UFC 3-280-04
17 DEC 2003
common coarse material used is anthracite coal. Garnet and ilmenite are generally used
in multi-media filters as the third, or possibly fourth, polishing layer. Most wastewater
applications, other than continuous backwash and traveling bridge filters, use dual me-
dia.
5-1.2.6.2 Although granular activated carbon may be used as filter media, usually its
principal purpose is to remove dissolved organics. As a result, when granular activated
carbon is used as filter media, the carbon acts to filter particulate from the water and
adsorb organic impurities in the water. The greatest disadvantage of granular activated
carbon, especially with regard to hazardous and toxic applications, is that the media's
adsorption capacity may be exhausted before its filtration capacity is exceeded. For
hazardous and toxic waste sites, activated carbon treatment should occur downstream
of the filtration unit. The activated carbon unit's principal function should be to remove
organic contaminants, not to filter particulate matter (see generally DG 1110-1-2).
5-1.2.6.3 Manganese greensand is a natural zeolite (glauconite) treated with man-
ganous sulphate and potassium permanganate, giving the media the characteristics of a
catalyst. Manganese greensand removal is ion-specific, removing soluble iron and
manganese by ion exchange, in addition to filtering out particulate material. Usually, a 1
to 4% solution of potassium permanganate (KMnO4) is fed upstream of the filters to oxi-
dize the soluble iron and manganese to insoluble ferric and manganic precipitates. The
majority of the oxides can be removed in the upper layers of the filter bed, which is
composed of conventional media (e.g., anthracite coal). Iron and manganese not re-
moved in the upper layers will be filtered out by the bed of manganese greensand. The
greensand can remove iron, manganese, and potassium permanganate in insoluble and
soluble forms. In this system, the manganese greensand acts not only as a physical fil-
tration media, but also as a catalyst in removing ions by chemical means. Solids can be
removed by periodic backwashing. The oxidative capacity of the bed is restored by con-
tinuous regeneration with potassium permanganate. It is important to note that chemical
feed rates should be proportional to influent rates. Excessive feed of potassium per-
manganate will result in a fully regenerated bed, leading to leakage of the potassium
permanganate causing a pink tinge in the filter effluent. Generally, iron and manganese
removal systems employ pressure filters. For more information on manganese green-
sand filters see EPA 570/9-91-004.
5-1.2.7 Filter Hydraulics. The flow of water through a granular medium filter with a
clean bed has similar hydraulic characteristics as flow through underground stratum.
Various empirical equations have been developed to compute the head loss attributable
to the flow of water through clean filter media of uniform size. See Metcalf & Eddy
(1991) for additional information on these and other equations. Several of these equa-
tions are presented below.
5-6
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