In rapid sand filtration, the typical water filtration rate ranges around 10 to 15 kilolitres per square metre per hour (equivalent to 10–15 m/h).

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Solve this multiple-choice question and choose the correct option.

Accepted Answer

Introduction / Context:Rapid sand filters (RSF) are widely used in municipal plants for turbidity removal after coagulation–flocculation and sedimentation. Their hallmark is a comparatively high filtration rate versus slow sand filters. Given Data / Assumptions: Medium: sand (effective size typically 0.45–0.7 mm). Operation: periodic backwashing restores headloss. Units: 1 kL/m2/hr equals 1 m/h. Concept / Approach:Standard design guidance places RSF rates roughly in the 5–15 m/h band; many plants adopt 10–15 m/h for balanced performance and run time between backwashes. Step-by-Step Solution: 1) Recognize RSF are designed for higher throughput than slow sand filters.2) Convert units: kL/m2/hr is numerically equal to m/h.3) Select the band aligning with common practice: 10–15 kL/m2/hr. Verification / Alternative check:Check headloss buildup and effluent turbidity; design manuals cite similar ranges for conventional RSF. Why Other Options Are Wrong: 0.1–1: too low; typical of slow sand filters.3–6: low for RSF; used in some specialized media.15–20 or 25–40: too high for standard RSF; risk turbidity breakthrough. Common Pitfalls:Confusing RSF with slow sand rates; ignoring unit equivalence; overdriving filters causing short runs. Final Answer:10 to 15 kL/m2/hr

In rapid sand filtration, the typical water filtration rate ranges around 10 to 15 kilolitres per square metre per hour (equivalent to 10–15 m/h).

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