ABSTRACT
Gravity separation refers to the removal of suspended solids whose specific gravity difference from that of water causes them to settle or rise during passage through a tank or basin under quiescent conditions. For the flocculent suspensions handled in wastewater treatment, particle contact and agglomeration continues during sedimentation. Sedimentation is the separation of suspended particles that are heavier than water from water by gravitational settling. It is a widely used unit operations in wastewater treatment. A large number of waste effluents and water comprise suspensions of solid particles in liquids. The application of filtration techniques for the separation of heterogeneous systems can be very costly. Continuous clarifiers handle a variety of process wastes, domestic sewage, and other dilute suspensions. They resemble thickeners in that they are sedimentation tanks or basins whose sludge removal is controlled by a mechanical sludge-raking mechanism. Dissolved-air flotation units commonly employ rectangular tanks with separate chain-and-flight scum and sludge collectors.
