Work out sludge volume index instantly with clear inputs, formula shown and shareable results.
Sludge volume index is the volume in millilitres occupied by one gram of settled sludge after 30 minutes. Below 100 indicates good settling, 100-150 is acceptable, and above 150 signals filamentous bulking. SVI also caps the MLSS a clarifier can handle, since settled volume cannot exceed the available depth.
Sludge volume index
SVI (mL/g) = settled volume (mL/L) x 1000 x dilution / MLSS (mg/L)
Filamentous organisms favoured by low dissolved oxygen, low F/M, nutrient deficiency, septic influent or high readily biodegradable substrate. Identification by microscopy points to the specific cause and remedy.
At high MLSS the sludge cannot settle freely and the result is meaningless. Diluted SVI or stirred specific volume index gives a comparable figure across concentrations.