The document discusses various methods of water purification on both large and small scales, detailing processes such as storage, filtration, and disinfection. It compares slow and rapid sand filters, outlines different disinfection techniques including chlorination and chemical methods, and describes household water purification methods like boiling and UV irradiation. Additionally, it provides guidance on disinfecting well water, including dosage calculations for bleaching powder and the importance of contact time for effective treatment.

1. Which one will you drink?????
Glass 1 Glass 2

2. WATER PURIFICATION
LARGE SCALE &
SMALL SCALE

3. Unsafe water-Diseases ???

4. Purification on a large scale
1. Storage
2. Filtration
3. Disinfection

5. Storage
• Physical:
90% suspended impurities settle down by
gravity in 24 hrs
• Chemical:
Aerobic bacteria oxidize organic matter.
From free ammonia to nitrates.
• Biological :
90% bacteria die out in 5-6 days.

6. Filtration
• 98-99% bacteria + impurities removed
• 2 types are there:
1. Slow sand/ Biological filter
2. Rapid sand /mechanical filter

7. Slow sand /Biological filter
1. Supernatant water
2. Bed of graded sand
3. Under drainage
system
4. System of filter
control valves

8. Sand bed
• Most imp part
• Sand grain
• Supported by gravel layer
• Purification process:
mechanical straining sedimentation,
adsorption, oxidation & bacterial action

9. Vital layer
• Slimy growth - consist of algae, plankton, diatoms,
bacteria
• SCHMUTZDECKE /vital/zoogleal/biological layer
• Formation of vital layer - Ripening of filter
• Removes organic matter
• Hold back bacteria
• Oxidize ammoniacal nitrogen into nitrates

10. Filter control valves
• Valves/ devices in outlet system
• Maintain constant rate of filtration

11. Cleaning
• Normally run weeks/ months without cleaning
• Bed resistance increases - fully opening of valve=
time to clean
• Supernatant water is drained off
• Sand layer cleaned by SCRAPING off top layer

12. Advantages
• Simple to construct
• Cheaper
• Quality of water is very high
• ( Total Bacterial count reduced by 99.9 to
99.99%)

13. Rapid / Mechanical Filter
• 2 types: 1. Gravity type (Paterson’s filter)
2.Pressure type (Candy’s filter)
Steps involved:
1. Coagulation
2. Rapid Mixing
3. Flocculation
4. Sedimentation

14. • Coagulation: raw water treated with alum.
• Rapid mixing: subjected to violent agitation in
mixing chamber
• Flocculation: slow stirring in a flocculation chamber
for 30 mins. Formation of thick Aluminium hydroxide
• Sedimentation: Detained in sedimentation
chamber for 2-6 hrs-flocculent precipitate with
impurities.
• Filtration: partly clarified water is now
subjected to rapid sand filtration

15. Flow diagram of rapid sand filter plant
River
Alum
Consumption
Chlorine
Mixing
Chamb
er
Floccul
ation
Chamb
er
Sedimentati
on Tank Filters
Clear
water
storag
e

16. Filtration
• Alum floc, not removed by sedimentation :
held back on sand bed form slimy layer
comparable to zoogleal layer.
• Adsorb bacteria, oxidation of ammonia
• Loss of head up to 7-8 feet: filter subjected to
wash named BACKWASHING need
daily/weekly washing (15min),
by reversing the flow of water ( dislodges the
impurities).

17. Advantage
• Can deal with raw water directly
• Occupies less space
• Filtration is rapid
• Washing is easy

18. Comparison of rapid and slow sand filter
Features Rapid sand filter Slow sand filter
Space Occupies less space Occupies large space
Rate of filtration 200 m.g.a.d 2-3 m.g.a.d
Effective size of sand 0.4-0.7 mm 0.2-0.3 mm
Preliminary treatment Chemical coagulation and
sedimentation
Plain sedimentation
Washing Back washing Scraping the sand bed
Operation Highly skilled Less skilled
Loss of head allowed 6-8 feet (2-2.5 m) 4 feet (1.5 m)
Removal of turbidity Good Good
Removal of colour Good Fair
Removal of bacteria 98-99 % 99.9-99.99 %

19. III. DISINFECTION
Ideal disinfectant
• Capable of destroying pathogenic organism within the
contact time
• Not unduly influenced by range of physical /chemical
properties of water
• Doesn’t leave products of reaction which make water
toxic
• Available at a reasonable cost
• Leaves residual concentration to deal
with possible contamination
• Amenable to detection by rapid/simple
tests

20. Chlorination
• Supplement and not substitute of sand filtration
• Kills pathogenic bacteria but no effect on spores and
viruses (except high dose)
• Oxidizes iron/manganese /hydrogen sulphide
• Controls algae
• H2O + Cl2  HCl + HOCl
• HOCl H + OCl
• HCl is neutralized by alkalinity of water
• Disinfection action due to HYPOCHLOROUS ACID and OCl
• Acts best at pH 7 as more HOCl

21. Principles of Chlorination
1. water should be clear/ free of turbidity
2.Chlorine demand should be estimated.
• Amount of Cl added- residual Cl at end of contact
period (60 Min) at a given temp/pH
• At which point the Cl demand of water is met called
Break point

22. 3. Presence of free residual Cl for a contact
period of 1 hr is essential to kill bact/viruses.
4. Min recommended free Cl is 0.5 mg/L for 1
hr. Gives margin of safety for subsequent
contamination.
5. Correct dose of Cl = Cl demand+ 0.5
mg/L residual Cl

23. Orthotolidine (OT) Test
• Both free & combined Cl can be determined
• Water containing Cl+ reagent= yellow
colour(intensity varies with conc. )
• Reaction with free Cl is fast
• Reading: within 10 sec=free Cl
after 15-20 min=both free and
combined Cl

24. Orthotolodine-arsenite (OTA) Test
• Modification of OT test to identify free and
combined Cl separately
• Error caused by iron/nitrites/ manganese by
producing yellow color can be overcome

25. PURIFICATION OF WATER ON A SMALL
SCALE

26. 3 methods
• BOILING
• CHEMICAL DISINFECTION
• FILTRATION
Others
ULTRAVIOLET IRRADIATION
MULISTAGE REVERSE OSMOSIS
Household purification of water

27. • Rolling boil
• 10-20 minutes
• Kills bacteria,spores,cysts and ova
• Removes temporary hardness
BOILING

28. • Bleaching powder
• Chlorine solution
• High test hypochlorite
• Chlorine tablets
• Iodine
• Potassium permanganate
CHEMICAL DISINFECTION

29. • Chlorinated lime
• 33% of available chlorine
• Unstable compound
• Stabilised bleach
Bleaching powder

30. • From bleaching powder
• 4kg bleaching powder (25% available chlorine) + 20
litre water
• 1 drop of this solution---For disinfection of 1 L water
Chlorine solution

31. • 60-70% available chlorine
• More stable
High test hypochlorite/perchloron

32. • Halazone
• Costly
• Single tablet(0.5gm)-20 litres
Chlorine tablets

33. • Emergency disinfection
• 2 drops(2% ethanol solution) for 1 litre clear water
• 20-30 minutes contact time
Disadvantage:
Physiologically active
High cost
Iodine

34. • Powerful oxidising agent
• Kill vibrio cholera
Potassium permanganate

35. • Effective against bacteria, yeast, viruses, fungi, algae,
protozoa etc
• mercury vapour arc lamps emitting uv radiation
Ultraviolet irradiation

36. Advantages:
• Short period
• No foreign matter introduced
• No taste and odour produced
• Overexposure doesn’t result in harmful effects
Disadvantages:
• No residual effect
• Expensive
• Lack of rapid field test for assessing treatment
efficiency

37. • Reduces the hardness, heavy metals – arsenic, lead,
mercury – and eliminates micro organisms
• Removes dust, mud, and sand from water
Multistage reverse osmosis

38. WELL WATER
CHLORINATION…

39. Well water disinfection..
• During epidemics and after natural disaster.
• Most effective and cheapest method-chlorination
• DO NOT USE KMNO4.
• Best done at night.
• During epidemics
well should be disinfected
daily..

40. FINDING THE VOLUME OF WATER IN THE WELL
(
( 1

41. Finding the amount of bleaching powder.
• Chlorine demand estimated using HORROCKS
APPARATUS.
• 2.5 g for 1000L

42. Horrock’s apparatus
• To find out dose of Bleaching powder required for
disinfection
• Contents: 1. 6 white cups (200 ml each)
2. one black cup with a circular mark
inside
3. 2 metal spoons (2 g when level
filled)
4. 7 glass stirring rods
5. One special pipette
6. Two droppers
7. starch-iodide indicator solution
8. Instruction folder

44. Well water chlorination
• A) Find the volume of water in a well:
• By formula/Roughly calculated by counting the
number of rings of water
• (B) Find the amount of bleaching powder required
for disinfection
• By HORROCKS APPARATUS./ Roughly 1 ring of water
requires 1 matchbox full of bleaching powder

45. • C) Dissolve bleaching powder in water :
• The bleaching powder required for disinfecting the well is
placed in a bucket (not more than 100 g in one bucket of
water) and made into a thin paste.
• More water is added till the bucket is nearly three-
fourths full.
• The contents are stirred well, and allowed to sediment
for 5 to 10 minutes when lime settles down.
• The supernatant solution which is chlorine solution, is
transferred to another bucket, and the chalk or lime is
discarded. (Note : the lime sediment should not be
poured into the well, as it increases the hardness of well
water)

46. • (D) Delivery of chlorine solution into the well:
• The bucket containing the chlorine solution is
lowered some distance below the water surface ,
and the well water is agitated by moving the bucket
violently both vertically and laterally.
• This should be done several times so that the
chlorine solution mixes intimately with the water
inside the well

47. • E) Contact period:
• A minimum contact period of one hour is allowed
before the water is drawn for use
• So always better to do chlorination during evening or
night time after usage of well ,so that water can draw
after the next morning after chlorination for
adequate contact time.
• Advice regarding drinking boiled water to be given
even if chlorination is performed

48. • If there is any waterborne disease outbreak or water
contamination exists,
• SUPER CHLORINATION should be done
• For super chlorination, double the amount of
bleaching powder is required
• So 2 match box full of bleaching powder required
for 1 ring of water
• Superchlorination should be done daily until the
outbreak is over
• other steps are similar