Gravity Thickener Solids Loading Calculator
Gravity thickeners are rated by solids loading, not flow. Enter your sludge feed and thickener size to check the loading rate against design ranges.
Thickener Loading
| Item | Value |
|---|
How the calculation works
Formulas
Solids fed (lb/day) = flow (gal/day) × 8.34 × TS% ÷ 100
Thickener area (ft²) = π × (diameter ÷ 2)² × number in service
Solids loading rate (lb/day·ft²) = solids fed (lb/day) ÷ area (ft²)
Solids fed (lb/day) = flow (gal/day) × 8.34 × TS% ÷ 100
Thickener area (ft²) = π × (diameter ÷ 2)² × number in service
Solids loading rate (lb/day·ft²) = solids fed (lb/day) ÷ area (ft²)
| Sludge type | Typical SLR (lb/day·ft²) |
|---|---|
| Primary sludge | 8 – 10 |
| Blended primary + WAS | 5 – 8 |
| Waste activated sludge | 3 – 6 |
Notes & limitations
Loading ranges are from Metcalf & Eddy gravity-thickener design guidance. WAS thickens poorly by gravity alone — many plants use dissolved air flotation or rotary drums for WAS and reserve gravity thickeners for primary sludge.
- Overloading shows up as a rising sludge blanket and solids in the overflow — watch blanket depth, not just the loading number.
- Solids loading, not hydraulic overflow rate, controls gravity-thickener performance. A dilute feed at the same flow loads the unit less.
- Septicity in the thickener (long detention, warm weather) can release phosphorus and generate odors — keep detention under ~24 hours where possible.
- This tool checks loading only; it does not predict thickened-solids concentration.
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