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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).

Difficulty: Easy

0.1 to 1 kL/m2/hr
3 to 6 kL/m2/hr
10 to 15 kL/m2/hr
15 to 20 kL/m2/hr
25 to 40 kL/m2/hr

Correct Answer: 10 to 15 kL/m2/hr

Explanation:

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.

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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