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Avoiding Recreational Water Illness Outbreaks

By Terry Arko

Enhanced Filtration

One viable and more affordable method that any aquatic facility can begin using immediately is enhanced filtration. The CDC and many aquatic experts have long considered filter enhancement with the use of specialty clarifiers as another preventive method. This technology uses two opposing biopolymers that quickly and effectively entrap micro-organisms such as E. coli and Crypto.

This method has been proven through an independent study conducted at Auburn University, which was presented at the World Aquatic Health Conference (WAHC) in 2005. The study showed very stable flocs of Crypto were able to form and be held in simulated sand filters. According to a presentation on "Cryptosporidium Removal from Swimming Pools by Sand Filters" by James Amburgey, Ph.D., an associate professor at the University of North Carolina at Charlotte, at the 2006 WAHC, there was a 99.99 percent removal of Crypto from pool water using sand filtration treated with the two-stage polymer.

There is a great deal of complicated physics going on in a depth filter, such as the sand bed, as it traps particulates suspended in the incoming water. Other influences include surface charge, particle size, conformation, rigidity, density and so on, on the nature of the path taken by the particles, and the frequency of their collisions and interactions with the filter medium. However, it is simple enough to understand the overall outcome: Smaller particles tend to make it through the bed and come out in the effluent, whereas the larger particles stand a greater chance of becoming stuck and trapped along the route.

Of course, all those retained particles alter the total amount of path available within the filter bed for the next influx of water. On the other hand, the filters should be periodically backwashed, which will restore the pathway for future entrapment. In this way, properly maintained depth filters do a fine job of keeping pool water free of much of the undesirable bits and pieces that become suspended in the media during normal use.

Giving pool filters the ability to trap more is the idea behind enhanced filtration products.

Enabling filter media to remove particles that were in the submicron range allows for the removal of microbial organisms. The most troublesome of those measure only a few microns or even less, and therefore routinely pass through filters with the flow of water.

Molecular weight, shape and charge, as well as absolute and relative concentrations of the biopolymers, plus timing of exposure, all turned out to be critical factors. Data from laboratory experiments conducted at Auburn University showed with the proper polymer treatment, inert particles (in this case, bentonite clay) could be flocculated into larger clumps, enabling many of the resulting aggregates to be removed in a single filter bed pass. Later experiments involving biological, as well as other inert particle types showed similar success, even to the extent suspensions of live Crypto cysts could be removed at a rate of 99.9 percent in a single pass through sand.

Accomplishing this required sequential treatment of pool water with two differently acting biopolymers—one charged positively, the other negatively. Using the right proportions and concentrations, this could be achieved reliably and repeatedly.

Here Is How It Works

Polymer molecules from stage one alter surface charges on small particles in the water, destabilizing the normal tendency they have to repel one another (and therefore keep separate, and fully suspended, indefinitely). The particles aggregate and become enmeshed in the lattice of long, cross-linked polymer molecules to form much bigger clumps. If the concentration of the cationic (positively charged) polymer is too low or high, this will not occur. Stage two polymers (negatively charged) then entangle the complexes, firming them up so they can withstand being trapped in the filter bed, until the filter is backwashed, removing them to waste.

The net effect is Crypto cysts, normally able to pass through sand bed and other particulate filter media, become trapped as cyst-polymer complexes and are removed. Crypto is not the only biological agent that can be trapped in this manner; other waterborne microbes (e.g. Giardia, E. coli) are similarly affected.

Stage one and two polymers can be used while bathers are present. With particle removal possible at the submicron level, overall water clarity also improves. This gives sand filters the ability to trap minute particles, and offers aquatic facility managers a new way to fight RWIs while improving water clarity.

Polymer additions for large pools can be accomplished by controlled metering, but a properly timed manual process is also entirely practical for smaller scale operations.

A Real-Life Example

Elise Knox, an aquatic facility operator in the Dallas/Fort Worth, Texas, region, along with a staffer, attended a CDC state aquatics seminar in an effort to be prepared with a plan to avoid a Crypto outbreak, and that she did when her area was hit hard with an outbreak in 2007.

"We knew we couldn't budget for UV filters in all of our pools, but we needed to prepare because an area-wide outbreak would be sure to affect us," Knox said. "In this case, we decided to use the enhanced filtration method. We were the first pool in the area to use it, in fact.

"We have used this method now for more than seven summers, and we've had the side benefit of excellent water clarity."

According to Knox, when the outbreak occurred, they hyper-chlorinated the pool water as per CDC recommendations. "Chlorine is not the be-all-and-end-all solution; it's a clean-right-now solution only," said Knox. "I like to compare hyper-chlorinating to washing a doorknob during flu season. The next person that comes along and sneezes on your doorknob, it's back to the same mess."

This facility's Crypto prevention plan also included methods to help keep it from entering pool water with the following: On weekdays, when children are most likely to come to the pool alone, a mandated restroom/hydration break at 3 and 5 p.m., was established. Every child age 7 through 17 is required to exit the pool for 30 minutes and are encouraged to stop at the water fountain for a drink and strongly encouraged to use the restroom (so they do not go in the pool). The facility also established a website for patrons to read about its prevention methods, as well as provide informative links on CDC's website.

"We've always concentrated on 'low tech' methods, but this really showed our staff why we actively work to enforce the 'shower before swimming' and 'no spitting or spouting' rules," Knox said. "We also displayed clever signs and funny posters the CDC has on their website for our facilities, reinforcing these same rules.

"In the end, our patrons actually thanked us for enforcing the rules. It was amazing how supportive our patrons became as we explained why we had breaks and required showers."

A Continuing Challenge

RWIs, especially Crypto, continue to be a major challenge for pool professionals. New water treatment technology and multiple water maintenance procedures are key to maintaining healthy water in aquatic facilities. These layers will include a residual of chlorine sanitizer, ozone or UV, regular dilution of pool water, and enhanced filtration of micro-organisms using the recommended polymer system.

Terry Arko has more than 30 years of experience in the pool and spa/hot tub industry, working in service, repair, retail sales, chemical manufacturing, customer service, sales, and product development. A certified pool operator (CPO) and CPO instructor through the National Swimming Pool Foundation (NSPF), Arko is currently a water specialist for NC Brands, parent company of SeaKlear and Natural Chemistry, which is a manufacturer of pool and spa products. For more information, visit www.ncbrands.com.