Sedimentation is gravitational separation of settleable ___ matter from wastewater.

• A. Suspended
• B. Dissolved
• C. Floating
• D. Colloidal

Answer: (A)

Sedimentation uses gravity to remove settleable suspended matter from wastewater. The solids that can settle out are the suspended solids that are heavy enough to fall to the bottom given enough contact time in a clarifier. Dissolved substances stay in solution and don’t settle by gravity. Floating material rides to the surface and is skimmed off rather than settled. Colloidal particles are so small and often stabilized that they don’t readily settle without processes like coagulation and flocculation. So the best fit for what sedimentation separates is suspended matter.