15 mg/l) is added during an epidemic such that it gives a residual of 1 to 2 mg/l beyond breakpoint is called super chlorination.
  
  • If chlorine is applied beyond the stage of break-point, then the water is called super-chlorinated.
  
  • It is most commonly added at the end of filtration.
  
  7. Dechlorination
  
  • When chlorine residue is high, excess chlorine will be removed by dechlorinating agent.