Environmental Engineering Reference
In-Depth Information
8.13.5 settling Tank effluent
8.13.5.1 BOD
5
and Total Suspended Solids
Testing for BOD
5
and total suspended solids is conducted variably
(daily, weekly, or monthly). Increases indicate that treatment perfor-
mance is decreasing; decreases indicate that treatment performance is
increasing.
8.13.5.2 Total Kjeldahl Nitrogen
Total Kjeldahl nitrogen (TKN) sampling and testing are variable. An
increase in TKN indicates that nitrification is decreasing; a decrease in
TKN indicates that nitrification is increasing.
8.13.5.3 Nitrate Nitrogen
Nitrate nitrogen sampling and testing are variable. Increases in
nitrate nitrogen indicate increasing nitrification or an industrial contri-
bution of nitrates. A decrease indicates reduced nitrification.
8.13.5.4 Flow
Settling tank effluent flow is sampled and tested daily. Results are
required for several process control calculations.
8.13.6 return activated sludge and Waste activated sludge
8.13.6.1 Total Suspended Solids and Volatile Suspended Solids
Total suspended solids and total volatile suspended solids concen-
trations of the mixed liquor suspended solids, return activated sludge,
and waste activated sludge are routinely sampled (using either grab or
composite samples) and tested, because
they are critical to process control. The
results of the suspended and volatile sus-
pended tests can be used directly or to
calculate such process control figures as mean cell residence time (MCRT)
or food-to-microorganisms (F/M) ratio. In most situations, increasing the
MLSS produces an older, denser sludge, and decreasing MLSS produces
a younger, less dense sludge.
Key Point:
The activated sludge aeration tank
should be observed daily to evaluate the type and
amount of foam, mixing uniformity, and color.
Note:
Control of the sludge wasting rate by maintaining a constant
MLVSS concentration requires maintaining a certain concentration of
volatile suspended solids in the aeration tank.
