The flotation is a separation technology, generally used for the treatment of process water and wastewater, to separate solid or liquid particles from the acqueous fraction.

To carry out this separation, air micro-bubbles are released at high pressure to the water to be treated and adhere to the suspended solids, facilitating their flotation to the top.
These bubbles are smaller than in other kind of flotation: smaller bubbles adhere to solids better. This is the most important type of flotation for wastewater treatment.

The separation occurs through the agglomerated particles migration to the water free surface
and it is conditioned by factors such as:

  • particles density
  • wettability
  • surface tension
  • temperature
  • pH

Destabilization of colloidal particles.
The double layer theory (Stern theory)
Colloids in the water are usually negatively charged.
A concentration gradient forms between the colloid’s surface and the solution (double layer). An electromotive force develops between the particles and the water: this is called «potential».
The potential difference between the shear plane and the water is called «Z potential» (ZP).

High ZP / no particles agglomeration: uniform dispersion, stable and free to flow.
Low ZP / van der Waals forces prevail on repulsion and agglomeration (unstable suspension).

Coagulation is the annulment of the Z potential.