MIL-HDBK-1005/16
drip trays, employing spill containment techniques, and
discarding oil only when it is no longer serviceable should be a
part of any oily waste control program. OWSs are not to be used
for spill containment.
5.5
Treatment Technology. Selection of the appropriate
treatment process for oily waste is dependent on the oil
classification. Under proper quiescent conditions, free oil can
be removed by gravity separation. Emulsified oil cannot be
removed by gravity separation unless it can first be converted to
free oil by breaking the emulsion. Emulsified oil may be removed
by air flotation, although the emulsion may also have to first be
broken for this process to be effective. Removal of soluble
(dissolved) oil generally requires biological treatment or
adsorption onto a solid phase sorbent such as activated carbon.
It should be noted that other pollutants, such as
solvents, phenols, dissolved metals, and other toxic and
hazardous pollutants, are not effectively removed by oil/water
separation technology and may require additional source control
or pretreatment.
Designers should also understand that lack of proper
maintenance is one of the biggest causes of OWS failure.
Designers must design for ease of maintenance so as to promote
adequate periodic maintenance. For example, buried cylindrical
separators are almost impossible to maintain and thus their use
is highly discouraged.
5.5.1
Gravity Separation. Two basic types of gravity OWSs
are in common use: a) conventional, rectangular-channel units,
commonly called API separators because they are usually based
upon design standards developed by the American Petroleum
Institute; and b) parallel plate separators. In either case,
removal is a function of residence time, specific gravity of the
oil, oil droplet size, fluid salinity, and fluid temperature.
Well designed and operated API gravity separators are
capable of removing oil globules with a diameter greater than 150
microns and achieving effluent levels of free oil as low as 100
mg/L. Parallel plate separators are generally designed to remove
oil globules greater than 60 microns in diameter, and can meet
effluent limits as low as 50 mg/L of free oil. The total oil
content of the effluent will be greater, depending on the amount
of emulsified and dissolved oil present. Other factors will also
affect the efficiency of oil removal, including oil-specific
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