Water purification techniques can purify water on a large, medium, or small scale. On a large scale, sources like rivers and lakes undergo screening, aeration, flocculation, sedimentation, filtration, and disinfection to remove contaminants. Methods include using coarse or fine screens, different types of aeration, adding chemicals like alum during coagulation, settling solids via sedimentation, and using sand or membrane filters along with chlorination, ozonation, or UV radiation for disinfection. On a medium scale from wells or springs, addition of chlorinated lime is used. Small scale purification involves boiling, adding chemicals like bleach or iodine, or demineralization through processes like reverse osmosis

1. WATER PURIFICATION
TECHNIQUES

2. WHAT IS WATER PURIFICATION ?
• Water treatment is the transition of dirty harmful ( contaminated ) water into
clean safe water ( Potable water).
• Freeing water from any kind of impurity it contains, such as contaminants or
microorganisams.

3. WHY PURIFY WATER ?
Water is of major importance to all living things.
To get rid of contaminants that can be harmful to our health.
The drinking water should be totally clean, pure and free of any disease causing MICROBES,
and that’s why it should be properly treated and DISINFECTED before using it for drinking
purpose.

4. METHODS OF PURIFYING WATER
LARGE SCALE
RIVERS
STREAMS
LAKES
MEDIUM SCALE
WELLS
SPRINGS
TANKS
SMALL SCALE
SMALL QUANTITY
DOMESTIC METHODS

5. PURIFICATION ON LARGE SCALE
When sources of water are Rivers, Streams, Lakes etc. Then water is purified by
a) Screening
b) Aeration
c) Flocculation
d) Sedimentation
e) Filtration
f) Disinfection
g) Storage

6. SCREENING
• Raw Material allows to pass through a screen having a large number of holes which removes the
small and large floating matters like Plastics, wooden material, leaves etc.
• Size of the floating substance should be greater than the hole size.
2 Types
Coarse Screen Fine Screen

7. SCREENING
COARSE SCREEN
• It is used when the raw water containing large
solid particles.
• It’s holes size is 6mm or larger
FINE SCREEN
• It is used when the raw water containing very
little sized solid particles.
• It’s holes size is 1.5 to 6mm

8. 2. AERATION
• Supply of air
• Water is brought in intimate contact with O2.
• Can be remove Odor/Gas like CO2, H2S and Fe2+.
• Basically used to treat ground water.
• Mainly there are 3 types of Aerators.
a) Spray nozzle aerator
b) Cascade aerator
c) Diffused air aerator

9. 3 TYPES OF AERATOR
SPRAY NOZZLE
AERATOR
 it is very costly
 maintenance required
 efficiency of releasing CO2 = 90%
H2S = 99%
CASCADE AERATOR
 it is very cheap.
 No maintenance required.
 Steps are made up of RCC ( Reinforced
Cement Concrete ).
 efficiency of releasing CO2 = 20% - 45%
H2S = 35%
DIFFUSED AIR
AERATOR
 it removes color and odor.
 it is very costly.
 maintenance required.

10. Diffused air aerator
Cascade Aerator

11. 3. COAGULATION/FLOCCULATION
• Main goal is to reduce the turbidity of the water.
• Removal of inorganic ( clay / silt ) and organic ( Algae, Bacteria, Virus, Protozoa and natural organic matters)
suspended in water by addition of some chemicals.
• Inorganic coagulants such as Aluminum sulfate ( Alum) or Iron(III) salts, such as Iron(III) chloride ( Ferric
chloride).
• When we add these chemicals to the water, form tiny sticky particles called “Floc” which attracts dirty particles.
• The combined weight of floc and suspended particles become heavy and sink to the bottom during sedimentation.
• Coagulation is a Rapid mixing process ( Detention time in seconds) and Flocculation is a gentle mixing process
• ( Detention time 15 to 45 minutes)

13. 4. SEDIMENTATION
• Using gravity to remove suspended solids from the water.
• The particles which is settle out from the suspension is called Sediment ( Sludge )
2 types
Plain Sedimentation
Sedimentation with
coagulation

14. PLAIN SEDIMENTATION
QUIESCENT TYPE
• Water is collected and kept in a tank
• Detention time is 24-36hrs
• Period of cleaning 8-12hrs
• Minimum 3 tanks required ( 2 operational &
1 standby)
CONTINUOUS FLOW TYPE
2 types
Horizontal
flow type
Vertical flow
type
Ex: Rectangular
sedimentation tank
Ex: Circular
sedimentation
tank

15. Vertical flow
type

16. 5. FILTRATION
• After separating most floc, the water is filtered as the final step to remove remaining suspended
particles and unsettled floc.
• Two commonly used filtration methods are :
 Sand filters
 Membrane filters

17. SAND FILTERS
RAPID SAND FILTER
• Most commonly used
• Water moves vertically through the sand
which often has a layer of activated carbon.
• To clean the filter, water passed upward
through the filter, opposite the normal
direction. It is called back washing.
SLOW SAND FILTER
• It is used where there is sufficient land and space.
• Water moves horizontally
• Constructed with finest sand at the top and gravels at
the bottom
• No backwash.
• Top layer of sand scrapped of when flow is eventually
obstructed by biological growth.

18. RAPID SAND
FILTER

19. MEMBRANE FILTERS
• Widely used for filtering both drinking water and sewage water
• It can remove all particles larger than 0.2µm
• They are widely used in drinking water industries.
• Available in wide range of defined pore size.
• Mainly made up of cellulose acetate.

21. 6. DISINFECTION
• To make drinking water free of any disease causing bacteria and other microbes.
3 methods
Chlorination Ozonation UV Radiation

22. CHLORINATION
• Chlorine is the most common cost-effective means of disinfecting water.
• The addition of a small amount of chlorine is highly effective against most bacteria, viruses, and
protozoa.
• But cysts (durable seed-like stages) formed by parasitic protozoa such as cryptosporidium and
giardia can survive chlorine.
• Chlorine is applied to water in one of Four forms:
Elemental chlorine (chlorine gas), hypochlorite solution (bleach), or dry calcium hypochlorite,
Chlorine tablet. All three forms produce free chlorine in water.

23. Elemental chlorine ( chlorine gas )

24. OZONATION
• Strongest disinfectant available.
• More effective against microbes than chlorination.
• Difficult to monitor and control under different condition.
• Process : Ozone (o3) is generated on-site at water treatment facilities bypassing dry oxygen or air
through a system of high voltage electrodes.

25. UV RADIATION
• When UV radiation penetrates the cell wall of an organism, it damages genetic material, and
prevents the cell from reproducing.
• Ultraviolet light is most typically generated from a low pressure or a medium pressure lamp
generating UV light.

27. PURIFICATION ON MEDIUM SCALE
• When sources of water are wells, springs, tanks etc.
• Then water is purified by the addition of bleaching powder/chlorinated lime as it is
 Cheep
 Easy to use
 Reliable and safe

28. PURIFICATION ON SMALL SCALE
• BOILING : For 5-10 minutes kills almost all organisms & removes temporary hardness.
• DISTILLATION : Not commonly used due to higher cost, used in labs. Etc.
BY ADDITION OF CHEMICALS :
• Bleaching powder
• Iodine solution
• KMnO4 (Potassium permanganate)
• Alum

29. DEMINERALIZATION
• Process of removing TDS from the water.
• Mainly used methods are :
 Membrane processes
a) Reverse Osmosis
b) Electodialysis
 Distillation

31. MCQ’S

32. 1) According to BIS the maximum permissible limit of dissolved solids in drinking water is
a) 1000 mg/l b) 500 mg/l c) 2000 mg/l d) 1500 mg/l
2) Indian Standard for drinking water is
a) IS 14543 b) IS 10500 c) IS 13428 d) IS 1165
3) Which of the following chemical is sometime added in the process of coagulation and
flocculation ?
a) Aluminum sulphate b) Aluminum oxide c) Calcium chloride d) None of these
4) The common methods used for disinfection in water treatment plants are
a) Chlorination c) UV light c) both (a) and (b) d) Phenolic solvent
5) Sedimentation is a physical process used in water treatment to
a) Remove particles that are less dense than water
b) Remove particles that are more dense than water
c) Remove the pertinacious material from the water
d) None of the above

33. 6) An addition of small dose of chlorine gas to the filtered water is known as
a) Sedimentation b) Filtration c) Coagulation d) Chlorination
7) The total dissolved solids (TDS) can be reduced by the following method
a) Distillation b) Reverse osmosis c) Ion Exchange d) all of the above
8) Devices remove materials which would damage equipment or interfere with a process.
a) Grit b) Screening c) Oxidation d) Reduction
9) Which is the primary force acting on the settleable particles ?
a) Gravitational force b) Centrifugal force c) Mechanical force d) Radial force
10) What is the product obtained when a coagulant is mixed with contaminated water ?
a) Sediment b) Acid c) Floc d) Grit
11) A reverse osmosis membrane is a semi permeable membrane that allows the passage of ?
a) Water b) Dissolved salts c) Organics d)Bacteria

34. 12) Which year was the safe drinking water act passed ?
a) 1990 b) 1992 c) 1994 d) 1996
13) Means the deactivation or killing of pathogens.
a) Reduction b) Disinfection c) Oxidation d) Pyrolysis
14) Which of the following is not a chemical disinfectant ?
a) UV b) Ozone c) Chlorine d) Bromine
15) Coliform bacteria in water is the indication of the presence of
a) Radio active waste b) Excess fertilizer c) Decaying animals and plants
d) Human feces
16) Which of the following substances are commonly used in a filter ?
a) Charcoal b) Sand c) both (a) & (b) d) Aluminium chloride

35. 17) The common methods used for disinfection in water treatment plants are
a) Chlorination b) UV light c) both (a) & (b) d) Phenolic solvent
18) As per BIS Standard, acceptable limit of the pH of drinking water is
a) 6.5 – 8.5 b) 5.5 – 7.5 c) 6.5 – 9.5 d) 7.5 – 9.5
19) What is TDS stands for ?
a) Total Diluted Solids b) Total Dissolved Solids c) Total Diagnosed Solids
d) Total Diffused Solids
20) The total dissolved solids (TDS) can be reduced by the following method
a) Ion Exchange b) Distillation c) Reverse Osmosis d) All of the above

36. THANKS