Very fine particles from the water do not settle no matter how long the water remains in resting state, because they are in colloidal equilibrium. These particles are negatively charged and repel each other. A chemical treatment method is used to obtain a better treatment effect.
By this method is meant the introduction into water of some substances that enter into a chemical reaction with substances dissolved in water. Compounds dispersing in the water in the form of positively charged fine particles, which neutralize the negative electrical charge of the particles which give turbidity to the water, are formed. In this way, their agglomeration into flocs occurs, namely larger flocculation that deposit quickly. The effect is high if a liquid agitation is introduced. This process is named coagulation – flocculation, and the substances used are named coagulants.
The choice of the optimal coagulant for water to be treated is determined based on laboratory research.