Flocculation is the set of physico-chemical phenomena that lead to the aggregation of particles to form flocs. This phenomenon is reversible, namely these flocs can be broken by, for example, vigorously stirring of the liquid to reach the initial colloidal solution.
Coagulation and flocculation are often inseparable. In fact, coagulation, by reducing the repulsive forces between the particles, favours their collision and the formation of aggregates; flocculation, by allowing the increase of aggregates, accelerates the separation of phases.
A polymer is a substance composed of high molecular weight molecules, made up of many identical small molecules, called monomers, linked by covalent bonds.
Flocculation is the stage in which destabilized colloidal particles (or particles formed during the coagulation stage) join together in agglomerations. The flocculation step can be applied in the water / wastewater treatment processes only in situations where the particles are already destabilized. As a result, it is a step that logically follows the coagulation.
The origin of the destabilized particles is varied and depends mainly on the origin of the water to be treated. These can come from the initial coagulation stage. The electric charge (+ or -) brought by the flocculant is selected according to the nature of the destabilized particles in water. In general, the selection is:
- anionic flocculant (-) for mineral particles
- cationic flocculant (+) for organic particles