Unit2 -Purification of water

1. Course Title: Public Health
Engineering
course code : 22303
Name of Faculty : Ms. A. S. Dungarwal
Lecturer in Civil Engg. Department,
SHHJB Polytechnic, Chandwad
Dungarwal A. S.

2. Unit Title:
Purification of Water
Course Outcome (CO) :
Estimate the Quantity of
drinking water and wastewater generated.
Weightage: 18 Marks
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3. Content…..
⚫Purification of water
⚫Clariflocculator
⚫Miscellaneous water Treatments
⚫Advanced water Treatment
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4. Purification Of water
⚫Water purification is the transition of dirty harmful
(contaminated) water into clear safe water.
⚫Water purification generally means freeing water
from any kind of impurity it contains, such as
contaminants or micro-organisms.
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5. Purpose of water treatment
⚫To remove the various impurities of raw water
⚫To bring the quality of water to required standard.
⚫To make the raw water odour free and colourless.
⚫To remove the dissolved gas and impurities.
⚫To get rid of contaminants that can be detrimental
or harmful to our health.
⚫Up to 60% of the human body is filled with water
⚫Therefore the quality of water we drink is very
important
⚫To make the water potable.
⚫To make the water fit for domestic purpose.
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6. Methods of purification of Public water
Methodsofpurificationof
water
Screening
Plain sedimentation
Sedimentation aided
with coagulation
Filtration
Disinfection
Aeration
Softening
Miscellaneous
treatment
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7. Screening
⚫The method of removing
the floating matter of large
sizes with the help of
screens is called as
screening.
⚫It must to remove the
large sizes material,
otherwise it choke the
small pipes and may
damage the pumps and
other equipment.
⚫Only floating material
remains on the screen.
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8. Types of Screens
Types of screen
Based on the size
of opening
Coarse
screen
Medium
screen
Fine
screen
Based on the
condition of screen
Movable
bar type
Moving
screen
Fixed
bar type
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9. Aeration:
The method of exposing the
large surface of water so as to
absorb more oxygen and to
remove unpleasant odour and
gases and to oxidize Fe and
Mn in water is called as
aeration.
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10. Objectives/ Purpose of aeration :
• To increase the oxygen constant in water which gives the freshness
to the water.
• To oxidise iron and manganeous get precipitated and removed
afterward.
• To kill the bacteria by the process of agitating during aeration up to
some extent.
• To evolve the gas such as H2S. CO2 and to remove the volatile
matter. These type of impurities causes bad taste and odour.
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11. Method of Aeration
1. Using foundation
2. Using Spray Nozzels
3. Cascades or gravity aerators or free fall aerators
(a) Circular type
(b) Inclined apron type
( c) Straight steps type
4. Trickling bends or Multiple trays
5. Using air diffusing
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12. 1. Using foundations:
• In this methods, water is
sprayed in the form of fine
spray under the effect of
fountain action by pressure.
• In fountains, very small
droplets of water are formed
and increase the water surface
area of contact with air so as
to absorb more oxygen.
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13. 2. Using spray Nozzles:
In such type of methods number of
nozzles are located in a pool of water
and these nozzles discharges water
under pressure of about 7 N/cm2 to 14
N/ cm2
• There is considerable loss of head.
• spray nozzles removes the gases
like CO2 and H2S at about 90%.
• There are two types of nozzles such
as
(i) Fixed type or (ii) movable type may
be used Dungarwal A. S.

14. 3. Cascade Aeration or Gravity Aeration or Free fall
Aeration:
• Cascade Aeration in also called as gravity aerator or free fall
aerator.
• In cascade aerator there is free of water. The water is allowed to
fall at a height of 1 m to 3 m.
• It is a simple type of cascade consisting of a series of 3 to 4
steps in the following form:
i. Circular cascade
ii. Straight steps cascade
iii. Inclined apron cascade
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17. Trickling bed or multiple trays
Cascade Aerator
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18. 4. Trickling beds or multiple trays
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19. 5. Aeration by using air diffusion
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20. Limitation of aeration
• water becomes corrosive
• There is a possibility of air born contamination in
water.
• only suitable and economical in warmer climate.
• Iron and manganese get precipitated only by aeration
only in absence of organic matter.
• This method is not suitable to reduce or remove tested
and odour caused by non-volatile substance such as
oils of algae and chemicals discharged in industrial
wastes.
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21. Sedimentation
⚫The method or process of removing suspended
particles of impurities by gravitational settling is
called as sedimentation. A basin or bath in which
sedimentation process is carried out is termed as
sedimentation tank.
⚫It is also termed as settling tank, settling basin or
clarifier
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22. Types of sedimentation
⚫Plain sedimentation
⚫Sedimentation with coagulation
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23. Coagulation
⚫Coagulation is a chemical technique which is directed
towards the destabilization of the charged colloidal
particles.
⚫It is a process of removing fine clay particles and
colloidal impurities from water by addition of
required amount of chemicals known as coagulants
before sedimentation.
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24. Process of Coagulation
⚫Feeding-
❑Dry feeding
❑Wet feeding
⚫Mixing
⚫Flocculation
⚫Clarification or Sedimentation
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25. Coagulants
⚫Coagulants are certain chemicals when added into the
raw water forming an insoluble precipitation having
ability to remove the very fine suspended matter &
colloidal particle.
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26. Types of coagulants
⚫Aluminium sulphate or Alum
⚫Sodium aluminate
⚫Chlorinated copperas
⚫Ferrous sulphate & lime
⚫Magnesium carbonate & lime
⚫Ferric coagulants
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27. Factors affecting coagulants
⚫Type of coagulant
⚫Time & method of adding or mixing
⚫Dose of coagulant
⚫Characteristic of water like pH, temperature, nature &
quantity of suspended matter
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28. Jar test
⚫The optimum dose of coagulants or approximate
dosage of coagulants can be determined by test called
as jar test .
⚫This test is carried out in the laboratory.
⚫Apparatus consist of :
1) 4 or more beaker (1 to 2 lit capacity)
2) Stirring paddles
3) Electric motor
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29. Types of sedimentation
tank
Shape
Squar
e
Circula
r
Rectan
gular
direction of
flow
Horizo
ntal
Flow
Vertic
al
Flow
batch
proce
ss
Fill &
Draw
type
Nature of
working
Fill &
Draw
type
Contin
uous
flow
type
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30. Fill & Draw type
⚫Rectangular in plan.
⚫Water is filled, allowed for retention period of 30 to 60 hrs
(normally 24 hrs) then clear water is drawn from outlet
⚫Empty the tank and cleaning of sediment is done.
⚫Needs more detention period, labours and supervision, More
than one tanks
⚫Not used nowadays
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31. •Horizontal Flow Type
A.Rectangular tanks with longitudinal flow
Continuous type:
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32. Circular with radial flow
i. Circular with central feed ii. Circular with peripheral feed
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33. •Vertical Flow Type
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35. Factors Affecting Sedimentation
Process
⚫Detention Time
⚫Size , Shape & Specific gravity of suspended particles
⚫Velocity flow of water
⚫Viscosity of water
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36. Clariflocculator
⚫The Coagulation
Sedimentation plan
sometimes called
clariflocculator.
⚫To reduce the cost and
increase the efficiency of
coagulation plant hence
this process is carried out
in same unit.
⚫It is more suitable to
install circular
clarrifloculator in water
treatment work.
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37. PROCESS OF SEDIMENTATION WITH COAGULATION
⚫Feeding the coagulant
⚫Dry feeding
⚫Wet Feeding
⚫Mixing of coagulant
⚫Mixing basin with baffle walls
⚫Mixing basin with mechanical means
⚫Mixing channels
⚫Hydraulic jump method
⚫Compressed air method
⚫Centrifugal pumping method
⚫Flocculation
⚫Sedimentation
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39. Filtration
⚫The process of passing the water through the beds of
such granular material (filters) is known as Filtration.
Objective:
❑ To remove colour, odour, unplesant taste.
❑ To remove bacteria.
❑ To remove iron & manganese
❑ To make the water sparking & aesthetically
attractive.
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40. Theory of Filtration
⚫Mechanical Straining
⚫Flocculation & Sedimentation
⚫Biological Metabolism
⚫Electrolytic Action
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41. Classification of Filters
Filters
Gravity
Filters
Slow Sand
Filters
Rapid Sand
Filters
Pressure
Filters
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42. Slow Sand Filter
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43. Efficiency of SSF:
⚫98 – 99% bacteria removal
⚫removes turbidity up to 50 ppm
⚫Only 20 – 25 % of color removal
⚫not so efficient in removal of colloidal matters
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44. Rapid Sand Filter
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46. Efficiency of RSF:
⚫35-40 ppm turbidity removal
⚫removes colour below 3 ppm
⚫Less efficient in iron and manganese removal
⚫not efficient in odour removal
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47. Pressure Filter
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48. ⚫Pressure water treatment filter is a RSF contained
under pressure in a steel tank,
⚫which may be vertical or horizontal, depending on the
space available.
⚫Similar to gravity filters, the media in pressure filter
is usually sand or a combination of media also called
multimedia filters.
⚫Filtration rates are similar to gravity filters.
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49. Slow Sand Filter Rapid Sand Filter
Coagulation Not required Required.
Area requirement Very large Small.
Economy High cost Cheap and economical
Flexibility in operation Not Possible Possible.
Skilled supervisors Not required Essentially required
Maintenance cost Small More
Cleaning period 1 to 3 months 2 to 3 days
Method of cleaning Scrapping the top layers Agitation and back washing
Construction simple Complicated
Suitability
For small towns and villages where
land cost is less.
For big cities where land cost is high
Efficiency
More efficient for bacterial removal
and less for turbidity and colour
removal
Less efficient for bacterial removal
and more efficient for turbidity and
colour removal.
Difference Between SSF And RSF
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50. Disinfection
⚫The Process of destroying the disease causing
bacteria, micro-organisms, etc. from the water and
making it safe for use is called disinfection or
sterilization of water.
⚫To kill pathogenic bacteria.
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51. Characteristics of a good disinfectants:
⚫Should be able to destroy all harmful bacteria
economically within the contact time and in the wide
range of temperature and pH values.
⚫It should not render the water toxic or impart colour
and odour.
⚫It should be easily available at reasonable cost.
⚫It should be safe to handle and method of application
should be simple.
⚫It should persist in residual concentrations as
safeguard
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52. Methods of Disinfection
⚫Boiling
⚫Chlorination
⚫Ozonisation
⚫Potassium Permanganate
⚫Ultra-violet rays
⚫Use of iodine and bromine
⚫Treatment with silver or Electro katadyn process
⚫Excess lime
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53. 1. Boiling:
• Bacteria can be destroyed by boiling it for long period.
• It is an effective method but practically not possible to
boil huge amount of public water supply.
• It can only kill the existing germs but cannot take care of
future contamination.
2. Treatment with excess lime:
• It increases the pH of water making it extremely alkaline.
This extreme alkalinity has been detrimental to the
survival of bacteria, thus killing them partially or
completely.
• Treatment like recarbonation for removal of excess lime
after disinfection.
• It does not ensure safety against future contamination.Dungarwal A. S.

54. 3. Treatment with ozone:
• Unstable allotropic of oxygen , and readily breaks into
normal oxygen and release nascent oxygen.
• This nascent oxygen is powerful oxidizing agent and remove
the bacteria and organic matter from water and also remove
color, taste, odour from the water.
•This is very costly, required electricity for the formation of
ozone and does not ensure safety against future
contamination.
4. Treatment with ultra-violet rays:
• Invisible rays having wavelength of 1000-4000 mµ.
• These rays highly effective in killing all types of bacteria ,
thus producing a truly sterilized water.
• This method is very costly and needs technical know-how.
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55. 5. Treatment with potassium permanganate:
• A popular disinfectant for disinfecting well water supplies in
villages.
• The addition of potassium permanganate to water, produces
pink color.
• However , if pink color disappears, it shows that that is organic
matter is present in water.
• More quantity of potassium permanganate should be added,
until the pink color stands.
• Does not remover 100% bacteria from water.
6. Chlorination:
• Most commonly used disinfectant because:
a. It is cheap, reliable, easy to handle, easily measurable.
b. It is capable of proving residual disinfecting effect for long
periods, thus proving complete protection against future
contamination. Dungarwal A. S.

56. Forms of Application of Chlorine
⚫Bleaching Powder
⚫Chloramines (Chlorine + Ammonia)
⚫Chlorine gas or liquid chlorine
⚫Chlorine dioxide
⚫Chlorine Tablets
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57. Forms of Chlorination
⚫Plain chlorination or simple chlorination: To raw
water
⚫Pre-chlorination:Before treatment
⚫Post chlorination: After treatment
⚫Double or multiple chlorination: Two or more point
⚫Super chlorination: Application beyond break point
⚫De-chlorination: Removing chlorine
⚫Break point chlorination or free residual chlorination:
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58. Dungarwal A. S.

59. Advantages of Break point chlorination
❖ It will remove taste and odour .
❖ It will have adequate chlorine removal .
❖ It will Destroyed all diseases causing bacteria.
❖ It will complete the oxidation of ammonia and other
compounds .
❖ It will remove colour due to organic matter.
❖ It will remove manganese.
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60. Residual Chlorine
❏Low level amount of chlorine remaining in the water
after a certain period or contact time after its initial
application is called as Residual Chlorine.
❏Residual Chlorine is the amount of chlorine which
remains in a water after a certain period or contact
time.
❏Three forms of residual chlorine:
❏Free Chlorine
❏Combined Chlorine
❏Total residual Chlorine
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61. Free Chlorine:
The concentration of residual chlorine in water present as
dissolved gas( cl2); hypochlorite ion and hydrochlorous acid is
called as Free chlorine.
Combined Chlorine:
•Free chlorine that has combined with ammonia (NH3) or
other nitrogen-containing organic substances.
•Typically, chloramines are formed .
Total Chlorine:
The sum of free chlorine and combined chlorine is called as
total chlorine
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62. Chlorine Test
❏ Orthotolidine test
❏ Starch-iodised Test
❏ Orthotolidine -Arsenile test
❏ Orthotolidine test is most common and easy
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63. Flow Diagram of water Treatment
Scheme
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64. Dungarwal A. S.

65. Softening of water
⚫ The Process of removing soluble calcium and
magnesium salts from hard water is known as softening
of water.
⚫ In these process, the soluble salts are converted into the
insoluble salts.
⚫ These insoluble salts are in the form of precipitation (or
sludge) which can be removed by Filtration and soft
water can be obtained.
❑ Types of hardness: 1)Temporary hardness
2)Permanent
hardness
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66. Harmful Effects of Hard Water
Some of the most common signs of hard water include:
● Linens and clothes look dull and feel rough.
● Ugly stains on white porcelain and scale buildup on
faucets
● Low water pressure from showers due to clogged pipes.
● Chalky, white residue or spots appear on dishes.
● Strains appearing in the shower.
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67. Temporary Hardness
❏ Hardness of water due to the presence of soluble
bicarbonates of calcium and Magnesium is called
temporary hardness.
❏ When water containing dissolved carbon dioxide passes
over solid carbonates (chalk or limestone deposits etc.),
these compounds get dissolved in water.
❏ Rainwater and distilled water are always soft because
they do not have dissolved (soluble) salts.
❏ Methods for Removing temporary hardness
❏ Boiling Of Water
❏ Addition Of lime
❏ By clark’s method
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68. ❏ Boiling
❏ Soluble bicarbonates are converted into insoluble carbonates
which are removed by filtration.
❏ Reactions: Ca(HCO3)2 → ΔCaCo3↓ + H2O + CO2
⇒ Mg(HCO3)2 → ΔMgCO3↓ + H2O + CO2
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69. ❏ Addition of lime
❏ By adding slaked lime [Ca (OH) 2] to hard water, insoluble carbonates
are formed.
❏ By Clark’s method
❏ Calcium hydroxide is Clark’s reagent. It removes the hardness of water
by converting bicarbonates into carbonate.
❏ Reaction: Ca(OH)2 + Ca(HCO3)2 → 2CaCO3↓ + 2H2O
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70. Permanent Hardness
❏ Permanent hardness in water is hardness due to the
presence of the chlorides, nitrates and sulphates of
calcium and magnesium, which will not be precipitated
by boiling.
❏ The lime scale can build up on the inside of the pipe
restricting the flow of water or causing a blockage.
❏ This can happen in industry where hot water is used.
❏ It is also known as NonCarbonate hardness.
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71. Methods of removing permanent
hardness
⚫ Soda-lime process
⚫ Zeolite process
⚫ Ion exchange method or demineralization
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72. Soda lime process
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73. zeolite process or Permutit
process
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74. Ion Exchange process
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75. Defluoridation technique
⚫ It is the method of removing the excess quantity of
fluoride from potable water.
⚫ Methods of defluoridation
⚫ bone charcoal
⚫ activated carbon
⚫ contact precipitation
⚫ Nalgonda technique
⚫ Activated alumina
⚫ soils, clays and minerals
⚫ lime Soda process
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76. Advanced water treatment
❏ Electrodialysis
❏ Reverse osmosis
❏ Solvent extraction
❏ Solar distillation
❏ freezing Method
❏ Distillation
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77. Electro dialysis method
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78. Reverse osmosis
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79. Ro System
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80. Freezing method
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81. Solar Distillation
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82. Distillation
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