In a properly operated sedimentation tank, the smallest particles are expected to settle toward which part of the tank within the detention time?

• A. Far end
• B. Near end
• C. On the surface
• D. Randomly distributed

Answer: (A)

In a sedimentation tank, particles settle at rates that depend on their size and density. Water flows from the near end toward the far end during the detention time, so larger, faster-settling particles drop out quickly and accumulate closer to the inlet side, while the smallest particles take longer to settle. Because they require more time, these fine particles continue with the flow further across the tank and settle toward the far end by the end of the detention period. So the smallest particles are expected to settle toward the far end.