The document discusses various methods of water disinfection and chlorination. It provides information on cholera outbreaks and advises people to follow hygiene practices like drinking boiled water and washing hands regularly. It describes small and large scale methods of water purification including filtration, disinfection, and chlorination. Chlorination is discussed in detail, including principles of chlorine action, definitions, recommended chlorine levels, and tests for chlorination. Methods like boiling, chlorination, ozonation, UV treatment and membrane processes are compared. Criteria for identifying problem villages and maintaining swimming pool sanitation are also outlined.

1. Water Disinfection
1
DR. MELBIN JAMES .S
SENIOR RESIDENT
Department of Community Medicine
SLIMS

2. VIDEO
2
DR .JOHN . L .LEAL

3. 3
CHOLERA OUTBREAK - Karaikal
People have been advised to follow hygiene
practices like consuming boiled water for drinking,
washing hands regularly, taking safe drinking water
in public places and hotels, using a public toilet and
avoiding open-air defecation, reporting any local
government Primary Health Centres
(PHC)/Community Health Centres (CHC) in case if a
person comes across any symptoms.
July 2022

4. 4

5. Water Purification
5
Small Scale Methods Large Scale Methods
2. Well Disinfection
3. Storage
1. Filtration ( Rapid and slow
sand filters)
1. Household purification of water
(Boiling , Chemical disinfection)
2. Disinfection of water

6. Disinfection Vs Sterilisation
Methods of disinfection
 Definitions and Sources of Chlorine
Chlorination of water and its uses
 Instruments and tests for chlorination
 Swimming pool and OHT sanitation
Related Health programmes

7. DISINFECTION
STERILISATION
7

8. • 1. Boiling - Best method – kills organisms and spores
• 2. Chlorination ( 2nd best) ----- Cl2 gas , Bleaching powder , Chlorine dioxide, Chlorine
tablets, Chloramines ( slow acting) – used in disinfection of water and surgical instruments
• 3. Ozonation
• 4. UV rays treatment
• 5. Membrane Process – RO filters
Methods of Disinfection of Water:
8

9. 2nd best because ( high doses needed on certain pathogens)
Not effective in small doses on
• Poliomyelitis
• Hepatitis A , Cryptosporidium , Helminth cysts and ova
• Bacterial spores and cyclops
9
CHLORINATION:
Disinfection property is mainly
due to HOCL ( 90%) > Ocl (10%)

10. PRINCIPLES & PROPERTIES :
10
DRINKING WATER CHLORINE ( CHLORINATED WATER)
Colorless Bactericidal , moderate virucidal and not sporicidal
Odorless with mild taste Best method in rural areas
Not turbid Very high ( <2ppm) – GI issues, bladder cancer , throat
irritation)
Free from pathogens, Floating
matter and suspended particles
Free/ Residual action – remains effective for next 2days
(safety during storage / distribution) ( unique feature)
PH -8 ( Slightly alkaline) Acts best at PH of 7 – most WBD diseases also the same
PH >8.5 – 90% of HOCL gets ionized to hydrogen ions
and hypochlorite ions
TDS <500 ppm 33% chlorine available in 100 g bleaching powder

11. • 1. Chlorine demand: Amount of Chlorine needed to destroy bacteria and oxidize all
organic matter and ammoniacal substances in water
• 2. Breakpoint chlorination : The point at which the chlorine demand is met ---on further
adding Cl beyond– it settles down as Free residual chlorine
• 3. Super chlorination : Addition of large doses of chlorine to heavily contaminated water
and removal of excess of chlorine after disinfection
• 4. Stabilised bleach : Bleaching powder mixed with excess of lime – retains strength
( bleaching powder exposed to sunlight /moistures --- loses it Cl- content)
SOME BASIC DEFINITIONS………..
11

12. 12
PHASE 1
PHASE 3
PHASE 2
PHASE 4

13. 13
FREE RESIDUAL CHLORINE LEVELS
Ppm ( mg/dl)
RECOMMENDED AREAS FOR CONTACT PERIOD
( 1 hr )
>0.5 ppm In Drinking water at home
>0.7 ppm Post disaster and water bodies ( outbreaks)
>1 ppm Swimming pools
>2 ppm To kill Cyclops

14. HORROCK’S APPARATUS
14
 Used for estimating the dose of bleaching powder needed to disinfect 455 Liters of
water --- Chlorine demand ( Mostly in wells)

15. • Contents of ‘Horrock’s Apparatus’
• 6 white cups, each of 200 ml capacity
• One black cup with a circular mark on the inside
• 2 metal spoons (each holds 2g of bleaching powder when filled up to the brim)
• 7 glass stirring rods
• One special pipette
• Two droppers
• Starch - iodide indicator solution
• Instruction folder
• Steps in Estimating the Required Dosage of Bleaching Powder for disinfecting water
1. One level spoonful (2g) of bleaching powder is placed in the black cup and made into a thin paste with a little water
The solution thus prepared is the ‘Chlorine Stock Solution’
2. The six white cups are filled with the water to be tested
3. Using the pipette provided with the apparatus, add one drop of the stock solution to the first cup, two drops to the
second cup, three drops to the third cup, and so on till adding six drops to the sixth cup.
• 4. Stir the water in the cups; use a separate rod for each cup
5. Wait for half an hour
6. Add three drops of starch-iodide indicator to each of the white cups
7. Development of blue color indicates the presence of free residual chlorine.
15

16. 16
INTERPRETATION :
If first cup develops blue colour: 1 spoonful (i.e. 2gm) of bleaching powder would suffice for
455 L of water
If the second cup develops blue colour: 2 spoonfuls (4 gm) of bleaching powder for 455 L of
water etc…..
If none of the cups develop a blue colour, this means that the chlorine demand of the water is
very high and it is better to use some method of clearing the water prior to chlorinating it
• If nth cup shows blue colour = n x 2g of bleaching powder is required for disinfection
Required Bleaching powder (gm) = Volume of water in litres x n x 2
455

17. 17
How many grams of bleaching powder is required to disinfect 3000 Litres of
water where 4th cup shows blue color change in Horrocks apparatus ?
53 g

18. 1. Orthotoluidine Test :
To check whether the water is chlorinated or not
Determines both Free and combined chlorine in water together
0.1 ml of reagent added to water with chlorine
Reading taken with 10 sec ( Free Cl-) and after 15-20 min ( Free and combined Cl)
Yellow color – matched with chloroscope
2. Orthotoluidine Arsenite Test :
Better test – since Free and Combined chlorine estimation separately
Unaffected by impurities ( Nitrites , iron , manganese)
TESTS FOR CHLORINATION :
18

19. CHLOROSCOPE :
19

20. • 400 ml of water mixed with 0.25g chlorine dioxide powder
• Dissolve and stir for few min
• Take 10ml of sample solution in test tube and add 2drops of OT reagent
• Turns yellow color measured against chloroscope - presence of level of chlorine
in water
Testing Chlorine content in water at Home level
20

21. • At field level – HI - once in 15days and daily in epidemics
• Bleaching powder kept tightly packed in dark room
• Sample of water taken and tested ( OT test along with chloroscope)
• Check the level of chlorination in water in tank
• Water added with Bleaching powder mixed like paste and diluted with water ( Chlorine solution)
• Chlorine water separated carefully by filtration
• Climb up and do chlorination for 1hr ---after that recheck with chloroscope again
• 1000 L water requires 4g bleaching powder ( even at syntex tank in home)
OVERHEAD TANK CHLORINATION
21

22. Swimming Pool Sanitation :
22
 HOCl –penetrate cell walls of bacteria/viruses- kills it
 Must be equipped with Rapid sand filter ( filtration <6hrs)
 Area > 24 sqft / swimmer
 IEC posters for regulations posted in appropriate places
 >15% water to be changed every day
 Free from communicable diseases – allow to swim
 Before swimming –empty bladder / use toilet outside pool
 Proper chlorination of the pool (> 1ppm free Cl-)
 Maintain pH of 7.4-7.8

23. All these techniques have No residual action unlike chlorination
1. OZONATION
• Powerful oxidant ----- strong virucidal – O3 gas ( 0.2-1.5 mg/dl)
• Used for chemical contamination of pesticides
2. UV rays treatment – 254 nm UV light damages RNA and DNA of organisms
3.Membrane process : Done in RO Filters using reverse osmosis , micro/ nano filtration techniques
OTHER METHODS OF DISINFECTION OF WATER :

24. 1. > 1.6 km access to water supply in rural plain areas and > 100m in hilly areas
2. >15m depth of water source ( bore)
3. Excess Salanity ( physical/ chemical contamination)
4. Water exposed to cholera / Guinea worm
Problem Village - Criteria
24

25. 25

26. 26

27. 1. All the following statements are true about breakpoint chlorination EXCEPT?
A. Free chlorine is released into water after breakpoint
B. Chlorine demand is amount of chlorine needed to kill bacteria , oxidise organic
matter and neutralize ammonia
C. 1 ppm free chlorine should be present in water after breakpoint has reached
D. Most commonly used form of chlorine is bleaching powder
2. Method of choice for purification of highly polluted water on large scale ?
A. Boiling
B. Chlorination
C. Superchlorination followed by Dechlorination
D. UV light treatment
MCQs
27

28. 3. Minimum recommended dose of free residual chlorine in water for routine chlorination ?
A. 0.5 ppm for a contact period of 1hr
B. 0.5 ppm for a contact period of 30min
C. 1 ppm for a contact period of 1hr
D. 2 ppm for a contact period of 30min
4. The colour produced in OT test is due to action of
A. Dissolved solids
B. Free chlorine
C. Combined chlorine
D. Free and combined chlorine
MCQ
28

29. 5. Access to water supply in Problem village criteria for distance in plain areas ?
A. >1.2kms
B. >1.5kms
C. >1.6kms
D. >1.7kms
6. Chlorination in small doses is not an effective disinfectant in all EXCEPT?
A. Polio virus
B. Bacterial cysts
C. Salmonellosis
D. Cyclops
MCQ
29

30. 7. Chlorine acts best at pH of ?
A. 6
B. 8
C. 7
D. 9
8. Minimum level of Chlorination in swimming pools ?
A. 1ppm
B. 1.5ppm
C. 2ppm
D. 0.5ppm
MCQ
30

31. Days to Remember..
• World Water Day- 22nd March
( 2023 THEME ---- “Accelerating Change”)
• International Decade for “Water for Life”
(2005 – 2015)
• Water Conservation Day - 19th November

32. Water Saving Tips in Home
Check at home for leaks, hidden
water leaks
Fix any dripping tap
Turn off tap while cleaning your teeth, shaving
or washing your face
Only use the washing machine when you can
put on a full load.
Use a sponge and bucket of water to
clean your car

33. 33

34. `
34