This presentation summarizes coagulation and flocculation techniques used in water treatment. Coagulation involves adding chemicals like alum to destabilize colloidal particles in water. Flocculation then aggregates these micro-flocs into larger macro-flocs that are easier to remove by settling. Jar tests are used to determine the optimum pH and coagulant dose. Various mixers like paddles and turbines are used for flocculation to induce velocity gradients and differential settling of the flocs.

1. Presentation on
Coagulation and Flocculation
Presented by:
Mr. Muhammad Azeem
Presented to:
Engr. Muhammad Sulaiman
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2. Outlines
 Purpose of Techniques
 Coagulation
 Coagulants
 Selection of Coagulant
 Amount of Coagulant
 Flocculation
 Types of Flocculation
 Flocculation Mixers
 Conclusion
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3. Purpose
 Settling of stabilized particles
 Destabilization of colloidal particles
 Increase the density of colloidal particles
 Reduction in repulsive forces between
particles
 Diminish the turbidity of water
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4. Coagulation
Coagulation is the destabilization of colloidal
and fine suspended solids by adding a chemical
coagulant such as alum in the water.
 Neutralization of negatively charged particles
 Micro-flocs formation
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+
Coagulant
Coagulation
Tank
Destabilization
of colloids

5. Coagulation
5
Coagulant Coagulation
Micro-flocs
Water
Rapid Mixing

6. Commonly Used Coagulants
Coagulant Formula
Aluminum Sulfate Al2(SO4)3 · 14H2O
Sodium Aluminate Na2Al2O4
Aluminum Chloride AlCl3
Ferric Chloride FeCl3
Ferric Sulfate Fe2(SO4)3
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7. Selection of Coagulant
A coagulant is selected on the basis of:
 Type of Coagulant (anionic, cationic)
 Molecular Weight (high)
 Charge Density (high)
 Toxicity (non toxic)
 Solubility (insoluble in neutral pH range)
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8. Type of Coagulant
Cationic:
 In the process of coagulation
 Positively charged coagulant
Anionic:
 In the process of flocculation
 Negatively charged coagulant used as
flocculent
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9. Amount of Coagulant?
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10. Jar Test
 Jar test is a laboratory procedure to determine
the optimum pH and the optimum coagulant
dose
 A jar test simulates the coagulation and
flocculation processes
 Fill the jars with raw water sample (500 or
1000 mL), usually 6 jars
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Determination of optimum pH:

11. Jar Test - Optimum pH
 Adjust pH of the jars while mixing using
H2SO4 or NaOH/lime (pH: 5.0; 5.5; 6.0; 6.5;
7.0; 7.5)
 Add same dose of the selected coagulant (alum
or iron) to each jar (coagulant dose: 5 or 10
mg/L)
 Rapid mix each jar at 100 to 150 rpm for 1
minute. The rapid mix helps to disperse the
coagulant throughout each container
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12. Jar Test - Optimum pH
 Reduce the stirring speed to 25 to 30 rpm and
continue mixing for 15 to 20 mins. This slower
mixing speed helps to promote flocs formation
by enhancing particle collisions, which lead to
larger flocs
 Turn off the mixers and allow flocs to settle for
30 to 45 mins
 Measure the final residual turbidity in each jar
 Plot residual turbidity against pH
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13. Jar Test - Optimum pH
13Optimum pH: 6.3
0
5
10
15
20
4.5 5 5.5 6 6.5 7 7.5 8
TurbidityRemaining
pH
Graph b/w Turbidity Remaining and pH

14. Jar Test - Optimum Dose
Optimum coagulant dose:
 Repeat all the previous steps
 This time adjust pH of all jars at optimum (6.3
found from first test) while mixing using
H2SO4 or NaOH/lime
 Add different doses of the selected coagulant to
each jar
(Coagulant dose: 5; 7; 10; 12; 15; 20 mg/L)
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15. Jar Test - Optimum Dose
 Rapid mix each jar at 100 to 150 rpm for 1
minute. The rapid mix helps to disperse the
coagulant throughout each container. Reduce
the stirring speed to 25 to 30 rpm for 15 to 20
mins
 Turn off the mixers and allow flocs to settle for
30 to 45 mins
 Then measure the final residual turbidity in
each jar
 Plot residual turbidity against coagulant dose 15

16. Jar Test - Optimum Dose
16Optimum Dose: 11.2 mg/L
0
5
10
15
20
0 2 4 6 8 10 12 14 16 18 20 22 24
TurbidityRemaining
Coagulant Dose (mg/L)
Graph b/w Turbidity Remaining and Coagulant Dose

17. Flocculation
Flocculation is the aggregation of micro-flocs
into macro-flocs to enhance their settling by
gravity sedimentation.
Anions are used as bridging media between
micro-flocs.
+ Flocculent
17
Micro-flocs Macro-flocs
….

18. Flocculation
18Coagulation Flocculation and
Settling
Micro-flocs
Slow Mixing

19. Types of Flocculation
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20. Types of Flocculation
 Micro Flocculation
 Macro Flocculation
Micro Flocculation:
 Due to random motion of fluid molecules
 Size range from 0.001 to about 1 µm
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Randomly Moving Molecules Flocs Formation

21. Types of Flocculation
Macro Flocculation:
 Size greater than 1 µm
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Macro Flocculation
Induced Velocity
Gradients
Differential
Settling

22. Induced Velocity Gradients
 Due to change in velocity of particles
 Fast moving particles overtake slow moving
particles
 Large particle formation due to stickiness of
particles
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L.P
S.P
Flocs Formation

23. Differential Settling
 Large particles overtake small particles
 Settling through gravity
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L.P
S.P
Flocs Formation

24. Polymeric Flocculation
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+
Polymer Micro-flocs Macro-flocs
Polymeric Flocculation

25. Hydraulic Flocculation
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 Due to the flow of water
 Horizontally Baffled Tank
 Vertically Baffled Tank
Horizontally Baffled Tank:
H2O
H2O
Horizontally Baffled Tank
Baffle

26. Hydraulic Flocculation
Vertically Baffled Tank:
Vertically Baffled Tank
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H2O
H2O
Baffle

27. Types of Flocculation Mixers
Following are the types of flocculation mixers:
 Static Mixer
 Paddle Mixer
 Turbine Mixer
Static Mixer:
 Static vanes or baffles for mixing
 Water passes through vanes or baffles
 Horizontally baffled tank (slide no. 25) 27

28. Paddle Mixer
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 Slow movement of paddles cause flocs formation
PaddlesMoving Shaft

29. Turbine Mixer
 Mixing due to the movement of blades
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30. Conclusion
 A coagulant is necessary to destabilize the
stable impurities of water
 Flocculation is necessary to develop the macro-
flocs of impurities that are settled down easily
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31. References
 Wastewater Engineering Treatment by Metcalf
Eddy
 Water and Waste Water Engineering by
Mackenzie L. Davis
 Unit Operations and Processes in
Environmental Engineering
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32. Thank
You

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