Flocculation

Flocculation is a process in which colloids come out of suspension in the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution. In the flocculated system, there is no formation of a cake, since all the flocs are in the suspension.

Overview

Flocculation is used in many applications in the chemical industry, such as in water treatment, to facilitate the removal of suspended solids. It is also used in brewing to gather the yeast in a beer brew. In soil science, flocculation is important for the structure of soils and their ability to hold water and air.

Mechanism

The process of flocculation is governed by the DLVO theory, which is based on the concept of zeta potential. The zeta potential is the electric potential at the shear plane, and it can be used to predict and control the stability of colloidal suspensions. When the zeta potential is reduced to a critical level, usually through the addition of a flocculating agent, the attractive forces exceed the repulsive forces, and the colloids come together to form flocs.

Applications

Water Treatment

In water treatment, flocculation is a major step that involves the addition of a flocculant to promote the formation of flocs. These flocs are then removed from the water by sedimentation and filtration.

Brewing

In brewing, flocculation has to do with the yeast. The yeast used in brewing tends to flocculate, or clump together, at the end of fermentation. This is a desirable characteristic as it makes the yeast easier to remove.

Soil Science

In soil science, flocculation is important for the structure of soils. Flocculation causes the clay particles to stick together, which improves the soil structure and its ability to hold water and air.

See Also

• Coagulation (disambiguation)
• Sedimentation (water treatment)
• Filtration
• Soil structure

Flocculation

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  Flocculation settling time
• 
  The coagulation and filtration processes at a drinking water treatment plant