Environmental Engineering Reference
In-Depth Information
8.10.4 seasonal variations
Seasonal variations in temperature, oxygen solubility, organism
activity, and waste characteristics may require several normal control
levels for the activated sludge process. During cold months of the year, for
example, aeration tank solids levels may have to be maintained at signif-
icantly higher levels than are required during warm weather. Likewise,
the aeration rate may be controlled by the mixing requirements of the
system during the colder months and by the oxygen demand of the sys-
tem during the warm months.
8.10.5 Control levels at startup
Control levels for an activated sludge system during startup are
usually based on design engineer recommendations or information
available from recognized reference sources. Although these levels pro-
vide a starting point, both the process control parameter sensitivity and
control levels should be established on a plant-by-plant basis. During
the first 12 months of operation, it is important to evaluate all potential
process control options to determine the following:
•
Sensitivity to effluent quality changes
•
Seasonal variability
•
Potential problems
8.11 visual indiCaTors for
influenT or aeraTion TanK
Wastewater operators are required to monitor or to make certain
observations of treatment unit processes to ensure optimum perfor-
mance and to make adjustments when required. When monitoring the
operation of an aeration tank, the operator should look for three physi-
cal parameters—turbulence, surface foam and scum, and sludge color
and odor—that aid in determining how the process is operating and indi-
cate if any operational adjustments should be made. This information
should be recorded each time operational tests are performed. Aeration
tank and secondary settling tank observations are summarized in the
following sections. Remember that many of these observations are very
subjective and must be based on experience. Plant personnel must be
properly trained on the importance of ensuring that recorded informa-
tion is consistent throughout the operating period.
8.11.1 Turbulence
Normal operation of an aeration basin includes a certain amount
of turbulence. This turbulent action is, of course, required to ensure
a consistent mixing pattern; however, whenever excessive, deficient, or
nonuniform mixing occurs, adjustments to air flow may be necessary, or
the diffusers may require cleaning or replacement.
