Which statement about the function of a secondary clarifier is true?

Which statement about the function of a secondary clarifier is true?

• A. To aerate the mixed liquor
• B. To settle and separate biological solids from treated liquor
• C. To chlorinate the effluent
• D. To mix influent with effluent

Answer: (B)

In a wastewater treatment process, the secondary clarifier serves as a gravity sedimentation stage after biological treatment. Its primary job is to let the biological solids settle out of the treated liquor so the liquid that exits the tank is clear enough for discharge or further treatment. The settled solids form sludge at the bottom, which can be recycled back to the aeration basin to maintain the biomass or wasted as surplus sludge. Aeration happens in the earlier basin, not in the clarifier, and disinfection (such as chlorination) typically occurs after clarification. Mixing influent with effluent would prevent solids from settling, so that option doesn’t describe the clarifier’s function.

In a wastewater treatment process, the secondary clarifier serves as a gravity sedimentation stage after biological treatment. Its primary job is to let the biological solids settle out of the treated liquor so the liquid that exits the tank is clear enough for discharge or further treatment. The settled solids form sludge at the bottom, which can be recycled back to the aeration basin to maintain the biomass or wasted as surplus sludge. Aeration happens in the earlier basin, not in the clarifier, and disinfection (such as chlorination) typically occurs after clarification. Mixing influent with effluent would prevent solids from settling, so that option doesn’t describe the clarifier’s function.