This document discusses coagulation and flocculation processes used in water treatment. It explains that coagulation uses chemicals like aluminum and iron salts to destabilize colloidal particles in water by neutralizing their negative charges. This allows the particles to agglomerate into larger flocs during flocculation. Flocculation is the process where these destabilized particles come together through gentle mixing. Jar tests are used to determine the optimum pH and coagulant dose needed for effective coagulation and flocculation in water treatment.

1. Topic-Coagulation and Flocculation in Water Treatment
BY
NAVEEN P. PATEKAR.

2. What is Coagulation?
Many of the contaminants in water and wastewater contain matter
in the colloidal form. These colloids result in a stable
“suspension”.
In general the suspension is stable enough so that gravity forces
will not cause precipitation of these colloidal particles. So they
need special treatment to remove them from the aqueous phase.
This destabilization of colloids is called “coagulation”.
Coagulation is the destabilization of colloids by addition of
chemicals that neutralize the negative charges

3.  The chemicals are known as coagulants, usually higher
valence
cationic salts (Al3+, Fe3+ etc.)
 Coagulation is essentially a chemical process
Typical colloidal characteristics for water and wastewater:
•· Size range: 10-3- 1 micron. (somewhere in the range
between a molecule and bacteria in size).
•· 50 – 70 % of the organic matter in domestic wastewater is
composed of colloidal matter.
•· In water treatment color, turbidity, viruses, bacteria,
algae and organic matter are primarily either in the colloidal
form or behave as colloids.

4. What is Flocculation?
Flocculation is the agglomeration of destabilized particles
into a large size particles known as flocs which can be
effectively removed by sedimentation or flotation.

5. 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
0.0001 (10 micron) Large colloids 0.3 m/y
0.000001 (1 nano) Small colloids 3 m/million y
Colloids – so small: gravity settling not possible
GravItysettlI
ng

6. Colloid Stability
------ ------
Repulsion
Colloid - A Colloid - B
 Colloids have a net negative surface charge
 Electrostatic force prevents them from agglomeration
 Brownian motion keeps the colloids in suspension
H2O
Colloid
 Impossible to remove colloids by gravity settling

7. COLLOIDAL INTERACTION

8. CHARGE REDUCTION :

9. Colloid Destabilization :
• Colloids can be destabilized by charge neutralization
• Positively charges ions (Na+, Mg2+, Al3+, Fe3+ etc.)
neutralize the colloidal negative charges and thus
destabilize them.
• With destabilization, colloids aggregate in size and
start to settle

10. COAGULATION AIM

11. Force analysis on colloids :
The integral of the
combined forces is
the energy barrier

12. FLOCCULATION AIDS

13. FLOC FORMATION WITH POLYMERS

14. Jar Tests
Determination of optimum pH
 The jar test – 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
 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)
Jar Test

15. Jar Test set-up
 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
and continue mixing for 15 to 20 mins
This slower mixing speed helps
promote floc 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
Jar Tests – determining optimum pH

16. Optimum pH: 6.3
Jar Tests – optimum pH

17. The optimum
coagulant dose and
mixing rate are
determined by
simulating both
coagulation and
flocculation in “jar
tests.”
Coagulation and Flocculation Practice

18. Typical layout of a water treatment plant

19. Inflow
Chemical
feeding
Inflow
Chemical
feeding

20. PADDLE FLOCCULATORS AT EVERETT
WTP (NOTE THE CMRS-IN-SERIES
ARRANGEMENT)

21. Cross flow Flocculator (sectional view)
Plan (top view)
L
H
W
Mechanical Flocculator

22. 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

23. Hydraulic Flocculation: Pipe

24. Flocculators integrated with settling

25. Flocculators both sides of settling

26. THANK
YOU.