Sedimentation in Water and Used Water Purification

Sedimentation is a physical water treatment process used to settle out colloidal and suspended solids in water under the influence of gravity. It is one of the widely used conventional water treatment methods. The terms sedimentation and settling are used interchangeably. A sedimentation basin is also referred to as a sedimentation tank, settling basin, or settling tank and as a clarifier. The process of removal of turbidity caused by fine suspended solids, colloidal impurities, and organic color from the raw water is termed as clarification which comprises coagulation, flocculation, and sedimentation steps. There are two basic forms of sedimentation based on the shape of the particles, unhindered and hindered settling. On the basis of concentration and tendency of particles to interact, there are four types of settling which can occur such as discrete particle, flocculant, hindered or zone, and compression settling. There are three basic geometrical shapes commonly used for sedimentation basins in water treatment: rectangular, circular, and square. The choice of selection of the shape of the basin mainly depends on the site conditions. Various configurations in each type of geometrical shape are presented along with their appurtenances. The high-rate clarifiers such as lamella clarifiers and tube settlers are also discussed. Comparison of various clarification systems such as lamella clarifier and sludge blanket clarifiers is also made with a detailed description on pulsator clarifier.