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.
This calculator also appears on ActivatedSludge.com, our consulting site. Results are for training and operator use; always follow your plant’s procedures.