Water treatment plants use various processes to purify water for human consumption and other uses. The key processes include screening to remove large solids, sedimentation to remove suspended particles, coagulation and flocculation to help sedimentation, filtration, disinfection to kill bacteria and other microbes, and sometimes aeration and softening. Together, these treatment steps aim to produce water that is safe to drink, aesthetically pleasing, and at a reasonable cost for consumers.

2. OUTLINE
Introduction
Objectives of water treatment
Conventional water treatment plant layout
Various Methods of purificationof water
Screening
Plain Sedimentation
Sedimentation aided with coagulation
Filtration
Disinfection
Aeration
Softening

3. Introduction
water suitable or
W
ater treatment is the process of
making acceptableforan end-use.
It removes existing water contaminants and so reduces their
concentrationthatthewaterbecomesfitforitsdesired application.
The amount & type of treatment process (Treatment Train )
dependsuponquality of rawwaterandvarious standards required
aftertreatment.

4. Objectives of water
treatment
The objectivesofwatertreatmentareto produce:
Waterthatissafeforhuman consumption
Waterthatisappealingaestheticallytothe consumer
Wateratareasonable cost

5. Indian Standards for drinking
water

6. Screenin
g
Coagulation
Flocculation
Sedimentation
Filtration
Disinfection
Storag
e
Distribution
Raw water
Alum Cl2
sludge
sludge
sludge
7

8. Functions of Water Treatment
Units

9. Selection of treatment process-
Train
The types of treatment required for different sources are given in the
following table:

10. Removeslargesolids
logs
branche
s rags
fish
Simpleprocess
mayincorporateamechanizedtrashremovalsystem
ProtectspumpsandpipesinWaterTreatment Plants

11. Plain
Sedimentation
Sedimentation is the removal of suspended particles
by gravitational settling.
 Types of Sedimentation Tanks
1) Fill And Draw Type
2) Continuous Flowtype

12. Shape of sedimentation
tank
1. Rectangular
tank with
horizontal flow.
2. Circular tank
with radial or
spiral flow.
3. Hopper bottom
tank with
vertical flow.

13. SEDIMENTATION
13
Water flows to a tank called a
sedimentationbasin
Gravity causes the flocs to settle to the
bottom
It would take a very long time for all
particles to settle out and that would
mean we would need a very large
sedimentationbasin.

14. Sedimentation aided with
coagulation
 Sedimentation added with comprises of three step
Addition of measured quantity of chemicals called
coagulants to water and their through mixing ( rapid
mixing ).
Formation of precipitate which coagulates and forms a
flow ( flocculation )
Sedimentation

15. Coagulants
AluminumSulfateAl2(SO4)3
FerrousSulfateFeSO4
FerricSulfateFe2(SO4)3
FerricChlorideFeCl3
LimeCa(OH)2
Aluminumsaltsarecheaperbut iron
salts are more effective over wider
pH range
15

16. AerationUnit
Work : Diffusion of Air
Removes odour and tastes
Oxidizes iron and manganese, increases dissolved oxygen content in
water, removes CO2 and reduces corrosion and removes methane and
other flammablegases.
Types of Aerators
1. Gravity aerators
2. Fountain aerators
3. Diffused aerators
4. Mechanical aerators.

17. Gravity Aerators (Cascades): In gravity aerators,
water is allowed to fall by gravity such that a large area
of water is exposed to atmosphere, sometimes aided by
turbulence.
AerationUnit

18. Injection or Diffused Aerators : It
consists of a tank with perforated
pipes, tubes or diffuser plates, fixed
at the bottom to release fine air
bubbles from compressor unit. Time
of aeration is 10to 30 min and 0.2 to
0.4 litres of air is required for 1litre
of water.
AerationUnit

19. Fountain Aerators : These are also known as spray
aerators with special nozzles to produce a fine spray. Each
nozzle is 2.5 to 4 cm diameter discharging about 18 to 36
l/h. Nozzle spacing should be such that each m3 of water
has aerator area of 0.03 to 0.09 m2 for one hour.
AerationUnit

20. Mechanical Aerators
flocculation are used.
: Mixing
Paddles
paddles
may be
as in
either
submerged or at the surface.
Aeration
Uni
t

21. Types of Mixing
Devices
 Mixings basins with baffle walls
`

22. Mixing Basins Equipped with Mechanicaldevicies

23. Flocculation
 Flocculation is a slow mixing or agitating process in which
the destablished colloidal particles are brought into
intimate contact in order to promote the floc formation .
 Rate of flocculation depends upon
 Types and amountof turbidity
 Types of coagulant
 Dosages of coagulant
 Mean velocity gradient in basin

24. Clariflocculat
or
Clarifier and flocculator are provided in single unit
called clariflocculator.
The flocculating chamber is provided in the centre
and clarifier component is formed by the peripheral
space.
Velocity of flow of water around 0.3 m/min.
Mechanical scrapper provided to remove sludge.

26. Filtration
The process of passing the water through the beds of
such granular material is known as filteraton
 Types of Filtration
Slow sand gravityfilter
Rapid sand gravityfilter
1. Rapid sand gravityfilter
2. Pressure filter

29. Method of disinfection
 Physical method
By heat
By U.V. rays
 Chemical method
Oxidizing chemicals
Metal ions
Alkalis and acids
 Minor method
Boiling of water
Treatment withexcess lime
Treatment withozone
Treatment with iodine and bromine
Treatment with ultra-violet rays
Treatment with potassium permanganate

30. Water softening
 Water is said to be hard when it contains relatively large
amounts of bicarbonates, carbonates, sulphates and
chlorides of calcium and magnesium dissolved in it.
 Types of Hardness
 Temporary hardness
 Permanent hardness

31. Types of Hardness
caused by dissolved
Temporary Hardness-
bicarbonates of Ca and Mg.
-AKA‘alkaline orcarbonate hardness’
Permanent Hardness – caused by dissolved
chlorides and sulphates of Ca, Mg, Fe and Aletc.

32. Removalof Hardness
Removal of temporary hardness
1.Boiling
2. By adding lime
Removal of temporary hardness
1.Lime-soda process
2. Zeolite process
3. Demineralization orDe-ionization process

33. Disinfection
The filtered water may
normally contain some
harmful disease producing
bacteria in it.
These bacteria must be
killed in order to make the
watersafe for drinking.
The process of killing these
Disinfection
bacteria is known as
or
Sterilization.

34. Methods of
Disinfection
 Boiling: The bacteria present in water can be destroyed by boiling it for a long
time. However it isnot.
 Treatment with Excess Lime: Lime is used in water treatment plant for
softening. But if excess lime is added to the water, it can in addition, kill the
bacteria also. Treatment like recarbonation for lime removal should be used
after disinfection.
 Treatment with Ozone: Ozone readily breaks down into normal oxygen, and
releases nascent oxygen. The nascent oxygen is a powerful oxidizing agent and
removes the organic matter as well as the bacteria from the water.
 Chlorination : The germicidal action of chlorine is explained by the recent
theory of Enzymatic hypothesis, according to which the chlorine enters the cell
walls of bacteria and kill the enzymes which are essential for the metabolic
processes of living organisms.