Coagulation and flocculation in watertreatment

1. 03/28/17 water treatment 1
Presented by :-
Prof. Kalpesh Solanki
Major Clean Up Water Treatment Processes:-
Coagulation , Flocculation, Filtration

2. Course Content
 Introduction
 Water treatment process or Methods
 Coagulation and flocculation
 Filtration

3. Introduction
Why it is needed?
 To kill all pathogenic germs, which are harmful to human health
 To remove the unpleasant and objectionable taste and odours
from the water
 To remove dissolved gases ,colour of water
 To make water fit for domestic, industrial, and commercial uses.
 To remove micro organism and colloidal matters
 To remove hardness of water
03/28/17 water treatment
3

4. Raw water collection
03/28/17 water treatment 4

5. Initial Stages
Screening - the removal of any floating objects like leaves,
branches, fishes , weeds, etc. from the water.

6. 03/28/17 water treatment 6

7. 03/28/17 water treatment 7
Sedimentation:
Removal of Suspended matters having higher
specific gravity than water and also fine suspended matter.

8. 03/28/17 water treatment 8
Aeration –
Dissolving oxygen into the water to remove smell
and taste, promote helpful bacteria to grow, and precipitate
nuisance metals like iron and manganese.

9. 03/28/17 water treatment 9

10. 03/28/17 water treatment 10
Spray aerators

11. Major Clean Up
• Coagulation and flocculation - causes the agglomeration
and sedimentation of suspended solid particles through
the addition of a coagulating agent (usually aluminum
sulfate and/or iron sulfate) to the raw water along with a
polymer to help form a floc.
• Filtration- Remove Micro-organism and colloidal matter
• Disinfection---Pre-chlorination and dechlorination - mostly
to kill algae that would otherwise grow and clog the water
filters. Also kills much of the remaining unprotected
bacteria.
• Softening- To remove hardness

12. 03/28/17 water treatment 12
COAGULATION & FLOCCULATION
 Removal of colloidal substances from water
 Potable water requirements:
health, aesthetics, economic
 Colloids
 Size of colloids - light waves
 Brownian motion
 Stability of colloids

13. 03/28/17 water treatment 13

14. 03/28/17 water treatment 14
Theory of coagulation
Coagulation is the destabilization of colloids by addition of
chemicals that neutralize the negative charges
 The chemicals are known as coagulants, usually higher
valence
 cationic salts (Al3+
, Fe3+
etc.)
 Coagulation is essentially a chemical process
Ionic layer compression
Adsorption and charge neutralization
Entrapment in a flocculent mass

15. 03/28/17 water treatment 15
 Relative coagulating power
Na+
= 1; Mg2+
= 30
Al3+
> 1000; Fe3+
> 1000
 Typical coagulants
Aluminum sulfate: Al2(SO4)3.14 H2O
Iron salt- Ferric sulfate: Fe2(SO4)3
Iron salt- Ferric chloride: Fe2Cl3
Polyaluminum chloride (PAC): Al2(OH)3Cl3

16. 03/28/17 water treatment 16
Aluminum Chemistry
1 mole of alum consumes 6 moles of bicarbonate (HCO3
-
)
Al2(SO4)3.14 H2O + 6HCO3
-
⇔ 2Al(OH)3↓+ 6CO2 + 14H2O + 3SO4
-2
•If alkalinity is not enough, pH will reduce greatly
•Lime or sodium carbonate may be needed to neutralize the
acid.
•(Optimum pH: 5.5 – 6.5)
With alum addition, what happens to water pH?
Al2(SO4)3.14 H2O ⇔ 2Al(OH)3↓+ 8H2O + 3H2SO4
-2

17. 03/28/17 water treatment 17
Alkalinity calculation
Al2(SO4)3.14 H2O + 6HCO3
-
⇔ 2Al(OH)3↓+ 6CO2 + 14H2O + 3SO4
-2
594 mg 366 mg
If 200 mg/L of alum to be added to achieve complete
coagulation. How much alkalinity is consumed in mg/L as
CaCO3?
594 mg alum consumes = 366 mg HCO3
-
200 mg alum will consume = (366/594) x 200 mg HCO3
-
= 123 mg HCO3
-
Alkalinity in mg/L as CaCO3 = 123 x (50/61)
= 101 mg/L as CaCO3

18. Al3+
species as a function of pH
03/28/17 water treatment 18

19. 03/28/17 water treatment 19
Iron Chemistry
FeCl3+ 3HCO3
-
⇔ Fe(OH)3↓+ 3CO2 + 3Cl-
With iron salt addition, what happens to water pH?
(Wider pH range of: 4 – 9; Best pH range of 4.5 – 5.5)
1 mole of FeCl3 consumes 3 moles of bicarbonate (HCO3)
If alkalinity is not enough, pH will reduce greatly due to
hydrochloric acid formation. Lime or sodium carbonate may
be needed to neutralize the acid. Lime is the cheapest.

20. Mixing device
03/28/17 water treatment 20
1- Mixing basins with baffle walls
2- Mixing basin with mechanical devices (Rapid mixing)

21. 03/28/17 water treatment 21
• Rapid or Flash mixing is the process by which a
coagulant is rapidly and uniformly dispersed through the
mass of water. This process usually occurs in a small basin
immediately preceding or at the head of the coagulation
basin. Generally, the detention period is 30 to 60 seconds and
the head loss is 20 to 60 cms of water. Here colloids are
destabilized and the nucleus for the floc is formed.
 Slow mixing brings the contacts between the finely
divided destabilised matter formed during rapid mixing.

22. Coagulation aim
03/28/17 water treatment 22

23. What is Flocculation?
03/28/17 water treatment 23
Flocculation is the agglomeration of destabilized particles
into a large size particles known as flocs which can be
effectively removed by sedimentation or flotation.

24. 03/28/17 water treatment 24

25. 03/28/17 water treatment 25

26. 03/28/17 water treatment 26
Why coagulation and flocculation?
Various sizes of particles in raw water
Particle diameter (mm) Type Settling velocity
10 Pebble 0.73 m/s
1 Course sand 0.23 m/s
0.1 Fine sand 0.6 m/min
0.01 Silt 8.6 m/d
0.00010.0001 (10 micron)(10 micron) Large colloidsLarge colloids 0.3 m/y0.3 m/y
0.000001 (1 nano)0.000001 (1 nano) Small colloidsSmall colloids 3 m/million y3 m/million y
Particle diameter (mm) Type Settling velocity
10 Pebble 0.73 m/s
1 Course sand 0.23 m/s
0.1 Fine sand 0.6 m/min
0.01 Silt 8.6 m/d
0.00010.0001 (10 micron)(10 micron) Large colloidsLarge colloids 0.3 m/y0.3 m/y
0.000001 (1 nano)0.000001 (1 nano) Small colloidsSmall colloids 3 m/million y3 m/million y
Colloids – so small: gravity settling not possible
GravItysettlIng

27. Fe species as a function of pH
03/28/17 water treatment 27

28. 03/28/17 water treatment 28
Hydraulic Flocculation
• Horizontally baffled tank
Plan view (horizontal flow)
• Vertically baffled tank
L
Isometric View (vertical flow)
L
W
H
The water flows horizontally.
The baffle walls help to create
turbulence and thus facilitate
mixing
The water flows vertically.
The baffle walls help to
create turbulence and thus
facilitate mixing

29. 03/28/17 water treatment 29
http://www.environmental-center.com/magazine/iwa/jws/art4.pdf
Hydraulic Flocculation

30. Hydraulic flocculators
03/28/17 water treatment 30

31. 03/28/17 water treatment 31
Hydraulic flocculators:
simple technology

32. 03/28/17 water treatment 32
Flocculators integrated with settling

33. 03/28/17 water treatment 33
Flocculators integrated with settling

34. 03/28/17 water treatment 34
Flocculators both sides of settling

35. Clarifier
• After Flocculation Water enters the settling tank which is
commonly called Clarifier.
Clariflocculator
In modern practice, flocculator and clarifier are
provided in one unit called Clariflocculator in which
chamber is provided in the center and clarifier
compartment is formed by the periferical space.
03/28/17 water treatment 35

36. 03/28/17 water treatment 36

37. 03/28/17 water treatment 37

38. Filtration
03/28/17 water treatment 38
The process of passing the water through the bed of such
granular materials is known as filtration.
Types of filter
1- The slow sand gravity filter
2- Rapid sand filter

39. Slow sand filters are used in water purification for treating
raw water to produce a potable product. They are typically 1
to 2 metres deep, can be rectangular or cylindrical in cross
section and are used primarily to treat surface water.
Filter through a 3 to 5 foot deep bed of unstratified sand
flow rate 0.05 gallons per minute per square foot.
Biological growth develops in the upper surface of the sand
is primarily responsible for particle and microbe removal.
Effective without pretreatment of the water by
coagulation flocculation‑ .
Periodically clean by removing, cleaning and replacing the
upper few inches of biologically active sand.
03/28/17 water treatment 39

40. 03/28/17 water treatment 40

41. Microbial Reductions by Slow Sand
Filtration
• Effective in removing enteric microbes from water.
• Virus removals >99% in lab models of slow sand filters.
– Up to 4 log10; no infectious viruses recovered from filter
effluents
• Field studies:
– naturally occurring enteric viruses removals
• 97 to >99.8 percent; average 98% overall;
• Comparable removals of E. coli bacteria.
– Virus removals=99 99.9%;‑
– high bacteria removals (UK study)
• Parasite removals: Giardia lamblia cysts effectively
removed
– Expected removals ~ 99%

42. Rapid sand filters
03/28/17 water treatment 42
Rapid sand filtration is a purely physical
drinking water purification method. Rapid sand filters (RSF)
provide rapid and efficient removal of relatively large
suspended particles. Two types of RSF are typically used:
Rapid gravity
Rapid pressure sand filters

43. 03/28/17 water treatment 43
•The biggest disadvantages of slow sand filter is that it
requires large area due to slow filtration rate.
•This Requirement make it uneconomical for places where
land is very costly in urban area. In order to reduce
requirement of space and to increase the rate of filtration , a
lot of research conducted which finally led to the developed
of rapid sand filter.

44. 03/28/17 water treatment 44
Rapid sand filters have filter rates 40 times those of slow
sand filters. The major parts of a rapid sand filter are:
• Filter tank or filter box
• Filter sand or mixed-media
• Gravel support bed
• Under drain system
• Wash water troughs
• Filter bed agitators

45. 03/28/17 water treatment 45

46. 03/28/17 water treatment 46
PRESSURE FILTERS
Pressure filters fall into two categories:
pressure sand and diatomaceous earth filters. Pressure
filters are used extensively in iron and manganese removal
plants. A pressure sand filter is contained under pressure in
a steel tank, which may be vertical or horizontal, depending
on the space available. As with gravity filters, the media is
usually sand or a combination of media, and filtration rates
are similar to gravity filters. Groundwater is first aerated to
oxidize the iron or manganese, and then pumped through the
filter to remove the suspended material.

47. 03/28/17 water treatment 47

48. Construction rapid sand filter
03/28/17 water treatment 48
1- Enclosure tank
2- Filter Media
3- Base material
4- Under Drainage system
5- Other appurtenances

49. Enclosure tank
03/28/17 water treatment 49
Rectangular in plan
Constructed either of masonary or of concrete , coated with
water proof material
Depth- 2.5 to 3.5 m
surface area- 10 to 50 m2
length to width ratio 1.25 to 1.35

50. Filter media
03/28/17 water treatment 50
 It consist sand layer -60 to 90 cm in depth
 Effective size of sand varies from 0.35 to 0.6 mm
 finer sand be used

51. Base material
03/28/17 water treatment 51
 Graded gravel
 total depth varies from 45 to 60 cm
Divided in to 4 to 5 layers
Size (mm) Depth
(cm)
2 to 5 5-8
5 to 12 5-8
12 to 20 8-13
20 to 38 8-13
38 to 65 13-20

52. Under drainage system
03/28/17 water treatment 52
Purpose:
 It collect the filtered water uniformly over the area of gravel
bed.
 It provides uniform distribution of backwash water without
disturbing the gravel bed and filter media.

53. Types of under drainage system
03/28/17 water treatment 53
1- Manifold and lateral System

54. 03/28/17 water treatment 54

55. 03/28/17 water treatment 55
Wheeler system

56. 03/28/17 water treatment 56
Leopald system

57. 03/28/17 water treatment 57

58. 03/28/17 water treatment 58
THANK
YOU