Wastewater contains suspended material, solid particles that can settle on their own, but we can also find very small particles of a colloidal kind with a size between 0.001 and 1 µm. It is not possible to divide these particles by decantation or flotation. Neither we could filter them because they would pass through any filter.
Each of these colloids contains particles stabilised by a series of equivalent charges on their surface, causing two adjacent particles to repel as two magnetic poles repelling each other. This prevents them from agglomerating to settle.
Coagulation is caused by the removal of electrical layers surrounding colloidal particles with the formation of microscopic nuclei. Flocculation consists of an agglomeration of destabilised particles in microflocules first and later in agglomerates called floccules.
The physical-chemical treatment of wastewater – by adding coagulant and flocculant – is aimed to altering the physical condition of these colloid substances that could remain stable indefinitely to convert them into particles subject to flotation/decantacion by division.
In the video we see that for breaking the stability of colloid particles and separate them easily we carry out three phases: Coagulation, Flocculation and Floating/Decantation.