This document discusses chlorination as the most important process for disinfecting water. Chlorine is identified as the ideal disinfectant because it provides residual sterilizing effects. The document outlines different chlorination methods including plain, pre, post, double, and break point chlorination. It also discusses dosages of chlorine, advantages of chlorine, and tests to determine chlorine residuals.

1. CHLORINATION
 By Pradumn Balaji Suryakar
 Government college of engineering aurangabad
 BE17F01F049

2. Introduction
 Presence of turbidities,colour, or minerals etc may not be
dangerous
 But presence of even a single harmful organism will definitely
prove dangerous
 So disinfection is the most important process
 Chemical used as a disinfectant must be able to give the
RESIDUAL STERILISING EFFECT ,so chlorine is most ideal
disinfectant

3. Minor methods of Disinfetion
1. Boiling of water
2. Treatment with excess lime
3. Treatment with Ozone
4. Treatment with iodine and bromine
5. Treatment with ultra-violet rays
6. Treatment with potassium permangate
7. Treatment with silver , called Electro-Katadyn process

4. Chlorination
Advantages
 Cheap
 Reliable
 Easy to handle
 Easily measurable
 Capable of providing
residual disinfecting effect
Disadvantage
 When used in more amount it
imparts bitter taste to the
water

5. Doses of Chlorine
 Dose depends upon the inorganic and organic impurities present
in water
 Inorganic impurities like S ,Fe ,Mn ,etc convert chlorine to
chloride (no residual oxidising power)
 Excess chlorine is consumed by ammonia to form chloramines
(combined chlorine)
 Chlorine consumed in above reaction represent the chlorine
demand of water
 Once it is satisfied , the chlorine will appear as free chlorine

6.  Free chlorine as well as the combined chlorine(Chloramines) will
cause germicidal action on bacteria and pathogens.
 The free chlorine will instantaneously kill pathogens ,while the
combined chlorine will provide long term germicidal effect
 Chlorine dose is increased during Rainy season and epidemics

7. Advantages of free chlorine
1. Can be easily stored for long period
2. Quite cheap and easily available
3. Occupies less space for storage
4. Low initial cost of installation
5. Very powerful disinfectant and may remain as residual
6. No need of skilled supervision
7. No sludge is formed

8. Types of Chlorination

9. Plain chlorination
 Only the chlorine treatment is given to water ,no other treatment
is given
 Helps in removing bacteria ,organic matter, and colour
 Used when turbidity is less than 20-30 mg/l
 May be used in emergencies also
 Normal dose of chlorine=0.5 mg/l

10. Pre chlorination
 Process of applying chlorine to
the water before filtration or
sedimentation –coagulation
 Helps in coagulation and reduces
loads on filters
 Reduces taste ,odour ,algae ,
other organisms
 Normal dose of chlorine=5-10
mg/l
Post chlorination
 Normal process of applying
chlorine in the end,when all the
other treatments have been
completed
 In water supplies ,it is adopted
after filtration
 Residual chlorine = 0.1 - 0.2
mg/l

11. Double chlorination
 Water is chlorinated twice
 Pre chlorination and Post chlorination is used
 Used when the water is highly turbid and contaminated

12. Break point chlorination
 Dose of chlorination beyond which any further addition of
chlorine will equally appear as free residual chlorine
 Chlorine reacts with ammonia present in water
 DPD test will indicate quantum of total residual chlorine
 Graph of Residual chlorine Vs Applied Chlorine is plotted and
shown

14. Details of graph
 Amount of residual chlorine is slightly less than that of addes
(AB)
 Beyond point B ,organic matter present in water starts getting
oxidised, so R.C. starts falling (BC)
 Beyond C, any further addition appear as free chlorine i.e nothing
is utilised….so C is called Break point
 Addition of chlorine beyond break point is called break point
chlorination

15.  It is essential to add chlorine beyond break point to ensure
residual effect
 Residual chorine is not easily removed except by sunlight
 So it take care of the future recontamination of water in
the distribution system

16. Super chorination
 Indicates the addition of excessive amount of chlorine
 Required in special cases of highly polluted water, during
epidemics of water borne diseases
 Used when water contains cysts of histolytica (organism)
 Residual chlorine = 1-2 mg/l
 Can be removed by dechlorinating agents like sodium
thiosulphate , activated carbon ,sulphur dioxide ,etc

17. Dechlorination
 Removal of chlorine from water
 Required when
superchlorination is done
 Amount of residual chlorine
changes from 1-2 mg/l to 0.1-
0.2 mg/l
 Economical
dechlorinator=Ammonia
 Dechlorinating agents
1. Sulphur dioxide gas
2. Activated carbon
3. Sodium thiosulphate
4. Sodium metabisulphate
5. Sodium sulphite
6. Sodium bisulphite
7. Ammonia

18. Tests to determine Chlorine Residuals
1. Orthotolidine test
2. D.P.D. test
3. Chlorotex test
4. Starch-iodide test

19. Reference
Water supply Engineering by S.K.Garg

20. THANK YOU