Water Conditioning & Purification Magazine

Swimming Pools of the 21st Century: Advanced Oxidation

By Nick Rancis

Crystal clear and safe water is, without a doubt, the primary objective for all swimming pool owners and operators. Swimming is one of the healthiest forms of exercise and an easy way to stay in shape. A properly designed and chlorinated swimming pool can not only keep the water free of harmful bacteria, but provide a safe environment for kids during hot summer months and especially at high bather and organic loading conditions.

At the same time, pool chemical exposures have sent thousands of swimming patrons and staff to the emergency room each year for treatment. High levels of chlorine coupled with a high bather load lead to a breeding ground for toxic chemical compounds known as disinfection byproducts (DBPs). DBPs give way to dangerous and potentially life-threatening situations, even when pool water looks safe. Furthermore, swimming pools should not be a burden on the natural or built environment. Discharging large quantities of water with a high chemical load should not be a frequent occurrence and should be minimized at all costs.

Pools of the 21st century must have the capacity to prevent these potential dangers of pool water chemistry quickly and effectively in order to truly create a healthy swimming experience for all. New advanced oxidation pool technologies help to minimize these health and environmental risks of a traditional chlorinated pool and are now commercially available.

Advanced oxidation

With the abundance of sanitation chemicals available on the market, it is no wonder that there is confusion about which is best, since few are created equal. While the most important factor is creating a safe and sanitary swimming environment, maintaining or minimizing the amount of toxic byproducts has been an industry concern for nearly a century. This has led to a continual search for solutions that deliver an effective means to lower chemical use and eliminate DBPs. Advanced oxidation processes (AOPs) are a key solution to meet this objective.

Initially created for the industrial, municipal and drinking water treatment markets, AOPs are, by definition, systems that produce large quantities of hydroxyl radicals (OH*) for treating water. Hydroxyl radicals are a potent, broad-spectrum, extremely short-lived oxidative species that oxidize and remove waterborne contaminants quicker and more completely than other water treatment methods (i.e., chlorine or UV). Typically, in the pool and spa space, hydroxyl radicals will chemically degrade oils, sweat, bacteria, viruses and toxic byproducts created by traditional chlorination or bromination disinfection processes. They will destroy microorganisms like Cryptosporidium parvum that are resistant to chlorine and bromine at concentrations typically found in pools and spas.

AOP systems, such as ozone, have been popular, although they have had limitations in economically scaling to certain flowrates or pool volumes. Other systems, such as a combination of ozone passed in front of a UV bulb, have also had success but electrical and maintenance costs have limited these products’ deployment in the pool sector. UV treatment on its own does not extensively oxidize organic matter commonly found in commercial swimming pools and thus is not classified as an AOP. Newer technologies, such as direct hydroxyl conversion discussed in this article, have brought to market an economical and scalable approach to hydroxyl radical creation through photolysis of oxygen directly into monoatomic oxygen and hydroxyl radicals. (This unique advantage of creating hydroxyl radicals via direct hydroxyl conversion translates into higher reaction and removal efficiencies compared to existing commercially available options. Hydroxyl radical rate constants with monocholoramine, for example, is 10,000,000 times that of monochloramine with ozone.)

Figure 1. Reduction of DBPs

Figure 1. Reduction of DBPs

Disinfection byproducts

Although chlorination of recreational water provides protection from most pathogenic aquatic microorganisms, there is a growing concern of human exposure to chlorinated DBPs created in these facilities. Initially proposed in 1953, numerous clinical studies have documented physiological ailments (i.e., lifeguard lung and asthma) among swimmers, especially in indoor swimming environments. These DBPs are created from the interaction between free chlorine and swimmer-introduced compounds (such as urine, saliva, skin sweat, lotions, etc); they are commonly associated with the chlorine smell and the cause of eye and lung irritation. Trihalomethanes (THMs) and haloacetic acids (HAAs) are two categories of well-documented and much-studied DBPs directly linked to negative health impacts in humans. DBPs can be absorbed by the body through inhalation, dermal contact and oral ingestion. (Numerous studies have shown an increase of DBP levels in human urine, sweat and blood from swimmers before and after swimming in commercial swimming pools.)

Figure 2. Advanced oxidation turned off—disinfection byproduct buildup

Figure 2. Advanced oxidation turned off—disinfection byproduct buildup

AOPs have shown to have a dramatic effect on reducing waterborne levels of THMs and HAAs. Chloroform, a type of THM, is of particular interest due to its known carcinogenic properties. Although not regulated in the US pool domain, US EPA regulates a maximum level of 80 ppb in drinking water THM levels. AOPs help minimize the risks associated with DBPs by actually oxidizing them away, treating water back to drinking-water quality. Figure 1 illustrates its success at doing so at a local 185,000-gallon indoor, commercial pool.

Interestingly enough, the corollary is also true of AOPs effect on DBPs when the system was turned off at the same pool. The data set in Figure 2 highlights the pool’s capacity to build up DPBs when the system was turned off. This build-up of HAA clearly shows two-times the surge in concentration when the system is turned off, which demonstrates the immediate benefit of supplementary, advanced oxidation protection from these byproducts.

Figure 3. Chlorine dynamics with and without advanced oxidation

Figure 3. Chlorine dynamics with and without advanced oxidation

Chlorine dynamics with advanced oxidation

High bather loads coupled with traditional chlorination systems have the potential to expose swimmers to highly fluctuating concentrations of chlorine. Typically, after a large loading event (such as a swim class or swim meet), a strong influx of chlorine will compensate for this bather load. Commercial swimming pools of the 21st century should not only be able to protect swimmers from these high and low ranges of chlorine use, but they should also be able to use chlorine more efficiently during such events.

Advanced oxidation is a proven technology at the pool scale to minimize the range of chlorine fluctuation 60 to 90 percent. Figure 3 shows data collected from a YMCA over the course of a year. The study is broken down into three parts:

  • Before AOP (direct hydroxyl conversion) system: chlorine maintained in between 0.5 and 5.0 mg/L
  • Phase I: After AOP (direct hydroxyl conversion): chlorine maintained between 0.5 and 3.0 mg/L
  • Phase II: After AOP (direct hydroxyl conversion) ORP set-point lowered to code minimum

The chlorine concentration before the installation of the AOP system ranged between 0.5 mg/L to 5 mg/L, with a standard deviation of 1.08mg/L. After installation, an immediate 60-percent decrease in the range of pool chlorine was observed. After day 111, a measured 88-percent reduction in the fluctuation of chlorine was observed, with a standard deviation of 0.13mg/L, coupled by an immediate 70-percent reduction in chlorine use at the facility. By maintaining tighter management of chlorine concentration, the system reduced the instability of chlorine levels during or after high bather loads. (Periodic oscillations in pool chlorine level will not only increase chlorine usage, but continually expose patrons and staff to higher than normal chlorine, chloramines and disinfection byproducts in both water and air.)

Environmental effects

Natural and man-made environmental wetlands and ecosystems are highly sensitive to even small fluctuations in chemicals and salt. Municipalities in wastewater treatment plants must protect themselves from anthropogenic influxes and discharges of water high in salt. Even at 10-percent concentration of seawater, saltwater pools have the capacity to wreak havoc on these highly sensitive biological systems, when discharged into the open environment. It is critical that water drained from saltwater pools is done in a manner that does not harm these complex biological systems. In practice, this has been a challenge for counties and states all across the country. Some states are beginning to regulate salt discharge limits to avoid costly upgrades to municipal wastewater treatment plants, while others are still searching for a better solution. Current regulations dictate saltwater pools be drained into sewer clean-out drains to avoid river discharge, but have had limited compliance.

Through the use of advanced oxidation, modern swimming pools can help conserve water and not burden the built and natural environment. Water lifespan is lengthened (through less dilution) and discharge water quality is greatly improved. By not requiring large quantities of salt or other chemicals, the inevitable discharge of water (treated with advanced oxidation) into the open environment is significantly better for wastewater treatment plants and the natural environment alike. If extrapolated to the millions of gallons of chemical-laden saltwater that are discharged, this translates into tremendous savings in wastewater treatment plant upgrades and preservation of natural wetlands and rivers near populated areas.

Conclusion

Advanced oxidation technology can help outdated, traditionally chlorinated or salt-chlorinated pools meet the demands of the 21st century. By helping to greatly reduce the amount of DBPs, advanced oxidation promotes a healthier swimming experience for swimmers and staff alike. Advanced oxidation also offers tighter control over the chlorine that is added to prevent large chlorine concentration swings, which can be harmful to patrons of the pool. This better control also leads to a dramatic reduction in chlorine usage. Furthermore, advanced oxidation helps to minimize the impact that traditionally chlorinated and salt-chlorinated pools have on both man-made and natural environments.

About the author

Nick Rancis, Chief Water Officer and co-Founder of Clear Comfort, is an accomplished microbiologist with more than a decade of experience in water technology, industrial microbiology, resource efficiency and technology transfer into the marketplace from universities and national labs. Rancis holds a BS in microbiology from Colorado State University and is the inventor and collaborator for seven issued patents. In addition, he has led resource recovery and microbial bioprospecting expeditions in extreme environments. A frequent speaker in the pool industry, university technology and startup accelerator spheres, Rancis is a leader in the water energy nexus and business strategy.

About the company

Clear Comfort manufactures and sells chlorine-free and low-chlorine pool and spa disinfection systems, inspired by the way our atmosphere cleans our air to bring you a clean, healthy pool without toxic chemicals. With headquarters and manufacturing in Colorado, Clear Comfort products are sustainable and US-made. The company provides an ideal solution for pool owners and aquatics facilities seeking to reduce chemicals and decrease pool system maintenance. For more information, visit www.clearcomfort.com.

About the product

Clear Comfort’s advanced oxidation technology produces powerful hydroxyl radicals that destroy contaminants on contact, including toxic DBPs commonly found in commercial swimming pools. The system also brings chlorine levels down to drinking-water levels and can reduce chlorine use by as much as 70 percent. This equates to several benefits for clients’ pools, including a reduction in chemical usage and exposure; a reduction in energy consumption and operational expense; a reduction in associated pool odors and irritants; and an improvement in air and water quality.

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