Why is flocculation slower than coagulation?

• A. To displace air.
• B. To inject more coagulant.
• C. To allow micro-flocs to grow into larger, settleable flocs without breaking apart.
• D. To rapidly mix water.

Answer: (C)

During water treatment, the process moves from coagulation to flocculation. Coagulation uses rapid mixing to quickly neutralize particle charges and form tiny clumps. Flocculation follows with slower, gentle mixing that gives these tiny clumps time to collide and stick together into larger, settleable flocs. If the mixing is too vigorous, those forming flocs are torn apart instead of growing, so the rate is purposely slowed to allow growth without breakage. This larger, settleable outcome is why flocculation proceeds more slowly but ends with better settling. The other options don’t explain the growth mechanism: displacing air isn’t the drive; injecting more coagulant relates to coagulation, not the slower growth stage; rapid mixing is characteristic of coagulation, not flocculation.