0

50

100

150

200

250

0 0.5 1 1.5 2

Retention time, tR (days)

Su

bstr

ate

, S

; B

iom

ass, X

(m

g/L

)

0

25

50

75

100

125

Tre

atm

en

t eff

icie

ncy (

perc

en

t)

S (mg COD/L)

X (mg VSS/L)

Efficiency (percent)

Lecture 17.xls 2/20/2006

StirredUnstirred

00 2

Solids Retention Time (days)

EFFECT OF SOLIDS RETENTION TIME, c, ON THE SETTLING PROPERTIES OF ACTIVATED SLUDGE

4 6 8 10

2000 mg/L-MLSS

12 14

Zone

Set

tling

Vel

ocity

, ft/h

r

4

8

12

16

20

Figure by MIT OCW.

Adapted from: WEF. Wastewater Treatment Plant Design. Alexandria, Virginia: Water Environment Federation, 2003.

0

1000

Aer

atio

n Ta

nkM

LSS

Con

cent

ratio

n, m

g/L

2000

3000

4000

5000

6000

1Return Sludge Ratio, R:Q

TYPICAL OPERATING RANGE FOR ACTIVATED-SLUDGE SYSTEMS

Common operating range

Suggested maximum

2 3

SVI = 50 SVI = 100SVI = 150SVI = 200SVI = 400

Figure by MIT OCW.

Adapted from: WEF. Wastewater Treatment Plant Design. Alexandria, Virginia: Water Environment Federation, 2003.

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