Environmental Engineering Reference
In-Depth Information
MillilitersofSettled Sludge
×
llilitersofSample
1000 mL
SSV
=
(8.3)
Mi
MillilitersofSettled Sludge
×
100
%SSV
=
(8.4)
Milli
ters of Sample
Note:
Running the settleability test with a diluted sample can assist
in determining if the activated sludge is old (too many solids) or bulk-
ing (not settling). Old sludge will settle to a more compact level when
diluted.
8.13.3.6 Flow
Monitoring flow in settling tank influent is important for determi-
nation of the mass balance.
8.13.3.7 Jar Tests
Jar tests are performed as required on settling tank influent and
are beneficial in determining the best flocculant aid and appropriate
doses to improve solids capture during periods of poor settling.
8.13.4 settling Tank
8.13.4.1 Sludge Blanket Depth
Sludge blanket depth refers to the distance from the surface of
the liquid to the solids-liquid interface or the thickness of the sludge
blanket as measured from the bottom of the tank to the solids-liquid
interface. Part of the operator's sampling routine, this measurement is
taken directly in the final clarifier. Sludge blanket depth is dependent
on hydraulic load, return rate, clarifier design, waste rate, sludge char-
acteristics, and temperature. If all of the other factors remain constant,
the blanket depth will vary with amount of solids in the system and the
return rate; thus, it will vary throughout the day.
Note:
The depth of the sludge blanket provides an indication of sludge
quality; it is used as a trend indicator. Many factors can affect the test
result.
8.13.4.2 Suspended Solids and Volatile Suspended Solids
Suspended solids and volatile suspended solids concentrations of
the mixed liquor suspended solids (MLSS), the return activated sludge
(RAS), and waste activated sludge (WAS) are routinely sampled and tested
because they are critical to process control.
