Technical Overview Water Filtration
There are three basic “families” of filtration. Media, Cartridge, and membrane. Explanations follow.
1. MEDIA WATER FILTRATION where the water flows through a column or BED of material referred to as the filter MEDIA.
A. Mechanical Water Filtration The filter media is selected by size to exclude any particles in the water that are larger than the spaces between the pieces of filter media. Sand filter would be an example. There is a generally a secondary condition that takes place which may do as much for the effectiveness of the filtration as the space between media particles and that is the attractive forces that exist between the material in the water (negatively charged) and the filter media (positively charged). In some cases the effect of these charges does more than the exclusion by space.
B. Reactive Water Filtration The filter media is selected because it or a coating on it has a natural attraction for one or more undesirable constituents in the water. Normally this type of constituent in the water is in the dissolved or ion state and not something that can be seen. An example would be a media rich in iron attracting arsenic in the water.
C. Catalytic Water Filtration Certain natural and coated media are used to cause dissolved ions in the water to combine with contaminates in the water to create a visible suspended solid in the water that can then be filtered out by the mechanical process. Activated manganese ore (Pyrolox) media removing ferrous (dissolved) iron is an example of this process.
The following is a list of common filtration media and application guides that will help in media selection and equipment sizing.
8-12 garnet.
Use. Support bed for other media. Course filtration of turbidity
Service flow-20 GPM/Ft2 .
Backwash flow -30 GPM/Ft2
Regenerant. None. Backwash only
Limitations. None
30-40 garnet
Use. Fine filtration of turbidity.
Service flow-8 GPM/Ft2
Backwash flow -18 GPM/Ft2
Regenerant. None. Backwash only
Limitations. None
Pyrolox
Use. Turbidity reduction. Clear water and red water iron removal. Manganese removal. Hydrogen sulfide removal.
Service flow-5 GPM/Ft2 .
Backwash flow -20 GPM/Ft2
Regenerant. Usually backwash only. Helpful to feed liquid chlorine when load of iron , etc. is high --- total iron, manganese, and hydrogen sulfide above 6 ppm. When feeding chlorine, ppm of chlorine must equal ppm of iron, manganese, and hydrogen sulfide combined
Limitations. pH 6.8 or above. Will not treat bacterial iron w/o chlorine feed.
Birm
Use. Turbidity reduction. Clear water and red water iron removal. Manganese removal.
Service flow-5 GPM/Ft2 .
Backwash flow -10 GPM/Ft2
Regenerant. Backwash only.
Limitations. Do not feed any chlorine. Do not expose to hydrogen sulfide. pH
must be above 6.8. Dissolved oxygen present
MTM
Use. Turbidity reduction. Clear and red water iron removal. Manganese removal. Hydrogen sulfide removal. Control of iron bacteria and organic iron.
Service flow-5 GPM/Ft2 .
Backwash flow -10 GPM/Ft2
Regenerant. Constant feed of chlorine, hydrogen peroxide or potassium permanganate.
Limitations. pH above 6.5.
Greensand Plus
Use. Turbidity reduction. Clear and red water iron removal. Manganese removal. Hydrogen sulfide removal. Control of iron bacteria and organic iron.
Service flow-6 GPM/Ft2 .
Backwash flow -12 GPM/Ft2
Regenerant. Constant feed of chlorine, hydrogen peroxide or potassium permanganate
Limitations. pH above 6.5
Activated Carbon. Acid washed. Coal or coconut based
Use. Turbidity reduction. Chlorine, volatile organic, taste, and odor removal.
Service flow-5 GPM/Ft2 .
Backwash flow -10 GPM/Ft2
Regenerant. None. Backwash only.
Limitations. No iron or bacteria in water.
Surface Enhanced Carbon. Acid washed. Coconut based.
a. Use. Turbidity reduction. Chlorine, chloramines, volatile organics, taste and odor removal.
b. Service flow-5 GPM/Ft2 .
c. Backwash flow -10 GPM/Ft2.
d. Regenerant. None. Backwash only
e. Limitations. No iron or bacteria in water.
Calcite. Crushed limestone
Use. Increase pH.
Service flow-4 GPM/Ft2 .
Backwash flow -10 GPM/Ft2
Regenerant. None. Backwash only.
Limitations. Correct pH at 6.2 or above. Adds calcium hardness to the water. Reacts slowly. May pack –as an alternative, consider up-flow
Corosex. Magnesium Oxide
Use. Increase pH.
Service flow-5 GPM/Ft2 .
Backwash flow -10 GPM/Ft2
Regenerant. None. Backwash only.
Limitations. Correct pH 5.2 to 6.1. Adds magnesium oxide to the water. Reacts rapidly and may over correct ---as an alternative consider up-flow.
KDF
Use. Increases life of activated carbon by four or five times. Removes some iron and manganese from the water.
Removes trace heavy metals. Mild effect on hardness removal
Regenerant. None.
Service flow-10 GPM/Ft2 .
Limitations. Use on pH 6.5 or above. Extremely heavy and difficult to backwash. Should use in an up-flow service tank as pre-filter to carbon filter only thus eliminate high flow backwash and also cost of a valve on the tank.
Filter AG
Use. Turbidity filtration.
Service flow-5 GPM/Ft2 .
Backwash flow -10 GPM/Ft2
Regenerant. None. Backwash only. Lighter than sand so consumes less water.
Limitations. Filters only to 40 microns. Plugged by bacteria
Filter AG Plus
a. Use. Turbidity filtration including ferric iron and many colloidal size particles. Filters to 5 micron
b. Service flow-16 GPM/Ft2 .
c. Backwash flow -15 GPM/Ft2
d. Regenerant. None. Backwash only
e. Limitations. Plugged by bacteria
Anthracite
a. Use. Turbidity removal and filter bed topping for other heavier filter media
b. Service flow-5 GPM/Ft2 .
c. Backwash flow -15 GPM/Ft2
d. Regenerant. None. Backwash only
e. Limitations. None. Inert material (hard coal)
ASM10HP
a. Use. Arsenic removal
b. Service flow-7 GPM/Ft2 .
c. Backwash flow -3.5 GPM/Ft2
d. Regenerant. None. Backwash only
e. Limitations. Chlorine must not exceed 0.3 PPM
H/A Media
a. Use. Fluoride removal
b. Service flow-6 GPM/Ft2 .
c. Backwash flow -5 GPM/Ft2
d. Regenerant. None. Backwash only
e. Limitations. Capacity is 40,000 part gallons per cubic foot. Material must then be discarded.
2. CARTRIDGE WATER FILTRATION
As the name implies, these are cartridges that fit within a pressure holding housing. They fit into two categories. Mechanical and media
A. Mechanical. Normally made of either a pleated specialty treated cellulose based material, wound string or an extruded polypropylene material. Available to filter as low as 0.1 micron and up to about 50 micron. The most popular seem the be the extruded polypropylene with multi depth — course 50 or 25 micron on the outside and down to 5 micron on the inside to provide extended life. They are rated as nominal (80% removal at micron rating) and absolute (99.9% removal at micron rating)
B. Media. For low flow rates and low total water volume it is becoming popular to place some of the previously discussed media into a cartridge. An example would be H/A media for fluoride removal at a point of use such as a sink. The options are almost limitless but the user should be aware of replacement costs both in material and labor.
3. MEMBRANE WATER FILTRATION
Ultra filtration-UF (0.006 to 0.20 micron) and micro filtration-MF (0.20 to 3.0 micron) membranes are increasingly popular in both the hollow fiber and spiral wound form. Mechanical filtration primarily with some removal due to the attractive forces between particles and the polymer used as the membrane material. Uses include commercial reverse osmosis pre-treatment , waste water tertiary solids removal and as microbiology barriers.
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