Coagulation and flocculation practices are essential pretreatments for many water purification systems.
In conventional coagulation-flocculation-sedimentation, a coagulant is added to the source water to create an attraction among the suspended particles. The mixture is slowly stirred to induce particles to clump together into “flocs.” The water is then moved into a quiet sedimentation basin to settle out the solids.
Dissolved air flotation systems also add a coagulant and flocculate the suspended particles; but instead of using sedimentation, pressurized air bubbles force them to the water surface where they can be skimmed off.
A flocculation-chlorination system has been developed as a point-of-use technology, especially for developing countries. It uses small packets of chemicals and simple equipment like buckets and a cloth filter to purify the water.
Finally, lime softening is a technology typically used to “soften” water—that is, to remove calcium and magnesium mineral salts. In this case, the material that is settled out is not suspended sediment but dissolved salts.