What is the correct order of the stages in standard municipal water treatment among coagulation, flocculation, filtration, and disinfection?

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

Answer: (A)

In municipal water treatment, the goal is to first destabilize and then remove particles, and finally kill any remaining microbes. Coagulation is done at the start to neutralize the tiny particles’ charges, allowing them to come together instead of staying dispersed. Next, gentle mixing in flocculation helps these destabilized particles form larger clumps, or flocs, making them easier to remove. After that, filtration physically strips away the remaining solids, producing clearer water. The last step is disinfection, which eliminates any microbes still present. So the best sequence is coagulation, flocculation, filtration, then disinfection. Doing disinfection before filtration would be less effective and could lead to byproducts, and reversing the order of coagulation and flocculation would hinder floc formation and particle removal.