considered (refer to NAVFAC P-916, User's Guide for the Handling,
Treatment, and Disposal of Oily Sludge and MIL-HDBK-1005/8 for
sludge handling systems).
3.9.2
Treatment Requirements. The level of required
treatment for oily wastewater depends on the discharge criteria
(POTW or navigable water).
3.9.2.1
Discharge to Publicly Owned Treatment Works (POTW).
Typical effluent quality requirements can be achieved by batch
treatment gravity separation processes to remove free oil from
wastewater. The oily waste is discharged into a short-term
storage/separation tank referred to as a load equalization tank
(LET). The waste is received for a predetermined number of days
and then allowed to sit quiescently for about 24 hours to ensure
optimum gravity separation. Free oil floats to the surface and
is skimmed off. Settleable solids sink and are scraped to a
hopper for withdrawal and disposal. Typical LET effluent
contains less than 50 ppm of oil and grease. Multiple LETs
should be provided for semicontinuous (fill and drawoff)
operation of the facility. The pretreatment scheme is shown in
Figure 12.
a) An induced gravity separator should be provided
for additional treatment when LET effluent contains more than 50
ppm of oil and grease. Provide a bypass around the induced
gravity separator. In an induced gravity separator, total flow
is distributed through numerous flow paths and formed by
inclined plates or tubes at laminar velocity. This increases
suspended solids contact, and it aids solids separation by
improving the flotation and settling characteristics of the
enlarged particles.
b) Design guidelines and criteria for these unit
processes are presented in paragraph 3.10.
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