Which statement best defines sedimentation in water treatment?

• A. Forcing water through membranes to remove particles
• B. Allowing heavier particles to settle out by gravity
• C. The chemical reaction that neutralizes charge on particles
• D. The process of adding chlorine to water for disinfection

Answer: (B)

Sedimentation is the physical removal of suspended solids by gravity as water sits in a quiet basin. After coagulation and flocculation, the heavier flocs settle to the bottom, forming a sludge layer while clearer water remains at the top. The process relies on gravity and time, with settling aided by low turbulence and enough residence time for particles to drop out. This step is distinct from filtration (forcing water through membranes to remove particles), chemical neutralization or charge destabilization (which occurs during coagulation), and disinfection (such as adding chlorine).