Are regenerative filters the wave of the future?

Paul Steinbach Headshot

Rage1 1109Eight enormous concrete bulkheads fill with water, then release it all at once, unleashing a surge that builds to a 9-foot-high, white-crested crescendo delighting thrill-seekers at Mt. Olympus Water & Theme Park in the Wisconsin Dells. The outdoor attraction, called Poseidon's Rage, debuted in 2007, and its popularity quickly spread beyond this resort town known as the water park capital of the world and into the YouTube universe, where video footage of the wave pool's fury circulated among thrill seekers everywhere.

As director of maintenance at Mt. Olympus, Jason Hammond's job is to prevent Poseidon's Rage from spreading Cryptosporidium's Revenge. That's why Hammond relies on four regenerative media filters to keep the pool's 1.5 million gallons of water sparkling and safe. The filters, which use perlite as the filter medium, represent a departure for Mt. Olympus, which features sand filters on all of its other water attractions.

The backwashing requirements of sand filters on a pool the size of Poseidon's Rage would be impractical, according to Hammond. "We'd have to use between 50,000 and 60,000 gallons of water a day to backwash high-rate sand filters on a 1.5 million-gallon pool," he says. "With the regenerative filters, we only use 5,000 gallons of water every two weeks."

And because water that goes down the drain carries with it all the heat and chemicals used to prepare it for use, those too must be replaced. "There's no product in the industry right now, worldwide, that has the potential benefits of this filter, whether it's ours or anybody else's," says Barry Gertz, president of Coventry, R.I.-based Neptune-Benson, which supplied the filters for Poseidon's Rage. "It all stems from the fact that this filter eliminates about 90 percent of the wastewater associated with sand filters - hundreds of millions of gallons of water a year."

Although this type of filtration system is the exclusive province of large commercial operations today, the same was once said of controls, advanced lighting systems, alternative sanitization methods and many other staples of the modern backyard pool.

Once a new technology is proven at the commercial level, it is often just a matter of time before it is adapted on a smaller scale. This is especially true of advancements, like regenerative filters, that save energy and resources.

Another benefit of regenerative filters - which utilize as a precoat media either perlite (fine, irregularly shaped particles formed by subjecting solid siliceous rock to extreme heat) or D.E. - is space savings relative to sand. In a large commercial equipment room, sand filters may take up to six times the floor space needed to achieve the performance of a single 60-inch-diameter regenerative filter.

Within that compact footprint are housed several hundred to several thousand finger-like flex tubes - stainless steel coils covered in a polyester braid mesh - that hang down from a tube sheet to serve as the regenerative filter's septa. The filter media is drawn from 25- or 50-pound bags through a hose and into the filter tank using a built-in vacuum-transfer system. When water pressure is introduced to the tank, the powder coats the tubes and grabs hold of contaminants as pool water circulates through at flow rates that may range from 85 to 2,800 gallons per minute. Because the filters operate primarily on the premise of surface-area filtration, as opposed to the depth filtration required of sand filters, pumps don't need to work as hard to maintain desired flow rates.

"That translates into pumping efficiency with respect to the electrical requirements of the pump," says Ken Bergstrom, president of Wayne, N.J.-based Filtrex. "Whereas a 25-horsepower pump might be necessary on a sand filter," adds Gertz, "we get away with a 20-horsepower pump. A sand filter is typically designed to handle 15 gallons of water a minute through every square foot of filter area. With our filter, it's about 1.2 to 1.5. It's going through at one-tenth the speed." And, Gertz adds, water in a regenerative filter is exposed to roughly 10 times the amount of media surface area as in a sand filter.

Where does the "regenerative" part come in? To expose the maximum amount of surface area of the chosen media - be it perlite or D.E. - the filters go through periodic "bump" modes, during which the water pressure is shut off and the dirty media is mechanically shaken off the septa tubes and into the bottom of the tank, where it is broken down and stirred up. When pressure is reintroduced via a closed loop that temporarily bypasses the pool's recirculation system, the same media, as well as the particulate matter it has captured so far, is forced to reattach to the septa tubes in an entirely different configuration as before. This is what differentiates regenerative filters from other precoat filters, which use the same media types, but in only one manual application at a time before the media becomes saturated with debris and requires replacement. (Turning the pump off and back on again will cause the media in these so-called static cake filters to drop and then reapply, but not necessarily in an even coat.) "The key is exposing new surface area," Bergstrom says. "We can use 90 to 95 percent of the total dirt-holding capacity of the media, as opposed to just the outer 10 percent."

The natural dirt-holding capacity of the types of microscopic media used in regenerative filters deserves a closer look. Research presented at the World Aquatic Health Conference in Cincinnati two years ago reveals that both D.E. and perlite, when tested repeatedly under ideal precoat filtration conditions, remove on average more than 99 percent of elusive and potentially deadly Cryptosporidium oocysts in a single pass.

Meanwhile, sand filtration, still the most widely used method of recreational water treatment, removed 31.3 percent of Crypto on average. Adding a maintenance-level dose of clarifier improved sand's performance, but the enhanced filtration conditions still only reached a Crypto-capture success rate of 61.1 percent. More comprehensive testing with pool clarifier products is being planned for the near future, according to University of North Carolina at Charlotte engineering professor James Amburgey, who conducted the tests.

This ability to capture Crypto, along with the enormous savings in terms of water, chemicals and energy, has allowed the system to capture market-share, as well.

Bergstrom, whose company stopped selling sand filters in the early 1970s, estimates that five percent of recreational water is currently treated using regenerative filtration. But given the fact that Filtrex's business doubled in the past year alone, he expects that number to expand rapidly in the near future.

"I think the real driver here is water quality," says Scot Hunsaker, president of St. Louis-based aquatics consultancy Counsilman-Hunsaker. Water has to be cleaner than it used to be, he says, "and we can do it with sand, but it takes more sand filters and lowering the flow rates and using polymers. We can trick out these filters to try to do the best we can, or we can look at a different filter medium that does it by its very nature."

The technology is continuing to develop, and like crystal clear pools a hot summer day, the regenerative filter market is becoming more crowded. In February 2008, Nemato Corp. of Whitney, Ont., through a licensing agreement with the Atlas Filter Company of South Africa, released a filter that employs rigid, more widely spaced septa, fiberglass components and a hydraulic pulse regeneration cycle that (similar to a traditional backwash, but without the water loss) dislodges the media by reversing flow through the septa as opposed to physically bumping them - all of which simplifies operation while stretching six filter runs across a calendar year, according to Nemato president Steve Andrews.

But for all their advantages, there are some tradeoffs associated with regenerative filters. Unlike sand, which as a medium doesn't require replacement en masse for years at a time, perlite and D.E. represent an ongoing operational expense. Hammond, for example, goes through 22 25-pound bags of perlite every two weeks, when it comes time to drain his four Poseidon's Rage filter tanks of their water and media contents. "They keep the water crystal clear, but the downside is the maintenance on them," says Hammond, who has trimmed the perlite replacement process from 10 hours to four in the time since the filters were installed. Says Hunsaker, " 'Regenerative' sounds like you get to keep on reusing the media, but you are basically just extending the filter run. You're putting off the inevitable of flushing that media down the drain and replacing it."

Flushing D.E. down the drain can be a bit tricky. Since it doesn't decompose (it's already millions of years old), local ordinances often require that used D.E. be strained, bagged and disposed of. And then there are the perceived health risks to the D.E. handler brought on by airborne crystalline silica. "There has never been a single case of cancer or death attributed to D.E. in the aquatics industry, and we've been using it since 1943," says Bergstrom, who adds that a filter serving a heavy bather load may require 100 pounds of D.E. to start, four to six regenerations a day and complete media replacement once a month. "I'm not going to try to scare off an operator from using D.E. - to take a one-in-three-trillion chance that he might get a whiff of D.E. and have it cause some lung problems, and trade that for the health of the bathers in the pool. You're still going to need sanitization and good operator training, but D.E. can provide a significant additional layer of protection for the health of the bathing public."

"We felt that the positives outweighed the negatives," says Hersheypark's Grubb. "We handle hazardous materials in other areas, as well, so it's just one more thing for which we have to follow the proper procedures."

Even perlite is classified as a nuisance dust, and EP Minerals' packaging recommends wearing a dust mask when working with either perlite or D.E. Says Walsh, "To put it in perspective, you are exposed to as much crystalline silica in the air at the beach on a windy day as you are when handling D.E."

Ongoing maintenance costs (not to mention an initial investment that may be substantially greater than with other filtration modalities) are more than offset by lifecycle savings, according to Bergstrom. "If you look at the amortization schedule on typical regenerative filtration versus sand filtration, you can recoup those costs, providing you take such typical energy-saving measures as installing a variable-speed pump," he says.

At the same time, as with any maturing technology, even initial investment costs are poised to come down. "It's happening as we speak," Gertz says. "We used to have 30 different models. Now we're down to five. Our repeatability in manufacturing is bringing these prices down, and we expect that to continue."

Not surprisingly, those supplying the recreational aquatics market with regenerative filters and media see regenerative media filtration as the industry's future. "I believe it is," says EP Minerals' Walsh. "Neptune-Benson believes it is. Filtrex believes it is."

Others do, too. "I think regenerative media filtration is going to continue to be a sought-after solution for improving water quality and minimizing operating costs," Hunsaker says. "And I think we're still seeing the first generations of this. We're going to continue to see this technology refined. We're going to see costs come down and performance go up."

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

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