TM 5-814-8
Packed bed, liquid void, low porosity
ties. It also demonstrated that the activated
media.
sludge process was better able to handle shock
Fluidized bed, liquid void, high porosity
loads. Although the system may not be applicable
fine media (sand, activated carbon).
for certain industrial waste applications unless
Most denitrification work has been conducted on
pretreatment is provided, it should be considered
for upgrading existing military treatment plants
submerged columns wherein the voids are filled
with the fluid being denitrified. The submerged
treating primarily domestic wastewater. The pro-
columns can be further subdivided into packed
cess has potential as a second stage unit with
bed and fluidized bed operations. Recently, a new
existing trickling filters to improve performance
type of column has been developed in which the
and also as a vitrification unit. The rotating
voids are filled with nitrogen gas, a product of
biological contractor can be considered as an
denitrification.
option, however, the use may be limited to add-on
d. Miscellaneous Biological Systems.
or advanced wastewater treatment capacity for
(1) Package plants. A number of so called
nitrogen removal until the RBC equipment reli-
"package plants" have been developed to serve
ability and economics have been improved.
the wastewater treatment needs of small installa-
(3) Activated biological filter. An activated
tions. Many of these units are available from a
biofilter (ABF) is a tower of packed redwood or
number of manufacturers. The small ones are all
other media which supports the growth of at-
factory fabricated and shipped as nearly complete
tached microorganisms. Influent wastewater is
units except for electrical connections and other
mixed with recycled solids from the clarifier and
minor installation requirements. These will serve
returned mixed liquor. The mixture is sprayed
a maximum population of 300 to 400. Larger
over the media and flows through the tower.
sized package plants are partially constructed in
Oxidation occurs in both the falling liquid film
the factory and then field erected. These types of
and in the attached growth. Less sludge is
facilities generally will serve larger installations,
produced from ABF treatment, diminishing the
up to about 1 mgd. Package plants are available
size of the final clarifier. Reduced life-cycle and
as biological treatment facilities and some new
land costs, compensate for high capital cost. ABF
units have been developed for physical-chemical
treatment achieves the same degree of effluent
treatment applications. Nearly all of the biological
quality as activated sludge process (39). Biologi-
units use the activated sludge process, principally
cal towers can be designed and operated with the
extended aeration and contact stabilization modi-
same parameters as activated sludge systems.
fications. The small physical-chemical package
ABF's are used for both domestic and industrial
plants have been developed mainly as "add on"
applications.
(4) Anaerobic denitrification filter. Denitrif-
units to existing biological facilities to provide
ication in attached growth anaerobic reactors has
additional removal of organic and inorganic con-
stituents. Physical-chemical package units are
been accomplished in a variety of column configu-
available for multi-media filtration, phosphorus
rations using various media to support the
removal, nutrient removal and activated carbon
growth of denitrifying bacteria. In the deni-
operations. For widely varying flows at small
trification column, the influent wastewater is
installations, a battery of physical-chemical units
evenly distributed over the top of the medium
might be employed. The on-off operation of these
and flows in a thin film through the medium on
installations would not be satisfactory for biologi-
which the organisms grow. These organisms
maintain a balance so that an active biological
cal units.
(2) Batch activated sludge. A batch activated
film develops. The balance is maintained by
sludge system utilizes a single tank reactor. The
sloughing of the biomass from the medium, either
typical treatment cycle consists of:
by death, hydraulic erosions or both. Sufficient
--fill, in which the wastewater is received.
voids are present in the medium to prevent
--react, which allows treatment reactions to
clogging or pending. The denitrification column
be completed.
must be followed by a clarification step to remove
-- settle, which separates the sludge from
sloughed solids. The various types of denitrifica-
the effluent.
tion columns currently available are summarized
draw, in which the effluent is discharged.
below:
--idle, the time period between discharge
Packed bed, nitrogen gas void space, high
and refill.
porosity media.
A batch activated sludge system combines the
Packed bed, liquid voids, high porosity
reactor and clarifier into a single unit. Sludge
media.
6-13
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