Which sequence represents the correct order of conventional surface water treatment units from raw water inlet to finished water outlet?
- ASedimentation → Coagulation → Filtration → Disinfection
- BCoagulation → Sedimentation → Filtration → DisinfectionCorrect
- CFiltration → Coagulation → Sedimentation → Disinfection
- DDisinfection → Coagulation → Filtration → Sedimentation
Solution
Concept
Sequence of surface water treatment
Formula
NONE
Step-by-step solution
1. Raw water treatment destabilizes fine colloidal particles via chemical flash mixing (Coagulation). 2. The flocculated particles settle under gravity in clarification basins (Sedimentation). 3. Clarified water passes through granular filters to trap residual fine turbidity (Filtration). 4. Disinfectant is finally added to kill pathogens before pumping into distribution (Disinfection). Answer: B
Explanation
Conventional surface water treatment follows a logical sequence: rapid mixing and flocculation with chemical coagulants (Coagulation), gravity settling of flocculated suspended matter (Sedimentation), granular bed filtration to capture fine residuals (Filtration), and chemical disinfection to destroy pathogens prior to storage.
Why the other options are wrong
A) Coagulation must precede sedimentation to aggregate colloidal particles into settleable flocs. C) Direct filtration of raw turbid water rapidly blinds filter media. D) Disinfection must follow filtration because suspended solids shield microbes from disinfectants.
Shortcut
Surface water treatment sequence: Coagulation -> Sedimentation -> Filtration -> Disinfection (C-S-F-D).
Common mistake
Placing sedimentation before coagulation in a conventional coagulated clarification plant.
Correct answer: B) Coagulation → Sedimentation → Filtration → Disinfection