What is the function of flocculator in the typical water treatment scheme for surface water ?
- ATo rapid dispersion of chemical coagulant(s) to encourage destabilization of colloids
- BTo permit the settlement of chemical ‘flocs’ along with colloidal particles
- CTo provide for gentle mixing of the destabilized colloids to promote agglomeration of colloids into large easily settleable flocsCorrect
- DTo remove the flocs and colloids which escape from the settlement in the secondary sedimentation tank
Solution
Concept
Function of the flocculator
Step-by-step solution
1. Rapid mix disperses the coagulant (a). 2. Flocculator: slow, gentle mixing so that destabilised particles collide and form large flocs (c). 3. Sedimentation tank: flocs settle (b). 4. Filter removes the escaping flocs (d).
Explanation
Gentle stirring in the flocculator builds flocs that are large enough to settle.
Why the other options are wrong
(a) is the rapid mixing unit, (b) is the sedimentation tank, and (d) is the filter.
Shortcut
Rapid mix → flocculator (slow) → settling → filter.
Common mistake
Choosing the rapid mix function.
Correct answer: C) To provide for gentle mixing of the destabilized colloids to promote agglomeration of colloids into large easily settleable flocs