Coagulation and Flocculation

Water is clarified using the processes of coagulation and flocculation, which remove suspended solids (turbidity) from water by causing the suspended particles to aggregate into a slime, that settles out of the water.

This technique is used in treating wastewater, both industrial and treated sewage, from municipal wastewater treatment plants. It is also used, as a first step, in treating raw water for industrial use, and in food and beverage production.

THE PROCESS
Coagulation uses salts such as aluminum sulfate (alum) or ferrous of ferric (iron) salts, which bond to the suspended particles, making them less stable in suspension, i.e., more likely to settle out. Figure 1 depicts the coagulation process in the resident tank by the diagonal lines.

Flocculation is the binding or physical enmeshment of these destabilized particles, and results in a slime that is heavier than water, which settles out in a clarifier. Flocculation agents are natural synthetic polymers and synthetic organic polymers used to form the flocculant.