TM 5-814-8
available sites. Other factors which are important
economic and feasible alternative to surface water
in site selection include climate, soil characteris-
disposal is an important factor for considering
tics and depth, topography, and hydrologic and
land applications.
geologic considerations. For land treatment appli-
c. Other. Several other methods of effluent
cations, the equivalent of secondary treatent
discharge are available depending on the circum-
should be provided. Normally, the chlorinated
stances at particular military installations. At
effluent from existing ponds or trickling filters at
facilities needing large quantities of cooling wa-
military installations can be applied to the land
ter, reuse of a well-treated (secondary) wastewater
without further treatment.
for such purposes is often practical. Similarly,
(a) Hydraulic capacity. Whenever possible,
water reuse occurs indirectly when discharge is to
the site should be selected so the pollutant
a stream rather than to the land. Reuse is also
removal capacity of the soils is the limiting factor
practiced quite often when treated effluents are
rather than the hydraulic capability. This will
used to spray golf courses, park facilities, and
minimize the land area needed. The hydraulic
other such areas which may exist at military
installations. In arid areas, effluent discharge
capacity will vary with each site since it is
dependent upon the type of soil, local precipita-
may approach zero with proper use of evaporation
tion and whether or not underdrains are provided.
ponds. Some wastewater treatment facilities now
Where agricultural crops are the means by which
utilize this technique of evaporation for final
the wastewater effluent is reused, an application
effluent disposal. Both water reuse evaporation
rate of about two inches per week seems to be a
methods should be considered in planning pollu-
controlling factor. The local precipitation, winter
tion control programs at military installations.
climate, type of crops and soils all dictate the
8-4. Solids handling systems
proper schedule and the area of land needed for
land application.
a. System alternatives. A line diagram of the
sludge handling and disposal systems which
wastewater irrigation that is not well defined is
should receive consideration at military installa-
the allowable nitrogen loading. Some nitrogen is
tions is presented as figure 8-2. The sludge
evaporated during application, the soil can elimi-
handling steps are arranged in sequential order
nate some, the crops can utilize a portion, but
from left to right with various alternatives under
nitrates can still be transported to the groundwa-
each major step. These systems are discussed in
ter. The acceptable nitrogen loading rate depends
this section and figure 8-1 shows the system
upon the type of soil and crop. It is often
which is applicable to most military installations
necessary to limit the nitrogen loading to the
considering the size and existing facilities. Avail-
amount that crops can assimilate in certain types
able references (55) and (125) can provide a
of soil. This may require a reduction in the liquid
comprehensive summary on detailed design crite-
loading rate in some areas and at certain times of
ria and extensive bibliographies on sludge han-
the year.
dling. Some design criteria are summarized in
(c) Phosphorus capacity. Some limitations
appendix B for sludge handling processes that
on long term use of sites for land treatment may
can be utilized to make preliminary cost-effective
develop from the phosphorus balance. The soil
comparisons with cost curves presented in appen-
can accumulate a certain amount, but after a
dix A.
period of time phosphorus will leach with the
b. Existing systems. Military facilities com-
renovated water. Special soil surveys are needed
monly have existing sludge handling facilities
to assess the life of a site when the phosphorus
consisting of anaerobic digestion plus dewatering
loading is considered.
and landfill or land spreading disposal. These
(d) Organic capacity. The biodegradable
handle settled solids from primary units or the
organics measured by the BOD test can be almost
totally removed by the soil matrix. This overall
combined solids from both primary and secondary
removal generally occurs in the upper 5 to 6
units. Evaluations of facility upgrading must
inches of soil, and the major filtration often
consider the interrelationship of the existing liq-
occurs in the top few centimeters.
uid and solids handling operations. For example,
(e) Beneficial use. In climatic zones where
where sufficient digester capacity exists, it may
irrigation is required, land application of effluents
be cost-effective to utilize a liquid treatment
from military installations handling primarily do-
p r o c e s s which produces more solids than another
mestic wastes is quite feasible. In areas where
alternative. When the sludge system is near
irrigation is of less benefit, the need for an
capacity, the choice of a particular liquid treat-
8-10
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