\[ \text{MLSS (kg)} = \text{MLSS conc. (g/L)} \times (\text{Aeration tank volume (m}^3\text{)} + \text{Secondary clarifiers volume (m}^3\text{)}) \]
\[ \text{MLSS (lb)} = \text{MLSS conc. (mg/L)} \times (\text{Aeration tank volume (MG)} + \text{Secondary clarifiers volume (MG)}) \times 8.34 \text{ (lbs/gallon)} \]
\[ \text{SS (kg/day)} = (\text{Flow of secondary effluence (m}^3\text{/day)} \times \text{Solids in secondary effluence (g/L)}) + (\text{Flow of waste sludge (m}^3\text{/day)} \times \text{Solids in waste sludge (g/L)}) \]
\[ \text{SS (lb/day)} = ((\text{Flow of secondary effluence (MGD)} \times \text{Solids in secondary effluence (mg/L)}) + (\text{Flow of waste sludge (MGD)} \times \text{Solids in waste sludge (mg/L)})) \times 8.34 \text{ (lbs/gallon)} \]
\[ \text{MCRT (days)} = \frac{\text{MLSS weight (mass)}}{\text{SS leaving activated sludge process (mass/day)}} \]