In a vortex-type grit chamber, where does the water–grit mixture primarily rotate?

• A. Around a vertical access, creating rotation about a vertical axis.
• B. Straight through a central pipe with no rotation.
• C. In a chaotic, non-rotational flow.
• D. Along the tank perimeter without any central rotation.

Answer: (A)

The key idea is that a vortex grit chamber uses a swirling flow to separate grit from the wastewater. The water–grit mixture is set into rotation around a central vertical axis, typically around a vertical access or centerline of the chamber. This vertical-axis swirl creates centrifugal forces that push the heavier grit toward the outer, lower part of the chamber where it can settle and be removed, while the cleaner water continues to move with the swirl and exits.

So the primary motion is around a vertical axis, not as a straight-through flow with no rotation, not chaotic, and not confined to the tank perimeter without central rotation.