What is the Sludge Volume Index?

Two 1 L samples of mixed liquor are taken from a lagoon. After settling for 30 min in a graduated cylinder, 250 mL of solids have settled out in the first sample. The total suspended solids concentration (MLSS) in the second sample is found to be 2300 mg/L.

(a) What is the sludge volume index?

(b) What is the theoretical required sludge recycle rate?  

Ans:

(a) From eq for SVI, SVI = 1000V_{settled, mL/L}/ X_mg/L

= (1000mg/g)(250ml/L)/2300mg/L = 109mL/g

(b) From Eq for, R = V_{settled, mL/L}/ 1000-V_{settled, mL/L}

250mL / 1000mL - 250mL = 0.33