TM 5-814-8
process may be necessary. The need for a single-
yses of the impact of an effluent on the stream
stage or two-stage process along with required
may be necessary.
lime dosages can only be determined from bench
b. Land application. Land treatment can be an
or pilot studies. Filtration of a lime clarified
effective means of providing advanced treatment
secondary effluent will generally result in effluent
for secondary effluents and shall be considered
phosphorus concentrations less than 1 mg/L be-
for military installations requiring a high degree
cause of the removal of phosphorus tied up with
of treatment. Approaches for spreading treated
the suspended solids in the effluent from lime
effluent on the land can be classified as either
clarification (142).
rapid infiltration-percolation, overland flow, or
(d) Additional suspended solids and organic
spray irrigation. Evaluation, design and costing
removal. Various combinations of lime clarifica-
m e t h o d s for land application are available
tion and/or filtration can reduce wastewater BOD
(53)(71)(72)(126). Regulatory agencies should be
to the 5 to 10 mg/L range, and suspended solids
consulted for specific project applications.
to 1 mg/L or less. In order to get the BOD below
( 1 ) Rapid infiltration-percolation. This
method consists of dosing spreading basins on an
5 mg/L, it is almost always necessary to use a
granular carbon adsorption step. Carbon will
intermittent basis to maintain high infiltration
adsorb most of the soluble organic compounds
rates. The main portion of the wastewater enters
that cause the remaining BOD. A properly de-
the groundwater after filtering and treatment by
signed and operated carbon adsorption step can
the soil, although there is some loss to evapora-
reduce the final wastewater BOD to as low as 1
tion. Soils are usually deep, permeable types such
to 2 mg/L.
as coarse textured sands, silty sands or sandy
(e) Land treatment. An alternative to the
silts.
several mechanical treatment processes following
(2) Overland flow. This technique is the con-
secondary treatment in table 8-2 is land applica-
trolled discharge, by spraying or other means, of
tion. Many military installations which have con-
effluent onto the land with a large portion of the
siderable land of the proper soil characteristics
wastewater appearing as run-off. Soils suited to
may find that land treatment is a cost-effective
overland flow are clays and clay silts with limited
alternative. With proper site location and opera-
drainability. The land for an overland flow treat-
tion, disposal of a secondary-treated effluent to
ment site should have a moderate slope. In the
the land will provide treatment equivalent to or
U. S., overland flow has been developed mainly for
better than that from a carbon adsorption system
treatment for high-strength wastewater, such as
or other mechanical facilities.
that from canneries. This process has not been
extensively used for the treatment of domestic
8-3. Effluent discharge alternatives
wastewater in the U. S., although Australia has
used it for this purpose for a number of years,
a. Surface water. Analysis of the impact of
with BOD and suspended solids removals of
wastewater discharge on the receiving surface
about 95 percent.
water (stream, lake, ocean, estuary) requires infor-
(3) Spray irrigation. This process is the con-
mation on a number of parameters for proper
trolled discharge of secondary treated effluent, by
formulation. For example, the impact of a dis-
spraying on land to support plant growth. Maxi-
charge on the oxygen resources requires knowl-
mum amounts of wastewater consistent with crop
edge of the deoxygenation rate of the wastewater;
yields may be applied. Although overland flow
reaeration rate of the stream; physical character-
and infiltration-percolation may have merit under
istics of the stream including flows, geometry and
special circumstances, irrigation is probably the
velocities; stream and waste temperatures; quality
best method for application to different soil types
of the stream prior to discharge; and characteris-
and cultural practices. In addition, irrigation
tics of other waste discharges along the stream.
maximizes nutrient benefits of the wastes. How-
Methods for analyzing the impact of effluents
ever, precautions and safeguards against contami-
discharged to surface waters are well documented
nation by aerosol dispersion of pathogenic organ-
(43)(147)(149). The impact of constituents other
isms or viruses by spray application is necessary
than those which affect oxygen can be evaluated
(7).
using some of the same analytical techniques as
indicated for oxygen. Normally in the U. S., State
(4) Design considerations. Some factors to be
and Federal pollution control regulatory agencies
considered when evaluating the applicability of an
will provide performance criteria for treatment
irrigation system are the amount of available
which negates the need for extensive stream
land, the need for reclaimed water, wastewater
surveys. In foreign locations, however, more anal-
characteristics and flow rates, and type of soil at
8-9
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