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Colloids are very low diameter particles which are responsible for the turbidity or the color of surface water. Because of their very low sedimentation speed the best way to eliminate them is the coagulation-flocculation processes. The aim of the coagulation is to destabilize the electrostatic charge in order to promote the colloids meeting.

Colloid features and origins:

The colloid diameter is between 1 µm and 1nm. The rate surface/volume give colloids very good adsorption properties for the free ions. This phenomenon of ion adsorption involves the presence of electronic charge at their surface which brings about some repulsion forces. That is why colloids are so stable into solution.

There are different origins: mineral substance dissolution, erosion, organic matter decomposition, farming wastes and wastewater.

The different kinds of colloids:

The hydrophobic colloids are responsible for water coloration and basically they have an organics origin with a R-NH2 or R-OH part. These electronegative parts create hydrogen links with the water molecules. This layer opposes itself to the colloid meeting and is a stabilization factor.

The hydrophilic colloids are from mineral origins. At their surface are concentrated negative charges which bring about an impossible agglomeration.

Basically the colloids are never 100 % hydrophilic nor 100 % hydrophobic, actually the percentage depends on their molecular constitution.

Colloid elimination:

In order to remove colloids from water the best solution is to perform like a first step a particle coagulation with a coagulant agent. The aim of this step is to destabilize the colloid electrostatic charge to promote the meeting and their future agglomeration during the flocculation step.

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