TM 5-814-8
time in the stabilization tank must be sufficient
--Low speed surface aerator as used in
to stabilize these organics. If it is insufficient,
the Carrousel system.
--Jet aeration.
unoxidized organics are carried back to the con-
--Diffused aeration with slow speed mix-
tact tank and the removal efficiency is decreased.
ers.
If the stabilization period is too long, the sludge
undergoes excessive auto-oxidation and loses
Clarification can be accomplished using a conven-
tional clarifier or by using an integral clarifier as
some of its initial high removal capacity. Increas-
ing retention period in the contact tanks increases
with the Burns and McDonnell system (159).
the amount of soluble organics removed and
Advantages of the CLR process include:
decreases required stabilization time.
The ability for the system to handle
(e) Extended aeration. The extended aera-
upset loading conditions.
tion process operates in the endogenous respira-
Produces low sludge quantities.
tion phase of the growth curve, which necessi-
C a n provide for vitrification and
tates a relatively low organic loading and long
denitrification.
Typically produces very good and sta-
aeration time. Thus it is generally applicable only
to small treatment plants of less than 1 mgd
ble effluent characteristics.
capacity (125). This process is used extensively
Simplicity of operation.
for prefabricated package plants. Although sepa-
The major disadvantages include the potential
rate sludge wasting generally is not provided, it
washout of the system by excessive hydraulic
may be added where the discharge of the excess
flows and the large land area and basin sizes that
solids is objectionable.
are required due to the typically high detention
times.
(f) Pure oxygen system. The variations set
forth in table 6-2, with the exception of the pure
(h) Nitrification. The kinetics and design
criteria for this system are already well defined.
oxygen system, represent flow models which are
Two important considerations are maintenance of
based on plug flow or completely mixed systems.
a proper pH and temperature. Nitrification is a
Some systems use a diffused air system, others
are more applicable to mechanical aeration, and
very temperature-sensitive system and the effi-
some variations are adaptable to either aeration
ciency is significantly suppressed as the tempera-
system. All of the systems, with the exception of
ture decreases. For example, the rate of vitrifica-
tion at pH of 8.5 and 50 degrees F is only about
the pure oxygen system, use air as the source of
25 percent of the rate at 86 degrees F. Treatment
oxygen. The principal distinguishing features of
facilities located in northern climates must be
the pure oxygen system are that it utilizes
high-purity oxygen as a source of oxygen and
sized at the appropriate loading rate to accom-
plish the desired effluent level if required to
employs a covered, staged aeration basin for the
provide year-round vitrification. The loading rate
contact of the gas and mixed liquor (49). To date,
the system has demonstrated its greatest applica-
significantly affects the capital costs for construc-
tion of the nitrification tanks. The optimum pH
bility and cost-effectiveness for treatment of high
has been determined to range between 8.4 and
strength industrial wastes and for large plants
treating domestic wastes. Thus, pure oxygen
8.6. However, for those wastewaters where it
would be necessary to provide chemical-feeding
systems for military wastewaters have limited
application.
facilities for pH adjustment, the cost-effective
alternative may be to provide additional tankage
(g) Continuous loop reactors. The continu-
ous loop reactor (CLR) is best described as an
to allow for the reduced biological activity when
extended aeration activated sludge process. The
the pH is not optimum.
process uses a continuously recirculating closed
loop channel(s) as an aeration basin. The reactor
cation, denitrification is a process which involves
is sized based upon the wastewater influent and
further removal of the nitrogen by conversion of
effluent characteristics with emphasis given to
the nitrate to nitrogen gas. This represents a
process for the ultimate removal of nitrogen from
the hydraulic considerations imposed by the basin
wastewater. As with vitrification, there are a
geometry. hydraulic detention times range from
10 to 30 hours and the mixed liquor concentration
number of system configurations that have been
in the basin is typically 4,000 to 5,000 mg/L. To
developed for denitrification. The most promising
provide the necessary oxygen to the system and
system alternatives include suspended growth
impart a horizontal velocity, several pieces of
and columnar systems (46). While there are ad-
vantages and disadvantages to either alternative,
equipment are available. These include:
--Brush aerators.
the more feasible system for military installations
6-10
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