Which type of sewage tends to produce gas bubbles that cause turbulence in a clarifier?

• A. Domestic
• B. Raw
• C. Industrial
• D. Septic

Answer: (D)

Gas production from anaerobic digestion is the main factor here. Septic sewage forms and digests organics without oxygen, producing gases like methane and carbon dioxide. Those gas bubbles rise through the wastewater as it sits in a clarifier, disturbing the settled solids and causing turbulence that interferes with proper settling. While other waste types can contain some dissolved gases, septic conditions generate bubbles more readily and in greater quantity, making turbulence in the clarifier more likely.