The main purpose of ___ is to remove turbidity.

• A. Coagulation/Flocculation
• B. Disinfection
• C. Aeration
• D. Filtration

Answer: (A)

Turbidity comes from tiny suspended particles that scatter light, and removing it requires getting those particles to stick together into larger clumps that can be separated from the water. Coagulation introduces chemicals called coagulants that neutralize the surface charges of colloidal particles, reducing the repulsion between them. Flocculation then uses gentle mixing to encourage those destabilized particles to collide and bond, forming larger aggregates called flocs. These flocs are much easier to remove by settling or filtration, so turbidity drops significantly.

Disinfection targets microorganisms, not how turbid the water is. Aeration mainly changes dissolved gases and taste/odor, not turbidity. Filtration can remove suspended solids and reduce turbidity, but it relies on the prior coagulation/flocculation step to make the fine particles large enough to be captured; the specific goal of coagulation/flocculation is to destabilize and aggregate particles to enable their removal.