What is the purpose of the spiral flow created by the injected air in an aerated grit chamber?

• A. Increase the flow velocity to keep grit suspended.
• B. Slow the flow to allow heavier grit to settle.
• C. Disinfect the wastewater.
• D. Concentrate solids at the surface.

Answer: (B)

The injected air creates a spiral, or swirling, flow that slows the overall velocity of the wastewater in the chamber. This slower, controlled motion gives heavier inorganic particles—grit like sand and small stones—time to settle to the bottom instead of being carried downstream. By removing this grit, downstream equipment is protected from abrasion and clogging, while lighter organic matter continues to move with the flow. Disinfection isn’t achieved by this process, and grit is not meant to concentrate at the surface in this setup; the goal is bottom settling of the heavier solids.