SVI (Sludge Volume Index) Calculator
Calculate the sludge volume index from a 30-minute settleability test and MLSS — the classic indicator of sludge settleability.
Sludge volume index
Formula
SVI (mL/g) = settled volume (mL/L) × 1000 ÷ MLSS (mg/L)
Use a 1 L graduated cylinder, unstirred, after exactly 30 minutes of settling.
SVI (mL/g) = settled volume (mL/L) × 1000 ÷ MLSS (mg/L)
Use a 1 L graduated cylinder, unstirred, after exactly 30 minutes of settling.
Interpreting SVI
| SVI (mL/g) | Settleability |
|---|---|
| < 100 | Good settling |
| 100 – 150 | Moderate; watch for trends |
| 150 – 200 | Poor; possible bulking |
| > 200 | Bulking sludge — investigate filamentous growth |