Primary Clarifier Removal Calculator
Primary clarifier performance follows the surface overflow rate. Enter your flow and basin geometry to estimate TSS and BOD removal.
Primary Clarifier Estimate
| Item | Value |
|---|
How the calculation works
Formulas
Surface area per basin (ft2) = π ÷ 4 × diameter2
Surface overflow rate (gpd/ft2) = flow (gpd) ÷ total area (ft2)
Removal % = linear interpolation of the typical SOR-vs-removal table below
Effluent (mg/L) = influent × (1 − removal ÷ 100)
Solids removed (lb/day) = 8.34 × flow (MGD) × (influent − effluent)
Surface area per basin (ft2) = π ÷ 4 × diameter2
Surface overflow rate (gpd/ft2) = flow (gpd) ÷ total area (ft2)
Removal % = linear interpolation of the typical SOR-vs-removal table below
Effluent (mg/L) = influent × (1 − removal ÷ 100)
Solids removed (lb/day) = 8.34 × flow (MGD) × (influent − effluent)
| Surface overflow rate (gpd/ft2) | Typical TSS removal | Typical BOD5 removal |
|---|---|---|
| 500 | 70% | 40% |
| 800 | 60% | 35% |
| 1,200 | 50% | 30% |
| 1,800 | 40% | 25% |
| 2,500 | 30% | 20% |
Notes & limitations
The SOR-vs-removal bands are typical values compiled from Metcalf & Eddy and WEF references for domestic wastewater. Real removal depends on influent character, temperature, and basin condition — treat the output as a planning estimate and confirm with plant data.
- Typical design: 800–1,200 gpd/ft2 at average flow, up to ~1,800–3,000 at peak hourly flow.
- Septicity, fats/oils/grease, and short-circuiting all degrade removal below the table values.
- Rectangular basins: use the equivalent-diameter hint above, or compute area directly as length x width and confirm it matches the total used here.
- This tool does not replace weir loading or solids loading checks for the secondary clarifiers downstream.
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