Environmental Engineering Reference
In-Depth Information
8.13.1.2 Temperature
Temperature is important because it indicates the following:
When the temperature increases …
•
Organism activity increases.
•
Aeration efficiency decreases.
•
Oxygen solubility decreases.
When the temperature decreases …
•
Organism activity decreases.
•
Aeration efficiency increases.
•
Oxygen solubility increases.
8.13.1.3 Dissolved Oxygen
The content of dissolved oxygen (DO) in the aeration process is crit-
ical to performance. DO should be tested at least daily (peak demand).
Optimum is determined for individual plants, but normal is from 1 to 3
mg/L. If the system contains too little DO, the process will become sep-
tic. If it contains too much DO, energy and money are wasted.
8.13.1.4 Settled Sludge Volume (Settleability)
Settled sludge volume (SSV) is determined at specified times during
sample testing. Both the 30- and 60-minute observations are used for
control. Subscripts (e.g., SSV
30
and SSV
60
) indicate the settling time. The
test is performed on aeration tank effluent samples.
MillilitersofSettled Sludge
×
Milliliters of Sample
1000 mL/L
SSV
=
(8.1)
MillilitersofSettled Sludge
×
100
%SSV
=
(8.2)
Milli
liters of Sample
Under normal conditions, sludge settles as
a mass, producing clear supernatant with
SSV
60
values in the range of 400 to 700 ml/L.
Higher values may indicate excessive solids
(old sludge) or bulking conditions. Solids in
well-oxidized sludge may rise after 2 or more hours; however, solids ris-
ing in less than 1 hour indicates a problem.
Key Point:
Running the settleability test with
a diluted sample can assist in determining if
the activated sludge is old (too many solids)
or bulking (not settling). Old sludge will set-
tle to a more compact level when diluted.
8.13.1.5 Centrifuge Testing
The centrifuge test provides a quick, relatively easy control test for
the solids level in the aerator but does not usually correlate with MLSS
results. Results are directly affected by variations in sludge quality.
