A ______ pump contains an impeller that rotates in a casing to pump large volumes of liquid through a pipe. This pipe is most commonly used for raw wastewater pumping; at lift stations, recirculation flows, for RAS/WAS, and final effluent pumping.

• A. Positive-displacement
• B. Submersible
• C. Centrifugal
• D. Diaphragm

Answer: (C)

Centrifugal pumps use an impeller spinning inside a casing to fling liquid outward and convert that velocity into pressure, producing large volumes of flow through a discharge pipe. This design fits wastewater systems where you need to move big flows—from lift stations and recirculation loops to return activated sludge and final effluent pumping. The impeller-in-a-casing description is the hallmark of a centrifugal pump, which is why it’s the best match for pumping large volumes of wastewater. Positive-displacement pumps crop up when you need steady, high-pressure flow at lower volumes, and diaphragm pumps are a type of positive-displacement; they aren’t the standard choice for moving large wastewater volumes. Submersible describes how a pump is installed, not the pumping mechanism itself.