The yield of rapid sand filter is ______to that of slow sand filter.

Slow sand filterRapid sand filterPre-treatmentEffluents from plain sedimentation coagulation, not req.Coagulation, flocculation, and sedimentation is the must.Filter SandD10 b/w 0.2 and 0.4 mmCu ⇒ 1.8 to 3.Gravel -30-75 cm thickD10 = 0.35 mm - 0.55 mmCu = 1.2 to 1.8Gravel-60-90 cm thickSize of each unitLarge such as 30m × 60 m.An area from 100-2000 m2.Less flexible on SHOCK loadingSmall 5m × 8m.Area < 100m2More flexible on shock loadingRate of filtration100 to 200 litres/hr/m23000 to 6000 L/hr/m2EfficiencyVery efficient in removing bacteria but less efficient in removing colour.Less efficient in bacteria (80-90%), very efficient in colour removal.Post-treatmentDisinfection is not must. ALMOST pure water obtained.Turbidity removal up to 50 ppmDisinfection is the must.Turbidity up to 35 ppm.Method of cleaningScrapping and removing the top 1.5 to 3 cm thick layer and washing down by hoses.Backwashing with or without compressed AIR. Qty of wash water req.0.2 to 0.6% of total filtered water is req. in every 1 to 3 monthsA large amount of total filtered water is req. in every 1 to 3 days. (1-5%) ∴ Rate of filtration (YIELD) of rapid sand filter is 30 times the rate of filtration slow sand filter.