By The Pool & Hot Tub Alliance

Proper sanitation helps keep pools free of microorganisms that can lead to and cause waterborne illnesses. Traditionally, the primary source of sanitation has been a halogen (chlorine or bromine). More recently, it has been determined that halogen-tolerant pathogens, such as Cryptosporidium, require the use of an additional means to disinfect pools.

The Pool & Hot Tub Alliance (PHTA) Recreational Water Quality Committee (RWQC) compiled the following information on the differences between and uses for secondary and supplemental disinfection systems. This article focuses on the equipment for secondary or supplemental treatment systems used in commercial pools as defined by ANSI/APSP/ICC-11 American National Standard for Water Quality in Public Pools and Spas.

Secondary disinfection systems
Secondary disinfection systems are installed in addition to the required primary disinfection systems and are required for increased risk aquatic venues. These systems are designed to achieve a minimum 3-log (99.9-percent) reduction in the number of infective Cryptosporidium parvum oocysts and other pathogenic microorganisms per pass through the secondary disinfection system at the maximum flowrate. These systems shall be listed and labeled to NSF/ANSI Standard 50 Equipment for Swimming Pools, Spas, Hot Tubs and Other Recreational Water Facilities by an American National Standards Institute (ANSI)-accredited certification organization and shall be installed according to the manufacturer’s directions. When listed as an NSF-approved system, it is classified as a sanitizer.

Increased risk aquatic venues have a higher risk of microbial contamination due to their primary users being children under the age of five and/or people more susceptible to infection, such as therapy patients with open wounds. All new construction or substantial alteration of the following increased risk aquatic venues are required to use a secondary disinfection system.

•Wading pools
•Interactive water play venues
•Other aquatic venues designed primarily for children under the age of five
•Therapy pools

Secondary disinfection systems may be installed on other aquatic venues. At present, secondary disinfection systems are either ozone or UV light systems. These systems require the use of a primary disinfecting halogen, such as chlorine or bromine.

Supplemental treatment systems
Supplemental treatment systems are not required in an aquatic venue for health and safety reasons but may be used to improve water quality and/or enhance overall system performance. These systems are designed to enhance water quality but are not required to achieve the minimum 3-log reductions, unlike secondary disinfection systems. Metal ion-based systems are often used as supplemental treatment systems. Ozone or UV light systems, however, can be considered supplemental systems when they are not required at an increased risk venue. Like secondary disinfection systems, supplemental treatment systems also require the use of a primary disinfecting halogen, such as chlorine or bromine.

Ozone secondary disinfection system
An oxidation reaction occurs once ozone has been dissolved in water. Once this reaction takes place, organic contaminants are destroyed and many dissolved metals become insoluble. Ozone is capable of killing all known microorganisms (including Cyrptosporidium and Giardia), destroying organic contaminants that may create chloramines and break down existing chloramines. This oxidation occurs immediately at the ozone gas injection point and continues in the return lines. A small residual (~0.1 ppm) of dissolved ozone may enter the pool, providing further oxidation. An ozone system is considered a pesticidal device under the US EPA Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and has a US EPA establishment number. The use of secondary systems in combination with a primary halogen should be used in accordance with manufacturer’s recommendations.

UV light secondary disinfection system
UV light systems use a process known as photolysis to inactivate microorganisms (including Cryptosporidium and Giardia). The intensity of the lamp and the flowrate through the unit will produce a dosage measured in mJ/cm3. UV light is most effective at a known wavelength of 254 nm.

Ultraviolet light and ozone supplemental treatment systems
Both ozone and UV light systems can also be used as supplemental treatment systems. They enhance both water and indoor air quality. Air quality has become critical in protecting swimmers, pool attendants, spectators or anyone spending time in an indoor pool environment. Both UV light and ozone systems have been proven to be effective in destroying chloramines in swimming pools and, therefore, improve indoor air quality. Both commercial ozone and commercial UV light systems are tested and listed under NSF/ANSI Standard 50. The device must meet the requirements of NSF 50, Disinfection Efficacy in Section 14.20 and must be used with a US EPA-registered sanitizer to impart residual concentrations in accordance with federal, state or local regulations. Supplemental systems in combination with a primary halogen should be used in accordance with manufacturer’s recommendations.

Metal-based systems
While metal-based systems have been recognized as US EPA-registered sanitizer systems when used with a primary halogen, the metal ionizer component has always served as a supplemental treatment system to the halogen. When operating, maintaining or servicing a water feature, it is always important to be aware of the requirements for that particular water feature and what treatment options you have available to ensure users have a safe and healthy aquatic experience.

The health and safety of pool users should always be at the forefront of successful pool and aquatic venue operations. As our understanding of waterborne pathogens improves, our disinfection systems also improve. UV light and ozone treatments provide an additional level of protection for users when used as either secondary or supplemental disinfection systems.

The Pool & Hot Tub Alliance protects and advances the common interests of the industry by providing education, advocacy, standards development, research and market growth to increase our members’ professionalism, knowledge and profitability.


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