Primary clarifiers remove solids from raw wastewater entering the WWTP.

• A. Primary
• B. Secondary
• C. Tertiary
• D. Quaternary

Answer: (A)

In wastewater treatment, solids removal happens in staged clarifiers. The primary clarifier is the first sedimentation tank that handles raw wastewater. Its function is to let settleable solids fall to the bottom and scum rise to the top, removing a large portion of solids before the water moves on to biological treatment. The clarified effluent then proceeds to the biological stage, where microbes treat the dissolved and suspended organic matter.

This is why the primary clarifier is the best choice: it specifically targets solids in the incoming, untreated wastewater. Secondary clarifiers come after the biological treatment to settle the biological biomass that forms there, tertiary clarifiers are used for polishing the effluent after biological treatment, and quaternary steps are not a standard part of the basicWWTP train.