Coagulation, Flocculation, and Sedimentation

Particles suspended in water naturally repel other particles. They cannot join to form larger particles that would settle more quickly. A coagulant, such as alum, is added to the water to overcome the repulsion between the particles. Flocculation involves gently mixing the water so that the particles can combine and form larger particles. During sedimentation, larger particles gradually sink to the bottom of the tank where they can be removed.