Sludge Volume Index

\[SVI=\frac{SV_{30}}{MLSS}\]

Variables

SVIsludge volume index (mL/g)

SV30settled sludge volume after 30 minutes (mL/L)

MLSSmixed liquor suspended solids concentration (g/L)

Description

What is this formula?

The Sludge Volume Index (SVI) evaluates the settling characteristics of activated sludge by relating settled sludge volume to biomass concentration.

When to use it

Use it when monitoring activated sludge systems, clarifier performance, sludge bulking, and biological treatment process stability.

Example

Data:

SV30 = 240 mL/L

MLSS = 3.2 g/L

Formula:

SVI = SV30 / MLSS

Substitution:

SVI = 240 / 3.2

Result:

SVI = 75 mL/g

Applications

Activated sludge operation, secondary clarifier evaluation, sludge settling analysis, wastewater treatment optimization, and process troubleshooting.

Note

SVI is an operational indicator. Low values generally indicate dense, well-settling sludge, while high values may indicate bulking sludge, filamentous growth, or poor settling performance. Interpretation depends on process type and operating conditions.