Which type of pump uses air to move wastewater?

• A. Air Lift Pump
• B. Centrifugal Pump
• C. Reciprocating Pump
• D. Diaphragm Pump

Answer: (B)

Using air to move wastewater is the principle behind an air lift pump. In this setup, compressed air is injected into a vertical pipe that contains wastewater. The air forms bubbles that mix with the liquid, reducing the overall density of the column. Because the air–liquid mix is less dense than the surrounding fluid, it experiences a buoyant force that pushes the mixture upward toward the surface or a discharge point. The air then escapes at the top, and the cycle continues. This method is advantageous in wastewater because it can handle solids and debris without moving mechanical parts in contact with the liquid, and it works well in deep sumps or wells.

Centrifugal pumps move fluid by imparting velocity with a rotating impeller, not by lifting with air. Reciprocating pumps push fluid with a piston or plunger in a cylinder, again using mechanical displacement rather than air lift. Diaphragm pumps use a flexible membrane driven to move fluid; while some can be air-actuated, the core action in those designs is the diaphragm movement, not raising the liquid through air-induced buoyancy.