Sedimentation is the next step in conventional filtration plants. (Direct filtration plants omit this step.) The purpose of sedimentation is to enhance the filtration process by removing particulates.
Sedimentation is the process by which suspended particles are removed from the water by means of gravity or separation. In the sedimentation process, the water passes through a relatively quiet and still basin. In these conditions, the flock particles settle to the bottom of the basin, while “clear” water passes out of the basin over an effluent baffle or weir.
Sedimentation involves one or more basins, called “clarifiers.” Clarifiers are relatively large open tanks that are either circular or rectangular in shape. In properly designed clarifiers, the velocity of the water is reduced so that gravity is the predominant force acting on the water/solids suspension. The key factor in this process is speed.
The rate at which a flock particle drops out of the water has to be faster than the rate at which the water flows from the tank’s inlet or slow mix end to its outlet or filtration end. The difference in specific gravity between the water and the particles causes the particles to settle to the bottom of the basin. Some plants have added baffles or weirs in their sedimentation basins to limit short-circuiting through the basins, promoting better settling.
