Which term refers to the solids that accumulate in sedimentation basins and form a layer?

• A. Sediment
• B. Sludge
• C. Slurry
• D. Dregs

Answer: (B)

In a sedimentation basin, the solids that settle out from the liquid and collect as a dense layer at the bottom are called sludge. The basin works by gravity to remove suspended particles, so they accumulate and form this bottom layer, which is then pumped out for disposal or further treatment. This term specifically describes the concentrated solids that settle and remain as a distinct layer, unlike the liquid above it which is clarified water.

Sediment refers to general material that deposits over time and isn’t limited to a bottom layer in a basin. Slurry means a thick mixture of solids suspended in liquid, not a separate bottom layer. Dregs are residues from various processes and aren’t the standard term used for the settled layer in a wastewater sedimentation basin.