Lamella Primary Clarifier

Inclined plate settler with dramatically increased effective settling area for compact, high-rate primary treatment.

Overview

The lamella (inclined plate) clarifier uses closely-spaced inclined plates to multiply the effective settling area, allowing much higher surface overflow rates (SOR) in a compact footprint. This technology is ideal for space-constrained sites or as a retrofit to increase existing plant capacity.

When to Use

• Space-constrained sites
• Capacity upgrades to existing plants
• High-rate primary treatment
• Storm water treatment
• Industrial pretreatment

Key Advantages

• 5-10× higher SOR than conventional clarifiers
• 60-80% smaller footprint
• Rapid construction (modular options)
• Effective for storm water peaks

Settling Theory

Inclined Plate Settling

The effective settling area is multiplied by the number of plate passages:

$$A_{effective} = A_{horizontal} \times n \times \cos(\theta)$$

Where:

• $n$ = number of plate channels
• $\theta$ = plate angle from horizontal (typically 55-60°)

Modified Hazen Theory

Particle removal in lamella settlers follows modified Hazen theory:

$$\eta = \frac{V_s}{SOR_{actual}} \times \frac{L}{d} \times \cos(\theta) \times \sin(\theta)$$

Where:

• $L$ = plate length (m)
• $d$ = plate spacing (m)
• $\theta$ = plate angle (°)

Simplifies to:

$$\eta = \frac{V_s \times L \times \sin(2\theta)}{2 \times SOR \times d}$$

Critical Settling Velocity

The minimum particle settling velocity captured:

$$V_{s,critical} = \frac{Q}{A_{effective}} = \frac{Q \times d}{W \times L \times n \times \cos(\theta) \times \sin(\theta)}$$

Design Equations

Effective Surface Overflow Rate

The actual SOR is much higher than conventional:

$$SOR_{actual} = \frac{Q}{A_{footprint}}$$

But the effective SOR considering plates:

$$SOR_{effective} = \frac{Q}{A_{effective}} = \frac{SOR_{actual}}{n \times \cos(\theta)}$$

Plate Geometry

Number of Channels: $$n = \frac{H_{plate zone}}{d + t}$$

Where:

• $H_{plate zone}$ = height of plate zone (m)
• $d$ = clear spacing between plates (m)
• $t$ = plate thickness (m)

Plate Length (vertical projection): $$L_{vertical} = L \times \sin(\theta)$$

Hydraulic Loading

Per-channel velocity: $$v_{channel} = \frac{Q}{W \times n \times d}$$

Design limit: $v_{channel} < 0.02$ m/s to prevent solids resuspension.

Sludge Slide-off

Plates must be angled to allow sludge to slide off:

$$\theta > \arctan(\mu)$$

Where $\mu$ = coefficient of friction (typically 0.7-1.0 for primary sludge)

Minimum angle: 50° (typically 55-60° used)

Parameters

Geometric Parameters

Parameter	Symbol	Unit	Range	Default	Description
Plate Length	L	m	1.0-3.0	2.0	Along flow path
Plate Spacing	d	mm	40-100	50	Clear spacing
Plate Angle	θ	°	50-70	60	From horizontal
Plate Thickness	t	mm	2-6	3	Material dependent
Plate Zone Height	H	m	1.5-4.0	2.5	Vertical extent
Tank Width	W	m	2-10	5	Flow width
Number of Tanks	N	-	1-4	2	For redundancy

Hydraulic Parameters

Parameter	Unit	Typical Range	Notes
Actual SOR	m³/m²/h	5-15	On footprint area
Effective SOR	m³/m²/h	0.5-1.5	On plate area
Channel Velocity	m/s	0.01-0.02	In plate channels
HRT (plate zone)	min	10-30	Shorter than conventional

Advanced Parameters

Parameter	Unit	Default	Range	Description
plateEfficiencyFactor	-	0.85	0.7-0.95	Account for edge effects
sludgeRemovalMethod	-	hopper	hopper/continuous	Collection method
flocculationZone	bool	true	-	Pre-settling zone
flocZoneHRT	min	10	5-20	Floc formation time
distributionMethod	-	weir	weir/manifold	Flow distribution

Particle Size Distribution

Lamella clarifiers effectively remove particles across the distribution:

Settling Velocity (m/h)	Conventional Removal	Lamella Removal
0.1 (colloidal)	5%	15%
0.5 (fine)	30%	60%
2.0 (medium)	85%	98%
5.0 (coarse)	98%	100%
10.0 (very coarse)	100%	100%

Removal Efficiencies

Primary Treatment Application

Parameter	Removal (%)	Notes
BOD	20-30	Lower contact time
TSS	50-70	Good solids removal
COD	20-35	Particulate fraction
NH₃-N	0	Not removed
Total P	10-15	Particulate only

With Chemical Addition

Parameter	Removal (%)	Notes
BOD	30-40	Enhanced
TSS	70-85	Excellent with chemicals
COD	30-45	Enhanced
NH₃-N	0	Not affected
Total P	70-90	Primary mechanism

Storm Water Treatment

Lamella clarifiers excel at storm water peaks:

Parameter	Removal (%)
TSS	60-80
Grit	95-100
Floatables	80-95

Configuration

Zones

graph TB
    subgraph Lamella Clarifier
        A[Inlet Zone] --> B[Flocculation Zone]
        B --> C[Plate Settling Zone]
        C --> D[Clarified Water Zone]
        C --> E[Sludge Hopper]
    end
    style C fill:#e1f5fe

1. Inlet Zone: Flow distribution and energy dissipation
2. Flocculation Zone: Gentle mixing for particle aggregation (10-20 min HRT)
3. Plate Settling Zone: Inclined plates for high-rate settling
4. Clarified Water Zone: Collection of treated effluent
5. Sludge Hopper: Collection of settled solids

Step-by-Step Setup

1. Define Flow Requirements

   • Peak flow capacity
   • Average flow for efficiency calc
   • Storm flow handling

2. Size Plate Zone

   • Select plate angle (55-60°)
   • Choose plate spacing (40-80mm)
   • Calculate required plate area

3. Add Support Zones

   • Inlet/distribution
   • Flocculation (if needed)
   • Sludge collection

4. Verify Hydraulics

   • Check channel velocity < 0.02 m/s
   • Verify effective SOR
   • Confirm sludge slide-off angle

Example Configuration

{
  "type": "primaryClarifierLamella",
  "parameters": {
    "tankLength": 8,
    "tankWidth": 5,
    "plateLength": 2.0,
    "plateSpacing": 50,
    "plateAngle": 60,
    "plateZoneHeight": 2.5,
    "numberOfTanks": 2,
    "chemicalDosing": false,
    "calculationMode": "advanced",
    "advancedParams": {
      "plateEfficiencyFactor": 0.85,
      "flocculationZone": true,
      "flocZoneHRT": 15,
      "sludgeRemovalMethod": "continuous"
    }
  }
}

Worked Example

Given

• Design flow: 5,000 m³/d (peak: 10,000 m³/d)
• Space available: 10m × 6m footprint
• Influent TSS: 350 mg/L

Design

Step 1: Plate Configuration

• Plate angle: 60°
• Plate spacing: 50mm
• Plate thickness: 3mm
• Plate zone height: 2.5m

Number of channels: $$n = \frac{2.5}{0.050 + 0.003} = 47 \text{ channels}$$

Step 2: Calculate Effective Area

Tank width: 5m, Plate length: 2.0m

$$A_{effective} = 5 \times 2.0 \times 47 \times \cos(60°) = 235 \text{ m}^2$$

Step 3: Check SOR

Footprint area: $A = 10 \times 6 = 60$ m²

At design flow: $$SOR_{actual} = \frac{5,000}{60} = 83.3 \text{ m³/m²/d}$$

$$SOR_{effective} = \frac{5,000}{235} = 21.3 \text{ m³/m²/d}$$

Equivalent to conventional: ✓

Step 4: Check Channel Velocity

Per-channel flow at peak: $$Q_{channel} = \frac{10,000}{86,400 \times 47} = 0.00246 \text{ m³/s per meter width}$$

$$v_{channel} = \frac{0.00246}{0.05} = 0.049 \text{ m/s}$$

⚠ Exceeds 0.02 m/s limit at peak - need larger plates or more tanks.

Step 5: Revised Design

Add second tank (2 × 60 m²):

$$v_{channel} = 0.025 \text{ m/s}$$ ✓ (marginally acceptable for peak)

Step 6: Estimate Removal

At effective SOR of 21 m³/m²/d:

• TSS removal: ~65%
• BOD removal: ~25%

Sludge Handling

Collection Methods

Hopper Collection:

• Sludge slides to hopper
• Batch withdrawal
• Simple, reliable

Continuous Removal:

• Scraper mechanism
• Continuous withdrawal
• Better for high solids loads

Sludge Characteristics

Parameter	Value	Unit
Concentration	1-3	% DS
Withdrawal Rate	0.5-2	% of flow
Density	1010-1030	kg/m³

Maintenance Considerations

Plate Cleaning

• Frequency: Every 3-12 months
• Methods: High-pressure water, air scour, manual
• Access: Removable plate packs preferred

Common Issues

Issue	Cause	Solution
Reduced efficiency	Plate fouling	Clean plates
Sludge buildup	Insufficient angle	Increase withdrawal
Short-circuiting	Poor distribution	Improve inlet
Algae growth	Light exposure	Cover tank

Comparison with Conventional

Parameter	Conventional	Lamella	Ratio
Footprint	100%	15-25%	4-7× smaller
SOR (actual)	30-50 m³/m²/d	150-300 m³/m²/d	5-10× higher
HRT	2-4 hours	15-45 min	4-8× shorter
TSS Removal	50-65%	50-70%	Similar
Capital Cost	100%	80-120%	Variable
Operating Cost	100%	90-110%	Similar

Applications

Retrofit/Upgrade

Ideal for increasing existing plant capacity:

$$Capacity_{new} = Capacity_{old} + A_{lamella} \times SOR_{lamella}$$

Can add 50-200% capacity with small footprint.

Storm Water Treatment

High-rate capability handles storm peaks:

• Flow equalization not always needed
• Rapid response to flow changes
• Good grit and floatables removal

Industrial Pretreatment

Compact size suits industrial applications:

• Food processing
• Paper mills
• Chemical plants

Best Practices

1. Plate Angle: Use 55-60° for reliable sludge release
2. Spacing: Wider spacing (80-100mm) reduces clogging risk
3. Flocculation: Include pre-flocculation zone for best results
4. Flow Distribution: Critical for even loading
5. Cleaning Access: Design for easy plate removal
6. Covers: Prevent algae in outdoor installations

Related Topics

• Circular-Primary-Clarifier
• Rectangular-Primary-Clarifier
• Lamella-Secondary-Clarifier
• Storm-Water-Treatment

References

1. Metcalf & Eddy (2014). Wastewater Engineering: Treatment and Resource Recovery, 5th Ed.
2. Yao, K.M. (1970). "Theoretical Study of High-Rate Sedimentation". JWPCF
3. WEF (2018). Design of Municipal Wastewater Treatment Plants, MOP 8
4. Parkson Corporation. Lamella Gravity Settler Design Manual
5. UK Water Industry Research (2003). High Rate Clarifiers in Sewage Treatment