MIL-HDBK-1138
Section 5:
OIL/WATER SEPARATORS
5.
5.1
Oil/Water Separators. Oil/water separators are
devices commonly used to separate oily waste products from
wastewater streams. They are typically installed in industrial
and maintenance areas to receive and separate oils at low
concentrations from wastewater generated during industrial
processes such as maintaining and washing aircrafts and vehicles.
The number of separators currently owned and operated by the
military is in the thousands. A large installation may have as
many as 150 units. In recent years, it has become clear that
many of the military's separators are not performing as
anticipated. Inadequacies have resulted from poor design,
improper selection of pre-manufactured units, misuse by
discharging inappropriate wastewaters or excessive quantities,
and lack of monitoring and maintenance.
5.2
Types of Oil/Water Separators. There are three
predominant types of oil/water separators: conventional gravity
separators, corrugated plate gravity separators, and flotation
separators. The overwhelming majority of oil/water separators
used are conventional gravity separators. Most units, regardless
of the type, are purchased as proprietary equipment from vendors.
Accordingly, the manufacturer's recommended O&M procedures should
be consulted and followed. A brief description of the main types
of oil/water separators follows.
The primary types of oil/water separators described in
this section are intended for the removal of free and de-
emulsified oils and greases, usually as a pretreatment method.
There are numerous other polishing oil/water separators marketed
for removal of trace quantities of oil and grease. These devices
include coalescing filters, oleophilic filters, and adsorption
devices. Operators should consult the manufacturer's proprietary
operations and maintenance guidance for these devices.
Gravity Separators. The process relies on the
5.2.1
different densities of oil, water, and solids for successful
operation. The wastewater is fed to a vessel sized to provide a
quiescent zone of sufficient retention time to allow the oil to
float to the top and the solids to settle to the bottom. Gravity
oil/water separators come in two configurations: conventional
gravity separators such as those designed in accordance with
guidelines established by the American Petroleum Institute (API)
and corrugated plate interceptors (CPIs).
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