A 1,000 mL settleometer test of mixed liquor yields a 30-minute settled sludge volume of 270 mL/L. If the aeration basin MLSS is 2,500 mg/L, what is the Sludge Volume Index (SVI)?

Formula Used: SVI (mL/g) = [30-Minute Settled Volume (mL/L) × 1,000] ÷ MLSS (mg/L)

Step-by-Step Mathematical Derivation:

1. Substitute test parameters: (270 mL/L × 1,000) ÷ 2,500 mg/L = 270,000 ÷ 2,500 = 108 mL/g.

⚠️ Common Exam Trap: Ideal SVI is between 80 and 150 mL/g. SVI over 150 indicates filamentous sludge bulking and poor clarifier settling.