This charge causes repulsion between particles and is referred to as the zeta potential. Metal oxide colloids are examples of hydrophobic solutions. For coagulation to occur, destabilization of the colloidal particles is necessary. Destabilization employs two mechanisms. The addition of electrolytes in solution reduces the net electrical repulsive force at the particle surfaces.
Flocculation facilitates bridging between particles.
There are two operations involved in the coagulation process. Mixing is the process wherein a dissolved coagulant material is rapidly dispersed with violent agitation throughout the water being treated. Flocculation involves the continuous agitation of wastewater at much slower velocities to allow for the agglomeration of very small particles into well defined flocs that settle readily. The most widely used coagulants for wastewater treatment are aluminum and iron salts. Waters high in organic matter are best treated with aluminum sulfate.