Sludge Volume Index (SVI)
Calculate the sludge volume index (SVI), SVI = (V₃₀ × 1000) ÷ MLSS, from the 30-minute settled sludge volume (mL/L) and the mixed-liquor suspended solids concentration (mg/L). The result, in mL/g, measures activated-sludge settleability: values of 50–150 mL/g indicate well-settling sludge, while values above 150 signal filamentous bulking that impairs clarification. Enter the settled volume and the MLSS concentration.
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Sludge volume index (SVI)
The sludge volume index (SVI, IVL in Portuguese) is the most practical test for telling whether activated sludge settles well. The procedure is simple: take one litre of mixed liquor, let it settle for 30 minutes in a graduated cylinder and read the volume occupied by the sludge (V₃₀, in mL/L). SVI = (V₃₀ × 1000) ÷ MLSS relates that volume to the solids concentration (MLSS) and gives the volume that 1 gram of sludge takes up after 30 min, in mL/g. The reading is straightforward: an SVI between 50 and 150 mL/g indicates dense, well-settling sludge; above 150 the sludge is light and bulky — the classic sign of filamentous bulking, in which filamentous bacteria overgrow and keep the floc from thickening, letting sludge wash over the clarifier weirs and degrade the effluent. A very low SVI, on the other hand, may point to old sludge and pin floc. Tracking the SVI over time is routine practice in running an activated-sludge treatment plant. Enter the settled volume and the MLSS concentration.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.