Goal and Mechanisms of Flocculation

Promote growth of flocs to a size that can be removed by sedimentation and filtration.





Sweep-Floc Coagulation







Goal and Mechanisms of Flocculation







Tapered Flocculation


All mechanical flocculation devices should be equipped with variable-speed drives having a range of up to 1:4 to meet variation in quality of feed water.



Inlets and Outlets


Detention time: 20-60 minutes for conventional and plate-and-tube settling




Flocculation: Operating Conditions

  G(sec-1) Mixing Time
  • Coagulation:
700-1000 30-60 sec
  • Flocculation:
20-80 20-60 min

Typical G-t for flocculation is 2 x 104 - 105




Vertical Turbine Flocculators




Horizontal-Shaft Flocculation Paddle Wheels








Paddle Wheel Flocculators




Mechanical mixing: Using different types of mechanical mixers to promote particles contacts and thus their agglomeration (Orthokinetic motion)





Horizontal-Shaft Flocculation Paddle Wheels






Horizontal-Shaft Flocculation Peddle Wheels (Cross-Flow Pattern)




Horizontal-Shaft Flocculation Peddle Wheels (Axial-Flow Pattern)




Design Criteria

Parameter Unit Value
Diameter of wheel m 3 - 4
Paddle board section mm 100 - 150
Paddle board length m 2 - 3.5
Apaddle board / tank section area % < 20

Paddle tip speed




Strong floc, 4

Weak floc, 2

Spacing between paddle wheels on same shaft m 1
Clearance from basin walls m 0.7
Minimum basin depth m 1 m greater than diameter of paddle wheel
Minimum clearance between stages m 1




Flocculation Basin




Vertical-Shaft Flocculation Peddle Wheels





Diffuser Walls






Hydraulic Flocculation









Baffled Channel Hydraulic Flocculation