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Coagulation and flocculation are two essential processes used in water treatment and various industrial applications to remove suspended solid particles from a liquid. They are often used in conjunction with each other. Coagulation is the initial step where destabilization of colloidal particles occurs. This is typically achieved by adding chemicals called coagulants, such as aluminum sulfate (alum) or ferric chloride. These coagulants neutralize the negative surface charges of the suspended particles, causing them to aggregate into small clumps. This process reduces the electrostatic repulsion between the particles, allowing them to approach each other.

Following coagulation, flocculation takes place. This is a gentle mixing process that encourages the small, destabilized particles to collide and adhere to one another, forming larger, heavier agglomerates called flocs. The mixing is slower than in coagulation, allowing for the growth of these flocs without breaking them apart. The increased size and weight of the flocs make them easier to remove from the liquid through subsequent sedimentation or filtration. Coagulation and flocculation are critical for improving water clarity, reducing turbidity, and preparing water for further purification steps. They are also employed in industries such as papermaking, mining, and food processing for solid-liquid separation.