SVI is the volume in mL occupied by 1 gram of mixed liquor after 30 minutes of settling. 80 to 150 mL/g is typical; above 150 means slow settling.
SVI
Formula
SVI, mL/g = (SSV30, mL/L x 1,000) / MLSS, mg/L SDI, g/mL = 100 / SVI
Inputs used
- 30 minute settled volume (SSV30) (mL/L)
- MLSS (mg/L)
- Dilution factor (1 if undiluted)
Worked example (White River WRRF, fictional)
- SVI = 310 x 1,000 / 2,620 = 118 mL/g
Tips
- Use MLSS from the same sample as the settleometer.
- If SSV30 is above about 800 mL/L, dilute 1:1 and enter a dilution factor of 2.
Results are estimates for operator use. Check units and inputs, and confirm decisions with plant data and procedures.