The solids inventory is the starting point for SRT, F/M and wasting calculations.
MLSS Inventory
Formula
Inventory, lb = Volume, MG x Concentration, mg/L x 8.34
Inputs used
- Aeration volume in service (MG)
- MLSS (mg/L)
- Volatile fraction (optional) (%)
- Clarifier volume (optional) (MG)
- Average clarifier solids (optional) (mg/L)
Worked example (White River WRRF, fictional)
- MLSS inventory = 3.6 x 3,000 x 8.34 = 90,072 lb
- MLVSS = 90,072 x 0.78 = 70,256 lb
Tips
- Use the volume of basins in service.
- MLVSS fraction is typically 70 to 85%.
Results are estimates for operator use. Check units and inputs, and confirm decisions with plant data and procedures.