Which process involves allowing solids to settle at the bottom of a treatment vessel?

Sedimentation is the process that involves allowing solids to settle at the bottom of a treatment vessel. This method is widely used in water treatment to remove suspended particles and impurities. In sedimentation, water is held in a tank or basin where the flow is slowed enough to enable heavier solids to overcome buoyancy and settle due to gravity. The settled solids, often referred to as sludge, can then be removed from the bottom of the vessel.

This process plays a crucial role in the primary treatment of water before further purification steps, such as filtration and disinfection, are employed. By effectively reducing the concentration of suspended solids, sedimentation enhances the efficiency of subsequent treatment processes and helps in improving water quality.

In contrast, filtration involves passing water through a porous medium to separate solids and other impurities, disinfectation refers to the process of killing or inactivating pathogens, and flocculation is a preceding step that involves the addition of chemicals to help small particles clump together, forming larger masses that can then be removed by sedimentation or filtration. Each of these processes serves a distinct purpose in the overall water treatment procedure, but sedimentation specifically targets the settling of solids.