A solid contact basin combines which processes?

• A. Coagulation and filtration
• B. Coagulation, flocculation and sedimentation
• C. Sedimentation and disinfection
• D. Filtration and aeration

Answer: (B)

A solid contact basin is designed to allow the particulates in the water to be treated in stages that build up into larger solids and then settle them out. In this type of basin, chemical coagulants destabilize tiny particles (coagulation), gentle mixing helps those destabilized particles clump together into larger flocs (flocculation), and the basin is designed to provide quiet conditions so those flocs can settle to the bottom (sedimentation). This combination removes a significant portion of suspended solids before the water moves on to disinfection or filtration.

Filtration and aeration aren’t primarily achieved in a solid contact basin, and disinfection is typically handled in a separate stage where the water is held to allow the disinfectant to act. Similarly, a basin focused on solids removal doesn’t perform filtration or aeration, and relying on sedimentation alone wouldn’t effectively remove the smaller, destabilized particles without the coagulation and flocculation steps.