TM 5-814-9
CHAPTER 6
WASTEWATER TREATMENT
Section I. GENERAL CONCEPTS
liter range in a sewage treatment waste stream
6-1. Overview
compared with 20 to 100 milligrams per liter in
CVWF wastewater.
The wastewater generated at a CVWF is widely variable in
quantity and quality. The frequency and duration on the system
6-2. Treatment system
will be site-specific. In addition, CVWF wastewater properties
differ greatly from those of a typical sewage waste-water. The
The water used to wash vehicles at CVWFs must be reason--
suspended solids concentration in a sewage wastewater usually
ably clean but is not required to be drinking water quality. All
is 200 to 400 milligrams per liter. In contrast, suspended solids
wastewater to be recycled or discharged to an offsite treatment
in CVWF wastewater will range from 100 to more than 20,000
system must first undergo primary treatment in a sediment basin
milligrams per liter.
to remove gross sediment, free oils and grease.
a.
a.
Typical sewage treatment collection systems and
A recycle system is a closed-loop system in which
plants are not equipped to handle the high sus-
wastewater is treated, circulated, and reused. Sec-
pended solids loading generated at a CVWF. A
ondary treatment of this wastewater is considered
typical sewage treatment wastewater will flow
essential to minimize pump O&M, meet all regula-
through the collection system without depositing in
tions, and protect the environment and health of the
the sewers because of the low solids content.
users. The waste water overflows from the sediment
However, the solids in a CVWF wastewater will
basin to a secondary treatment system consisting of
deposit readily in the collection system if proper
either an equalization basin, followed by intermit-
precautions are not taken. This buildup occurs
tent sand filters or a lagoon system, and wash water
primarily because of the large amount of solids and
supply basin.
the fact that they are generally heavy compared with
b.
those in a sewage wastewater. These precautions
In a nonrecycle (or discharge) system, the sediment
include steeper slopes, higher velocities and a
basin is followed only by an equalization basin, if
flusher system in the collection system. The wash
required, to bring the discharge to a quality and
facility will discharge a large volume of silt, clay,
quantity that complies with requirements of the off-
sand, and gravel, and an array of solid debris, such
site treatment plant.
as ordnance, rags, rocks, and ration cans. This type
c.
of material does not normally occur in such large
A water supply basin may also be required in a
volumes in a sewage treatment wastewater.
discharge system if the water source cannot meet
the immediate demands of the wash facility. If water
b.
The wastewater from a CVWF also will contain
is not recycled, a good quality, reliable watersource
higher levels of grease and oils than a typical
must be used. If a discharge system Is being
sewage treatment wastewater. Therefore, oil re-
considered, the designer should consider the flow
moval equipment must be installed at a CVWF
and quality requirements of the installation's
waste treatment facility. The biological oxygen
sewage treatment plant authority and design the
demand (BOD) and chemical oxygen demand
onsite treatment system and conveyance accord-
(COD) are usually in the 200 to 400-milligram per
ingly.
Section II. DESIGN PARAMETERS
6-3. Criteria
6-4. Wash period (Tw)
In designing the wastewater treatment system for the CVWF,
The wash period is the continuous time, in hours, that the
the hydraulic floor will dictate the size of the collection and
CVWF is expected to operate each time the facility is used. This
treatment system needed. Local water supply and weather
time is not the minimum or maximum time that individual
conditions also affect the choice of treatment systems. In regions
vehicles spend at the facility; it is the time during which the
with a limited water supply, strict water conservation and reuse
facility is expected to be operated (see chap. 3). The wash
techniques need to be reviewed before deciding to recycle the
period does not include the time required to fill and drain the
water. Factors to consider in designing the treatment system are
prewash bath (when included) or to clean the facility. The
the wash period, cleanup time, water usage factor, wash,
installation must establish an operating schedule of the CVWF
stormwater, water flow demand, and wastewater volume.
based on projected facility demand.
6-1
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