UFC 3-280-04
17 DEC 2003
tions, then care should be taken to ensure that the manufacturer's warranty is not
voided. For package systems, it is preferable for the designer to review the manufac-
turer's available system parameters and options and to write the specifications so that
they fall within the ranges described in this design guide.
5-1.2.1 Types of Media. The designer will typically provide a filter equipment or me-
dia supplier with information about the filter media size, layer depth or performance, or
all three. The supplier will calculate the clean bed head loss for the designer. The equa-
tions discussed can be used to determine whether the information supplied by the
manufacturer is accurate.
The filter media provide the surface upon which particles are separated from
the waste stream. The media are specified on the basis of material, size, shape, and
specific gravity and will be selected on the basis of the waste stream and required efflu-
ent quality. The most commonly used granular media materials available for filtration
are silica sand, crushed anthracite coal, and garnet or limonite (high density sands).
Manganese greensand is used when soluble iron or manganese must be removed. Ac-
tivated carbon and ion exchange resins may be used to filter out solids in conjunction
with their primary role of removing dissolved compounds. It is important to note that
some resin beads are subject to particulate attack, which fractures the resin bead.
Reliable filter performance depends on the proper selection and maintenance
of filter media and the effective operation of the process. The different types of media
can be used alone or in combination with one another. The following media properties
are important in establishing the filter performance characteristics:
Media size and size distribution.
Media density.
Media shape.
The hydraulics of filtration, as well as filter backwashing, are influenced by these prop-
erties.
5-1.2.2 Media Size and Size Distribution. Filter media size affects filter performance
in two conflicting ways. Smaller grain size improves particulate removal, but accelerates
head loss development and may shorten run time if the filtration cycle is determined by
reaching terminal head loss. Conversely, larger grain size causes somewhat poorer
particulate removal, but lowers the rate of head loss development.
5-1.2.2.1 Filter media size can be defined in several ways. In the United States, filter
media are characterized by the effective size and the uniformity coefficient. A sieve
analysis of a sample of the media determines these values. The sieve analysis should
be done in accordance with the American Society for Testing and Materials (ASTM)
Standard C136-96.
5-1.2.2.2 The effective size (ES) of the sieve is defined as the opening size for which
10% by weight of the grains are smaller in diameter. The effective size is determined by
5-3
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