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SVI calculator

SVI tells you how well your activated sludge settles. You need the 30-minute settled sludge volume from the settleometer and the MLSS of the same sample.

SVI (mL/g) = 30-min settled volume (mL/L) × 1,000 ÷ MLSS (mg/L)

    Worked example

    A 1-liter settleometer shows 250 mL of settled sludge after 30 minutes. MLSS is 2,500 mg/L. What is the SVI?

    1. SVI = 250 × 1,000 ÷ 2,500 = 100 mL/g

    Answer: 100 mL/g

    Common mistakes

    • Forgetting the × 1,000, which converts mg to g.
    • Using MLVSS instead of MLSS.

    Check your exam's reference sheet for its exact constants. Some use 3.14 instead of 3.1416, which changes answers in the last digit.