Design Manual › Secondary › Lamella / Tube
FREE ENGINEERING TOOL · SECONDARY
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.
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.
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 →Response within 24 hours · Inputs stay in your browser — nothing is uploaded.
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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