UFC 3-280-04
17 DEC 2003
steps: precoat application, filtration of water, and removal of the spent filter cake. For
precoating a thin layer, approximately 1.5 to 3 mm (0.06 to 0.12 in.) of the filter media is
applied to the septum before the feed is introduced to the system. This thickness can be
achieved by applying approximately 0.5 to 1 kg/m2 of diatomite or perlite to the septum
(0.10 to 0.20 lb/ft2). This precoat serves to protect the filter septa from blinding caused
by the filtrate and also serves to bridge the larger septa pores. This bridging reduces the
size of filtrate particles removable from the feed stream. For additional information, refer
to TM 5-662.
5-3
CARTRIDGE FILTRATION
5-3.1
Description of Unit. Disposable cartridge filtration uses pleated or non-
pleated disposable filter media. As a rule of thumb, a cartridge filter system should be
expected to handle a solids loading of 1 to 2 mg/L TSS at the cartridge system's design
flow. For example, a 10-in. long 4-in. pleated filter, sized with an absolute rating of 10
microns, is rated for a flow of up to 1 L/s (15 gpm). At 2 ppm, such a filter would retain
approximately a third of a pound of solids per day. This will mean that the filter element
may have to be changed every day. A cartridge system can handle greater solids load-
ings, such as10 or 20 mg/L suspended solids, but the number of filters cannot be sized
based on the listed flow capacity. The best performance will be obtained when the filter
capacity is sized by dividing the rated flow capacity per filter by the TSS concentration in
mg/L and using that number to determine the number of filters required for a given flow.
5-3.1.1 Each filter medium is usually associated with a particular removal rating,
ranging from sub-micron up to 150-micron particles. The cartridges are often cylindrical,
with the media configured as pleated woven fabric or as a non-woven depth medium.
The medium is bonded to plastic or metal hardware. Housings are available in plastic,
lined metal, or metal construction to meet various operating conditions of pressure,
temperature, and waste stream compatibility.
5-3.1.2 Cartridge filters are usually composed of a porous medium or fabric that is ei-
ther pleated or configured for depth filtration. Depth-style cartridges may be either:
String wound, which does not have a fixed or uniform pore structure.
Molded fiber, which does have a uniform pore structure.
High efficiency, with continuously graded pre-filter layers in decreasingly
smaller pore sizes.
5-3.1.3 Pleated filters generally feature a fabric medium that is folded in either
triangular or crescent shaped pleats. There are also laterally pleated media with folds
perpendicular to the axis of the filter. Figure 5-9 shows a typical pleated cartridge media
cross section. An example of a multi-unit cartridge filter media housing is shown in Fig-
ure 5-10.
5-3.1.4
Typically, pleated elements are rated for a higher flow rate than depth filters
of the same size configuration because pleated filters offer a greater surface area to the
incoming waste stream flow. Of the pleated filters, the crescent pleat offers greater sur-
5-29
Previous Page
