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Zeolite filter media: Setting a new standard for water filtration
High purity zeolite has the physical, mineral properties needed for efficient water filtration.
Over the past 50 years, advances in granular filter media water filtration have been achieved by using smaller mesh size sand combined with garnet or garnet/anthracite (multimedia) to achieve a nominal 12 to 15µ rating and to improve bed design and fluidics.
High purity zeolite media is now available that achieves a <5µ nominal rating.
Structure and properties
Mineralogically, there are about 40 known types of natural zeolites (hydrated silicates) of which clinoptilolite is the most common.
Clinoptilolite is classified as a crystalline, aluminum, silicon, oxide mineral (Berkhout 2002; Rempel, 1996).
This report describes a high purity 14 x 40 mesh, approximately 55 lb/cu. ft. bulk weight, clinoptilolite (zeolite) from the western US that has a high porosity, high surface area, a micro-crystal structure, and is abrasion resistant.
This zeolite media is classified under 21CFR Part 182.2729 and under 40 CFR Part 180 as GRAS (Generally Recognized As Safe). It is also listed under NSF Standard 61.
Performance and advantages
Since the mid-1970s, lab and field test data reports in the US have indicated that zeolite filtration media has consistently outperformed sand, sand/anthracite and multimedia in both pressure vessels and gravity filtration tests (e.g., Foreman:1985: Johnson & Petersen, 2001 Hansen, 1997:, Johnson et al, 1997; Fuger, 2003).
Generally, the zeolite filter beds have 1.7 to 1.9 times the solids loading capacity/ft3 and superior filtration performance versus multimedia.
Based on more than 100 lab and field tests (2/3 using pressure vessels and 1/3 using gravity beds) since the mid-1990s representing commercial, residential and industrial water filtration projects, it has been concluded that high purity zeolite media is superior to conventional granular media.
Our test results using pressure vessels indicate
For solids loading capacity, high purity zeolite surpassed multimedia, sand/anthracite and sand;
Zeolite more effectively removes fine particles in the 0.5µ to 10µ range that escape conventional medaiI).
Similar results were observed for gravity beds. Some representative examples of high purity zeolite filter performance are provided below
Prefilter for GAC
Municipal water supplied to a restaurant contained elevated iron and other fine particles. Cartridge (5µ) filters rapidly loaded and caused reduced water flow to the GAC beds and chiller
A backwashing zeolite filter (10" diameter vessel with a 24" bed depth) was installed and tested by an independent engineer and technical consultant
The feedwater had 0.1µ to 10µ particles (average SDI or silt density index = 4.3)
The zeolite bed effectively removed the iron particles. The product water particles were in the 0.1µ to 2.3µ range, with an average SDI = 0
Bottled water plant
A bottled water plant pumped groundwater to four 48"diameter pressure vessels that feed two RO units.
The multimedia reduced the well water SDI by an average 5 percent compared to 45 to 50 percent SDI reduction for the zeolite media.
The sand/garnet was replaced with an equal volume (545.5 ft3) of 14 x 40 mesh zeolite. The zeolite, when operated at the same flow rate (2.5 gpm/ft2), removed greater than 98 percent of the turbidity versus approximately 20 percent for the sand/garnet.
The zeolite has provided superior filtration for two years.
Flow rates, backwashing guidelines
For pressure vessels, a 36" bed depth is generally used with undergravel, plus approximately 50 percent freeboard, similar to multimedia beds
The optimum service flow rate for pressure vessels ranges from 12 to greater than 20 gpm/ft2 of bed area, depending on the water filtration application
For example, use 12 gpm/ft2 for RO and GAC pre-filtration; use 15 gpm/ft2 to achieve low turbidity well water, surface water and for industrial projects; and 18 to 20 gpm/ft2 rate to get high water volume for projects with lower filtration requirements
Since virgin zeolite has "fines" from mine production, it is important to backwash it prior to placing in service
The backwash rule-of-thumb is to achieve 35 percent bed expansion using a backwash rate of 20 gpm/ft2 until the water is clear for new zeolite, and for six minutes for routine operational backwash cycles
Alternatively, air scour can be used with water to reduce backwash water usage
[ltr]Zeolite has a wide range of applications:
[ltr]* Water filtration
* Heavy metal removal
* Swimming pools
[ltr]* Ammonia in municipal sludge
* Heavy metal removal
* Septic leach fields
[ltr]* Odor control
* Confined animal environmental control
* Livestock feed additives
[ltr]* Nurseries, Greenhouses
* Tree and shrub transplanting
* Turf grass soil amendment
* Reclamation, revegetation, landscaping
* Silviculture (forestry, tree plantations)
* Medium for hydroponic growing
[ltr]* Household odor control
* Pet odor control
[ltr]* Absorbents for oil and spills
* Gas separations
[ltr]* Site remediation/decontamination
[ltr]* Ammonia filtration in fish hatcheries
* Biofilter media