MIL-HDBK-1005/16
Section 5:
OIL/WATER SEPARATORS
5.
5.1
Section Overview. This section addresses military
applications of oil/water separators (OWSs). It provides general
information on OWSs, as well as specific information on determining
the need for an OWS, principles of oil/water separation, OWS design
criteria, and selection of OWS technology. Emphasis is given to
conventional and parallel plate gravity OWSs, which are the
prevailing types installed at military bases. Other technologies,
such as flotation, filtration, and adsorption are also briefly
discussed. These topics are not addressed in the WEF MOP 8.
5.2
Oil Classification. Oily wastewaters are generated in
the industrial and maintenance areas of military installations
from such activities as aircraft and vehicle maintenance and
washing. The oils present in wastewaters may be of several
types, including gasoline, jet fuel, diesel fuel, lubricants, and
miscellaneous detergents. Regardless of type, they are typically
classified into three major categories: free, emulsified, and
dissolved.
5.2.1
Free Oil. Free oil consists of discrete globules
large enough to rise as a result of buoyant forces and form an
oil layer on top of the water. Theoretically, oil globules as
small as about 20 microns can be classified as free oil.
However, research indicates that the size of oil globules must be
approximately 150 microns or greater to be effectively removed in
a conventional gravity separation chamber.
5.2.2
Emulsified Oil. Emulsified oil exists as smaller
droplets, approximately 1-20 microns, which form a stable
dispersion in the water and are incapable of rising to form a
separate oil layer without additional chemical treatment.
Dissolved oil is soluble in water and is also incapable of
removal by gravity separation.
5.2.3
Oily Wastes. Oily wastes discharged at military bases
may include any or all of these classifications. While most of
the oily waste is originally in the free state, the cleaning
agents commonly used in the washing of floors, vehicles,
aircraft, and other equipment at military installations are
designed to increase the solvency of oil in water, and they cause
the oil to become emulsified. Additionally, free oil can be
mechanically emulsified through excessive agitation and
turbulence, such as that caused by high velocities or pumping.
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