Formation and collapse of gas bubbles due to low pressure; can cause pitting and noise.

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

Answer: (B)

Cavitation is the phenomenon where the liquid pressure drops below its vapor pressure, causing dissolved gases to form tiny bubbles. When these bubbles move into higher-pressure areas, they collapse violently, sending shock waves and microjets that can abrade metal surfaces. In wastewater equipment such as pumps and impellers, this collapsing action leads to pitting and loud, banging noise due to the rapid pressure fluctuations. To prevent it, maintain adequate suction head and proper flow to keep pressures above vapor pressure and use equipment designed to resist cavitation. The other options don’t describe this gas-bubble formation and collapse: a centrifuge separates solids and liquids by rotation, chlorination is a chemical disinfection process, and bulking relates to sludge settling, not cavitation.