Wastewater math
SVI in mL/g from the 30 minute settled sludge volume in mL/L and the MLSS in mg/L.
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The formula
SVI, mL/g = (SSV₃₀, mL/L)(1,000 mg/g) ÷ MLSS, mg/LWPI Formula/Conversion Table (2023), Printed page 5 of 10, Sludge Volume Index
Worked example
A 1 L settleometer reads 300 mL after 30 min. The MLSS is 2,500 mg/L. What is the SVI?
A 1 L cylinder reading of 300 mL is 300 mL/L.
Multiply by 1,000 mg/g: 300 mL/L × 1,000 mg/g = 300,000.
Divide by the MLSS: 300,000 ÷ 2,500 mg/L = 120 mL/g.
Answer: 120 mL/g
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