Question

Coagulation-flocculation with alum is performed

• A. immediately after chlorination
• B. immediately before chlorination
• C. before rapid sand filtration
• D. after rapid sand filtration

Answer 1

The correct option is C before rapid sand filtration

Coagulation and Flocculation is done before filtration.

Filtration can be done either by slow sand or rapid sand filters.

The removal of chemical solids is easier than removing turbidity solids from surface water, and thererfore, higher filtration rates can be used.

This allows the use of smaller filters which reduce the treatment plant size and treatment capital cost.