What is also called clarification and involves the removal of settleable solids by gravity?

The process known as clarification involves the removal of settleable solids through the action of gravity, and this is specifically referred to as sedimentation. In sedimentation, suspended particles in water are allowed to settle to the bottom of a tank or basin due to gravitational forces. As the particles settle, they form a layer of sludge at the bottom, effectively clarifying the water above it. This process is critical in drinking water treatment, as it helps to remove large particles and impurities, improving water quality before further treatment steps take place.

In contrast, the other processes listed have different purposes: sterilization refers to the destruction of pathogens, filtration is a physical removal of particles using a medium, and flocculation involves the aggregation of particles to form larger clumps (or flocs) that can then settle out, but it is distinct from the gravitational settling process itself. Therefore, the accurate identification of sedimentation as clarification underlines its role in the initial stages of water treatment.