Sludge Volume Index (SVI)
How well activated sludge settles, as an index in mL/g, and what that index means.
Example
You enter
- SV30 (mL/L; volume after 30-min settling) 300
- MLSS (mg/L) 2500
You get
- SVI (mL/g) 120
- 30-min settled fraction 30 %
Checked against published worked examples from: USEPA / WEF.
Details, formula, and sources
ScopeSVI = SV30 * 1000 / MLSS in mL/g, with operator-typical operational bands (typical / pin floc / filamentous / bulking). Companion to the SRT and F:M ratio checks.
Formula or tableSVI (mL/g) = (SV30 mL/L * 1000) / MLSS mg/L. Bands: < 80 pin-floc / under-aerated; 80-150 typical CAS; 150-200 filamentous developing; > 200 bulking.
Source and editionUSEPA Wastewater Operator Training (public domain); WEF Manual of Practice No. 11 by name.
Free accessepa.gov for operator-training materials.
What governsEstimate. Operator of record and primacy agency govern.
API field namessv30_ml_per_l, mlss_mg_per_l, svi_ml_per_g, sv30_settled_fraction
- Settled-volume procedure 30-min Imhoff cone or 1 L cylinderUSEPA / WEF method
- Companion F:M srt-fm-ratio tile provides the F:M / SRT pairv4 srt-fm-ratio (already shipped)
- Bulking threshold SVI > 200 mL/g indicates the sludge will not settle in conventional secondary clarifier residence timesWEF MOP 11 operator guidance