What type of solids does a clarifier remove?

• A. Dissolved solids
• B. Floating and settled
• C. Colloidal solids only
• D. All solids including dissolved

Answer: (B)

Clarifiers work by letting solids separate from the liquid through gravity. Heavier solids settle to the bottom and are removed as sludge, while lighter materials rise to the surface and are skimmed off as scum. Dissolved solids remain in solution and pass with the effluent, not being removed by settling. Colloidal solids are too fine to settle unless they form larger flocs through coagulation and flocculation. So the solids actually removed by a clarifier are the floating material at the surface and the solids that settle at the bottom.