What is the purpose of coagulation-flocculation in wastewater treatment?

• A. Destabilizes colloids; flocculation aggregates particles into larger flocs for efficient sedimentation.
• B. Adds chemicals to dissolve organic matter.
• C. Removes dissolved nutrients by filtration.
• D. Increases temperature to accelerate chemical reactions.

Answer: (A)

Coagulation-flocculation is all about getting suspended, tiny particles out of the water by making them easier to remove. First, coagulants are added to neutralize the electrical charges on colloids, so the particles no longer repel each other. Then a gentle mixing phase (flocculation) encourages these destabilized particles to collide and stick together, forming larger clumps called flocs. These bigger aggregates settle more readily in a sedimentation basin or can be filtered out, leading to clearer water and better efficiency of downstream treatment steps. This approach specifically targets suspended solids and turbidity, rather than dissolving organic matter, removing dissolved nutrients by filtration, or heating the water.