As solids settle to the bottom of a sedimentation basin, what develops?

When solids settle to the bottom of a sedimentation basin, the material that accumulates there is referred to as sludge. This process occurs during the treatment of drinking water, where larger particles and sediments in the water are allowed to settle under the influence of gravity. Over time, these particles aggregate and sink to the bottom of the sedimentation basin, forming a thick layer. This layer is composed of the settled solids, which can include various contaminants, organic materials, and other particulate matter.

The presence of sludge is a critical part of the water treatment process, as it effectively removes suspended solids from the water. This sedimentation process is essential for ensuring that the water being treated meets the necessary standards for clarity and quality before undergoing further treatment steps such as filtration or disinfection.

In contrast, while options like the scum layer and clear water layer describe other components of the sedimentation process, they do not refer specifically to the accumulation of settled solids at the bottom. The scum layer typically consists of floating debris and oils, while the clear water layer is the treated water that remains above the sludge and scum after sedimentation has occurred.