MIL-HDBK-1005/9A
3.10.7.1 Multimedia Filtration. Systems are available that
operate by gravity or under pressure. Select equipment on basis
of operating costs and the availability of space for installation.
Pressure filters operate at higher loading rates and require less
installation area than gravity units with comparable capacity. In
colder climates, consider enclosing the system indoors. The
system should have automatic backwashing capabilities, initiated
by sensing a predetermined head loss across the filter bed.
Treated effluent is normally recycled for surface wash and
backwash water supply. A suitably sized reservoir should be
provided downstream from the filtration unit to hold the required
volume of effluent for the backwashes. Backwash wastewater should
be recycled to either the LET, DAF, or IAF unit. Depending on the
desired flow configuration, adequate capacity must be included in
either the LET, DAF, or IAF unit to receive the periodic backwash
recycles flows. Refer to Figure 23 for typical sections of
gravity and pressure multimedia filtration units, respectively.
a) The principal design variables for multimedia filter
design for oily waste treatment are as follows:
Design Parameter
Design Value
Bed depth
24-36 in. (610-914 mm)
Filtration rate
3-8 gpm/ft2 (122-326 L/min⋅m2)
Gravity
12-18 gpm/ft2 (489-
Pressure
733 L/min⋅m2)
15-20 gpm/ft2 (611-815 L/min⋅m2)
Backwash rate
3-6 sft3/min/ft2 (0.9-
Air scour flow rate
1.8 m3/min/m2) @ 12
(if necessary)
psig (83 kPa)
Filter media
Combination sand, gravel,
anthracite (garnet optional)
Pressure drop
Clean
2-4 psig (13.8-27.6 kPa)
Loaded
8-12 psig (55.2-82.7 kPa)
2-6 lb/ft2/hr (9.8-
Filter solids loading
29.3 kg/m2⋅hr)
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