A lamella clarifier stacks inclined plates or tubes in a tank so that particles only need to settle a short vertical distance onto a plate, multiplying the effective settling area in a small footprint. Capacity is set by the total projected (horizontal) plate area and the surface loading rate the flocs can tolerate, which depends heavily on good coagulation and flocculation upstream.
What is a lamella clarifier and why use one?
Key takeaway: A lamella clarifier (inclined plate or tube settler) removes settleable solids in a fraction of the footprint of a conventional clarifier by giving particles many short settling paths onto inclined surfaces. Its capacity depends on the total projected plate area and a surface loading rate suited to the floc you produce upstream, so design starts with the chemistry and the settling characteristics of your water.
Conventional clarifiers need large surface areas because a particle must fall the full depth of the tank before the water carries it out. Lamella clarifiers solve this by stacking inclined plates a few centimeters apart. This article covers the principle, the projected area concept, loading rates, plate angle, upstream treatment, sludge handling and typical applications.
How does an inclined plate settler work?
The theory comes from ideal settling basin analysis: a particle is removed if its settling velocity is greater than the flow rate divided by the settling surface area. The depth of the basin does not appear in that relationship — only the area does. Inclined plates exploit this by adding settling surface without adding footprint.
The flow path typically works like this:
- Flocculated water enters the clarifier through a feed zone and is distributed below the plate pack.
- Water flows upward between the inclined plates (counter-current flow, the most common arrangement).
- Particles settle a short vertical distance onto the upper surface of the plate below.
- Settled solids slide down the plate, against the upward flow, into the sludge hopper.
- Clarified water leaves at the top through collection launders or orifice channels that spread the draw-off evenly.
- Sludge is withdrawn from the hopper by gravity or pump for thickening and dewatering.
Even flow distribution across every plate channel is essential. If a few channels take most of the flow, their local loading is far higher than the design value and solids carry over.
What is projected settling area?
Each plate contributes its horizontal projection to the settling area:
Projected area = number of plates × plate length × plate width × cos(θ)
where θ is the plate angle from horizontal. Some design methods include an efficiency factor to account for flow non-uniformity and entrance effects, so the effective area used in design is somewhat lower than the geometric figure.
The practical result is that a lamella pack can provide many times more effective settling area than the plan area of the tank it sits in. This is why lamella units are popular in skid-mounted plants and space-limited industrial sites.
Plate spacing and length
Typical plate spacing is in the range of about 50–100 mm. Closer spacing packs in more area but increases the risk of clogging with heavy or sticky sludge. Longer plates add area per plate but make the pack taller. The supplier should match spacing to your expected solids concentration.
What surface loading rate should be used?
The surface loading rate (also called overflow rate or hydraulic loading rate) is the flow divided by the effective projected area, usually expressed in m³/m²·h (equivalent to m/h). It must be lower than the settling velocity of the flocs you want to capture.
Because loading rates depend strongly on the water and the chemistry, designers base them on jar tests, settling tests or experience with similar water. The ranges below are typical starting points expressed on the projected plate area; quoting on tank plan area gives much higher numbers, so always check which basis a figure uses.
| Application | Floc character | Typical loading on projected area |
|---|---|---|
| Potable water with good coagulation | Light alum or ferric floc | About 0.3–0.6 m/h |
| Metal hydroxide precipitation (electroplating) | Moderately dense floc | About 0.3–0.8 m/h |
| Mining and mineral process water | Dense mineral particles | Up to about 1.0 m/h or more |
| Lightweight biological or organic solids | Fragile, slow settling | At the lower end, often below 0.3 m/h |
Treat these as indicative and confirm with testing. Overloading is the most common cause of poor lamella performance.
Why is the plate angle usually 55–60°?
The angle is a compromise between settling area and self-cleaning:
- Flatter plates (for example 45°) give more projected area per plate, but sludge tends to stick and accumulate.
- Steeper plates (above about 60°) shed sludge easily but lose projected area, since cos θ falls.
- Around 55–60° most sludges slide reliably down the plates while retaining good projected area.
Sticky sludges such as some metal hydroxides or oily solids may need the steeper end of this range, plus access for periodic washing.
Why does coagulation and flocculation matter upstream?
A lamella clarifier can only remove what has been made settleable. Fine clay, colloids, dissolved metals and emulsions settle too slowly on their own. Upstream treatment typically includes:
- pH adjustment — essential for metal hydroxide precipitation, where each metal has an optimum pH range.
- Coagulation — rapid mixing with a coagulant such as aluminum or iron salts to destabilize particles.
- Flocculation — slow mixing with a polymer flocculant to build large, strong flocs.
- Gentle transfer — low-velocity pipework or channels into the clarifier so flocs are not broken up.
Many packaged lamella units include integrated coagulation and flocculation tanks with mixers. Jar testing your actual water is the best way to choose chemicals and doses before finalizing the design.
How is the sludge hopper designed?
Settled solids collect in a conical or pyramidal hopper under the plate pack. Good hopper design features:
- Steep walls — typically 50–60° or steeper so sludge flows to the outlet.
- Adequate volume — enough storage to thicken sludge between withdrawals.
- Withdrawal control — timer-controlled valves, sludge pumps or, on larger units, a scraper or thickener rake.
- Sludge concentration — the hopper partially thickens sludge, reducing the volume sent onward.
Withdrawing sludge too rarely lets the blanket rise into the plates; withdrawing too often sends thin sludge to dewatering. Hopper sludge is typically dewatered on a filter press or screw press — see our sludge dewatering equipment.
Where are lamella clarifiers used?
| Application | Purpose | Notes |
|---|---|---|
| Electroplating and metal finishing | Remove precipitated metal hydroxides | Precise pH control is critical |
| Mining and quarrying | Clarify process water and recover water for reuse | Heavy solids may need robust sludge removal |
| Potable water pre-treatment | Remove turbidity before filtration | Often combined with coagulation and sand filters |
| Industrial process water | Treat cooling tower blowdown, wash water | Compact skid packages common |
| Wastewater tertiary treatment | Phosphorus removal with chemical dosing | Follows biological treatment |
For light solids, oils and grease that tend to float rather than settle, dissolved air flotation is often the better choice. In municipal and domestic wastewater, lamella settlers are frequently integrated into package sewage treatment plants as secondary or tertiary clarifiers, and drum filter screening can protect them from fibers and debris.
What data do you need to design one?
Before requesting a design, collect:
- design and peak flow rates (m³/h),
- influent TSS, turbidity and, for industrial water, metal concentrations and pH,
- required effluent quality,
- results of any jar or settling tests,
- available space and whether the unit will be indoors or outdoors,
- preferred materials (carbon steel with coating, stainless steel, or FRP/PP plates).
If you do not yet have jar test results, a supplier can usually suggest a test procedure or evaluate samples. Designing on assumed settling data without testing risks an undersized unit, so it is worth investing in this step before procurement, especially for industrial water whose chemistry varies by shift or batch.
Request a lamella clarifier proposal
Send your flow rate, water analysis and target effluent quality to inquiry@waste-water-equipment-factory.com, WhatsApp +86 176 2154 1688, or reach us through our contact page. Our engineers will recommend projected area, plate configuration and upstream dosing for your lamella clarifier.
FAQ
Why are lamella plates set at 55–60 degrees?
At around 55–60° the settled sludge slides down the plates by gravity and into the hopper without manual cleaning. Flatter angles give more projected area but let sludge accumulate, while steeper angles reduce the projected area.
What is the projected area of a lamella clarifier?
It is the horizontal projection of all the plates: number of plates × plate area × cosine of the plate angle. This projected area, not the tank footprint, is used to calculate the surface loading rate.
Do lamella clarifiers need chemicals?
For most industrial and potable water uses, yes. Coagulants and flocculants form larger, faster-settling flocs; without them, fine and colloidal particles settle too slowly to be removed reliably.
What is the difference between a plate settler and a tube settler?
Both use inclined surfaces to reduce settling distance. Plate packs are usually rigid and spaced for easier access, while tube settler modules are lightweight honeycomb blocks often used to upgrade existing tanks.
