Which phenomenon can occur when rapid pressure changes near a pump or valve cause gas bubbles to form and collapse, possibly producing noise?

• A. Centrifuge
• B. Bulking
• C. Buffer
• D. Cavitation

Answer: (D)

When a liquid experiences rapid pressure changes near a pump or valve, dissolved gases can come out of solution and form vapor bubbles. As the pressure then rises again, these bubbles collapse violently, producing noise and often vibration or even damage to equipment. This phenomenon is cavitation. It happens when local pressure drops below the liquid’s vapor pressure, letting bubbles form, and upon rebound, those bubbles implode with significant energy. In wastewater systems, cavitation around pumps and throttling valves is a common concern because it can reduce efficiency and wear down impellers and other components.

Other terms don’t describe this process: a centrifuge uses spinning to separate materials, bulking refers to poor sludge settling due to microbial issues, and a buffer relates to pH stabilization or a buffering tank. Cavitation precisely explains the formation and collapse of gas bubbles caused by rapid pressure changes near pumping equipment.