Treatment of water

INTRODUCTION
 The extent of treatment required to be given to a particular water depends
upon the characteristics & quality of the available water & also upon the
quality requirements for intended use.
 In general public water supplies are designed from the view point of the
quality requirements for drinking water, & simultaneously, they should be
made reasonably suitable for industrial purposes like steam generation,
dying, brewing, etc.
 Available water must be made safe, good in appearance, & attractive
to human taste & tongue.
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TREATMENT OF WATER
 The complete process of removal of
undesirable matter, in order to make the
water acceptable for domestic or Industrial
use, is commonly termed as TREATMENT
OR PURIFICATION OF WATER.
 The object of water treatment is to remove or
reduce these impurities up to acceptable
standards, before water is supplied to the
public.
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OBJECTIVES OF TREATMENT OF
WATER
 To Removal of all Pathogenic germs contained in untreated water
 To Remove all unpleasant tastes & odour from water
 To Remove the dissolved gases, colour of water
 To make water fit for domestic purposes
 To Remove corrosive properties of water which affect pipes
 To Remove Suspended & Floating material.
 To Remove Harmful Bacteria.
 To Remove Hardness.
 To make water suitable for a wide variety of industrial purposes
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LOCATION OF WATER TREATMENT
PLANT
The treatment plant should be located near the town to which water is to be
supplied, so that treated water needs to travel a small distance after
treatment.
This will prevent the water quality to deteriorate after treatment.
The Treatment plant should be located away from any source of pollution.
The water should be tapped from the upstream of the point of disposal of
city waste discharging to the river acting as source of water.
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LOCATION OF WATER TREATMENT
PLANT
 If the source is at a lower elevation than the distribution area, the treatment plant
may be located near the source.
 The plant should be easily accessible for the persons connected with operation and
maintenance works.
 If the natural topography permits, the treatment plant should be located at higher
elevation and the water supply may be achieved by gravity.
 The treatment plant should be so located that there should be enough space all
around for future expansion.
 The plant should be made a hygienic as possible.
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LAYOUT OF WATER TREATMENT
PLANT
The following process are required in a WTP starting from sources of water to the
distribution zone in order of sequence :
1) Screening
2) Plain Sedimentation
3) Sedimentation with coagulation
4) Filtration
5) Disinfection
6) Aeration
7) Softening
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METHOD OF PROCESS
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LAYOUT OF WATER TREATMENT
PLANT
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WATER TREATMENT PROCESS AND
IMPURITIES
PROCESS IMPURITY REMOVED
 Screening Floating matter
 Plain Sedimentation Large suspended Solids
 Sedimentation with coagulation Fine suspended Soilds
 Filtration Colloidal Solids
 Disinfection Pathogenic bacteria
 Aeration Taste, odour
 Softening Hardness Dhara Dattani 10

PRIMARY,SECONDARY AND
TERTIARY TREATMENT
 Primary Treatment
 Makes wastewater (w/w) compatible for secondary treatment
 Employs physical operations and chemical processes
 Secondary Treatment
 Employs biological processes mainly for biodegradable organic matter removal
 Tertiary Treatment
 Make secondary effluent fit for reuse (agric., incl. or mun. reuse)
 Employ physical operations and chemical/biological processes
 Preliminary treatment
 Making water/wastewater compatible for pumping and passing through the
(water/wastewater/sewage) treatment plant
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CLASSIFICATION OF SCREENS
 Coarse screens (6-150 mm)
— used in the preliminary treatment of wastewater to protect pumps, valves, pipelines and other
appurtenances from damage or clogging by rags and large objects
— hand cleaned or mechanically cleaned
— Often may not be needed (characteristics of wastewaters may determine)
• Fine screens (<6 mm)
— Often used after coarse screens
— May be to protect process equipment or to eliminate materials that inhibit beneficial use of bio solids
— Fine screens can be static wedge wire, drum or step types
• Micro screens (<50 microns)
— used principally for the removal of fine solids from the treated effluent
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2. SEDIMENTATION
 Many impurities suspended in water having Sp.Gr greater than 1 and are held in
suspension by virtue of the turbulence or currents maintained in the water
 When the currents are retardered by offering storage to the water ,these impurities
tend to settle down at the bottom of the tank. This is principle of sedimentation
process.
 These are two types of sedimentation :
i. Plain Sedimentation
ii. Sedimentation with Coagulation.
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SEDIMENTATION
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SEDIMENTATION
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SEDIMENTATION
SOURCE : www.google.comDhara Dattani 17

SEDIMENTATION
 Particles settle down more rapidly in water at high temperature than at low
temperature
 MATERIAL REMOVED
 Suspended matter – 60%
 Bacteria-75%
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PURPOSE OF SEDIMENTATION
 To remove coarse dispersed phase.
 To remove coagulated and flocculated impurities.
 To remove precipitated impurities after chemical treatment.
 To settle the sludge (biomass) after activated sludge process / tricking filters.
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PLAIN SEDIMENTATION
 When Impurities are separated from suspending fluid by action of natural forces alone,
Gravitational and natural aggregation of the settling particles, without the aid of coagulants,
it is called plain sedimentation.
 ADVANTAGES OF PLAIN SEDIMENTATION:
 It lightens the load on subsequent.
 Impurities can be controlled in better way because plain sedimentation delivers uniform
quality of water.
 The cost of clearing the chemical coagulation basin is reduced.
 Less quantity of chemicals are required in the subsequent treatment process.
 No chemical is lost with sludge discharged from the plain settling basin.
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TYPES OF SEDIMENTATION TANKS
 Depending upon operation
1. Fill and draw type tanks
2. Continuous flow type tanks
 Depending upon shape
1. Rectangular tank
2. Circular tank
3. Hopper bottom tank
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IMPORTANT FACTORS OF
SEDIMENTATION TANK
 PERIOD OF DETENTION : 6-8 hours
 DEPTH OF TANK : 3-6 metre
 VELOCITY OF FLOW : 5mm/s or 30 cm/min
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SEDIMENTATION WITH
COAGULATION
 When chemicals (coagulants) are added to induce or hasten aggregation of the
settling of finely divided suspended matter, colloidal substances and large
molecules, the operation is called sedimentation with coagulation or clarification.
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RECTANGULAR TANK
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COAGULANT AGENT
SOURCE : www.google.comDhara Dattani 25

CHEMICALS USED FOR
COAGULATION
 Aluminium sulphate
 Ferrous sulphate
 Chlorinated copperas
 Magnesium carbonate
 Polyelectrolytes
 Sodium aluminate
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FILLAND DRAW TYPE TANK
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FILLAND DRAW TYPE TANK
 This tank is also called Quiescent or internment type sedimentation tank.
 In this water is filled with incoming water and allowed for rest for certain time.
 During this period suspended particles settle down at bottom of tank.
 Detention period is 24 hours
 At the end of the period, the clear water is discharged from outlet valve.
 After this process, cleaning process takes place, which taken 6-8 hours.
 Thus whole cycle takes place of 30-36 hours (approx.)
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CONTINOUS FLOW TYPE TANK
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CONTINOUS FLOW TYPE TANK
 Velocity of flow is reduced, a large amount of suspended impurities can be easily removed
from water.
 This is principle of continuous flow type sedimentation tank,
 In this type of tank, water enters the tank from one end and as it travels towards at the other
end, its velocity is broken or reduced by means of baffle walls. These walls in openings at
different levels.
 The velocity of flow is so adjusted that time taken by a particle of water to move from end
to the other is slightly more than that required for the settlement of suspended impurities in
water.
 The water flows practically in the horizontal direction, with a maximum permissible
velocity of 0.3 m/sec.
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ADVANTAGES
 Because of continuous flow, less wastage of water
 As it is arranged in series hence anyone of them may be clean or for washing purpose.
 Process of sedimentation is continued so there is no requirement of labour expect in
cleaning purpose.
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CIRCULAR TANK WITH RADIAL
FLOW
 These are generally not used in plain sedimentation, but are mostly used in sedimentation
with coagulation.
 The section through a typical type of radial flow circular tank.
 water enters in this tank through the central inlet pipe placed inside the deflector box. .
 The deflector box deflects the water downwards and then it goes out through the holes
provided in the sides of the deflector box.
 The water flows radially from the deflector box towards the circumference of the tank where
an outlet is provided on the periphery.
 All the suspended particles settle down on the sloppy floor and clear water goes through the
outlet.
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CIRCULAR TANK WITH RADIAL
FLOW
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CIRCULAR TANK WITH
RADIAL FLOW
 The sludge is removed by scrapper which continuously moves around the floor at a very
small velocity.
 The maximum velocity of the scrapper should not exceed 4.5 m/hour.
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CIRCULAR TANK WITH SPIRAL FLOW
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CIRCULAR TANK WITH SPIRAL FLOW
 In this case, the inlet is provided at the circumference and directed at an angle between a
radius and a tangent.
 The outlet, provided in the form of a submerged weir is also provided at the outer
circumference.
 Water while moving at very low velocity allows its suspended impurities to settle in the
tank, which can be removed from the sludge outlet.
 The clear water is drawn over a small weir type outlet.
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HOPPER BOTTOM SETTLING TANK
WITH VERTICAL FLOW
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HOPPER BOTTOM SETTLING TANK
WITH VERTICAL FLOW
 In this type of tank, water enters in the tank from the top into deflector box.
 After flowing downward inside the deflector box the water reverses its direction
and starts flowing downward around the deflector box.
 The suspended particles having specific gravity more than one, not follow the water
at the time direction, and settle reversing its the bottom, from where they are
removed through sludge outlet pipe under hydrostatic pressure.
 These tanks are mostly used in sedimentation with coagulation process.
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MIXING DEVICES
 After adding coagulants in water, the next operation is to mix them thoroughly in
water dispersed into the entire mass of water.
 This violent agitation water can be achieved by means of mixing devices.
 Mixing can be done by the following devices :
1. Mixing basins with baffle walls
2 Mixing basin with flash mixer
3. Narrow mixing channel with flume
4. Centrifugal pump
5. Compressed air agitation walls
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MIXING BASINS WITH BAFFLE WALLS
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 In this type of device, the mixing basins or tanks with baffle walls are provided to mix water
with the coagulant.
 Such basins are of two types :
 (i) Horizontal or round the end type
 (ii) Vertical or up and down type
 the plan of a horizontal or round the end type mixing basin.
 The water moves flows horizontally for a short distance and by the action of baffles, it
makes a turn and moves further.
 It ultimately reaches outlet end of the tank shown by arrows.
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 Distance between baffle walls- 60-100 cm
 Velocity of water-15-30cm/sec
 Detention period 20-50minutes
 In this method, the mechanical means are used to mix raw water with the coagulant a typical
'flash mixer' in which the raw water and coagulant are agitated vigorously by a paddle
operated by an electric motor.
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FLOCCULATION
 The best floc will form when the mixture of water and coagulant are violently Aggitate
followed by a relatively slow and gentle stirring to permit build up and agglomeration of
floc particles.
 From the mixing basin, the water is, therefore, taken to a flocculation is called a flocculator,
where it is given a slow stirring action.
 Rectangular tanks fitted with paddles operated by electric motor are used as flocculator.
 Flocculators are slow starring mechanism, which forms floc.
 The paddles are remove at very slow speed of about 2-3 RPM
 The paddles may revolve on vertical or horizontal shaft and detention period is 30-60
minutes.
 A typical flocculator fitted with slowing moving paddles
 The water coming out from flocculator is taking out in sedimentation tank
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FLOCCULATION
ADVANTAGES
 Requirements of chemical reduced
upto 10-40%
 Better floc formation
 Less capacity of tank is required
 More flexibility in operation, because
it can be easily controlled.
 Very small loss in head of water
 Can be easily installed in existing
plants.
DISADVANTAGES
 Dead spaces in corners
 Low velocity near shaft of paddles
 Bad short circuiting
 Requires supervision and maintenance.
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CLARIFLOCCULATOR / CLARIFIER
 After flocculation water enters the settling tank, which is commonly known as
clarifier.
 In this operation the floc which has been formed in the flocculation is allowed to
settle and is separated from the water.
 This is done by keeping the water in the sedimentation tanks which are also known
as coagulation tanks or basins.
 The design of clarifiers is similar to that of plain sedimentation tanks, except that
the detention time in this case is lower.
 The detention time of about 2.5 to 3 hours is commonly adopted with an overflow
rate of 1 to1.2 m per hour.
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CLARIFLOCCULATOR / CLARIFIER
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PREPARING AND ADDING CO-
AGULAT(ALUM)
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JAR TEST
 The sample of raw water o be tested is placed in a number of jars or beakers having
capacity of about 500 millilitres.
 Normally six jars are used. Different amounts of coagulants are then added to each
jar.
 The driving unit is started. The paddles connected with driving shaft through
stirring m placed inside the jars, are thus made to rotate.
 The formation of floc in each jar is noted. The amount of coagulant in the jar which
products a good floc with the least amount to coagulant, indicates the optimum
dosage.
 The speed of paddles and the time of mixing may also be varied for different tests
during determining this least optimum dosage.
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AERATION
 Aeration of water is done to accomplish the following objectives
 It removes taste and odours caused by gases due to organic decomposition
 (ii) It increases dissolved oxygen (DO) content of the water.
 (iii) It removes hydrogen sulphide, and hence odour due to this is also removed
 (iv) It decreases carbon dioxide content of water, and thereby reduces its corrosive
and raises its pH value.
 (v) It converts iron and manganese from their soluble states to their states, so that
these can be precipitated and removed.
 (vi) Due to agitation of water during aeration, bacteria may be killed
 (vii) It is also used for mixing chemicals with water.
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TYPES OF AERATORS
1. GRAVITY
AERATOR
2.SPRAY
AERATORS
3.AIR DIFFUSER
BASIN
CASCADE
AERATOR
INCLINED APRON
SLAT TRAY GRAVEL BED
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MECHANICALAERATORS
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FILTERATION
 Screening and sedimentation process removes a large percentage of the suspended
solids, organic matter and a small percentage of bacteria.
 If sedimentation with coagulation is used, the percentage removal of colloidal
particles is increased.
 But however, the resultant water will not be pure, and may contain some very fine
suspended particles and bacteria.
 For removing bacteria, colour, taste, odour and for producing clear and sparkling
water, filters are used.
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THEORY OF FILTERATION
 MECHANICAL STRAINING
 SEDIMENTATION
 BIOLOGICAL ACTION
 ELECTROLYTIC ACTION
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FILTER MATERIALS
 SAND
 GRAVEL
 ANTHRACITE
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FILTER MATERIALS
 Sand :
 It shall be obtained from rocks ,traps, basalts, Etc
 It should be free from clay, loam, lime & organic matter
 Its size should be uniform and of same nature
 It should be placed in hydraulic acid for 24 hrs and shall not weight lose more than
5% of its original weight.
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FILTER MATERIALS
 Depth of sand bed :
 Depth of sand bed minimum to 60-90 cm
 Why 60 cm depth of sand is preferred ?
 It divides very finest particle in initial stage of filter
 It gives uniform rate of flow
 It provides good support for the topmost layer of sand bed.
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FILTER MATERIALS
 2. Gravel
 Density must be 1600kg/m3
It is used below sand bed layer
It shall be rounded shape
It is placed in 5-6 layers
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TYPES OF FILTERS
GRAVITY FILTERS
PRESSURE FILTERS
SLOW SAND FILTER
RAPID SAND FILTER
HORIZONTAL
PRESSURE FILTER
VERTICAL
PRESSURE FILTER
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SLOW SAND FILTERS
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SLOW SAND FILTERS
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SLOW SAND FILTERS
Clean slow sand filter without supernatant water layer.
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SLOW SAND FILTERS
Underdrain and support media.
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SLOW SAND FILTERS
Removal of Schmutzdecke.
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SLOW SAND FILTERS
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SLOW SAND FILTERS
 Slow sand filter' was the earliest type of filter introduced in 1829. 'Slow sand filters'
so called because the rate of filtration through them may be 1/20 or less of the rate
of Filtration through rapid gravity filters or pressure filters. Because of low
filtration rate, they require large area of land and are costly to install.
 They are well suited for rural areas in less of filtration developing countries because
of its simple operation and maintenance procedures.
 The effect of the slow sand filter is to remove turbidity by straining and to remove
bacteria by biological action.
 It is not particularly effective in removing colloidal matter.
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SLOW SAND FILTERS
 Filter media
 Base material
 Under drainage system
 Appurtenances
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SLOW SAND FILTERS
 Enclosure tank :
 It consists of an open water tight rectangular tank, made of masonry or concrete.
The floor has slope of 1 in 10 to 1 in 200 towards the central drain. The depth of
tank from 2.5 to 3.5 m. The plan area of tank may vary from 100 to 2000 m2.
 Filter media
 The filter media consists of sand layer 90 to 110 cm thick. The effective size of
sand Filter media the sand from 0.20 to 0.35 with a common value of 0.30. The
uniformity coefficient of sand s from 2 to 3, the common value being 2.5.
 The finer the sand, better will be bacterial efficiency but slower will be the
filtration.
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SLOW SAND FILTERS
 Base material : The base materials are gravel, and it supports the sand. Gravel is
placed on the top under drainage system
 The depth varies from 30to 75 cm.
DEPTH SIZE
TOP MOST LAYER-15 cm 3 mm to 6mm
Intermediate layer 15 cm 3 mm to 6mm
Bottom layer-15 cm 3 mm to 6mm
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SLOW SAND FILTERS
4. Under drainage system
 Base material and filter media are supported by under drainage system.
 Under drainage system collects filtered water and delivers it to the reservoir
 Laterals – earthenware pipes of 7.5 to 10 cm dia.
 Spacing of laterals- 2 to 3 m c/c
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SLOW SAND FILTERS
Under drainage system
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SLOW SAND FILTERS
5. Appurtenances
 Measuring head loss through Gauge.
 Controlling depth of water above filter media
 Maintaining constant rate of filtration through the filter
 Telescopic tubee for maintaining constant discharge
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ADVANTAGES & DISADVANTAGES
ADVANTAGES
 Very effective removal of bacteria,
viruses, protozoa, turbidity and heavy
metals in contaminated fresh water
 Simplicity of design and high self-help
compatibility
 If constructed with gravity flow only,
no (electrical) pumps required
DISADVANTAGES
 Turbidity (<10-20 NTU) and low algae
contamination. If then pre-treatment
may be necessary
 Cold temperatures lower the efficiency
of the process due to a decrease in
biological activity
 Very regular maintenance essential
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ADVANTAGES
 Local materials can be used for
construction
 No necessity for the application of
chemicals
 Easy to install in rural, semi-urban and
remote areas,
 Long lifespan (estimated >10 years)
DISADVANTAGES
 Chemical compounds (e.g. fluorine)
are not removed if added
 May require electricity
 Requirement of a large land area, large
quantities of filter media and manual
labour for cleaning, Low filtration rate
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RAPID SAND FILTERS
Valv
e no. Name ofValve
1 Inlet valve
2 Filtered water storage tank valve
3 Waste water valve to drain water from
inlet number
4 Wash water storage tank valve
5 Waste water valve to drain water from
main drain
6 Compressed air valve
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RAPID SAND FILTERS
 Essential Features :
 1. Enclosure tank
 2. Filter Media
 3. Base material
 4. Under Drainage System
 5. Appurtances
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RAPID SAND FILTERS
 1. Enclosure tank :
 Smaller in size, therefore can be placed under roof.
 Rectangular in shape and constructed of concrete or masonry.
 Depth – 2.5 to 3.5
 Surface area – 10 to 80 m2.
 L/B ratio – 1.25 to 1.35.
• Designed filtration rate - 3000 to 6000 lit/m2/hr
Number of filter units= (given by Moral equation) (2 filters unit minimum)
N= 1.22√Q
Q= million litres per day
N= number of units
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RAPID SAND FILTERS
2. Filter media
 Should be free from dirt, organic matter and other Suspended Solid.
 Depth of sand media – 0.6 to 0.9 m
 Effective size – 0.35 to 0.6 mm (Common value 0.45)
 Uniformity coefficient – 1.2 to 1.7 (Common value -1.5)
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RAPID SAND FILTERS
Layer Depth Grain Size
Top Layer
15cm
2mm to 6 mm
Intermediate Layer 6 mm to 12 mm
Intermediate Layer 12 mm to 20mm
Bottom Layer 20mm to 50mm
3. Base materials :
Multiple layer of Graded Gravel Layers (4-5 Layers)
Each layers of 10-15 cm thick
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RAPID SAND FILTERS
4. Under drainage system
 It collects filtered water uniformly over the area of gravel bed
 It provides uniform distribution of backwash water without disturbing the gravel
bed and filter media.
 Types of Under Drainage system:
 Perforated pipe system
 Pipe and strainer system
 Wheeler system
 Wagner system
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RAPID SAND FILTERS
 5. Appurtenances :
 Wash water troughs
 Air compressor
 Rate controller
 Head loss Controller
 Metering for measuring flow of water
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BACKWASHING
 Amount of Water Required : 2 % to 5% of total water filtered
 Washing period - 24-48 hours
 Rate of washing – 15-90cm/minute
 Time taken for back washing – 15 minutes
 Rate of filtration of Rapid Sand filter : 30 times more than Slow sand filter
- 3000-6000 l/hr/m2
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ADVANTAGES
 Turbid water may treat
 Operation is continuous
 Land required is less compared to slow
sand filter
DIS-ADVANTAGES
 Requires skill person
 Less effective in bacterial removal
 Mud balls are formed on the sand bed
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PRESSURE FILTER
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PRESSURE FILTER
 Small rapid sand gravity filter placed in closed vessel
 Pressure applied is more than atmospheric pressure
 PRESSURE RATE : 300-700 kn/m2
 Rate of Filtration : 6000-15000 l/hr/m2
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ADVANTAGES
 It’s a compact unit
 Suitable for small water works only
 Requires smaller area for installation
 Small number of fittings are required
 Seimentation and co-agulation are
avoided
 Rate of filteration is more due to its
pumping pressure
DIS-ADVANTAGES
 Overfall capacity of plant is samll
 Due its higher cost cannot use for large
quantity of water
 It is less efficient in removing bacteria
& turbidity
 Requires additional pumps
 Back washing is difficult due to its
circular shape.
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DISINFECTION OF WATER
 The process of killing the pathogenic bacteria from the water and making it safe to
user is called DISINFECTION.
 It does not mean total destruction of all living organisms in water
 When the aim is to kill all the micro organisms in water so as to make it sterile(no
bacteria present in water) process is known as sterilization.
 The filtered water which is obtained either from slow sand filter or rapid gravity
filter may contain some harmful disease producing bacteria in it.
 Before the water is supplied to the public it is almost necessary to kill all the
disease causing bacteria.
 The chemicals or substances which are used for killing the bacteria are known as
disinfectants and the process of killing the bacteria is known as DISINFECTION
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REQUIREMENTS OF IDEAL
DISINFECTANT
 It shall kill pathogenic bacteria
 It should act rapidly
 It shouldn’t change quality of water
 It should be easy and economic
 It should not make water poisonous
 It should not require high skill
 It should be safe to handle
 It must be capable of being dissolved in water
 It must be able to leave some residual of concentration
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MINOR METHOD OF DISINFECTION
1. Boiling of water
2. Excess lime treatment
3. Treatment with UV-Rays
4. Treatment with ozone
5. Treatment with iodine and bromine
6. Treatment with potassium permanganate
7. Treatment with silver, called electro-Katadyn process
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 Boiling of water :
 Removes the present bacteria
 Kills the micro-organism
 It is uneconomical due to large consumption of fuel
 It doesn’t make sure for future recontamination
Dhara Dattani 95

 Addition of lime :
 In forms of Calcium oxide (CaO) and Ca(OH)2 quick lime/slag lime
 Addition of lime leads to PH>9.5 ,causes alkalinity
 Re-carbonation (Adding carbon di-oxide in water) is done to remove alkalinity
 If we add dosage of lime upto 14-40mg/lt it will reduces bacterial load upto 99.3%.
Dhara Dattani 96

 Treatment with UV-rays :
 Electric current is passed through mercury in quartz bulbs and it generates uv rays
 It removes present bacteria by sterilization method
 It doesn’t impart any taste in water
 Used in small swimming pools
 Highly costly
Dhara Dattani 97

 Treatment with ozone
 O3 02 + o
 Ozone= oxygen + Nascent oxygen (powerful oxidising agent & removes Organic matter )

Dhara Dattani 98
Advantages Dis-advantage
It removes color, & organic matter Nascent oxygen is unstable
It gives pleasant taste to water It doesn’t have residual capacity
Dosage of O3 2-3 ppm so that residual
capacity is 0.1 ppm when it is in contact
period of 10 min
 Ozonise – apparatus /equipment used for
producing ozone is very costly
It doesn’t make sure for future
recontamination

 Treatment with Bromine & Iodine Pills :
 Dosage up-to : 8ppm
 Kills existing Bacteria
 Doesn’t take care of future contamination
 Its hand and cheaply available
Dhara Dattani 99

 Treatment with KMNO4
 It is used in village for well water which is less contaminated with bacteria.( kills only
present bacteria)
 It improves the taste of water and also kills bacteria up-to 98% adding this it also kills 100%
cholera disease( water born) bacteria
 KMNO4 is added in to full fill bucket (water taken from well). The water turns into pink
colour, after that mix that water into the well. If pink colour disappeared, it implies that
organic matter is present. Hence more KMNO4 is added till pink colour becomes stable. The
well is not used for 48 hours.
 If this water(KMNO4) used more and more in household purpose, utensils coloured will be
brown.
 Dosage rate : 1-2 mg/lt.
 Contact time period: 4-6 hours
Dhara Dattani 100

 Treatment with silver or electro-katadyan Process:
 Strong Germicidal action
 Dosage 0.05-0.1mg/lt
 Contact period may vary from 15mins to 3 hours
 Neither imparts any taste and odour to the water nor it produces effect on human
body.
 The method ,however removes algae and its germicidal property is retained for a
considered time, this is safeguard against future recontamination
Dhara Dattani 101

CHLORINATION
 It kills the present existing bacteria
 It possess residual capacity
Dhara Dattani 102

CHLORINATION
 Chlorine in its various form is invariably universally used for disinfecting public
water supplies.
 It is cheap ,easy, reliable and capable for producing residual disinfecting effects
 Main disadvantage if used in higher rate it tastes bitter in water
 DOSE OF CHLORINE :
 Chlorine and chlorine compounds, by virtue of their oxidising power, first reacts
with organic as well as inorganic impurities present in water.
 The amount of chlorine consumed the oxidation of these impurities, before any
disinfection is achieved is known as chlorine demand of water.
 After the chlorine demand is fulfilled, chlorine will appear as free available residual
chlorine
Dhara Dattani 103

TYPES OF CHLORINATION
 Plain chlorination
 Pre-chlorination
 Post chlorination
 Double chlorination
 Super chlorination
 Break point chlorination
 De chlorination
Dhara Dattani 104

 PLAIN CHLORINATION
 It only indicates that only chlorine treatment is given to Raw water
 After chlorination treatment water is distributed to next unit
 Mainly plain chlorination is used in hilly areas ,where natural springs and lakes of
water is available.
 Dosage : 0.50mg/lt
Dhara Dattani 105

 PRE-CHLORINATION :
 Treatment is given in high turbidity water
 Treatment is given before filtration process
 Sometimes, also used before plain sedimentation process
 This is done to reduce less use of coagulants and less load on filters
 Dosage rate should be adjusted that chlorine residual must be of 0.1 to 0.5ppm
when it enters to filtration process
Dhara Dattani 106

 POST CHLORINATION :
 The term post suggests the process, that chlorine must be added into water after the process
of filtration and before water supplies to the public.
 Dosage of chlorine is so adjusted that residual of chlorine must be available up-to 0.1-0.2
ppm before it supplies to Public.
 DOUBLE CHLORINATION :
 Double chlorination name suggests that , Double or multiple application of chlorine at two
or more points in the purification process.
 Chlorine is just applied before sedimentation and also applied after filtration process (Pre
chlorination+ post chlorination).
 Used only at highly contaminated zone or more bacteria and organic matters are present.
Dhara Dattani 107

 BREAK POINT CHLORINATION :
 It is a point where all the impurities present in
water such as reducing compounds organic
compound and ammonia are oxide by chlorine and
the chlorine is added further acts as a disinfectant
to kill pathogenic bacteria.
Dhara Dattani 108

 BREAK POINT CHLORINATION :
 Up-to A : chlorine reacts with reducing compounds – no
residual chlorine
 A to B : chlorine reacts with organic impurities and nitrogen
compound like ammonia to form chlor-organics and
chloramines. (Combined chlorine residuals)
 B to C : Partial destruction of chloro-organics and chloramines
 C : Breakpoint chlorination – All the reducing substances,
organic impurities and ammonia are oxidised and further
residual chlorine acts as a disinfectant to destroy the
pathogens.
 Beyond C: Total residual chlorine (free and combined
chlorine) – acts as a disinfectant.
Dhara Dattani 109

 SUPER CHLORINATION :
 Super chlorination is used beyond the stage of Break point chlorination
 Required in specially more polluted areas or where more water borne disease
 Huge quantity of chlorine is added into super chlorination so 1-2 mg/lt of residual
beyond break point chlorination
 It gives strong odour & taste into treated water which can be removed by De-
chlorination
Dhara Dattani 110

 De-chlorination :
 The process of removing excess chlorine from water before distribution to public,
to avoid chlorine tastes.
 It is mainly used after super-chlorination process
 Residual remains in dichlorination is : 0.1-0.2 mg/lt
 De-chlorine agents :
 Sulphur di-oxide gas
 Activated carbon
 Pottasium permagnate
 Sodium-(bio/thio) sulphate
Dhara Dattani 111

WATER SOFTENING
 Removal of hardness from water is known as water softening
 Water is said to be hard when it contains large amount of bicarbonates, carbonates,sulphayes
and chlorides of calcium and magnesium dissolved in it. It requires more consumption of
soap in producing lather and washing of clothes in hard water than soft water
 NECESSITY OF WATER SOFTENING :
 More quantity of soap is consumed
 Fabric of clothes are destroyed in hard water
 Causes serious difficulties in producing paper, rayon, ice industry etc
 It causes formation on boilers
 It makes food tasteless
 It causes clogging and choking of house plumbing system due to hardness of salt presents in
water Dhara Dattani 112

TYPES OF HARDNESS
 Permanent hardness
 Temporary hardness
Dhara Dattani 113

TYPES OF HARDNESS
TEMPORARY HARDNESS :
 The temporary hardness is also known as carbonate hardness and is mainly due to
presence of bicarbonates of calcium and magnesium.
 The permanent hardness is also known as non-carbonate hardness and is mainly
due to presence of sulphates, chlorides and nitrates of calcium and magnesium.
Dhara Dattani 114

TYPES OF HARDNESS
 HARDNESS COMPOUNDS
Dhara Dattani 115
Causing Temporary Hardness Causing permanent Hardness
Calcium bi-carbonates (Ca(HCO3) Calcium sulphate CaSO4
Magnesium bi-carbonate Mg(HCO3 )2 Magnesium sulphateMgSO4
Calcium chlorideCaCl2
Magnesium chloride MgCl2

TYPES OF HARDNESS
Removal of Temporary Hardness :
1. By boiling
2. By adding lime
Removal of Permanent Hardness :
1. Lime-soda process
2. Zeolite process
3. Demineralization
Dhara Dattani 116

REMOVAL OF TEMPORARY HARDNESS-
BY BOILING
WHEN BOILED :
Ca(HCO3)2
 Calcium and magnesium elements presents in water
 which settles down when water is get heated
 So, By boiling Temporary hardness is removed
Dhara Dattani 117
Removing Temporary Hardness
CaCo3 + CO2+ H2O
Heat
Calcium hydrogen
carbonate
Calcium
carbonate
Carbon di-oxide
Water

REMOVAL OF TEMPORARY HARDNESS-
ADDITION OF LIME
 The magnesium carbonate is fairly Dissolved in water which cannot be removed by
boiling ,but can be removed by addition of lime
 Mgco3 + Ca(OH)2 = Mg(OH)2 + CaCo3 Settles down
 Similarly, Magnesium Bi-carbonate
 Mg(HCO3)2 + Ca(OH)2 = Ca(HCO3)2 + Mg(OH)2
 Ca(HCO3) + Ca(OH)2 = 2CaCO3 + 2H2O (Water)
Dhara Dattani 118
Soluble Hydrated Lime Insoluble Insoluble

METHOD OF REMOVING PERMANENT
HARDNESS -LIME SODA PROCESS
 Lime [Ca(OH)2] + Soda [Na2CO3] Water
 Removing
 1. Lime - Carbonate Hardness
 2. Soda - Non-carbonate Hardness
Dhara Dattani 119
Calcium Carbonate [CaCO3] and
Magnesium Hydroxide [Mg(OH)2]
Removing Water

 Zeolite Removing Hardness
Dhara Dattani 120
SALT & CLAY HYDRATE & SILICATE OF
SODIUM & ALUMINUM
Nat+ ion > Ca+ & Mg NO HARDNESS
SAND REPLACES ZEOLITE
HARDNESS - BASE EXCHANGE PROCESS
OR ZEOLITE PROCESS

 DISADVANTAGES:
 NOT SUITABLE FOR HIGHLY TURBID WATER
 IT IS COSTLY
Dhara Dattani 121
HARDNESS - BASE EXCHANGE PROCESS
OR ZEOLITE PROCESS

Dhara Dattani 122
REMOVINGALLTYPES OF MINERALS
REMOVINGALLTYPES OF HARDNESS
THIS TREATED WATER IS CALLED=
DEMINERALIZATION
Uses : For Industrial Purpose
Steam Resisting In High Pressure Boilers
HARDNESS - DEMENIRALIZATION OF
WATER

Dhara Dattani 123
END OF CHAPTER-3

Treatment of water

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