Advanced oxidation provides alternative to chemical disinfection in pools
Swimming is a safe and effective way to get exercise. It builds endurance, improves circulation and increases muscular flexibility and balance. Beneficial at any age, swimming burns more calories than jogging. In long-term studies, children who swim frequently have been shown to become active, healthy adults.
Over the past decade, however, an increase in pool chemical exposures has sent thousands of swimmers to emergency rooms each year. According to the Centers for Disease Control and Prevention, in some cases these hospital visits are tied to chlorine overuse and the formation of toxic compounds known as disinfection byproducts (DBPs). DBPs can lead to potentially life-threatening elements, even when the water looks safe.
A properly designed and chlorinated swimming pool should keep the water free of harmful bacteria and provide a safe environment for exercise and recreation, especially with high bather and organic loading conditions. Pools of the 21st century must have the capacity to quickly prevent the potential dangers of pool water chemistry and create a healthy swimming experience.
Furthermore, swimming pools should not be a burden on the natural or built environment. Discharging large quantities of water with a high chemical load into the water supply should be avoided. Advanced oxidation now is available to minimize the health and environmental risks of traditional chlorinated pools.
With the abundance of sanitation chemicals available on the market, it is no wonder there is confusion about which is best. While creating a safe and sanitary swimming environment is important, maintaining or minimizing toxic byproducts always has been an industry concern. This has led to a continual search for solutions to effectively lower chemical use and eliminate DBPs. Advanced oxidation processes (AOPs) can help resolve these concerns.
Stemming from the industrial water treatment sector, AOPs are systems with the ability to create large quantities of hydroxyl radicals to treat organic contaminants and microorganisms on contact in water. While popular, AOP systems, such as ozone systems, have economical limitations in scaling to certain flow rates or pool volumes. Other systems, such as a combination of ozone and ultraviolet (UV) light, which involves passing ozone in front of a UV bulb, also have had success, but electrical and maintenance costs have limited deployment in the pool sector. UV treatment alone 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, offer economical and scalable approaches to hydroxyl radical creation through photolysis of oxygen directly into monoatomic oxygen and hydroxyl radicals.
In addition to large a large hydroxyl radical output, direct hydroxyl conversion creates a low level of hydrogen peroxide on site to provide a safe and effective level of residual protection in the pool. This byproduct, at a concentration of 1 to 3 ppm, replaces daily chlorination in residential pools and the need to manually add chlorine.
A Danger in Disguise
The well-known odor of chlorinated pools is a danger in disguise. DBPs are associated with the chlorine smell and are created by the interaction between free chlorine and swimmer-introduced compounds like urine, saliva, sweat, lotions, cosmetics and dirt. Chloramines, trihalomethanes (THMs) and haloacetic acids (HAAs) are three categories of well-documented and much-studied DBPs. They are directly linked to negative health impacts in humans and can cause eye and lung irritation. 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 pools.
The U.S. Environmental Protection Agency regulates a maximum level of 80 ppb of THMs in drinking water. AOPs minimize the risks associated with DBPs by oxidizing them and treating water to drinking quality. The advantage of creating hydroxyl radicals via direct hydroxyl conversion translates to higher reaction and removal efficiencies. The hydroxyl radical rate constant with monocholoramine, for example, is 10 million times that of monochloramine with ozone.
Saltwater pools could be called by another name: chlorinated pools. It is a myth that saltwater pools are chlorine-free. Sodium chloride is manually added to the body of water at roughly 10% of the concentration found in the ocean, approximately 3,000 ppm. A saltwater chlorinator is installed in-line after the pool heater to create chlorine gas from available chloride, hydrogen gas and sodium hydroxide to produce hypochlorous acid (HClO). The chlorine found in a saltwater pool is chemically identical to chlorine delivered by normal pool chlorination methods such as bleach or chlorine tabs (calcium hypochlorite or trichlor). This creation of chlorine can result in the formation of DBPs such as chloramines, THMs and HAAs. Furthermore, salt is corrosive and can irreversibly damage pool surfaces and materials.
Natural and man-made environmental wetlands and ecosystems are sensitive to small fluctuations in chemicals and salt. Municipalities with wastewater treatment plants must protect themselves from anthropogenic influxes and discharges of water with high salt.
Even at 10% the concentration of seawater, saltwater pools have the capacity to wreak havoc on sensitive biological systems when discharged into the environment. It is critical that water drained from saltwater pools is done in a manner that does not harm complex biological systems. In practice, this has been a challenge across the country. Some states have begun regulating salt discharge limits to avoid costly upgrades to municipal wastewater treatment plants, while others are still searching for solutions. Current regulations dictate saltwater pools be drained into sewer clean-out drains to avoid river discharge, but compliance is limited.
Through the use of advanced oxidation, modern swimming pools can conserve water and avoid damaging the environment. Water lifespan is lengthened through less dilution and discharge water quality is improved. The inevitable discharge of water treated with advanced oxidation into the open environment is better for wastewater treatment plants and the environment because the process does not require large amounts of salt or chemicals. The process creates savings for wastewater treatment plants and preserves natural wetlands and rivers near populated areas.