What step usually follows the addition of coagulants?

• A. Screening
• B. Coagulation
• C. Coagulation and Flocculation
• D. Disinfectant added

Answer: (C)

After adding coagulants, the water undergoes rapid mixing to start coagulation, which neutralizes charges on tiny particles and destabilizes them. This is followed by gentler mixing that promotes growth of those destabilized particles into larger clumps, a process called flocculation. Together, these two steps form larger, settleable flocs that can be removed by sedimentation or filtration, so the usual step after dosing coagulants is coagulation and flocculation. Screening happens earlier in the process to remove larger debris, and disinfectant is added later, after treatment and filtration.