Flocculation and sedimentation are processes used to separate suspended solids from water. Flocculation involves the addition of chemicals to destabilize particles and cause them to cluster together into larger flocs. Careful control of mixing is needed to build up floc size without shredding. Sedimentation allows flocs to settle out of solution by gravity in tanks with distinct zones. The type of sedimentation depends on factors like particle settling behavior and concentration. Together, flocculation and sedimentation are important steps in water and wastewater treatment.

1. FLOCCULATION
&
SEDIMENTATION
ERIN DAVIS
SEM 7 BT

2. INTRODUCTION
• Processes are used to separate the suspended
solids portion from the water.
• The suspended particles vary considerably in
 source
 composition charge
 particle size
 shape
 density
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4. FLOCCULATION
• Process where colloids come out of suspension in the
form of floc or flake
• Due to :
1.the addition of a clarifying agent
2.spontaneously
• Occur in successive steps
intended to overcome the
forces
• Stabilizes the suspended
particles, allowing particle
collision and growth of floc.
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7. FLOCCULATION PROCESS
• A gentle mixing stage, increases the particle size from
submicroscopic microfloc to visible suspended particles.
• slow mixing
The microflocs are brought into contact with each other.
• Collisions
microfloc particles cause them to bond to produce larger,
visible flocs called pinflocs.
• The floc size continues to build through additional
collisions30-08-2015 7B.TECH BIOTECHNOLOGY

8. • Interactions occur with inorganic polymers formed by the
coagulant or with organic polymers added.
• Macroflocs are formed.
• High molecular weight polymers, called coagulant aids
added
o It helps to
 bridge
 bind
 Strengthens the floc
 add weight
 increase settling rate.
• Floc has reaches it optimum size and strength.30-08-2015 8B.TECH BIOTECHNOLOGY

9. Operational Considerations
Flocculation requires careful attention
• mixing velocity and amount of mix energy.
• prevent the floc from tearing apart or shearing, the
mixing velocity and energy input are usually
tapered off as the size of the floc increases.
• Once flocs are torn apart, it is difficult to get them
to reform to their optimum size and strength.
• The amount of operator control available in
flocculation is highly dependent
 type and design of the equipment.
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10. Flocculants
(flocculating agents)
- Also known as flocking agents
- Chemicals that promote flocculation
by causing colloids and other suspended
particles in liquids to aggregate,
forming a floc.
• Flocculants are used in water treatment processes to
improve the sedimentation or filterability of small
particles.
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11. • Selection of flocculant depends upon the
1. nature of the suspended solid to be removed
2. the raw water conditions
3. the facility design
4. the cost of production
• Considerations must be given
1. to required effluent quality,
2. effect upon down stream treatment process
performance,
3. method and cost of sludge handling and disposal
4. net overall cost at the dose required for effective
treatment.
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12. SEDIMENTATION
• Sedimentation is the tendency for particles in suspension to
settle out of the fluid in which they are entrained and come
to rest against a barrier.
• It may be due to gravity , centrifugal acceleration or
electromagnetism.
• Sedimentation may take place in a pre-sedimentation
device such as a reservoir, grit basin, debris dam, or sand
trap
• Take place in a rectangular sedimentation basin, a double-
deck rectangular basin, a clarifier, or a solids-contact
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14. • Four zones :-
Each zone has its own unique purpose.
 inlet zone
controls the distribution and velocity of inflowing water
 settling zone
the bulk settling takes place
 sludge zone
the sludge collection occur. Sludge may be disposed in sewer
or stream or may be conditioned and then thickened before
being transported to a landfill.
 outlet zone
controls the outflowing water
• Each zone should provide a smooth transition between the zones.
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15. CLASSIFICATION OF SEDIMENTATION
• Type 1 sedimentation
 Characterized by particles that settle discretely at a constant settling
velocity.
 They settle as individual particles and do not flocculate or stick to other
during settling.
 Example: sand and grit material
• Type 2 sedimentation
 Characterized by particles that flocculate during sedimentation
 Due to their constantly changing size their settling velocity changes.
 Example: alum or iron coagulation30-08-2015 15B.TECH BIOTECHNOLOGY

16. • Type 3 sedimentation ( zone sedimentation)
 Particles are at a high concentration (greater than 1000 mg/L)
such that the particles tend to settle as a mass .
 a distinct clear zone and sludge zone are present.
 Example: lime-softening, sedimentation, active sludge
sedimentation and sludge thickeners.
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