LAMELLA DESIGN FUNDAMENTALS
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Design Criteria for Lamella Settlers in Clarifier Tanks

Arbiol Mühendislik Lamella Hesap Standartları ve Teknik Rehber

One of the most fundamental physical processes in water and wastewater treatment technologies is the removal of suspended particles by gravity settling. Today, due to high costs, Lamella (Inclined Plate) Systems, which offer a modern geometric solution, are preferred.

1. Fundamental Logic of Sedimentation and Footprint Requirements

For a sludge particle to separate from water, it must reach the bottom of the tank and settle there. The factor determining efficiency is not the depth of the tank, but the total BASE area. Lamella systems provide significant efficiency by increasing the existing tank base area by 9 to 16 times, depending on the selected model.

Lamella with Multi-Story Building Analogy

If you build single-story detached houses to accommodate 50 families on a plot of land, you would need a massive area (think of this as the base of a tank without lamella). However, if you build a high-rise apartment building on the same plot by utilizing vertical space, you can fit all the families into a smaller plot (we can think of this as a tank with lamella).

Without expanding the BASE area covered by the tank, we can create a much wider "projection (effective) area" by inserting inclined plates inside. By arranging inclined plates in the tank, we are effectively producing thousands of square meters of artificial "floors" and effective base area.

2. Lamella Plate Quantity and Area Calculation Method

The most fundamental engineering concept in lamella systems is the Projection Area (Horizontal Projected Area). Since the plates are inclined at 60 degrees, the active surface that determines the settling efficiency of the water is calculated based on the projection of the actual plate area in this alignment.

Single Plate Area Calculations:
  • Actual Surface Area: Width x Length
  • Projection Area (60°): Actual Area x cos(60°) = Actual Area x 0.50
Example: While the actual area of a 1.0m x 1.2m plate is 1.2 m², the Projection Area is 0.60 m².
Formula for Required Plate Quantity:
1. Total Projection Area = Flow Rate (m³/hour) / Target Velocity (m/hour)
2. Plate Quantity = Total Projection Area / Single Plate Projection Area
Engineering Calculation and Verification Example (Q = 100 m³/hour):

Let's select our target in-plate velocity as exactly 0.50 m/hour:

  • Required Total Projection Area: 100 / 0.50 = 200 m²
  • Required Plate Quantity (for 0.60 m² projection): 200 / 0.60 = 333.3 → 334 Plates

✓ Verification Check: 100 m³/hour / (334 x 0.60 m²) = 0.499 m/hour. (Perfectly validates the safe range of 0.40 - 0.60 m/hour!)

3. Surface Overflow Rate (SOR) Limits by Design Standards

Source Lamella System Type Surface Loading (SOR) Hazen Velocity
Clean Water NONE Conventional Settling 1.0 – 2.0 m/hour No Plate
Domestic Wastewater NONE Conventional Settling 0.9 – 1.5 m/hour No Plate
Clean Water YES Lamella Settling 4.00 – 6.00 m/hour 0.40 – 0.60 m/hour
Industrial Wastewater YES Lamella Settling 3.00 – 5.00 m/hour 0.30 – 0.50 m/hour
Domestic Wastewater YES Lamella Settling 6.00 – 8.00 m/hour 0.60 – 0.80 m/hour

4. Critical Design and Material Selection Recommendations

Material Thickness by Plate Length
  • For plates up to 115 cm in length: 1.0 mm thickness
  • For plates up to 140 cm in length: 1.2 mm thickness
  • For plates up to 170 cm in length: 1.5 mm thickness
  • For plates 200 cm and longer: At least 2.0 mm thickness
  • Production exceeding 2 mm is possible with special techniques but is not recommended due to cost factors.
Module Geometry and Angle Optimization
  • Module Volume: Should be between 1.5 m³ and 2 m³ for ease of site installation, service, and operation.
  • Outer Frame: 304 Quality stainless steel is suitable (316 is unnecessary and very expensive depending on the function).
  • Frame Profile Size: Varies depending on module size. For a 1.5 m³ module, 2-2.5 mm is sufficient; for 2 m³, 2.5-3 mm is sufficient.
  • Frame Geometry: Frame width (Wx) is important. The production width and axial distance of the lamella model to be used are decisive. Lamella vertical (Hx) height of 100-104-120 cm are the most commonly used dimensions. Module length (Lx) is determined while staying within frame volume criteria. For quick advice on module dimensions: info@arbiol.com.tr
  • Inclination Angle: The plate inclination angle must be 60 degrees for the sludge to slide down automatically.
Material and Design Preference by Purpose
  • Drinking Water Plants: The first choice should be PP (Polypropylene) due to food safety criteria, and the plate color should be selected as Blue.
    Note: PP material offers a more advantageous structure than PVC with its high strength, flexibility, temperature resistance, long life, and superior surface quality.
  • Wastewater Plants: Technically, the first choice is still PP. However, PVC can be preferred as an economical alternative in projects with high budget sensitivity.
  • Assembly and Operation: To provide ease of service and prevent floating problems caused by buoyancy in water, lamella modules must be designed as Framed Type.
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