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Media Filter (Sand / Dual-Media) Design

The standard tertiary polishing step. Set the flow, filtration rate and media, and get the filter area, bed dimensions, clean-bed headloss (Kozeny-Carman) and the backwash rate and volume — for the polishing stage after biological treatment.

1Duty & media

Rapid sand 5–8 m/h; dual-media / multimedia up to 10–12 m/h. Bed 0.6–1.2 m. Always ≥2 units.

Avg flow Q^[1] (1k–500k)m³/d

Media^[1]

Rate v^[1] (5–12)m/h

Filters n^[1] (2–12)

Bed depth L^[1] (0.6–1.2)m

d₁₀^[2] (0.4–1.2)mm

Porosity ε^[2] (0.4–0.5)

Temp T^[3] (15–34)°C

Backwash v_bw^[1] (30–60)m/h

BW duration^[1] (5–15)min

Results — area, headloss & backwash

Total filter area

—m²

Clean-bed Δh

—m

Backwash vol

—m³

Item	Value	Basis

2Cell geometry & backwash

Cells are laid out L:W ≈ 1.5–2 (or square for dual-media). One cell is taken offline for backwash.

Parameter	Value	Unit

Order note

Quote the filter instruments at factory price

A filter cell needs headloss (differential pressure), effluent turbidity, level and flow — plus the backwash-valve controls. We supply them at the manufacturer's ex-works price; margin is the export rebate only.

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Sources & parameter basis

[1]	Metcalf & Eddy — rapid sand rate 5–8 m/h (up to 12 for dual/multi), bed 0.6–1.2 m, ≥2 cells, backwash 30–60 m/h × 5–15 min; air-scour 50–60 m/h.
[2]	Kozeny-Carman clean-bed headloss: Δh = 180·(1−ε)²/ε³ · (ν·v·L)/(g·d_s²); sand d₁₀ 0.4–0.6 mm, anthracite 0.8–1.2 mm; ε ≈ 0.4–0.5.
[3]	Kinematic viscosity ν(T): 1.00e-6 m²/s @20°C, 0.80e-6 @30°C (drops ~2 %/°C, lowering headloss).

Full derivation and worked example: Media-Filtration-Calculation-Sheet.md. The filter is the polishing step of advanced treatment — run it after the biological stage.

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