Wastewater New York State Practice Exam

Which type of pump injects compressed air into a discharge line to raise solids through sludge density differential?

1. Rotary Lobe

2. Peristaltic

3. Air Lift

4. Submersible

The correct answer is: Air Lift

The type of pump that injects compressed air into a discharge line to raise solids through sludge density differential is the air lift pump. This pump operates on the principle of using buoyancy to lift solids. By introducing compressed air at the bottom of the discharge line, it creates a mixture of air and liquid that reduces the density of the sludge, allowing it to be lifted through the discharge line more effectively. The air bubbles decrease the overall weight of the sludge column below them, enabling the solids to rise and be transported to the desired location. In contrast, rotary lobe pumps utilize rotating lobes to move fluids and are not designed for solids lifting using air. Peristaltic pumps function by compressing and releasing tubes to push fluids through and do not use air injection to enhance solids movement. Submersible pumps are designed to be submerged and typically move fluids without the assistance of air to lift solids. Therefore, the air lift pump is distinct in its operational mechanism and is specifically designed for the application described in the question.