What is the main function of the secondary clarifier, and what happens to the settled solids?

What is the main function of the secondary clarifier, and what happens to the settled solids?

• A. To remove biomass from treated water; settled solids pumped as sludge to RAS or WAS.
• B. To oxidize organics in the effluent.
• C. To chemical precipitate phosphorus.
• D. To increase temperature.

Answer: (A)

The secondary clarifier mainly serves to separate suspended solids from the treated water after the biological treatment. It uses gravity to let the biomass settle to the bottom, producing clearer effluent that exits from the top. The material that settles forms sludge at the bottom; this sludge is partly returned to the aeration basin as Return Activated Sludge to maintain the microbial population, and the excess sludge is sent out as Waste Activated Sludge for digestion or disposal. The clarifier does not oxidize organics, precipitate phosphorus chemically, or raise temperature; those functions occur in other parts of the treatment process.

The secondary clarifier mainly serves to separate suspended solids from the treated water after the biological treatment. It uses gravity to let the biomass settle to the bottom, producing clearer effluent that exits from the top. The material that settles forms sludge at the bottom; this sludge is partly returned to the aeration basin as Return Activated Sludge to maintain the microbial population, and the excess sludge is sent out as Waste Activated Sludge for digestion or disposal. The clarifier does not oxidize organics, precipitate phosphorus chemically, or raise temperature; those functions occur in other parts of the treatment process.