This presentation provides with information regarding the processes , methods , applications of Water Treatment and simple design of water treatment filters. It incorporates chlorination, aeration, and other miscellaneous methods for water treatment

1. Ch-6 Water Treatment
Group members:
Mani (079)
Manisha(080)
Manoj(081)
Meman(082)
Nabin(083)
Narace(084)
Tutor:
Asst. Prof. Shukra Raj Paudel
Department of Civil Engineering
IOE, Tribhuvan University
2019-01-22
1

2. At the end of the presentation, students will learn about
Objectives of the presentation
1. Types of filters and their working principle
2. Methods of disinfection
3. Chlorination and its types and methods
4. Temporary & permanent Hardness in water
5. Aeration of water and its methods
6. Miscellaneous treatments of water
2

3. Presentation outline
6.6 Filtration
6.7 Disinfection
6.8 Softening
6.9 Miscellaneous treatment
3

4. 6.6 Filtration
Filtration is separation of solids from fluids by using a
porous medium through which only the fluid can pass.
In water supply scheme, this porous medium is usually
sand supported on a bed of gravel.
http://www.svensktvatten.se
Simple filter diagram
4

5. 6.6.2 Types of filters
Slow sand
filters
Rapid sand
filters
Pressure
filters
Slow sand filter water treatment plant, AssosaRapid sand filter in Bret lake, SwitzerlandPressure sand filter used in Pune, India
The first modern
rapid sand filter
was operated in
1920, in the
USA
5

6. Rapid sand filters
• Most commonly used filters.
• Faster than slow sand filters
• Filtration rate :3000-6000 lit/hr/m2
• Smaller than slow sand filters
http://napier-reid.com/products/gravity-filtration-systems/
Unfiltered water flows
under gravity , so these
are also called rapid
gravity filters
6

7. Enclosure
tank
Filter
media
Base
material
Under
drainage
system
Appurtenances
Parts of rapid sand filter
Enclosure tank
Perforated pipes
Under drainsCentral drain
Base material
Gravel
Filter media
Sand
Wash trough
7

8. 8

9. 2. Filter media Sand
• Thickness of 60 to 75 cm
• Effective size varies from 0.45 to 0.70 mm
• Cu varies from 1.3 to 1.7 (avg-1.5)
• Higher value of effective size and lower Cu causes
increase in void spaces resulting in higher rate of
filtration.
1. Enclosure tank
• Rectangular ,water tight
• Made of stone or brick masonry or concrete.
• Depth of 2.5 to 3.5 m
• Length to width ratio is 1.25 to 1.35
• Surface area of 10 to 50 m2
9

10. D60 = Cu x D10 D10 = effective size
Cu = Coeff. of uniformity
D60 = desired value of filter sand
Pusable = 2(P60 - P10 ) Pusable = % of usable sand
P60 = % of sand smaller than D60
Preparation of filter sand
Ptoo fine = P10 -10% Pusable
Ptoo fine = P10 -0.1 [2(P60 - P10 ) ]
Ptoo fine = 1.2 P10 -0.2 P60
Ptoo coarse = P60 - 40% Pusable
Ptoo fine = P60 -0.4 [2(P60 -P10 ) ]
Ptoo fine = 1.8 P60 -0.8 P10
10

11. The sizes of sand
below D too fine and
above D too coarse can be
removed by Sieving .
The finer portion can
also be removed by
Sand Washer
Higher
effective
size
Lower
Cu
Increased
voids
Higher
rate of
filtration
11

12. https://www.in-eko.com/products
12

13. Estimation of thickness of sand bed
• Sand bed should be thick enough to prevent
breakthrough by floc
• The minimum thickness is calculated using
Hudson formula ;
•
Qd3h
𝐿
= Bi x 29323
Where Q = rate of filtration in m³
d = sand size in mm
h = terminal loss of head in cm
L = thickness of sand bed in m
Bi= break through index
Minimum depth of sand bed : not less than 60 cm
13

14. 3. Base material Gravel
• Supports the filter media
• Consists of 45 to 60 cm of gravel bed
• Gravel bed is graded in layers in ascending order
Layer Thickness size
Top layer 15 cm 2-6mm
Intermediate
layer
15 cm
15 cm
6-12mm
12-20mm
Bottom layer 15cm 20-50mm
Total 60 cm
14

15. Estimation of gravel size gradation
Required depth ‘L’ in cm of a component gravel layer
of size ‘d’ mm can be computed by empirical formula:
L = 2.54k (log10 d) ; k ranges from 10-14
Example: If k= 12; d=2mm, L1 is given as
L1 = 2.54 x 12x log10 2 = 9.2 cm
Thus thickness of layer of gravel of size 2 mm to be
provided at top is 9.2 cm.
15

16. Similarly, for gravel of size 5mm, L2 is given as
L2 = 2.54 x 12x log105 = 21.3 cm
Thus the thickness of next layer of gravel of size
5 mm is (21.3-9.2)=12.1 cm
The same process is repeated upto 50mm,
And thickness of layers are calculated
16

17. Can u guess ?
a?
b?
c?
17

18. 4. Under drainage system
• Used to collect filtered water uniformly.
• Provides uniform distribution for backwash.
• Delivers filtered water to clean water reservoir
• Consists of central drain or manifold and lateral drains
18

19. Perforated system Pipe strainer system
Perforations are provided
at the bottom of laterals ,
30o with vertical
Perforations are provided
at the top of laterals with
strainers
Requires more water for
backwashing.
600 liters/min/m2 of filter
area
Requires comparatively
less water.
250 liters/min/m2 of filter
area
High velocity wash Low velocity wash
Water from wash water
overhead tank is used for
backwashing
Compressed air is used
for purpose of back
washing
Underdrains are basically of two types 19

20. 1. Ratio of length to diameter < 60
2. Spacing of laterals ,15 - 30 cm
3. CSA of manifold =1.5 to 2 x sum of CSA of laterals
4. Dia of perforations = 5 - 12 mm, 30o with vertical
5. Spacing of perforations = 80 mm for 5 mm dia
200 mm for 12 mm dia
General rules for design of under drainage system
20

21. 6. Ratio of TA of perforations to filter area = 0.003
7. Ratio of TA of perforations to CSA of laterals
< 0.5 for 12mm dia &
< 0.25 for 5 mm dia
21

22. 5. Appurtenances
a. Wash water trough
• at upper portion of filter tank to collect back wash water.
• spacing is kept 1.2 to 2 m
• top edge of trough should be above the highest elevation
of sand in expanded form to prevent washing away of sand.
• Free board of 5 cm should be provided.
• For fixing the size of trough
Q= total water received by trough in m3/s
b= width of trough in m
h= depth of water n trough in m
Q= 1.376 bh3/2
22

23. Perforated
pipesUnder drainsCentral drain
Wash trough
23

24. b. Air compressor
• to carry out agitation of sand grains during back
washing.
• Used in pipe and strainer system
• Should have capacity of supplying compressed air
at 0.60 to 0.80 m3 per m2 of filter area for 5 mins
c. Rate control device
• to maintain constant rate of filtration irrespective
of head loss.
• Simplex rate controller automatically controls the
rate of filtration
24

25. 25

26. d. Miscellaneous accessories
• Head loss meters
• Flow rate meters
• Valves
https://en.wikipedia.org/wiki
26

27. Filtration
proceeds
Trapping of particles
in sand pores
Increase in
head loss
Decrease in
filtration rate
Back washing
27

28. Back washing
• When maximum allowable head loss of 2.5 to 3 m is
reached backwashing is required.
• It is done to remove trapped materials
and rejuvenate filter sand.
• Filtered water is used
• Not exceeding 2-3% of treated water
• Should be done for 10 mins at 600 lit/min/m2
• Should be done in 1 to 3 days for 10-15 mins as rapid
sand filters get clogged faster
28

29. http://www.hitachi.com/businesses/
29

30. 1. Close valve 1
2. Close valve 2
3. Open valve 6
4. Close valve 6
5. Open valve 4
6. Close valve 4
7. Close valve 3
8. Open valve 1
9. Close valve 5
10.Open valve 2
11.Open valve 1
30

31. Surface wash
• Top layer of sand is dirtiest and requires more cleaning.
• Back washing is not sufficient
• Wash water is applied from top using high pressure
water jets
• Two types
a) fixed type surface wash
b) rotary type surface wash
• Rate of surface wash : 200 to 400 lit/min/m2
under pressure of 20 to 30 m water head
31

32. Efficiency of Rapid sand filter
• less efficient in the removal of
bacterial load.
• Remove about 80 to 90% of
bacterial load
Bacterial load
• Can remove turbidity to the
extent of 35 to 40 ppm.
• Water should be pretreated in
coagulation sedimentation tank
Turbidity
• The intensity of colour can be
brought down below 3 on cobalt
scale
Colour
32

33. https://www.khnwatertreatment.com/
33

34. Numerical problem
Ex 6.13 Design a rapid sand filter for a population of 60000
nos for a newly growing urban area.
34

35. 35

36. Numerical problem
Ex 6.14 A city has a population of 150,000 with a water
supply rate of 150 lpcd. Determine the number and size of
rapid sand filters required. Assume required data suitably.
36

37. 37

38. These are type of rapid sand filters in closed
cylindrical tanks through which water to be treated
is passes under pressure of 0.3 to 0.7 N/m2
Pressure filters
Diameter : 1.5 – 3m
Length or Height: 3.5 – 8 m
Difference in operation of rapid sand & pressure filter is:
Coagulated raw material is fed directly to filters without mixing,
flocculation and sedimentation in case of pressure filters
38

39. 1.Horizontal type 2. Vertical type
Two types
39

40. https://www.environmental-expert.com/
40

41. Features of pressure filters
• Convenient for small schemes like swimming
pool and colonies
• Not suitable for public supply scheme due to
less efficiency
• Less efficient in terms of bacterial removal,
color and turbidity removal
• Higher rate of filtration than rapid sand filters.
6000-15000 liters/hr/m2 of filter area
41

42. 6.7 Disinfection
Filtration alone doesn’t make water safe for
drinking purpose
Water disinfection means the removal, deactivation
or killing of pathogenic microorganisms.
The substance or agent used for disinfection is
called Disinfectant.
42

43. 6.7.1 Methods of Disinfection
• Boiling method
• Excess lime treatment
• Iodine treatment
• Bromine treatment
• Ozone treatment
• KMnO4 treatment
• Silver treatment
• Ultra violet ray treatment
43

44. Methods Key points
Boiling
method
• 15 mins of boiling kills all bacteria.
• Most effective method.
• But only applicable in domestic scale.
• Does not prevent future possible contamination.
Excess lime
treatment
method
• Bacteria & E-coli do not survive in pH>9.5 & pH<3
• Lime addition increases ph of water & kills
bacteria for disinfection
• Amount of lime added = 10-20 ppm.
• excess lime need to removed by recarbonation.
Iodine
treatment
• I2+ water= Hypoiodous acid(HIO) acts as
disinfectant.
• HIO gives hypoiodite ion (IO) , also disinfectant
• I2, HIO, IO all increases ph of water
• Usual dose=8mg/L contact time= 5 mins
• Costlier than Cl so used only for domestic
purpose.
44

45. Methods • Key points
Bromine
treatment
• Br2+ water= Hypobromous acid(HBrO) acts as
disinfectant.
• HBrO gives hypobromite ion (OBr) , also
disinfectant
• Bacterial effect of Br2 is similar to that of
chlorine
• Higher cost & less effectiveness so used in
small scale
Ozone
treatment
• Ozones breaksdown to give O2 and [O]
• Uses Nascent oxygen (O) to kill bacteria &
effectively oxidizes organic matter
• Produced at point of use.
• Usual dosage=2 to 3 ppm contact time= 10
minutes
45

46. Methods Key points
Silver
treatment
• Silver is powerful disinfectant
• Destroys bacterial spores & algae present in
water
• Used as silver salt or passing potential through
silver electrodes
• Used in Electro-katadyn process
• Expensive process . Used in small installations
Ultra violet ray
treatment
• Effective for killing bacteria & algae spores
• Requires large exposure area and long time
• UV rays from mercury vapor lamps kill bacteria
• Wavelength of light used: 0.490-0.149 microns
• Depth of water<10 cm; turbidity< 20 NTU
• Effective method but costly. Used in small
installations
NTU= Nephelometric Turbidity Unit
46

47. Method Keypoints
KMnO4
treatment
• KMnO4 is a powerful oxidizing agent
• Effectively removes taste producing organic matter
• Specially effective in cholera bacteria
• Used in rural areas for waters extracted from wells
• Normal dosage= 1to 2 mg/L contact time= 6-4 hrs
• Imparts pink color to water
• Treated water should not be used within 48 hrs of
treatment
https://www.walmart.ca/en
47

48. 6.7.2 Chlorination
• most commonly used method of disinfection.
• Chlorine or its compounds used as disinfectant.
• Cheap, reliable, easy to handle and soluble in water.
• Cl2 + H2O HOCl + H+ + Cl- (Hydrolysis rxn)
• HOCl H+ + OCl- (ionization)
48

49. Nascent oxygen theory Enzymatic hypothesis
theory
Chlorine on water produces
nascent oxygen [O] and
oxidizes unicellular
organisms and kills them
Chlorine penetrates through
cell wall of organisms and
reacts with enzymes
essential for bacterial life
• Theories that explain disinfection action by
chlorine are as
1. Nascent Oxygen theory
2. Enzymatic hypothesis theory
49

50. • The addition of chlorine doesn’t produce any
significant change in pH value of water due to its
buffering capacity
• Hypochlorous acid (HOCl) and Hypochlorite ion (OCl- )
are the disinfecting agents
• Undissociated HOCl is 80-100 times more powerful
than OCl-
• HOCl, OCl- and Cl2
existing in water are
defined as free
residual chlorine.
50

51. pH of water above 3
100% HOCl
Further increase in pH
HOCl  OCl-
% of HOCl decrease
% of OCl- increases
pH of water above 9.5
100% OCl-
51

52. • What is Chlorine Demand?
• The amount of chlorine consumed in killing
pathogenic organisms as well as oxidation of
organic compounds and organic materials present
in water is Chlorine Demand of Water.
• What is Residual chlorine?
• Amount of chlorine remaining in water after
chlorine demand has been fulfilled.
Terms to be familiar with 52

53. • What is Dosage of chlorine?
• The dose of chlorine which leaves a residual
chlorine of 0.2 mg/ litres at end of 10 mins of
contact period is the optimum dose of chlorine.
• What is Contact Time?
• The time taken to kill the pathogenic organisms
after the application of chlorine is called contact
time. It is about 10 minutes for free chlorine but
can go upto 30- 60 minutes for combined chlorine
Chlorine dose = Chlorine demand + Residual chlorine
53

54. • What is Combined Available chlorine?
• These are compounds formed when free chlorine reacts
with ammonia, protein, amino acids, phenol , etc in
water to form chloroamines and chloro- derivatives
• Mono chloramine and dichloramine have 25 times less
disinfecting power than free chlorine
• Trichloramine has 0 disinfecting property
54

55. Ex 6.15 For disinfecting water supply, it is required to treat one
million litres of daily water supply with 0.6 ppm of chlorine, if the
beaching powder containing 35% chlorine is used as
disinfectant, calculate the amount of bleaching powder required
per day. (IOE, 2061 poush).
Solution,
Quantity of water to be disinfected= 1MLD =1 x 106 liters/day
Chlorine dose required= 0.6 ppm = 0.6 mg/l
Quantity of chlorine required= =0.6 kg/day
Bleaching powder contains 35% of chlorine required
So,quantity of bleaching powder requires= =1.71 kg/day
0.6 x 1 x 106
106
0.6
0.35
55

56. 56

57. 6.7.3 Types of Chlorine
Types
Bleaching powder
Chloramines
Chlorine gas or liquid
chlorine
Chlorine dioxide gas
57

58. 1. Bleaching
powder
or
Hypochlorite
• Bleaching powder is chlorinated lime .Ca(OCl)2.
• Ca(OCl)2 Ca++ + 2OCl-
(Hydrolysis)
• H+ + OCl- HOCl (HypoChlorination)
• Bleaching powder contains 30 to 35 % available
chlorine
• 0.5 to 2.5 kg per million liters of water is
required.
• Used for small installations like swimming pool
and colonies.
2.
Chloramines
• Chloramines are compounds formed by reaction
between ammonia and chlorine.
• Reactions are slow so treated water should be
supplied after 20mins to 1 hour.
• No bad taste or odor like in case od free
chlorine.
58

59. 3.
Chlorine
gas
or
Liquid
chlorine
• Cl gas may be fed directly to water supply or
first dissolved in small flow of water & the
chlorine solution is fed to water supply.
• Choking and corrosion of pipes may take place
by use of Cl gas.
• A chlorinator is used to supply regulated
quantity of chlorine.
• Types: a) Pressure type gravity fed b) Vacuum
type chlorinator.
4.
Chlorine
dioxide gas
(ClO2)
• 2NaClO2 + Cl2 2NaCl + 2ClO2
• ClO2 is a very effective and powerful
disinfectant and has 2.5 time the oxidizing
power of chlorine.
• Dosage: 0.5 to 1.5 ppm.
• High cost of production makes it uneconomical.
59

60. 6.7.4 Forms of Chlorine
Depending upon the stage of treatment at which
chlorine is applied
Plain chlorination
Pre-chlorination
Post- chlorination
Double or multiple chlorination
Break point chlorination
Super chlorination
Dechlorination
60

61. 1) Plain Chlorination
• only chlorine treatment is done to water and supplied
to consumers.
• removes bacteria, color impurities, algae growth
• Dosage = 0.5 to 1 ppm
2) Pre-chlorination
• treatment of raw water with chlorine before water
enters the sedimentation tanks.
• improves coagulation and reduces the quantity of
coagulants required
• Reduces taste and odor impurities and controls algae
growth.
• Reduces bacterial load on filters and maintains longer
filter runs
• Prevents putrefaction of sludge in purification tank
61

62. 3) Post- chlorination
• Addition of chlorine after all the purification treatments
are done.
• Dosage should be such that 0.1 to 0.2 ppm of
residual chlorine occurs at point of entry into
distribution system.
• Provides protection against contamination in the
distribution system.
62

63. 4) Double or Multiple chlorination
• Chlorine is applied to water at two points in the
purification process
• This is adopted when raw water is highly
contaminated with large amount of bacteria
• When chlorination is done in two phases as, pre
chlorination and post chlorination, it is called double
chlorination
• If done more than twice ,called multiple chlorination
63

64. 5) Break point chlorination
• it is the application to chlorine to water with chlorine dose equal
to or slightly higher than that at which break point occurs.
At Zero chlorine demand applied
chlorine occurs as residual
chlorine. This is represented by
Line A(45o slope)
Point C: maxm residual chlorine
Point D: break point
Break point is the point on applied residual chlorine
curve where all the residual chlorine is free chlorine
64

65. Advantages of break point chlorination
1. Removes taste and odour
2. Removes bacteria
3. Leaves desired residual chlorine
4. Completes oxidation of ammonia and
other compounds
5. Removes manganese
Break point is affected by free ammonia present in water
65

66. 6) Super chlorination
• Chlorine is applied to water beyond the stage of break
point.
• Residual chlorine of 0.5 to 2 ppm after break point.
• Removes odour and taste
• Rentention period : 30 to 60 mins
• Commonly done at the end of treatment process
• Excess Cl imparts unpleasant smell & taste
• Adopted when there is epidemic in locality.
66

67. 7) Dechlorination
• The process of removing excess chlorine from water.
• Adopted to avoid chlorinous taste and smell
• (Na2S2O3) sodium thiosulphate, (Na2S2O5 )sodium meta
bisulphate, (SO2 ) Sulphur dioxide may be used
• SO2 +Cl2+2H2O  H2SO4 +2HCl
• Ammonia( NH3) converts Cl to chloramines
• Activated carbon can also be used in powder form
• Aeration , exposure to sunlight ,Mg metal is also used
67

68. Remember
Dechlorination?
Here is why we
need it.
68

69. Factors
effecting
efficiency of
chlorination
Turbidity
Presence of
metallic
compounds
Ammonia
compounds
pH of
water
Temperature
Time of
contact
Concentration
of
microorganisms
69

70. Factors Key points
1. turbidity Decreases free residual chlorine
suspended matter consume chlorine
2.Presence
of metallic
compounds
Fe and Mn consume large amount of Cl to
oxidize and forms precipitate
Less chlorine is available for disinfection
3. Ammonia
compounds
Forms chloramines which is less effective
than free chlorine.
Less Cl available for disinfection
Decreases speed of disinfection
And requires more chlorine
4. pH of
water
At higher pH, more OCl- and less HOCl- is
present
Higher pH decreases efficiency of
chlorination
70

71. Factors Key points
5.Temperature
of water
Reduction in temperature decreases the
efficiency of chlorination
Requirement of residual chlorine increases
with decrease in temperature
6. Time of
contact
Bacteria are not instantly killed by chlorine
Certain contact time is required for efficient
killing of bacteria
Contact time for free chlorine: 30 mins
Contact time for combined Cl: 60 mins
7.
Concentration
of micro
organsims
Microrganisms include bacteria or viruses
Effective removal of E- coli means
satisfactory disinfection.
Virus require longer contact time and higher
concentration of chlorine for disinfection
E- coli cause intestinal diseases in human beings
71

72. 6.8 Softening of water
• Process of removing hardness from water.
• Hardness prevents the formation of lather with soap.
• Hardness of water is caused by the presence of
bicarbonates, sulphates, chlorides and nitrates
Ca,Mg,Sr
Hardness of
water
Temporary
hardness
Permanent
hardness
72

73. Removal of temporary hardness
1. Boiling Method
Ca(HCO3)2 → CaCO3 + CO2 + H2O
Mg(HCO3)2 → MgCO3 + CO2 + H2O
This method is not economically feasible
So not in practice.
Suitable only for domestic purpose.
73

74. 2. Lime treatment Method
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 +2H2O
Mg(HCO3)2 + Ca(OH)2 → CaCO3 + MgCO3 + 2H2O
Removal of Temporary Hardness
https://infograph.venngage.com
• These precipitates are
insoluble in water
• Removed by
sedimentation tanks or
filtration units
74

75. Removal of Permanent Hardness
1.Lime soda method
2.Zeolite method
3.Deionization method
These methods can also be used to
remove temporary hardness
75

76. Lime Soda method
Advantages Disadvantages
Simple and economical Large quantity of sludge
Less coagulant required Requires skilled provision
Increases pH , decreases
corrosion of pipes
Incrustation of pipes and
clogging of filters
Iron and manganese are
reduced
Hardness is not completely
removed
Kills pathogens
Lime [Ca(OH)2] and sodium carbonate [Na2CO3] (or
soda ash) are used
76

77. Zeolite method
Ion exchange resin called Zeolite
(2Sio2.Al2O3.Na2O) is used.
Naturally available Zeolite is called
Green sand or Glauconite
Advantages Disadvantages
No sludge formed Unsuitable for highly turbid
water
Compact design requires less
space
Unsuitable for water containing
Fe & Mn
Zero hardness can be achieved Not suitable for acidic water
Automatic process and low
initial cost
Damage to Zeolite & equipment
occurs
Free from danger of excess
chemicals
Bacterial growth can occur in
beds
77

78. Deionization method
In this method, another Zeolite called Zeo-karbs are
used. These exchange all cations including sodium
from hydrogen.
78

79. 6.9 Miscellaneous treatment
These are treatments dealing with the removal of iron ,
manganese, dissolved gases, color, odor, taste which
still remain in water after application of previous
treatments.
1. Aeration
2. Removal of iron and manganese
3. Removal of color, odor, taste
79

80. 6.9.1 Aeration
Water is brought in intimate contact with
air so that it can absorb oxygen.
Carbon dioxide along with other gases
are released.
Source :Bob Lusk OutdoorsSource:Indiamart
80

81. Purpose of aeration
• Removes taste and odour from
organic decomposition.
• Increases Dissolved Oxygen
Content.
• Reduces CO2 content and raises
pH value.
• Fe and Mg are converted to
insoluble states and can be
precipitated and removed
• Kills bacteria to some extent
81

82. Method of aeration
Aerators are used for aeration.
1. Free fall aerators or gravity aerators
a) cascade aerators
b) inclined apron aerators
c) slat tray aerators
d) gravity bed aerators
2. Spray aerators
3. Air diffuser basins
https://www.youtube.com/watch?v=sMj4ESEsI6k
82

83. Cascade aerator
• Consists of series of steps
of concrete or metal.
• Water is allowed to fall
through height of 1 to 3
meters
• 50 – 60% reduction in CO2
content
• Examples are weirs and
waterfalls
83

84. Inclined apron aerator
• Water is allowed to fall along and inclined plane studded
with riffle plates
• Breaking of sheets of water causes agitation of water &
consequent aeration
84

85. Slate tray erator
• Most commonly used type
• Consists of closely stacked
superimposed wood slat
trays.
• Aeration takes place during
the falling of water from one
tray to another.
• 4-9 trays with spacing of
300 to 750 mm spacing.
• 65- 90% CO2 reduction
85

86. 86

87. Gravel bed Aerator
• Most effectively removes
CO2
• Water is allowed to
trickle down cascading
bed of coke, limestone,
or anthracite as air is
blown upwards
• Thickness of gravel bed
vary from 1 to 1.5 m.
87

88. Spray Aerators
• water is distributed into air in
the form of small droplets by
means of orifices or nozzles
mounted on a stationary pipe
system
• Nozzles have diameter
varying from 10 to 40 mm at
interval of 0.5 to 1 m
• Reduces CO2 by 70-90 %
88

89. Air diffusion
• Compressed air is blown through network of perforated
pipes from the bottom of aeration tank (3 to 5 m in
depth).
• Rising air bubble cause aeration.
89

90. 6.9.2 Removal of Iron and Manganese
• Iron and manganese are generally presented in water
either in suspension as hydrate oxide or in solution as
bicarbonates.
• Hydroxides can be removed by normal treatments but
bicarbonates in special treatment.
According to NDWQS,
Iron and manganese should not be
more than 0.3 to 0.2 mg/l
NDWQS is National Drinking Water Quality Standards.
90

91. Effects of Fe & Mn
Unpleasant odor and taste
Straining & Corrosion of pipes
Pipe blockage
Red and brown colored water
Iron induces bacterial growth
Chemical reaction in industrial works
91

92. Unpleasant smell and taste
Straining and corrosion in pipes Blockage in pipes
https://www.expressdrainagesolutions.co.uk/
92

93. Red and brown colored water
https://idahowatersolutions.com
Iron induced bacterial growth
https://www.nature.com/articles/ismej2016
186.pdf?origin=ppub
93

94. 1) Aeration followed by sedimentation and filtration
Aeration
Coagulation
Sedimentation
Filtration
Aeration converts dissolved ferrous
and manganese compounds to
insoluble form
4Fe(HCO3)2 + 2H2O + O2 4Fe(OH)3 + 8CO2
6Mn(HCO3)2 + 3O2 6MnO2 + 2CO2 + 2H2O
Methods of removal of Fe and Mn 94

95. 2) Base exchange method
Manganese Zeolite is used for treatment.
Water passes through bed of
manganese zeolite.
Fe and Mn substitute Na
ions in zeolite
Insoluble hydroxides of Fe
and Mn are formed
Zeolite beds fliter the
insoluble hydroxides
Removal of Fe and Mn
KMnO4 is used to regenerate the zeolite beds
95

96. 3) Chlorination followed by sedimentation and filtration
Oxidation of Fe and
Mn by Chlorine
Precipitation of
hydroxides of Fe
and Mn
Sedimentation
Filtration
Removal of Iron
and Manganese
from water
96

97. Organic
&
vegetable
matter
Industrial
waste &
domestic
sewage
Dissolved
gases
Dissolved
mineral
matter
Micro-
organisms
6.9.3 Removal of color, odour and taste
Objectionable color, odour and taste may be caused due to
97

98. Methods of removal of color odour & taste
1. Treatment by activated carbon
2. Treatment by using copper sulphate
Activated carbon
• can be used as filter
media or fine powder feed.
• It absorbs the organic
compounds and removes
color taste and odour
• Usual dosage varies from
5 to 20 mg/l
Copper Sulphate
• Used in powder or crystal
form
• Controls growth of algae
bacteria and aquatic weed
• Usual dosage varies from
0.3 to 0.6 mg/l
98

99. https://www.elgalabwater.com/
https://naturalake.com/reasons-to-
reduce-copper-sulfate/
99

100. Lets take a quiz
What kind of aerator is this?
100

101. I am X. I kill 99.99% germs
I spare that 0.01 % So it can deliver a message
To tell all the other germs what happens when u go in
drinking water supply
Who is X?
101

102. Do u know what this is?
102

103. How can u help Bob?
103

104. Thank you!
Namaste
105