Water Treatment MCQ with answer and solution

Concept

Effective sand particle size for rapid filters

Formula

NONE

Step-by-step solution

1. Rapid sand filters utilize coarser filter media compared to slow sand filters to allow higher filtration rates. 2. The effective particle size (D10) for sand used in rapid sand filtration typically ranges from 0.35 mm to 0.55 mm. 3. This size range ensures proper bed porosity and filtration efficiency. Answer: B

Explanation

Rapid sand filters utilize coarser filter media compared to slow sand filters to achieve higher filtration rates. The effective size of the sand particles used in these filters typically ranges between 0.35 mm and 0.55 mm. This particle size provides adequate pore spaces for rapid water passage while ensuring effective straining of impurities.

Why the other options are wrong

A) Sand particles ranging from 0.20 to 0.30 mm are typically used in slow sand filters. C) An effective size of 0.60 to 0.65 mm is larger than the standard range for rapid sand filter media. D) Particle sizes from 0.65 to 0.75 mm are common in dual-media or coarse filter beds rather than standard rapid sand filters.

Shortcut

Rapid sand filter effective particle size is 0.35 to 0.55 mm (Slow sand is 0.20 to 0.30 mm).

Common mistake

Confusing the effective sand size for rapid sand filters (0.35–0.55 mm) with the finer sand size used in slow sand filters (0.20–0.30 mm).