Supernatant is the term for which portion of the wastewater after solids have settled?

• A. Clear liquid remaining after sediment settles
• B. The sludge at the bottom of the clarifier
• C. The air carried in the liquid
• D. The dissolved solids in the water

Answer: (A)

Supernatant is the clear liquid that remains on top after solids have settled in a clarifier. When the heavier solids settle to the bottom, forming sludge, the lighter liquid above becomes the supernatant. This portion is the liquid that has been clarified of most settled solids, though some fine particles may still be present. The bottom layer is sludge, not the supernatant. The air carried in the liquid refers to entrained gas, not a separate liquid layer, and dissolved solids are substances dissolved in the water, not a distinct layer. So the top liquid, after settling, is the supernatant.