Activated Sludge Process - Wastewater Operators - page 323

8.14.1 settled sludge volume

Settled sludge volume (SSV) is the volume that a settled activated
sludge occupies after a specified time. The settling time may be shown
as a subscript; for example, SSV 60 indicates that the reported value was
determined at 60 minutes. The settled sludge volume can be determined
for any time interval; however, the most common values are the 30-min-
ute reading (SSV 30 ) and 60-minute reading (SSV 60 ). The settled sludge
volume can be reported as milliliters of sludge per liter of sample (mL/L)
or as percent settled sludge volume:

Settled Sludge Volume (mL)

Sample Volume (L)

Settled Sludge Volume (mL/L) = (8.5)

Note: 1000 milliliters = 1 liter.

Sample Volume (mL)
1000 mL

(8.6)

Sample Volume (L) =

/L

Settled Sludge Volu me (mL) × 100

%Settled Sludge Volume = (8.7)

Sample Volume (mL)

 Example 8.1

Problem: Using the information provided below, calculate the SSV 30 and
%SSV 60 :

Time Milliliters

Start 2500

15 minutes 2250

30 minutes 1800

45 minutes 1700

60 minutes 1600

Solution:

1800mL
2.5L

SSV = = 720mL/L

30

1600mL1 × 00

2500 mL

%SSV = = 64%

60

8.14.2 estimated return rate

Many different methods are available for estimating the proper
return sludge rate. A simple method described in the operation of
Wastewater Treatment Plants: a field Study Training Program (Kerri
et al., 2007) uses the 60-minute percent settled sludge volume (%SSV 60 ),
which can provide an approximation of the appropriate return activated