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Settling Velocity & Clarifier Sizing Calculator

Calculate particle settling velocity, clarifier surface area, solids flux, and removal efficiency using Stokes and Newton drag laws. For primary, secondary, lamella, and DAF clarifier design.

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Settling Velocity & Clarifier Sizing Calculator

Enter your process parameters below to calculate design values. All calculations follow industry-standard methodologies.

m³/day
mg/L
µm (micrometres)
kg/m³ (typical 1050-2650)
kg/m³ (998 @ 20°C, 1000 default)
Pa·s (0.001 @ 20°C)
m³/m²·hour (typical 0.5-2.0 for primary, 0.5-1.0 for secondary)

Clarifier Design Parameters

Surface loading rates (overflow rates) are the primary design parameter for clarifiers. Primary clarifiers typically operate at 1-2.5 m³/m²·h for municipal wastewater. Secondary clarifiers after activated sludge operate at 0.5-1.0 m³/m²·h due to lighter sludge. Lamella clarifiers can achieve 3-5 m³/m²·h effective rate due to the reduced settling distance. DAF units operate at 3-10 m³/m²·h with air flotation assistance.

  • Primary clarifier: 1.0-2.5 m³/m²·h
  • Secondary clarifier: 0.5-1.0 m³/m²·h
  • Lamella clarifier: 3.0-5.0 m³/m²·h
  • DAF unit: 3.0-10.0 m³/m²·h
  • Weir loading: < 10 m³/m·h (circular)

Settling Theory

Particle settling follows Stokes law for small particles (Re < 1) where drag is viscous. For larger particles, the drag coefficient increases and Newton law applies. In practice, real clarifiers achieve lower removal than ideal theory due to turbulence, density currents, and wind effects. Safety factors of 1.5-2.0 are commonly applied to theoretical area calculations. Temperature affects water viscosity and thus settling velocity.

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