Which sequence best describes standard water treatment steps?

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

Answer: (D)

In water treatment, each step builds on the previous one to remove particles efficiently. Coagulation adds chemicals that neutralize the charges on tiny particles, allowing them to come together during flocculation into larger clumps. Those clumps then settle out in sedimentation, so much of the solid material is removed before the water moves on. After sedimentation, the water passes through filtration to catch remaining particles, and finally disinfection kills microbes to ensure safety. This order—coagulation, flocculation, sedimentation, filtration, disinfection—maximizes removal of contaminants at each stage. Starting with sedimentation would miss the chance to form and remove large flocs first, letting more material pass to filtration and reducing overall effectiveness.