Activated Sludge SVI Calculator

The Activated Sludge SVI (Sludge Volume Index) Calculator helps wastewater treatment plant operators and environmental engineers determine the settling characteristics of activated sludge. SVI is a critical parameter for monitoring and controlling the activated sludge process in wastewater treatment plants.

The Sludge Volume Index (SVI) is calculated as:

$$SVI = \frac{SV_{30} \times 1000}{MLSS}$$

where SV30 is the volume of settled sludge after 30 minutes (in mL/L) and MLSS is the mixed liquor suspended solids concentration (in mg/L). An SVI between 80 and 120 mL/g generally indicates good settling sludge.

For related calculations, explore our MLVSS Calculator for volatile suspended solids analysis and the Wastewater Calculator for comprehensive treatment plant calculations.

Frequently Asked Questions

What is a good SVI value for activated sludge?

A Sludge Volume Index (SVI) between 80 and 120 mL/g is generally considered good for conventional activated sludge systems. Values below 80 may indicate dense, possibly over-oxidized sludge, while values above 150 suggest poor settling characteristics often caused by filamentous bulking.

How do you calculate SVI?

SVI is calculated by taking a 1-liter sample of mixed liquor from the aeration tank, allowing it to settle for 30 minutes in a graduated cylinder, recording the volume of settled solids (SV30 in mL/L), and dividing by the MLSS concentration (in g/L or mg/L with appropriate conversion).

What causes high SVI in activated sludge?

High SVI (poor settling) is most commonly caused by filamentous organism growth, which can result from low dissolved oxygen, low F/M ratio, nutrient deficiencies, or septic wastewater. Other causes include viscous bulking from extracellular polymers and pin floc from over-aeration.

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Activated Sludge SVI Calculator

Activated Sludge SVI Calculator

Frequently Asked Questions

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