This slide only contains the water treatment processes in the water supply system. This is based on the IOE syllabus.

1. 127, Rudra Khadka
128, Rupak Pokhrel
129, Safal Poudel
131, Sagar Bhandari
132, Sagar Bist
Tutor:
Asst. Prof. Shukra Raj Paudel
Department Of
Civil Engineering
IOE, Tribhuvan University
15 DEC 2019
Group Members:
127, Rudra Khadka
128, Rupak Pokhrel
129, Safal Poudel
131, Sagar Bhandari
132, Sagar Bist
15 DEC 2019
Water Treatment
Tutor:
Asst. Prof. Shukra Raj Paudel
Department Of Civil
Engineering
IOE, Tribhuvan University
1

2. Objectives of Presentation
● Students will be able to learn about the following
things:
❖ Process involved in filtration of water.
❖ Types of filter.
❖ Disinfection and its methods.
❖ Chlorination, its forms and types.
❖ Removal of hardness of water.
❖ Aeration.
2

3. Outlines of Presentation
❖ Types of filters.
➢ Slow sand filters
➢ Rapid sand filters
➢ Pressure filters
❖ Disinfection.
❖ Softening of water.
❖ Miscellaneous treatment of water
➢ Aeration
➢ Removal of iron and manganese
➢ Removal of color
3

4. Types of Filters
➢ On the basis of rate of filtration and
driving force to overcome the frictional
resistance there are 3 types:
○ Slow sand filters (gravity type)
4
○ Rapid sand filters
○ Pressure filters
powerplastics.cz

5. 6.6.2.1 Slow Sand Filter
● Earliest and slowest type of filtration type
● Requires large areas of land and large quantity of sand.
● No use of chemicals for water treatment.
● Raw water of turbidity <20NTU can be fed without
treatment.
● It consists of following parts:
1. Enclosure tank
2. Filter media
3. Base material
4. Under drainage system
5. Appartenances
5

6. Source: Water supply engineering book of Prof. Dr. Bhagwan R Kansakar
6

7. Elements of Slow Sand Filter
1. Enclosure tank
● Rectangle tank of stone, brick and concrete.
● Depth: 2.5-4m Area: 50-100sq.m
● Filtration rate: 100-200lit/hour/sq.m
2. Filter media
● Sand layer: 90-100cm thick with 0.25-0.35mm sand
size.
● Cu: 3-5
● Finer the and more the efficiency of filtration.
● Sand shouldn’t contain more than 2% of ca and mg
as carbonate.
7

8. 3. Base media
⮚ Gravel bed of 30-75 cm thick to support filter media.
⮚ This bed is laid in layers – 15 cm thickness.
Layers Thickness (cm) Size (mm)
Top layer 15 3 - 6
Intermediate
layer
15 6-20
15 20- 40
Bottom layer 15 40- 60
8

9. 4. Under drainage system
⮚ Collects the filtered water.
⮚ Lies below gravel bed.
⮚ Consists of lateral and central drains.
5. Appurtenances
⮚ Installed for efficient working.
⮚ Made to regulate the inflow to filter tank so as to
maintain constant depth ( 1- 1.2 m).
⮚ Includes vertical air pipes through layer of sand,
devices for controlling depths etc.
9

10. Source: Water supply engineering book of Prof. Dr. Bhagwan R Kansakar
10

11. Working of Slow Sand Filter
Water of
sedimentation
tank
Filter
media
Drainage
system
Inlet chamber
Outlet
chamber
Clear water
storage tank
11

12. Cleaning of Slow Sand Filter
● Needs to be done after 1-3 months of use.
● Each cleaning reduces sand depth due to loss so when
depth reach 600mm new fresh Sand is used.
Top layer of sand is
scrapped manually up
to depth 15-30 mm
Removed sand
are dried
Water in filter
tank is
drained off
Dried sand is
put back in.
12

13. Efficiency of Slow Sand Filter
1. Bacterial filtration : highly efficient (98% -
99%).
2. Turbidity: to the extent about 50 ppm can be
removed.
3. Color: removes 20-25%
4. Colloidal matter: not much efficient.
13

14. Merits and Demerits
Merits Demerits
Simple to construct. Old fashioned.
Cheaper and no need of
skilled manpower
Maintenance cost is high.
Highly efficient for
bacterial filtration.
Very slow and steady
process.
14

15. 15
Solution:
Base year = 2068
Population at base year, P =10,000
per capita demand of water =150 lpcd
Assume design period = 15 years
Annual population growth rate, r =1.5%
Design year = Base year + Design period = 2068 + 15 = 2083
Population in 2083,P2083 = P(1+r/100)n
=10000(1+1.5/100)15=12502
Water demand in design year, Q = Population * per capita
demand =12502*150 = 1875300 liters/d = 78137.5
liters/hr
Average water consumption rate 150 lpcd in an urban
area. Design a slow filtration unit for a community
having the population of 10,000 at base year 2068. (IOE,
TU, 2068 Baishakh)
15

16. 16
Assume filtration rate = 150 liters/hr/m2. Filtration rate
should be 100 – 200 liters/hr/m2.
Surface area , As = Q/Filtration rate = 78137.5/150 = 520.92 m2
Provide 3 units of slow sand filters including one stand by unit.
Surface area of each unit, As = 520.92/2 = 260.46 m2
Assume L/B = 2
As = L * B = 2B2 = 260.46 m2
B = (260.46/2)1/2 = 11.41 m, Say 11.5 m
L = 2*B = 23 m
Provide depth as follows.
Free board = 0.5 m
Water depth = 1 m
Sand depth = 1 m
Gravel depth = 0.6 m
16

17. 17
Water demand in design year, Q = Population*per capita demand =
18696*60 =1121760 liters/d=46740
Assume filtration rate = 150 liters/hr/m2. Filtration rate should be
100-200 liters/hr/m2.
Surface area, As = Q/Filtration rate = 46740/150 = 311.60 m2
Provide 3 units of slow sand filters including one stand by unit.
Surface area of each unit, As = 311.6/2 = 155.80 m2
Assume L/B = 2
As = L*B = 2B2 = 155.80 m2
B = (155.80/2)1/2 = 8.82 m, Say 8.90 m
L = 2*B = 2*89=17.8 m
17

18. 18
Provide depth as follows.
Free board = 0.5 m
Water depth = 1 m
sand depth = 1 m
Gravel depth = 0.6 m
Depth for under drain pipe = 0.2 m
Total depth = 3.3 m
Provide 3 numbers of slow sand filters of 17.8 m*8.9 m*3.3 m
18

19. 6.6.2.2 Rapid Sand Filters
● Most commonly used in large water supply schemes.
● Raw water is fed in filter after treating sedimentation and
coagulation.
● Consists of following parts:
I. Enclose tank
II. Filter media
III. Base material
IV. Under drainage system
V. Appurtenances
19
19

20. 20
20

21. Parts of Rapid Sand Filter
1. Enclosure tank
⮚ Water tight rectangular tank of stone/brick/concrete.
⮚ Depth: 2.5- 3.5 Area: 10-50sq.m
⮚ Small filter units are provided depending on total
surface area of filter i.e. (min- 4 for large and 2 for
small plants).
⮚ Length to width ratio: 1.25 – 1.35
⮚ Rate of filtration: 3000-6000 liters/hour/sq.m.
21

22. 2. Filter media
⮚ Sand layer: 60-70cm thick with sand size(0.45-0.70
mm)
⮚ Cu: 1.3 – 1.7
Higher the
effective
size
Lower the
Cu
High the
rate of
filtration
22

23. Preparation of Filter Sand
● Done by sieve analysis.
● Size specification can be computed as follows:
Let,
D10,D60 = desired effective size of sand
P60,P10 = % of stock sand for respective effective size.
Then D60 = Cu*D10 Pusable = 2(P60 – P10)
For specific component of filter sand 1/10 of usable sand below
And 2/5 of usable sand above
Ptoo fine = P10 – 0.1Pusable
Ptoo fine = P10 – 0.12(P60 – P10)
Ptoo fine = 1.2P10 – 0.2P10
23

24. And,
Ptoo coarse = P10 + 0.4Pusable
Ptoo coarse = P10 + 0.4 * 2(P60 – P10)
Ptoo coarse = 1.8P60 + 0.8P10
From sieve vs cumulative % curve, the grain size D10 and
D60 is determined.
Size below D10 and above D60 are removed by sieving.
And yet finer can be removed by sand washer’s help.
24

25. Source: Water supply engineering book of Prof. Dr. Bhagwan R Kansakar
25
25

26. 26
source:sswm.info

27. Estimation of Thickness of Sand Bed
● Should be such that the flock do not break
through the sand bed.
● Can be calculated by Hudson formula:
(Q(d^3)h/L)=Bi*29323
where, Q=rate of filtration in
m^3/hr/m^2;
d= sand size in mm;
h= terminal loss of head in m;
L=thickness of sand bed in m;
Bi=break through index whose value ranges
between 4*(10^-4) to 6*(10^-3) depending on
response to coagulation and degree if
pretreatment in filter influent
27

28. Estimation of Gravel Size Gradation
● Estimated by empirical formula:
l =2.54*k* log10d
where k varies from 10-14
Example, for l1 d=2mm with k=12
=2.54 * 12* log102 = 9.2cm
For l2 d=5mm,
= 2.54*12* log105 = 21.3cm
And , thickness of next layer of gravel of size
5mm=
(21.3-9.2)=12.1 cm.
28

29. 3. Base materials
⮚ Gravel layers: 45- 60 cm.
⮚ Arrangements are same as of slow sand filter.
4. Under drainage system
⮚ Collects filtered water uniformly.
⮚ Provides uniform distribution of back wash water
without disturbing upsetting the ground bed and filter
media.
⮚ 2 systems are commonly used:
I. Perforated pipe system
II. Pipe and strainer system
29

30. I. Perforated pipe system
● Similar to slow sand filter drainage system.
● Consists of lateral and central drains made of mostly
cast iron.
● Lateral drains are provided with perforation of diameter
5-12mm
● Lateral drains are supported on concrete blocks of
thickness 4-5 cm.
● Economical but requires more quantity of water for back
wash i.e. about 600 lit/min/sq.m area.
● This is known as high velocity wash.
30

31. Source: Water supply engineering book of Prof. Dr. Bhagwan R Kansakar
31
31

32. ● Rules for designing the under drainage system
containing manifolds and laterals
⮚ Length to diameter ratio < 60.
⮚ Spacing of laterals: 15-30 cm.
⮚ CSA of manifold=(1.5-2) *sum of CSA of laterals.
⮚ Diameter of perforation: 5-12mm and staggered at angle
30 degree with vertical axis of pipe.
⮚ Spacing of perforation: 80mm for 5mm dia. and 200 for
12mm dia.
⮚ ratio of TSA of perforation to TSA of laterals < 0.5 for
12mm dia. and <0.25 for 5mm dia.
32

33. II. Pipe and strainer system
● Central drain and lateral drains attached to either side.
● Lateral drains are provided with strainers at the top.
● Lateral drains spacing: 15-30 cm
● Compressed air is used for purpose of back wash so
result in saving water i.e needs only 250 lit/min/sq.m.
● Its called low velocity wash.
33

34. 4. Appurtenances
a) Wash water troughs:
● Provided at upper portion of filtration tank to collect
back water wash.
● Design as free falling weirs or spillways.
for falling rectangular trough, following expn. Is used for
fixing size of trough.
Q=1.376*b*h(3/2)
where, Q= total water received by trough in m3/s
b=width in m
h= depth of water in m.
34

35. b). Air compressors
⮚ Used during back wash.
⮚ Supplies compressed air at rate 0.6-0.8 m3/min/m2 area
for 5 minutes.
c). Rate control device
⮚ Maintains constant rate of filtration.
⮚ Simplex rate controller is commonly used.
d). Miscellaneous accessories
⮚ Other like head loss indicator, flow rate measuring
devices ,manometers,etc.
35

36. • Simplex rate controller:
Valve control rate of flow
Small pipe⮚ pressure at throat of
venturi tube to diaphragm.
Valve is controlled by movable weight
Source: Water supply engineering book of Prof. Dr. Bhagwan R Kansakar
36

37. Working and Back Washing of Rapid
Filters
⮚ Controlled by six valves:
Valve 1=inlet valve
Valve 2=filtered water storage tank
Valve 3=wastewater valve to drain water from inlet
chamber
Valve 4=wash water storage tank valve
Valve 5= wastewater valve to drain water from outlet pipe
Valve 6=compressed air valve
⮚ For common working of filter valve 1 and 2 are opened
only.
37

38. Back Washing
● Usually done when loss of head through the filter bed
reach 2.5-3m.
● Done by passing air and water upward through filter
bed.
● Water used for back wash should be filtered water.
● Should be done frequently 1 to 3 days interval.
● Normally it takes 30 minutes time.
38

39. Operation During Back Washing
39
CLOSE V1
CLOSE V2 OPEN V6
CLOSE V6
OPEN V4 &
V3
CLOSE V6CLOSE V3
OPEN V1
and V5
CLOSE V5.
OPEN V2
and V1

40. Surface Wash
● Usually accomplished by applying wash
water or mechanical agitation near surface of
sand in filter.
● Wash water is applied from above in form of
high pressure water jet.
● 2 system used usually:
I. Fixed type surface wash system
II. Rotary type surface wash system.
40

41. Efficiency of Rapid Sand Filter
● Bacterial load: less efficient than SSF about
80-90%.
● Turbidity: can be removed upto extent 35-40
ppm.
● Color: highly efficient .Intensity of colour can
be brought down below 3 on Cobalt scale.
41

42. 42

43. 43
Example 6.13
Design rapid sand filter for a population of 60000
nos for a newly growing urban area. (IOE, TU,
2069 Chaitra) .
Solution:
Population,P=60000
Assume per capita demand of water = 100 lpcd
Water demand in design year,
Q=Population* per capita
demand=60000*100=6000000 litres/d
Assume that 3% of filtered water is required for filter

44. 44
backwashing and 30 min is required for backwashing
of filter.
Then design flow, Q=6000000/(1-0.03)*(1/(24-
0.5))=263215.62 litres/hr
Assume filtration rate=5000 litres/hr/m2. Filtration
rate should be 3000-6000 litres/hr/m2.Surface area,
As=Q/Filtration Rate= 263215.62/5000=52.64 m2
Provide 3 units of rapid sand filters including one
stand by unit.
Surface area of each unit ,As=52.64/2 =26.32 m2
As= L*B =1.3 B2=26.32 m2

45. 45
B=√(26.32/1.3) =4.50 m
L=1.3 *B=1.3*4.50+5.85 m
Provide depth as follows.
Free Board=0.5m
Water Depth=1.6m
Sand Depth=0.6m
Gravel Depth=0.6m
Depth for under drain pipe=0.2m
Total depth=3.5m
Provide 3 numbers of rapid sand filters of

46. 46

47. 47
Example 6.14
A city has a population of 150000 with a water
supply of 150 lpcd . Determine the number and size
of rapid sand filter required. Assume necessary
data suitably.(IOE, TU, 2063 Poush)
Solution:
Population , P=150000
Per Capita demand of water =150 lpcd
Water demand in design year,
Q=Population*per capita demand
=150000*150=22500000 liters/d
Assume that 3% of filtered water is required for filter
backwashing and 30 minutes is required for
backwashing of the filter.

48. 48Then design flow,Q=(22500000/(1-0.03))*(1/(24-0.5)
=987058.57 litres/hr
Assume filtration rate=5000 litres/hr/m2. Filtration
rate should be 3000-6000 litres/hr/m2.
Surface area,As =Q/Filttration
rate=987058.57/5000=197.41 m2
Provide 6 units of rapid sand filters including one
stand by unit.
Surface area of each unit,As=197.41/5=39.48m2
Assume L/B=1.3 [should be 1.25-1.35]
As= L*B=1.3 B2= 39.48 m2
B=√(39.48/1.3) =5.51 m, Say 5.60 m
L=1.3 * B =1.3 * 5.60 = 7.28 m, Say 7.30 m

49. 49Provide depth as follows.
Free board = 0.5 m
Water depth = 1.6m
Sand depth = 0.6 m
Gravel depth= 0.6 m
Depth for under drain pipe = 0.2 m
Total depth = 3.5 m
Provide 6 numbers of rapid sand filters of 7.30 m
*5.60 m *3.50 m.

50. Differences between Rapid and Slow
Sand Filter
Item Slow sand method Rapid sand method
Pre treatment Plain sedimentation Coagulation , flocculation
and sedimentation
Base material Gravel(3-65mm size) bed:30-
75cm
Gravel(2-50mm)
bed: 45-60 cm
Filter sand
•Effective size
•Thickness of bed
•Cu
0.25-0.35mm
80-100cm
3-5
0.45-0.7mm
60-75cm
1.25-1.35
Under drainage
system
Lateral drains are spacing at 2
to 3 m. And they are open
jointed.
Lateral drains are
spacing at 15 to 30 cm.
Size of tank 50-1000sq.m. 10-50sq.m.
Rate of filtration per hr 100-200lit/sq.m 3000-6000lit/sq.m.
cost Installation low ,maintenance
high
opposite
50

51. manpower Not skilled Skilled required.
Efficiency
•Turbidity
•Bacterial load
Low, 50ppm
98-99%
Any level can be feed.
80-90%
suitability Rural areas and small
towns
For towns and big cities.
Loss of head
•Initial
•final
10cm
80-120cm
30cm
250-350cm
Method of cleaning scrapping Back washing
Cleaning interval 1-3 months 1-3 days
51

52. Pressure Filter
⮚ Type of rapid sand filter enclosed in steel
cylinder tank where water passes under
pressure.
⮚ May but horizontal or vertical.
⮚ Diameter (1.5-3m) and height (3.5 -8 m).
⮚ All operation and process are same as RSF
except coagulated raw water in it is fed to
filter without mixing, flocculated and
sedimentation.
⮚ Rate of filtration(6000-15000L/hr/m2) is faster
than RSF.
⮚ High cost ,inefficient and relatively poor
52

53. 53
Source: Water supply engineering book of Prof. Dr. Bhagwan R Kansakar

54. 54
source: Engineeringnotes

55. 6.7. Disinfection
• The treatment by which the disease producing bacteria
present in water are killed is known as disinfection.
• The substance or agent used for disinfection of water is
known as disinfectant.
• The treatment by which all kinds of bacteria i.e. Both
disease producing and non-disease producing are killed
is called sterilization.
55

56. 6.7.2. Methods of Disinfection
1. Boiling method
2. Excess lime treatment
3. Iodine treatment
4. Bromine treatment
5. Ozone treatment
6. Potassium permanganate treatment
7. Silver treatment
8. Ultra violet ray treatment
56

57. 1. Boiling Method
www.zeopad.com
• This is the most effective
method of killing bacteria
but impracticable in large
scale.
• Most of bacteria are
destroyed when the water
has attained of about 80°C
temperature.
• Prolonged boiling is
unnecessary and wasteful.
57

58. 2. Excess Lime Treatment
• Treatment of lime is given to the water for the removal of
dissolved salts.
• Excess lime added to water works as disinfecting
material.
• When pH value is about 9.50, bacteria can be removed
to the extent of 99.93 per cent.
• Lime is to be removed by re-carbonation after
disinfection.
58

59. 3. Iodine and Bromine Treatment
• Use of iodine or bromine is limited to small water
supplies such as swimming pools, troops of
army, private plants, etc.
• Dosage of iodine or bromine is about 8 p.p.m.
• Contact period with water is 5 minutes.
• Available in the form of pellets or small pills.
59

60. 5. Ozone Treatment (302 =203)
• Nascent oxygen is very powerful in killing bacteria.
• Ozone is unstable and does not remain in water when
reaches the consumer.
• Dosage of ozone is about 2 to 3 p.p.m. To obtain
residual ozone of 0.10 p.p.m
• contact period is about 10 minutes.
60

61. 6. Potassium Permanganate
Treatment(KMnO4)
• It is a powerful oxidising agent, effective in killing cholera
bacteria.
• Used to disinfection of water of village wells and ponds.
• The treated water produces a dark brown coating on
porcelain vessels and this is difficult to remove except with
scratching or rubbing.
• Dosage is about 2.1 p.p.m
• Contact period of 4 to 6 hours.
61

62. 7. Silver Treatment
• Silver is used to disinfect bacterial spares
algae from water stored in jars.
• Metallic silver is placed as filter media. Water
get purified while passing through theses
filters.
• Dosage of silver varies from 0.05 to 1 p.p.m.
• Contact period is about 10 minutes to 1
hours.
• It is costly and limited to private individual
houses only.
62

63. 8. Ultra-violet Ray Treatment
Source: Synergy boreholes
● For generating these rays,
the mercury is enclosed in
one or more quartz bulbs
and electric current is then
passed through it.
● The water should be
passed round the bulbs
several times .
● Depth of water over the
bulbs should not exceed 10
cms.
63

64. Kinetics of Disinfection
Ideal conditions for the factors affecting kinetics of
disinfection
•All cells of a single species of organisms are discrete units
which are equally susceptible to a single species of
disinfectants.
•Both cells and disinfectants are uniformly dispersed in
water.
•The disinfectant doesn’t change in chemical composition
and concentration during time of contact.
•Water doesn’t contain any interfering substance.
64

65. Disinfection is a function of following three factors:
a)Time of contact
b)Concentration of disinfectant
c)Temperature of water
a. Time of contact
•Important factor affecting the destruction of organisms
•According to chick’s law: the rate of kill of organisms is
proportional to the number of organisms remaining in water at
any time ‘t’ i.e. dN/dt=-kNi
Where, N= number of organisms killed up to an time t
Ni= number of organisms remaining in water at any time t
k= dieoff coefficient
65

66. Performing integration, we get
T=(2.303/K)*log10(N0/(N0-N))
•Modified equation of Chick’s equation is
T=[(2.303/K)*log10(N0/(N0-N))]1/n
Where n= dilution coefficient
b. Concentration of disinfectant
•By change in concentration, rate of killing of organisms is
affected
•Relation between concentration and time required for
killing a desired percentage of organisms can be
expressed by: Cnxtp=k
where, C= concentration of disinfectant
tp=time for a constant percentage of kill of organisms
66

67. For n>1, rapid decrease in the efficiency of disinfectant
with the reduction in concentration
For n<1, contact time is more important than
concentration
For n=1, both the contact time and concentration affect
the efficiency of disinfectant to the same extent
c. Temperature of water
•Increase in temperature results more rapid killing of
organisms
•Relationship between time and temperature that affects
the given percentage of kill can be expressed as:
Log10(t1/t2)=[E(T2/T1)]/(2.303*RT1T2)
67

68. Where , t1, t2 are time for given percentage of kill at
temperatures T1 and T2 in Kelvin
E is activation energy in J/mol, of cal/mol
R is gas constant= 8.314 J/mol*K, or 1.99 cal/mol*K
•Typical values of E at pH of 7 for aqueous chlorine and
chloramines are 34332 and 50242 J/mol
•Value of E increases with increase in pH
•Lower the temperature, higher is the time required for
achieving a percentage of kill for a concentration of
disinfectant
68

69. 6.7.3. Chlorination
Source: www.thewatertreatments.com
● The method in which
chlorine is used as an
disinfectant to kill the
harmful organism in
water is called
chlorination.
1. Nascent oxygen theory
2. Enzymatic hypothesis
theory
69

70. Nascent oxygen theory
Chlorine in water produces nascent oxygen which
oxidizes unicellular animals and kills them.
Enzymatic hypothesis theory
Chlorine first penetrates through the cell wall of the
organisms and then react inside with the enzymes which
are essential for bacterial life.
As enzymes become ineffective, the bacteria gets
destroyed.
70

71. Action of Chlorine
•Hypochlorous acid (HOCl) and hypochlorite ions(OCl-)
accomplish disinfection in water
•The un-dissociated HOCl is about 80-100 times more
powerful as disinfectant than OCl- ion.
Cl2 + H2O HOCl + H+ + Cl- (Hydrolysis)
HOCl H+ + OCl- (Ionization)
71

72. Combined available chlorine
The free chlorine can react with compounds such as
ammonia, proteins, amino acids and phenol that may be
present in water to form chloramines and chloro-derivatives
which constitute the combined chlorine.
NH3 + HOCl NH2Cl (mono chloramine) + H2O
NH2Cl + HOCl NHCl2 (dichloramine) + H2O
NHCl2 + HOCl NCl3 (trichloramine) + H2O
Chlorine demand
The amount of chlorine consumed in killing pathogenic
organisms as well as oxidation of inorganic and organic
materials present in water is known as chlorine demand of
water.
72

73. Residual chlorine
It is the amount of chlorine remaining in water after
chlorine demand has been fulfilled.Safeguard water in
distribution system.(0.2 mg/l after 10 mins)
Free available chlorine
The chlorine existing in water as hypochlorous acid,
hypochlorite ions and molecular chlorine is defined as free
available chlorine.
Dosage of chlorine
Chlorine dose = chlorine demand + residual chlorine
Contact time
The time taken to kill the pathogenic organisms after the
application of chlorine is known as contact time.
73

74. Relative Effectiveness of Components of
Free Available Chlorine
www.nzdl.org
● Decrease in % of HOCl with
increase in pH.
● Effectiveness of chlorine
decreases with increase in
pH.
● Effectiveness of chlorine for
disinfection decrease with
increase in temperature.
74

75. Temperature(‘C
)
0 5 10 15 20 25
Kix108 (mol/lit) 1.5 1.7 2.0 2.2 2.5 2.7
Table:- 6.4
75

76. 76

77. Worked out examples
77
Example 6.15)
For disinfecting water supply it is required to treat one
million litres of daily supply with 0.6 ppm of chlorine. If
bleaching powder containing 35% chlorine is used as
disinfectant calculate the amount of bleaching powder
required per day.
Solution:
Quantity of water to be disinfected = 1MLD=1x10^6
litres/ day
Chlorine dose required = 0.6mg/l
Quantity of chlorine required =
(0.6x1x10^6)/10^6=0.6kg/day
Bleaching powder contains 35% of chlorine
Therefore, quantity of bleaching powder
required=0.6/0.35=1.71kg/day.

78. 78
Solution:
Quantity of water to be disinfected
=30000m^3/day=30x10^6 litres/day
Chlorine dose required = 15kg/day = 15x10^6 mg/day
Doses of chlorine =(15x10^6)/(30x10^6)= 0.5 mg/litre
Residual chlorine = 0.2 mg/l
Therefore, chlorine demand of water
= chlorine dose- residual chlorine = 0.5 - 0.2 = 0.3mg/l
Example 6.16)
Chlorine usage in the treatment of 30000 cubic meters of
water per day is 15 kg/day. The residual chlorine after 10
minutes contact is 0.2 mg/litre. Calculate the doses of
chlorine in mg/l and chlorine demand of water.

79. 6.7.4. Types of Chlorine
❖ As bleaching powder or hypochlorite
❖ As chloramines
❖ As chlorine gas or liquid chlorine
❖ As chlorine dioxide gas
79
vasuchemicals.com
Liquid Chlorine

80. 1. Bleaching Powder
● This is chemically calcium hypo-chlorite Ca(0Cl)2 is
chlorinated lime, containing about 33.5% of
chlorine(Punmia,2010). The process of chlorination
using hypo-chlorites in called hypo-chlorination. When
introduced to water calcium hypo-chlorite reacts as
follows:-
Ca(OCI)2 +H20 2HOCI + Ca(OH)2
● in the same way in which Sodium hypo-chlorite reacts
that is:-
NaOCI + H20 HOCI + NaCI
80

81. 2. Chloramines
⮚ Chloramines are compounds produced by combining
chlorine and ammonia.
• NH3 + HOCl → NH2Cl+ H2O Monochloramine
• NH2CL + HOCl → NH2Cl2+ H2O Dichloramine
• NH2CL2+ HOCl → NCl3+ H2O Trichloramine
⮚ The disinfecting reaction is slower.
⮚ Water treated with chloramines should be supplied to
consumer about 20 minutes to 1 hour.
81

82. 3. Chlorine Dioxide Gas
• Extreme soluble in water and does not form
trihalomethanes.
• Must be generated on-site:
• Prepared by passing chlorine gas through sodium
chlorite
2NaCLO2+ CL2 → 2CLO2+ 2NaCL
• The dose of chlorine dioxide required for effective
removal of taste and odor varies from 0.5 to 1.5 ppm.
82

83. 4. As Chlorine Gas or Liquid Chlorine
⮚ There are two methods of applications of chlorine to
water to be disinfected:
1. Chlorine gas may be fed directly to the point of
application to the water supply
2. Chlorine gas may be dissolved in a small flow of
water and the chlorine water is fed to the point of
application.
83
83

84. 6.7.5. Forms of Chlorination
1. Plain Chlorination
2. Pre- Chlorination
3. Post- Chlorination
4. Double Or Multiple Chlorination
5. Break Point Chlorination
6. Super- Chlorination
7. De-chlorination
84

85. 1. Plain chlorination
• Only chlorine treatment is given for disinfection.
• Usual dose is between 0.5 to 1 ppm.
• It is used when raw water contains turbidity less than 10
NTU.
• Helps to remove bacteria and colour from water also
control growth of algae.
1. Pre-chlorination
• Chlorine is added before any treatment.
• It controls growth of algae and reduces the quantity of
coagulants required.
• Reduces bacterial load in filter.
• Dose of chlorine should be such that residual chlorine is in
between 0.1 to 0.5 ppm.
85

86. 3. Post-chlorination
• Application of chlorine after all the other treatment for
purification.
• It protects water from contamination in the distribution.
• Dose of chlorine should be such that residual chlorine
must be 0.1 to 0.2 PPM before it enters distribution
system.
4. Double or multiple chlorination
• Double chlorination is combination of pre and post-
chlorination.
• When chlorination is done more than two times, it is
called multiple chlorination.
86

87. 5. Break Point Chlorination
• Point at which nearly all the residual chlorine is free
chlorine.
• Determine by lab test , generally occurs at 3 to 7
PPM of chlorine.
• Affected by ammonia present in water.
• Adequate chlorine is incorporated into the water to
achieve the breakpoint, keeping the water well
chlorinated and appropriate for its intended use.
• At this point there is complete oxidation of ammonia
and other compound
• Manganese is also removed
87

88. 6. Super chlorination
• Application of chlorine beyond the stage of break point.
• Dose should be such that residual chlorine lies between 0.5
to 2 PPM.
• Usually used when there is epidemic in residences.
7. Dechlorination
• Process of removing of excess chlorine.
• At the end small amount of residual chlorine must remain in
water.
• Generally ammonia, sodium bisulphite, sodium sulphite,
sodium thiosulphate are used.
• This is generally required when super-chlorination has been
practiced.
• Ammonia is best because it forms chloramines.
88

89. B. Relation Between Residual and Applied
Chlorine
89
Source: slideplayer.com

90. 90
● If there is no chlorine demand, relation is indicated by line
having slope of 1.
● Generally, water has some chlorine demand so relation is
indicated by curve
● With the increase in applied chlorine, the residual chlorine
also increases till it reaches a peak point

91. ● When peak point is reached, sudden decrease in residual
chlorine occurs with further increase in applied chlorine.
91
Break Point
● At break-point, the residual chlorine is minimum and
further increase in applied chlorine results increase
in residual chlorine.

92. 6.7.6 Factors Affecting Efficiency of Chlorination
1. Turbidity
• Makes difficult to obtain residual chlorine
• Destruction of bacteria in suspended particles is
uncertain
2. Presence of metallic compounds
• Compounds of Fe and Mn utilize large amount of
chlorine
3. Ammonia compounds
• Combined available chlorine is formed
• Combined chlorine is less effective than free
available chlorine.
92

93. 4. pH Value of water
• High pH value reduces the effectiveness of chlorine
5. Temperature of water
• Reduction in temperature reduces killing power of
chlorine
6. Time of contact
• Less contact time required for free chlorine
7. Type, condition and concentration of micro-
organisms
• E-coli bacteria ensures disinfection
• Bacteria in clumps and their higher concentration
93

94. 6.8 Softening
● Removal of hardness
● Bicarbonates, Sulphates, Chlorides and Nitrates of Ca
and Mg causes the hardness
TYPES
6.8.1 Removal of Temporary Hardness
6.8.2 Removal of Permanent Hardness
94

95. 6.8.1 Removal of Temporary Hardness
● By boiling
▪ When water is boiled
Bicarbonate decomposes
to Carbonate
Ca(HCO3) + Heat ⟹ CaCO3⇩ + CO2 + H2O
Mg(HCO3) + Heat ⟹ MgCO3 ⇩ + CO2 + H2O
95
http://slideplayer.com/slide/8512346/

96. ● Lime treatment method
▪ Lime is added to the hard
water.
▪ Carried out either hot or
cold.
▪ CaCO3 and MgCO3 get
precipitated.
96
Source: Cienciabit: Cienciay Tecnología.(youtube)
Ca(HCO3) + Ca(OH)2 CaCO3 + 2H2O
Mg(HCO3) + Ca(OH)2 CaCO3 + MgCO3 + H2O

97. 6.8.2 Removal of Permanent
Hardness
1. Lime Soda Method
2. Zeolite Method
3. Deionization Method
1. Lime Soda Method
● This method is used to remove permanent hardness of
water.
● Calcium and Magnesium ions are precipitated by the
addition of lime Ca(OH)2 and soda ash Na2(CO3).
● Carried out either hot or cold.
97

98. 98
98
98

99. Advantages
● Simple & economical.
● Amount of coagulant is
reduced for coagulation
process.
● Increase pH of water
which reduce the
corrosion of pipes.
Disadvantages
● Large amount of sludge is
formed.
● Requires skilled
manpower.
● Cannot remove hardness
of zero, so cannot be
used in dyeing industry.
99
Raw water Lime Soda
Reaction tank
Filters
Storage
99

100. 2. Zeolite Method
➔ Complex compound of Aluminum Oxide, Silica, Soda
(2SiO2.Al2O3.Na2O) (Na2Ze).
Natural zeolite:- Green sand (7500 gm hardness/m3)
Artificial zeolite:- Permutit ((35000 gm hardness/m3)
➔ Found in nature or synthesized in lab.
➔ Also known as ion exchange or base exchange
method.
➔ Hardness causing ions(Ca+2,Mg+2) are retained by
Zeolite as CaZe and MgZe and water gets soften.
➔ Carried out in vessel like Rapid Sand filter.
0

101. 75-150 cm
250 lit/min
Source:Slideshare.com
101

102. Advantages Disadvantages
Sludge isn’t formed so no
disposal problem
Doesn’t work for turbid water
Doesn’t require skilled
manpower
Unsuitable for water
containing Fe and Mn.
Zero hardness water is
obtained
Can’t be used for acidic water
Economical process should be operated carefully
to protect zeolite
Automatic process Likelihood of growth of
bacteria on bed of zeolite
102

103. 3. Deionization Method
● In this process, H2Z is used. H is hydrogen and Z is
organic part.
● Water after this process is free from mineral salt.
● Useful for water of turbidity <10NTU.
● Cations like Ca, Mg and Na are exchanged with
Hydrogen ion.
H2Z + Ca(HCO3)2 ⟹ CaZ + 2CO2 + H2O
H2Z + CaSO4 ⟹ CaZ + H2SO4
H2Z + CaCl2 ⟹ CaZ + 2HCl
Similar reactions with Mg and Na salts.
103

104. The acidity of water can be removed by
1. diluting treated water with raw water
2. neutralizing treated water with alkaline substance
3. by absorbing with De-acidite(DOH)
2DOH + H2SO4 ⟹ D2SO4 + 2H2O
DOH + HCl ⟹ DCl + H2O
Regeneration of Hydrogen Content
CaZ + H2SO4 ⟹ H2Z + CaSO4
MgZ + HCl ⟹ H2Z + MgCl2
104

105. Regeneration of De-acidite
D2SO4 + Na2CO3 + H2O ⟹ 2DOH +Na2SO4 + CO2
DCl + Na2CO3 + H2O ⟹ 2DOH +NaCl + CO2
5

106. 6.9 Miscellaneous Treatment
● Performed to remove iron, manganese,
dissolved gases, colour, odour, taste etc.
present after the normal treatments.
TYPES
1. Aeration
2. Removal of Iron and Manganese.
3. Removal of Colour, Odour, and Taste.
106

107. 6.9.1 Aeration
● Process of bringing water in intimate contact of air.
● Removes tastes and odour caused by the gases due to
decomposition.
● Increases the dissolved oxygen of water and decreases
CO2 in water.(pH increases)
● Bacteria may be killed to some extent.
TYPES
1. Free fall aerators or gravity aerators.
2. Spray aerators
3. Air diffuser basins
107

108. 1. Gravity Aerators
Source: http://www.appropedia.org
⮚ Cascade Aerator
▪ Simplest freefall aerator
▪ Contains series of
aerators.
▪ CO2 reduced by 40-60%
⮚ Inclined Apron Aerator
▪ Water is allowed to fall
in inclined plane.
▪ Aeration is caused by
agitation of breaking of
sheet of water.
108

109. ⮚ Salt Tray Aerator
▪ Commonly used aerator.
▪ Square or round in
shape.
▪ Series of wood trays.
▪ Reduction od CO2 is
about 65-90%.
109
109
Source: Textbook of Water Supply Engineering

110. ⮚ Gravel Bed Aerator
▪ Thickness of gravel
bed may vary from
1-1.5m.
▪ This way of
cascading is more
efficient for CO2
removal than other
method.
110

111. 2.Spray Aerator
• Water is sprayed
through nozzles
and broken into
mist or droplets.
• Nozzles have
diameters from
10-40mm.
• Reduces CO2 by
70-90%.
Source:http://www.ag.auburn.edu
111

112. 3.Air Diffusion Aerator
• Water pipe is
inserted into the
tank and
compressed air is
blown.
• Amount of
dissolved oxygen
increases in
water.
Source:.diversifiedpondsupplies.com
112

113. 6.9.2 Removal of Iron and Manganese
● Effects
▪ Unpleasant taste and odour in water.
▪ Water becomes red or brown in colour.
▪ Causes growth of bacteria, corrosion of plumbing
work etc.
● Suspended Iron and Manganese are remove by
normal treatment method but soluble Fe and Mn need
special treatment method.
113
1. Aeration followed by filtration
4Fe(HCO3)2 + 2H2O + O2 4Fe(OH)3 + 8CO2
6Mn(HCO3)2 + 3O2 6MnO2 + 2CO2 + 2H2O

114. 2. Base exchange method
● Useful when Iron and Manganese in large amount.
● Fe and Mn are removed by Manganese Zeolite.
● Bed must be washed by Potassium Permanganate
Z-MnO2 + Fe2+ Z-Mn2O3 + Fe3+
Z-Mn2O3 + KMnO4 Z-MnO2
3. Chlorination followed by sedimentation and filtration
● Iron and Manganese are removed by oxidation using
chlorine and then sedimentation followed by filtration.
2Fe2+ + Cl2 + 6H20 2Fe(OH)3 + 6H+ + 2Cl-
Mn2+ + Cl2 + 6H20 MnO2 + 4H+ + 2Cl-
4

115. 6.9.3 Removal of Colour, Odour and
Taste
⮚ Colour, odour and taste in the water may be
due to
• Industrial and domestic waste.
• Organic matter
• Dissolved gases
• Dissolved minerals
• Microorganism
Source: listaka.com
115

116. 1. Treatment by Activated Carbon
● Charcoal that has been heated or otherwise treated to
increase its adsorptive power
● Preparation
Charcoal + Heat(1200˚C) Activated
Carbon
● Uses
▪ Carbon adsorbs organic compounds which will
remove colour, odour and taste
▪ Adsorbs micro-organisms to some extent.
116
P2O5/N2

117. ● Used in two ways
1. Can be used instead of sand bed in rapid sand filter.
1. Can be used in powder form
1. Along with coagulant.
2. Before entering filter.
3. Before any treatment.
Dose varies from 5-20 mg/l however the optimum is
determined from test result.
117

118. 2. Use of Copper Sulphate
● Control growth of algae, bacteria and aquatic weed.
● Applied by dragging under water or spraying.
● Dose may vary from 0.3 to 0.6 mg/l.
● Detrimental to fish if used in excess.
118

119. 119

120. 120