| Filtration Medium |
Basic Characteristics |
Discussion |
| Activated Alumina |
Density (lb/ft³): 43
Bed depth (inches): 36+
Service flow (gpm/ft²): 1-2
Backwash flow (gpm/ft²): 8-10 |
Activated Alumina is “a mixture of amorphous and
gamma aluminum oxide” that is used for removal of arsenic,
fluoride, selenium, silica and humic acids. For arsenic and fluoride
treatment, low pH (5.5-6) is superior. It can be regenerated with sodium
hydroxide. |
| Anthracite |
Density (lb/ft³): 50
Bed depth (inches): 24-36
Service flow (gpm/ft²): 5
Backwash flow (gpm/ft²) 12-18: |
Crushed anthracite coal has long been a favorite
medium-weight filter for sediment reduction. It is now most often used
with sand and other media in multi-media filters. |
| Birm |
Density (lb/ft³): 46
Bed depth (inches): 30-36
Service flow (gpm/ft²): 3.5-5
Backwash flow (gpm/ft²): 10-12 |
Birm is a manufactured medium consisting of plastic coated
with magnesium oxide. It is designed for iron and manganese
reduction. It causes iron and manganese to precipitate (change from a
dissolved state to a particulate), then filters out the particulate.
It can be used with or without an oxidizer. Its success without
an oxidizer depends a great deal on the amount of dissolved oxygen in
the water. (Testing for dissolved oxygen isn't easy, so trial and error
is often the best policy.) |
| Calcite (Crushed marble) |
Density (lb/ft³): 100
Bed depth (inches): 24-30
Service flow (gpm/ft²): 2-6
Backwash flow (gpm/ft²): 10-12 |
Calcite is crushed marble. It is naturally occurring
calcium carbonate. It is used to raise the pH of acidic water. Since it
is dissolved only in acidic water, it is self-limiting. When acidic
water reaches neutral pH, no more calcite is dissolved. |
| ChemSorb (Natural Zeolite) |
Density (lb/ft³): 55
Bed depth (inches): 24-30
Service flow (gpm/ft²): 12-18
Backwash flow (gpm/ft²): 11-13 |
ChemSorb is a unique granular zeolite filter media.
It is a natural product mined in the western U.S. It offers sediment
filtration down to <5 microns and backwashes well and has an excellent
service rate. |
| Corosex |
Density (lb/ft³): 100
Bed depth (inches): 24-30
Service flow (gpm/ft²): 5-6
Backwash flow (gpm/ft²): 10-12 |
Like calcite, Corosex, which is magnesium oxide, is used
to correct low pH situations. Unlike calcite, it has a tendency to
overcorrect, especially if the flow rate is low. It is preferred for
very low pH and for very high flow rates. |
| Filter-Ag |
Density (lb/ft³): 25
Bed depth (inches): 24-36
Service flow (gpm/ft²): 5
Backwash flow (gpm/ft²): 8-10 |
Filter Ag is a manufactured lightweight sand substitute, which
weighs about 1/4 as much as sand. Its main function is removal of
suspended solid but it is also used at times for iron reduction. |
| Filox-R |
Density (lb/ft³): 114
Bed depth (inches): 20 minimum
Service flow (gpm/ft²): 13.5-22
Backwash flow (gpm/ft²): 16-23.5. |
Filox-R is a processed natural medium known for the purity of
its active ingredient (it's 80% manganese dioxide), its durability, and its high
oxidation/filtration capacity. It is used for iron, manganese, and
hydrogen sulfide reduction. It has an extremely long life and high service
flow rate capacity. It has a high pH range of operation and imparts no
taste or odor to treated water. |
| Garnet |
Density (lb/ft³): 140
Bed depth (inches): 10+
Service flow (gpm/ft²): 10
Backwash flow (gpm/ft²): 25-30 |
Garnet is a natural medium used most often in multi-media
filters. It is very fine and filters down to the 10-20 micron range. |
| Granular Activated Carbon (GAC) |
Density (lb/ft³): 25
Bed depth (inches): 24-36
Chlorine removal Service flow (gpm/ft²): 3-5
Organic removal flow (gpm/ft²): 1-3
Backwash flow (gpm/ft²): 8-10 |
Granular carbon is the standard media for most
chemical reduction situations. Its high surface area gives it massive
adsorptive capacity. It can be manufactured from animal bones, wood,
and petroleum, but most carbon is produced from anthracite coal or coconut
shells. Go here for more information about
filter carbon.
|
| KDF55 |
Density (lb/ft³): 171
Bed depth (inches): 10+
Service flow (gpm/ft²): 30
Backwash flow (gpm/ft²): 30 |
High purity copper/zinc granules that use redox
(exchange of electrons) to remove chlorine and heavy metals. KDF55 is 50%
copper and 50% zinc. This grade of KDF is most often used for chlorine and
heavy metals reduction. It also
has bacteriostatic properties. Has an unusually high flow rate, but
also requires a strong backwash stream. Cannot be used in
“aggressive” water and is often preceded by some form of neutralization. |
| KDF85 |
Density (lb/ft³): 1741
Bed depth (inches): 10+
Service flow (gpm/ft²): 15
Backwash flow (gpm/ft²): 30 |
High purity copper/zinc granules that use redox
(exchange of electrons) to remove chlorine and heavy metals. KDF85 is 85%
copper and 15% zinc. This grade of KDF is most often used for iron,
manganese and hydrogen sulfide reduction. It also
has bacteriostatic properties. It has an unusually high flow rate, but
also requires a strong backwash stream. Cannot be used in
“aggressive” water and is often preceded by some form of neutralization. |
| Manganese Greensand |
Density (lb/ft³): 85
Bed depth (inches): 30-36
Service flow (gpm/ft²): 2-5
Backwash flow (gpm/ft²): 12-15 |
Manganese greensand is a purple-black filtration medium
made from naturally occurring greensand coated with manganese. It serves
as a catalyst to precipitate hydrogen sulfide, iron and manganese.
It can be continuously regenerated with chlorine and/or a purple
liquid called potassium permanganate, or it can be intermittently
regenerated with potassium permanganate alone. |
| MTM |
Density (lb/ft³): 27
Bed depth (inches): 24-36
Service flow (gpm/ft²): 3-5
Backwash flow (gpm/ft²): 8-10 |
MTM is a granular manganese dioxide filtering medium that
works in much the same way as manganese greensand and is regenerated also
with chlorine and/or potassium permanganate. The main difference is
that it is lighter and therefore can be backwashed more easily and has a
higher service flow rate. |
| Multi-media (multi-layer) |
Density (lb/ft³): 92
Bed depth (inches): 36
Service flow (gpm/ft²): 10
Backwash flow (gpm/ft²) 15 |
Multi-media filters consist of several layers—usually
three to five—of different media. The media are loaded by
density—the most dense in the bottom of the tank, the least dense on top.
This produces a filter with excellent flow rate and and relatively easy
backwash properties that will filter down to ten microns.
The most common media mix is (top to bottom): anthracite, filter sand,
garnet 30 X 40, garnet 8 X 12, and gravel. This is a typical
mix, though many others are common. |
| Pyrolox |
Density (lb/ft³): 125
Bed depth (inches): 24+
Service flow (gpm/ft²): 5
Backwash flow (gpm/ft²): 25-30 |
Pyrolox is a mined ore—manganese dioxide—used for
manganese, iron and hydrogen sulfide reduction. Like Birm,
greensand, and MTM, it acts as a catalyst to oxidation. Waters low in
dissolved oxygen can use the catalytic properties of Pyrolox. It
must be backwashed aggressively, although no regenerant is needed.
The leading causes of filter failure when using Pyrolox are inadequate
backwashing and low dissolved oxygen. |
| Sand |
Density (lb/ft³): 100
Bed depth (inches): 18-30
Service flow (gpm/ft²): 3-5
Backwash flow (gpm/ft²): 15-50s |
Filter sand is naturally occurring sand that is high in
silica and low in calcium. It is graded and washed. It can be
used independently or as part of a multi-media filter. Sand filters are
believed to be the oldest man-made filters and they imitate a common
natural filtration technique. |
Information in this chart is taken largely from an excellent article by
James A. Hunt: “Filtration Media: Making the Right Choice. A Reference Guide
for Dealers” that can be found in the May 2001 issue of Water
Conditioning and Purification magazine.