GATE 2025 ES – Question 45
Water and Wastewater Treatment and Management · Water Treatment · 2 marks · Multiple select
Which options remove solids from water? Select all that apply.
- Chlorination
- Coagulation–flocculation–sedimentation followed by slow sand filtration
- Chlorination followed by aeration
- Slow sand filtration
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Show answer and explanation
Correct answer: (B) Coagulation–flocculation–sedimentation followed by slow sand filtration; (D) Slow sand filtration
Explanation
Coagulation destabilizes colloids, flocculation enlarges them, sedimentation removes settleable flocs, and filtration retains residual particles. Slow sand filtration also removes suspended solids by itself. Chlorination primarily disinfects and aeration primarily transfers gases; neither listed chemical/gas-treatment option supplies the intended solids separation. Select **B, D**.
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