By Dave Purkiss
There is an increasing trend toward using alternate filter medias in sand and DE (diatomaceous earth) filters. Zeolite and recycled glass are being touted as efficient replacements for sand, while perlite and cellulose are promoted as eco-friendly alternatives to DE. How do you know that these products will perform as claimed?
NSF/ANSI Standard 50-2009 contains the criteria for evaluation and testing of many material and product types for pool, spa, and water-park applications. The standard contains requirements for pool filters, chemical generators, skimmers, UV systems and water quality test devices as well as many other products. The standard also contains criteria for evaluating filtration media including alternatives to sand and DE.
In many areas, disposal of DE via the sanitary sewer is not allowed due to impact upon water treatment facilities and piping systems. Claims of performance benefits and cost savings from using alternatives to sand have prompted facility operators to consider use of these alternate medias.
NSF developed criteria to evaluate the use of alternate media in pre-coat (DE) filters and sand-type filters. This involves testing the media in filters that have previously demonstrated compliance to NSF 50.
The filters are charged or filled with the alternate media and put through a series of tests including:
- Head-loss testing
- Verify pressure loss through the filter and assess media migration.
- Filter–media-cleanability testing
- Challenge filter media with a known contaminant loading then conduct manufacturer-recommended backwashing.
- Turbidity reduction testing
- Perform filtration with a known contaminant loading.
- Assess reduction of turbidity over five volumetric turnovers.
- Ensure at least a 70 percent reduction in challenge turbidity.
When criteria was being developed for alternative pre-coat medias such as perlite and cellulose, there was a concern that cellulose may not be as durable and last as long as the mineral type medias of DE and perlite. An additional cellulose–media-longevity test was developed, therefore, where two identical pre-coat filters are run in a side-by-side comparison–one is charged with DE and the other cellulose. The cellulose media must last at least as long as DE before a recharge is needed.
Requirements and uniformity
Alternate medias for sand type filters, such as glass and zeolite, must also meet head loss, cleanability and turbidity reduction requirements mentioned above. In addition, media is certified to a particular size range and uniformity coefficient. The media also needs to demonstrate stability during backwashing cycles, requiring that media is not lost and the bed-level remains level after backwashing.
NSF Standard 50 also requires media to comply with drinking water material requirements ensuring that the media does not add any contaminants to water in excess of US EPA drinking water standards. If the media meets all of these requirements, it can be certified to NSF/ANSI Standard 50 for use in any NSF 50-certified filter designed for that application (i.e. sand-type or pre-coat filter).
The drinking water material requirements of NSF 50 that apply to any pool material in excess of 100 square inches (645 cm2) require complete traceability on materials to ensure that they are not contaminated. This restricts the use of recycled glass to only new glass that comes from a specific product manufacturer.
Companies that have filtration medias that are currently (September 2009) certified to NSF/ANSI Standard 50 include:
Purifiber – North Tonawanda, NY
Trivitro Corporation – Kent, WA
EP Minerals – Reno, NV
Harborlite – Santa Barbara, CA
Industrial Insulation Group – Brunswick, GA
Zeotech Corporation – Ft Worth, TX
A list of all pool, spa and other recreational water products that have been certified by NSF to NSF/ANSI Standard 50 can be found at: http://www.nsf.org/Certified/Pools/
About the Author
Dave Purkiss is General Manager of the Recreational Water Certification Program at NSF International. Purkiss has served NSF in a variety of technical and business functions over his 20 year career, including current additional General Manager roles in NSF’s Standard 60 and Standard 61 Certification Programs. He can be reached at 1-800-NSF-MARK or via email [email protected].