Flocculation

About coagulant particles aggregates form, which are known by the name of micro flocs. However, these have not yet micro flocs sufficient size to settle. Therefore, by the flocculation which will be produced an agglomeration of coagulated colloidal matter and finely divided matter in suspension as a result of collision and adhesion between particles, generating larger flocs already be eliminated by sedimentation or flotation.

The rate of aggregation is determined by the speed at which collisions occur between particles and the effectiveness of the collisions between particles permit aggregation.

Such a physical process of power by a slow mix, that must be high enough to prevent settlement and low enough to prevent rupture of the flocs already formed. A number of the reagents that enabling the process may be added. These additives are coagulation aids, namely the organic polymers described above, able to increase their the size of the flocs generated and improve the sedimentation and well-classified of the water.

Normally, the organic reagents generate more volume of sludge and require a greater volume of soda to neutralize the mixture.

The addition of proper polyelectrolyte as assistants coagulation and flocculation, it can contribute to lower treatment costs for small doses used and increased efficiency. On the other, if the wrong type polyelectrolyte is chosen floc obtained has a higher sedimentation rate and allows formation of more homogeneous and compact sludge.

The flocculation is also an essential part in the chemical precipitation systems, resulting in increased size of the crystals formed and thus promoting their removal.

As was the case in the coagulation, there are different flocculation mechanisms as follows:

1) By thermal or Brownian motion (perikinetic flocculation). It is a movement associated to the temperature of the particles very slowly making them move, randomly through the fluid. The flocculation will be happen when the particles collide with one another. Due to the slow process, there are no application in a wastewater treatment plant (WWTP), you have to building very large vats.

2) By differential sedimentation. The particles are aligned vertically at different speeds sedimenting collide to form a larger floc. This particle entrainment occurs mainly in the sludge sedimentation and flotation. The larger particles settle more quickly and density and smaller drag. This is taken into account for the design of decanters.

3) By the movement of the fluid (orthokinetic flocculation). Through a gentle agitation that will not break the floc, the particles are carried by the fluid motion, which generates collisions between particles and is forming larger flocs.