If a gravity grit removal system is operated at a velocity significantly lower than the recommended value, what problem is most likely?

• A. Grit will not settle properly, and solids may exit with the effluent
• B. Grit will settle too quickly
• C. Grit will dissolve into wastewater
• D. Grit will corrode equipment

Answer: (A)

In gravity grit removal, the flow velocity is chosen to let heavy grit settle out while lighter organic matter stays in suspension and moves on with the rest of the wastewater. If you operate at a velocity significantly lower than advised, the flow pattern won’t effectively direct and transport the grit into a proper settling zone. The result can be improper separation, with grit and other solids remaining entrained in the flow and slipping out with the effluent.

This is why the most likely problem is solids exiting with the effluent due to insufficient residence time and poor separation in the grit chamber. Grit dissolving or corroding components aren’t related to this hydraulic issue, and grit settling too quickly isn’t the expected outcome when the velocity is reduced.