Select the correct statement with respect to a slow sand filter.

Question

rrbpapers · Accepted Answer

The effective size and uniformity coefficient are the most important sand parameters in determining the filtration rate.

Item	Slow sand filter	Rapid sand filter
Rate of filtration	Low Rate of Filtration (1 to 4 to 8m³)(m²d)⁻¹	High Rate of filtration (100 to 400m³)(m²d)⁻¹
Surface Area	Larger surface area (200 - 2000 m2)	Smaller surface area (80 - 200 m2)
Depth of bed	0.3 m gravel 1.0 - 1.5m sand	0.5 m gravel 0.60 - 1.8m of sand anthracite
Pre-treatment	Pre-treatment not required	Pre-treatment compulsory
Post-treatment	Post-treatment optional	Post-treatment compulsory
Size of sand	Sand filter characteristics Grain size - 0.15 to 0.30 mm Coefficient of uniformity (grain) - 1.8 to 2.5 or 3.	Sand filter characteristics Grain size - 0.35 to 0.55 mm Coefficient of uniformity (grain)- 1.2 to 1.7
Drainage	Drainage: Lateral Drainage System	Drainage: Central Drainage System

The filtering medium has effective size 0.45 to 0.7 mm