present as soluble, colloidal, and suspended solids.
plished by pressure spraying with water or clean-
ing compounds to remove surface films, followed
The pollutant contribution in sewage is usually
expressed as a per capita contribution. A study of
by scrubbing with brushes and cleaners to loosen
foreign matter, and finally rinsing thoroughly
data reported by 73 cities in 27 states in the
with water to remove emulsified oils and dirt. An
United States (96) during the period 1958-1964
showed a sewage flow of 135 gal/capita-day and a
alkaline, water-based cleaner normally is used.
B O D and suspended solids content of 0.20
Wastewater flows and concentrations are highly
lb/capita/day and 0.234 lb/capita/day, respectively.
variable. This is due primarily to the type vehicle
being washed, type of washing operation, amount
of water used, inclusion or exclusion of storm
shown in table 3-6. It should be recognized that
water, variation in type of cleaning agents, and
the presence of industrial wastes in a domestic
sampling procedures used. Automobile and
system may radically alter these concentrations.
ground vehicle washing requires 30 to 50 gal of
These levels may be expected to vary by about a
water per vehicle. Washwater characteristics de-
ratio of 3 over a 24-hour period. Flow and BOD
loadings generally peak between 1400 and 1900
termined from ground vehicles are presented in
hours. The lowest loadings generally occur be-
table 3-7. Principal wastewater constituents in-
clude free and emulsified oils, suspended dirt and
tween 0300 and 0500 hours.
oxides, phosphates, detergents, and surfactants.
Table 3-6. Average characteristics of domestic sewage
(b) Aircraft are routinely washed to remove
(mg/L unless noted otherwise)
foreign material from the aircraft surface. The
survey results indicate significantly higher waste
loads than those experienced during ground vehi-
cle washing. BOD values ranging from less than
100 to several thousand mg/L and oil and grease
levels of less than one to several thousand have
(2) Wastes from paint stripping operations.
Aircraft and other vehicles are stripped of paint
periodically as routine maintenance in preparation
Settleable Solids (mL/liter)
for repairs or overhaul. Aircraft are usually re-
painted every three or four years to prevent
Free Ammonia (as NH3)
corrosion of metallic surfaces. The paint-stripper
Total Phosphorus (as P)
is brushed on and allowed to set on the painted
Sulfates (as SO.)
surfaces, causing the paint to swell and blister.
Alkalinity (as CaCO3)
This loosened paint is then removed with a high
pressure water spray. Modern paints are stripped
with a phenolic paint remover, while the older
c. Characteristics of industrial wastewater. In-
paints are removed by strippers containing
mostly methylene chloride (dichloromethane) and
quantity. The purpose of this section is to de-
hexavalent chromium with additional surfactants,
scribe the characteristics of major industrial dis-
thickeners, and wetting agents. Flows and charac-
charges and particularly those discharges found
teristics are highly variable. For example, approx-
on military installations. The major portion of
imately 3,350 gallons of paint-stripper, 715 gal-
wastewaters from most military installations are
lons of which is phenolic paint-stripper, are used
domestic in nature. However, military industrial
for large aircraft; while smaller aircraft may
wastewaters are produced from operations such
require some 300 gallons of stripper. It is esti-
as photographic processing, metal plating, laun-
mated that from 45 to 75 gallons of water are
dry, maintenance, and munitions manufacturing.
required to rinse each gallon of paint-stripper.
(1) Aircraft and vehicle washing.
The principal pollutants from a phenolic aircraft
(a) Ground equipment is routinely washed
paint-stripping wastewater and the ranges of
to remove any accumulated oil film, grease, metal
oxides, salts and dirt. This is normally accom-
concentration are presented in table 3-8.