Technical Report

nextSand Filter Media

A report on the performance advantages of high purity nextSand over conventional filter media for pressure and gravity filtration applications.

Tod S. Johnson, Ph.D.
George A. Desborough, Geologist

June 1, 2004

Background: Enhanced Particle Removal.

Improving water filtration performance translates to improved water quality and bottom-line cost savings. The dominant factor for particle removal from water using granular filter media is physical inertial impaction [i.e., direct, physical interception of the particle(s)]. Over the past 50 years, improvements in granular-media water filtration have been achieved by: a) using smaller mesh size sand to remove finer particles, b) by combining sand with garnet or garnet and anthracite (i.e. “multimedia” beds) which resulted in a lower nominal filtration range of 12-15μ for multimedia; and c) by improving the fluidics design of beds and vessels. Further enhancements in performance for granular filter media can be achieved by modifying the particle characteristics in the feed water stream or increasing the filter media surface structure and/or surface area to enhance particle inertial impaction.

Clinoptilotlite Mineral Structure & Properties

Mineralogically, there are about forty known types of natural zeolites (hydrated silicates) known in the world. Clinoptilolite is one of these types but varies greatly in both structure and purity. It is recognized that high-purity clinoptilolite has ideal characteristics for use as water filtration media. In 2002 there were seven, open pit, clinoptilolite mines in the Western USA producing ~46,000 metric tons of product, with varying mineral composition used for agriculture, soil-amendment and other uses (Verta 2002). In 2003 only three clinoptilolite mines in the Western USA produced granular media for water filtration applications. Only one of these mines produces high purity clinoptilolite, and is the sole supplier of next Sand filter media.

The clinoptilolite used for next-Sand is mined, crushed, sieved (e.g. 14 x 40 mesh) and kiln dried. Natural, high purity next Sand filter media has the high surface area and high porosity in addition to surface micro-crystals that makes it an ideal filter media. The ultra-high surface area and surface micro-structure of next Sand significantly increases the probability for inertial impaction of particles for particle removal from water compared to conventional filter media.

High purity clinoptilolite silicate structures are characterized by low solubility in water and acid; low to moderate Specific Gravity, with comparatively high hardness. Based on crystallography, the basic atomic structure of next Sand media consists of four (4) atoms of oxygen equally spaced. With this tetrahedral crystal structure (Si2O4) oxygen atoms are shared with other Si2O4 structure to form the unique crystal framework (Fig. 1).

Fig 1. next Sand crystal structure.

Table I lists characteristics for the high purity, hard next Sand filter media used in the water filtration tests outlined in this report. Figure 2 illustrates the typical micro-crystal structure (0.1 to 1μ spacing between surface crystals) of next Sand.

Mineralogically, clinoptilolite is classified as a crystalline aluminum oxide/silicon oxide, mineral consisting of hydrated Ca2 (Na2 or K2) Al8Si28O72•24 H2O (Berkhout review; Rempel, 1996). Based on XRay Diffraction Analysis (XRD) of the mineral purity of natural clinoptilolite filter media sold in the USA the mineral content ranges from ~70 wt/% to >95 wt%. High surface area is important for the next Sand filter media. Unpublished surface area measurements in 1999 for clinoptilolite filter media from the Western USA, based on analytical measurements (Gemini Model 2360, Micrometrics, Inc., Norcross, GA) indicated: a) that the clinoptilolite used for water filtration ranges from 14 to 29m2/g; and b); the presence of mineral contaminants negatively impacts the surface area. The surface area of next Sand shown in Table I is indicative of next Sand’s high purity.

Table I.

Physical properties of next Sand filter media.

Dry Bulk Weight 55 lb/ft3
Mesh Size 14 x 40
Color Light green-gray
Surface Area 26-27 m2/gm
Surface Charge Net Negative
Bed Void Volume 55-58%
Thermal Stability 500°C
Binding Material Opal SiO2nH2O
Uniformity Coefficient > 2.0

The high purity clinoptilolite used for next Sand is classified under 21CFR Part 182.2729 & 40 CFR Part 180 as GRAS (Generally Recognized As Safe), and is listed under NSF/ANSI 61

next Sand Hardness & Media Longevity

The hardness, i.e., resistance to abrasion of zeolite filter media is determined by the clinoptilolite mineral purity, where higher purity is a favorable characteristic. In addition, the binding (or cementing/bonding) properties of the mineral impurities in the next Sand granules are important for abrasive resistance and water insolubility. Table II lists some of the common mineral impurities detected in clinoptilolite from the Western USA. Mica is ubiquitous in clinoptilolite deposits in the Western USA, but if the wt % is <0.25, then this would not be expected to compromise the granule hardness. On the contrary, mineral granules with 2.5 wt% or higher, would be expected to “break down” in the filter bed. Generally, if: a) the clinoptilolite purity is >85%; b) the smectite (e.g., clay) and mica are undetectable; c) calcite is <0.25 wt%; and d) the mineral is void of water soluble and/or “weak” shear-force mineral contaminants; and e) the clinoptilolite crystals are strongly bonded, then the media would be expected to be resistant to abrasion. Conversely, when significant clay, mica quartz and/or water-soluble impurities are present the mineral hardness is compromised. Table II lists the common mineral contaminants found in Western USA clinoptilolite deposits and the expected effects on abrasion resistance. The rare high purity of the next Sand mineral sets it apart from all other known clinoptilolite deposits and the presence of Opal in next Sand’s mineral structure provides superior strength and stability.

Table II.

Common clinoptilolite contaminants and effects on media abrasion resistance.

The authors have not observed a single case of high purity next Sand media undergoing bed loss (attrition) in pressure vessels or gravity flow beds over the past several years representing ~10 water filtration projects and numerous test evaluations.

However, we are aware of “breakdown” occurring for clinoptilolite from other Western USA clinoptilolite deposits. These breakdowns were attributed to the presence of smectite (clay), calcite and/or weak shear-force mineral contaminants. These findings support the claim that the high purity mineral used in next Sand is a unique form of clinoptilolite with ideal properties for water filtration.

Only high purity next Sand media has the quality and purity needed to achieve reliable filtration performance and filter bed longevity.

Figure 2.

High magnification SEM showing micro-crystals (0.2 to 0.9μ spacing) on next Sand media.

Performance & Advantages of next Sand Filter Media.

Since the mid-1970’s lab and field test data has been accumulating in the USA that demonstrated the utility of high purity clinoptiolite as a water filtration media. next Sand has out-performed conventional sand and sand/anthracite media for both pressure vessels and gravity filtration beds (Foreman, 1985, McNair et al, 1987; Hansen, 1997; Johnson et al, 1997; Johnson & David 1999). Generally, the next Sand filter beds operate at less than half the hydraulic loading rate of 20 x 40 mesh sand and 50% of sand/anthracite or multimedia. Interestingly, next Sand media has proved effective for removal of Giardia lamblia cysts and E. coli bacteria, where sand failed (McNair et al, 1987; Foreman, 1985). Since 1985 scattered reports and numerous technical and engineering studies have demonstrated the utility of high purity next Sand as a water filter media.

Since the mid-1990’s, next filtration technologies inc. (NFTI) has conducted >100 next Sand filter media lab and field tests. next Sand has been successfully used for well water, drinking water, surface water, pre-reverse osmosis (R/O) and industrial wastewater filtration applications. The NFTI water filtration tests used 14 x 40 mesh next Sand media vs. 20 x 40 mesh sand, sand/anthracite (1:2 ratio) or multimedia. Two-thirds of the tests utilized pressure vessels at 12-20 gpm/ft2 and onethird of the tests, gravity flow at 2-4 gpm/ft2 flow rates. Table III Summaries the NFTI filtration test results obtained for high purity next Sand vs. conventional, filter media. The test results indicate the following.

First, that the solids loading capacity of next Sand media was superior, with declining performance as follows; >multimedia>sand/anthracite>sand. next- Sand had 1.5-2X higher solids loading capacity per ft3 than multimedia beds.
Second, next Sand is a superior water filtration media, particularly for removing fine particles in the 0.5μ to <10μ range that escape conventional media.
Third, next Sand functions as a true depth filter.
Fourth, next Sand beds reduce the backwash frequency compared to conventional granular media and,
Fifth, the superior solids loading capacity and filtration performance of high purity next Sand applies to both pressure vessel and gravity flow beds.

Table 2.

next Sand vs. conventional media performance (pressure vessels)

Filter Media Filter Rating (nominal) Solids Loading Capacity
Sand (20x40 mesh ~20 micron 1X
Sand/Anthracite (20x40 mesh & Anthracicte ~15 micron ~1.4X
Multimedia1 ~12 micron ~1.6X
next Sand (14x40) <5 micron ~2.6X
1 Multimedia bed volume-#12 garnet (9%), #50 garnet (18%), 20x40 mesh sand (30%), GAC (43%)

Real-World Performance of next Sand

An example of the superior fine particle filtration performance of next Sand is provided in Figure 2. The histogram plot shows filtration results for turbidity (NTU) removal of river water clay & TOC particles for next Sand vs. multimedia.

The mid-2004 field tests were conducted in Houston, TX testing NTU for six consecutive filtration days (8 hrs filtration per day with backwash cycles at the end of each day). The next Sand filtrate averge NTU was 70% less than the multimedia filtrate indicating that next Sand more efficiently removed the turbid particles. Several other next Sand applications are provided below.

Figure 2.

next Sand vs. multimedia removal of surface water turbidity (NTU). Feed water & filtrate are plotted for next Sand vs. multimedia representing six 24 hr, D) pressure vessel runs @ 12 gpm/ft2.

Bottled Water Plant

A major bottled water plant in Mexico, pumped ground water to four, parallel filtration vessels (48”dia/ea, 3 ft bed ht) that serve as pretreatment to two RO units. A two month, “on-line” test was carried out using two of the filter vessels filled with next Sand and two filled with multimedia tracking the feed water and filtrate SDI’s. The results indicated that next Sand reduced the SDI by 50% while multimedia reduced the SDI by just 5%. The next Sand media provided superior pre-filtration for the RO equipment for one year without any problems or bed loss.

Drinking Water Plant

A resort on San Juan, Island, Pacific Northwest installed a new drinking water plant to supply drinking water to the resort and local residential customers. The design engineers conducted pilot tests and worked with the Washington State Public Health Department, then installed a 220 gpm system to remove colloidal and micro-particles from lake water (4-19°C). Three parallel gravityflow, next Sand filter beds (3 ft bed ht, with 12” under gravel) have operated at ~4 gpm/ft2 flow rate for two years, filtering DAF decant water and providing high quality (<0.25 NTU, <1 mg/l TOC’s ) drinking water.

Cooling Tower Makeup Water

A major chemical plant in South Texas pumps river water for cooling tower make-up water but had periodic turbidity problems due to rain events. Filter pilot tests indicated that the turbidity was predominantly colloidal and that next Sand filter media removed >98% of the turbid particles. The customer replaced the sand and garnet media in a gravity filter unit with 30,000 lbs (545.5 ft3) of next Sand. The next Sand media continues to provide superior filtration performance after several years operating at 2-3 gpm/ft2 flow rate, including periods of high turbidity “spikes”.

Boiler Feed Makeup Water:

An electric power plant in Louisiana installed a well water pumping station water treatment facility and new RO equipment to provide boiler feed makeup water. Multimedia was specified for use in two carbon steel pressure vessels (750 gpm/ea, 3 ft bed ht) as pretreatment to the RO equipment. The plant start-up was delayed several months due to failure of the multimedia system to meet the RO filtrate volume and SDI specifications. The two multimedia beds were replaced with equivalent volumes of 14 x 40 mesh next Sand media. The next Sand media has consistently performed to the original strict design specifications for the RO feed water and low SDI for over two years. No significant next Sand bed loss has been observed.

“Produced Water” Filtration

An oil company operating in Texas and New Mexico wanted to convert unusable oil production produced water into reusable irrigation water. Early in 2004 a water treatment and filtration pilot test was conducted at the oil product site. The produced water was processed for oil/water separation, flocculation, clarification then filtration using two, parallel pressure vessels (72 inch dia.), with next Sand operating at ~10-12 gpm/ft2. The filtrate was used directly as feed water for an RO unit which recycled the water as agricultural irrigation water.

Summary & Conclusions

The unique high purity clinoptilolite used for next Sand has the physical and mineral properties needed for reliable and efficient water filtration applications. next Sand is a direct replacement (volume for volume) for sand, sand/anthracite or multimedia in pressure vessels or gravity beds. next Sand has a lower dry bulk weight of 55lb/ft3 than sand or garnet, which translates to lower freight costs.

next Sand performs as a true depth filter–the water flows through the porous crystalline matrix as well as around the next Sand granules in the filter bed. Based on published reports and NFTI lab and field data the following conclusions can be made for next Sand filter media. First, next Sand is a superior filter media compared to sand, sand/ anthracite, sand/garnet or multimedia. Second, next Sand is cost-competitive with multimedia and eliminates the requirement for warehousing, shipping and loading multiple media layers into the vessel. Further, next Sand has several other advantages vs. conventional granular media, which are:

next Sand is inert and stable over pH range <1 to <12. The unique high purity of next Sand ensures superior hardness and abrasion resistance for longest media life.


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