Filtration Nation: Sand Questions

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This edition of Filtration Nation examines sand filtration from different perspectives and considers its position in the ongoing three-way battle with cartridge and D.E. for market share — which continues to evolve under the traditional forces of water clarity, cost, longevity, equipment pad footprint and ease of maintenance. In drought-stricken areas of the country, water efficiency has recently been added to the criteria.

Sand filtration has long been a favorite option on commercial pools, where tremendous volumes of water pass through filtration systems and an automated backwash can keep operations simple. But on smaller residential pools, cartridge and D.E. have more attractive advantages. Even in these segments, market share continues to shift.

Contributors to this article include:

Dan Lenz, vice president and service department manager of Chicago-area builder All Season Pools & Spas
Terry Arko, water specialist at SeaKlear, a division of HaloSource, Bothell, Wash.
Mike Fowler, commercial marketing manager for Pentair Commercial, Sanford, N.C.
Jeff Boynton, sales and marketing manager at Delta UV, Gardena, Calif.

How is sand holding up compared to D.E. and Cartridge? Is there any spillover from the commercial segment?

LENZ: The trend for a dozen years in our area has been a migration away from sand (and D.E.) towards cartridge. Where commercial operators have found cartridges at home to be a benefit, they want to move their sand or D.E. systems to cartridge. Unfortunately in Illinois, this process involves a lengthy and costly permitting process from the State of Illinois Health Department, and that often causes them to keep their existing systems.

ARKO: Cartridge filters have become more popular on residential pools [compared to sand] because of efficiency (down to 10 micron). Also, they are more convenient to work with and don't require backwashing.

Commercial facilities with high water volume and velocity can be a problem for cartridge filters due to the fact that debris can be forced into the media and back into the pool. The high velocity and turnover is hard on the cartridges as well and most commercial cartridges have a six month life. The small footprint of a cartridge filter and the water savings do make them an attractive option, though.

Does sand filtration have a future — or will it be gone in 10 to 15 years due to its lack of fine particle filtration and its waste-water backwash.

Lenz: I think it will have a future, but its use will continue to decrease. There are some (few) occasions that an installation is better served with sand. If we are dealing with areas prone to a lot of airborne particulate, or in a case where animals that shed might be in the pool (We built a "dog pool" this year for a client at a doggy day care center and have built horse pools as well.), a cartridge filter can clog up quickly. Using sand in these cases is really a must.

Fowler: In my opinion, sand filtration will stick around. Sand filters are simple and easy to maintain and they last forever. Sand filters might require a few new parts over the years, but it's typical for them to work fine for 35 to 40-plus years.

Arko: I don't believe we will see sand filters go away soon, but we may see modifications to the media as we already have in the case of Zeolite and glass. Newer enhancement products and upgraded chemical treatments along with ozone or UV systems can help to lengthen the time between backwashes. Sand filters continue to be attractive because they are less expensive and fairly simple to operate. However, the micron removal rate of even high rate sand filters is only down to 25 microns.

Because of this, in a commercial facility there can still be a threat of chlorine-resistant protozoa such as Giardia and Cryptosporidium passing through the media. In the recently published Model Aquatic Health Code the CDC recommends "enhanced filtration" using a coagulant to help the sand media to pick up and capture the smaller micron particles. Since a majority of commercial facilities still rely on sand, it is imperative to incorporate the maintenance use of polymer-based clarifiers to ensure adequate removal of harmful protozoa and bacteria.

Any tips or tricks for filtration efficiency?

Lenz: When upgrading from sand to cartridge filters, ensure the filter capacity you select will require the least amount of in-season maintenance. If the filter is too small, it will have to be disassembled and cleaned too frequently. Also, choosing too small a filter for the size of an existing pump can cause damage to the new filter.

On the other hand, going too large can cause the filters within the tank to not be fully utilized. If you open the tank on a 500-sq.-ft. filter that is using a ¾-hp circulation pump, you'll often see only the lower one-half to two-thirds of the filters have actually had water flowing over them.

Fowler: When filling sand filters, be sure to use a mix of pea-gravel and sand. Having a layer of pea-gravel at the bottom gives nice spacing around the laterals so the water has an easy pathway. Also, be sure that you haven't oversized the pump for the filter. If water is pumping into the filter too fast, then the filter can't filter the water efficiently.

Boynton: Make sure the filter is properly calibrated to the pump's flow speed, and make sure the sanitizer is properly sized to the flow rate as well.

Arko: Any filter's efficiency can be improved with a simple maintenance dosing of an effective non-petroleum coagulant clarifier. Clarifiers help to keep the filter operating more efficiently and the water cleaner. Regular use of a natural based clarifier will keep filters cleaner, reduce the need for frequent backwashes and lower chemical use.


Invaders In the Sand

New antimicrobial sand seeks to kill microbes living in the sand filter bed

The goal of the recreational water industry is to provide safe, clean water for bathers. Mostly this is accomplished through the use of sanitizers that treat the water — but what about the sand filter bed? Is that a potential base of pool contamination? And if so, should it be disinfected in order to better protect bathers? U.S. Silica, a sand filter media supplier based in Frederick, Md., believes so, and has developed a product to kill microbes living in the grainy media of sand filters.

MysticBlue is pool filter sand treated to destroy microorganisms in the sand bed. Each grain is covered with a coating that eradicates algae, bacteria and pathogens in the sand filter bed, which leads to a safer, cleaner pool, according to Dale Grove, senior technical product developer at US Silica, Hagerstown, Md.

"As far as we know," he says, "we're the first company to offer this type of treatment for sand. There are cartridge filters that use media that has an antimicrobial treatment, but we believe this is the first antimicrobial treatment for sand."

Service pros with long experience using ordinary sand as a filter medium may wonder: What problem does this solve? Doesn't the chlorine/sanitizer regimen kill and oxidize microbes and pathogens in the pool?

"The sanitizer does not get all of them," responds David Weller, technology director at US Silica. "Sometimes the concentration is too high — there's just too much bacteria in the pool for the chlorine to keep up with it.

"Keep in mind, a low level of chlorine is distributed throughout the pool water; it's not added to the filter area, and at that point, once these microbes start growing, they form a biolayer over the colony, a film which protects the interior. Once you develop biofilm around the microbes, your pool water and its chemicals just divert around the colony without penetrating it. And it will just keep growing."

For evidence of the problem, Weller points to a CDC report on research done in the Atlanta metro area during 2012 summer swimming season. That summer, backwash samples were collected at 162 sand-filtered public pools. Bad actors such as Pseudomonas, Giardia, Crypto and E. Coli were detected in 58 percent of the samples.

"Basically what the CDC report talks about is the fecal matter and all sorts of nasty stuff that comes off bathers in the pool — all that comes around and collects in the filter," Weller says. "So now you have a site and source of contamination. Bacteria and microbes can grow there.

"So the thought behind this product is — beyond just removing debris, you want to have something in the filter bed than can combat bacteria and microbes. If you don't have some kind of antimicrobial treatment on the sand, bacteria will grow in the sand bed because it has a high surface area and collects everything from the pool."

Cations And Anions

Weller is clear that the development was driven by the goal of fighting bacterial growth in the sand bed, but product trials have shown an added benefit of improving filtration.

"The coating puts a cationic, or positive, charge on the outside layer of the grains of sand. Mother nature is mostly anionic, or negatively charged. And of course the opposite charges attract, and that may help it filter better," he says.

In most ways, MysticBlue is used like regular sand, except in the filter bed cleaning process. Weller cautions users not to use an anionic sand cleaner on MysticBlue because of its cationic coating.

"Otherwise, use it like you would normal sand," Weller says, "and for the normal period of time before replacement. And of course, you would continue your normal maintenance routine of backwashing to keep the sand bed clean as debris piles up."


Comments or thoughts on this article? Please e-mail [email protected].

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