FLOCCULATION
NUR ISTIANAH,ST.MT.,M.Eng
INTRODUCTION
Flocculation: primary particles to
approach close enough together, make contact and progressively form larger
agglomerates
Transport Mechanisms
• Brownian motion: for relatively small particles which follow random motion and collide with other particles (perikinetic motion)
• Differential settling: Particles with different
settling velocities in the vertical alignment collide when one overtakes the other
Design of Flocculator
(Slow & Gentle mixing) Flocculators are designed mainly to provide enough interparticle contacts to achieve particles agglomeration so that they can be effectively removed by sedimentation or flotationMechanism
• arises from thermal agitation (Brownian movement)
• Naturally random process
• Assumed particle in radial motion
Perikinetic flocculation
• arises from induced velocity gradients in the liquid
• Mechanical supports
Orthokinetia
flocculation
Velocity gradient
• Passage around baffles
• Mechanical agitation
• Granular filter bed
Cross flow Flocculator (sectional view)
Plan (top view) L
H
W
Mechanical Flocculator
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
Hydraulic flocculators: simple technology
Hydraulic Flocculation: Pipe
Hydraulic Flocculation: Pipe
Mechanical flocculators
Mecahnical
flocculators
Mechanical
flocculators
Flocculators integrated with
settling
Flocculators integrated with
settling
Flocculators both sides of
settling
Flocculator perforated wall (in
background)
Velocity of flocculator
• The greater the velocity gradients induced in the liquid the more particle contacts there will be
within a given time.
• However, the greater the velocity gradients the smaller will be the ultimate floe size due to a
continuous breakdown of the larger flocs. Hence, for a given velocity gradient there will be a limiting flocculation time beyond which floc particles will not grow further.
• The lower the velocity gradient the longer will be the time needed to reach the optimum floe size, but the larger will be the final floc size.
Consideration of Flocculation
• The principal parameters governing the effective degree of flocculation are the retention time
and velocity gradients applied also type of coagulant and flocculant
• These parameters influence the rate and extent of particle aggregation and the rate and extent of break-up of these aggregates
Consideration of Flocculation
• Having assessed each chemical combination alternative in terms of both destabilization
(clarification) efficiency and flocculation
efficiency, some form of final choice in terms of overall economics is required.
Typical layout of a water treatment plant
REFERENCES
• Solid Liquid Separation Equipment Selection and Process Design
• Coagulation and floculation
• Coagulation and Flocculation in Water Treatment By J(Hans) van Leeuwen
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