238/33310–15FE Reference Handbook 10.4 · Environmental · Activated Sludge

Handbook formula

Sludge Volume Index (SVI)

SVI ~ 50–150 mL/g is healthy; >>150 suggests bulking (filaments). MLSS is mixed-liquor suspended solids. Used with recycle and clarifier design.

(mL/g)
Sludge volume index
(mg/L)
Mixed liquor SS

Step-by-step solved example

30-min settled volume 250 mL in a 1 L cylinder, MLSS=2500 mg/L. SVI?

QAOR = Q/A
Settleometer: settled sludge volume vs MLSS → SVI.
  1. 1. mL/L

    250 mL/L.

  2. 2. SVI

    250×1000/2500=100 mL/g (good).

Answer: SVI = 100 mL/g

10 practice questions

0/10 correct

1.SVI=200 mL/g indicates

2.If MLSS doubles at the same settled volume, SVI

3.F/M uses

4.A 1 L settleometer is the

5.MLVSS is typically about

6.Return sludge concentration is higher so that

7.Settled 180 mL/L, MLSS=1800: SVI=

8.Secondary clarifier overflow rate is

9.Chlorination of RAS is sometimes used to

10.Units mL/g because