Lamella / Tube Settler Clarifier

Stack inclined tubes or plates into a clarifier and every square metre of plan area does the work of several. That is the pitch — and it is real. This tool derives the multiplier from the tube geometry rather than assuming one, then checks the two things that actually kill these installations: turbulence in the channels, and sludge that will not slide down the plates.

1Duty & existing asset

Use the retrofit area to answer "how much more can my existing clarifier take?" — the question that usually motivates a lamella installation.

Avg flow Q^[1] (1k–300k)m³/d

Peak factor^[1] (1.5–3)×

MLSS^[1] (2–5)g/L

RAS R^[1] (0.5–1.5)×

SOR on A_eff^[2] (30–50)m³/m²·d

Existing area^[1] (any)m²

2Tube / plate geometry

The multiplier is not a magic number — it falls out of how much horizontal projected settling area fits into one square metre of plan area: L·sinθ·cosθ / d, derated by an efficiency factor.

Inclination θ^[3] (55–70)°

Spacing d^[3] (25–80)mm

Length L^[3] (0.6–1.5)m

Coverage^[3] (0.5–0.85)—

Efficiency η^[4] (0.35–0.8)—

Viscosity ν^[5] (0.8–1.1)10⁻⁶ m²/s

Depth below^[1] (2–4)m

Tanks^[1] (1–8)ea

Results — area & footprint

Plan area needed

—m²

Area multiplier

—×

Apparent SOR

—m³/m²·d

Item	Value	Basis

3Flow regime & sludge slide

Two failure modes dominate real installations: turbulence inside the channels, and sludge that refuses to slide down the plates and accumulates until the channels block.

Item	Value	Basis

4Retrofit — what the existing tank gains

Same tank, same footprint. The number that decides whether a lamella retrofit is worth the capital is how much extra flow it buys.

Item	Value	Basis

Operating envelope & maintenance

Item	Value	Basis

5Instrument schedule

A lamella retrofit concentrates the same duty into a smaller volume, which makes the blanket level and the effluent clarity more sensitive, not less.

Point	Instrument	Why here

Quote the lamella clarifier instruments at factory price

Blanket level, effluent turbidity, MLSS and RAS flow — all mappable to our catalogue and supplied at the manufacturer's ex-works price (our margin is the export rebate, not a markup on the device).

Request a quote for this duty ← Conventional Activated Sludge Chlorine Disinfection →

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Sources & parameter basis

[1]	METCALF & EDDY / EPA — secondary clarifier: peak SOR 30–50 m³/m²·d on the effective settling area, SLR 100–250 kg MLSS/m²·d, RAS 0.5–1.5×, MLSS 2–5 g/L.
[2]	Sizing on the effective area keeps the same SOR criteria as a conventional tank — the tubes do not change the settling physics, they multiply the area available for it.
[3]	Horizontal projected area installed per m² of plan area = L·sinθ·cosθ/d, multiplied by the coverage fraction. Tube modules: inclination 55–70°, spacing/diameter 25–80 mm, length 0.6–1.5 m, coverage 0.5–0.85.
[4]	Efficiency factor η 0.35–0.8 covers inlet disturbance, wall effects and short-circuiting. Use the lower end for biological sludge, which is lighter and more easily re-suspended than a water-treatment floc.
[5]	Flow regime: Reynolds number Re = v·d/ν on the channel velocity; keep Re below about 500 and preferably below 200 so the flow in the channels stays laminar. ν ≈ 1.0×10⁻⁶ m²/s at 20 °C, ≈0.8×10⁻⁶ at 30 °C.
[6]	Sludge slide: the inclination must exceed the sludge–plate friction angle; 55° is the usual minimum, and 60° is the common specification.

Full derivation and worked example: Lamella-Secondary-Calculation-Sheet.md. Try dropping the inclination to 45° — the projected area per m² actually rises (sinθ·cosθ peaks at 45°), but the sludge stops sliding. That trade-off is why nobody builds them at 45°.

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