SLR is the mass of solids applied to a clarifier per unit area. It controls thickening.
Clarifier Solids Loading Rate
Formula
SLR, lb/d/ft² = (Q + RAS, MGD) x MLSS, mg/L x 8.34 / Area, ft²
Inputs used
- Influent flow (MGD)
- RAS flow (MGD)
- MLSS (mg/L)
- Clarifier diameter (ft)
- Clarifiers in service (units)
- Or total area (overrides diameter) (ft²)
Worked example (White River WRRF, fictional)
- Solids applied = (8.0 + 4.0) x 3,000 x 8.34 = 300,240 lb/d
- Area = 25,447 ft²
- SLR = 300,240 / 25,447 = 11.8 lb/d/ft²
Tips
- Include RAS in the flow: (Q + RAS) x MLSS.
- Compare with state point limiting flux for the current SVI.
Results are estimates for operator use. Check units and inputs, and confirm decisions with plant data and procedures.