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The use of Ozone to disinfect swimming pools and spas has been a practice in Europe for over 50 years. With more than 500 Ozone treated pools, the European Community (EC) now considers Ozone treatment a standard method of pool disinfection. Some countries require mandatory compliance with the German Din. 19643, a comprehensive codes standard that covers all aspects of pool design and water quality including the use of Ozone for disinfection. Other countries, such as England, have established their own standards concerning the treatment of pool water. The British Effluent and Water Association (BEWA), for example, has established a "Code of Practice" that details the design and use of Ozone water treatment systems for swimming pools. California and Oregon provide guidelines on the treatment of swimming pools with Ozone. Currently, however, there is no comprehensive standard on the design and use of ozone in swimming pools within the U.S.
Over the past five years, the U.S. pool and spa industry has become increasingly interested in using ozone as a supplemental disinfectant to traditional chlorine and bromine-based water treatment. The high bather loads of large, recreational water parks have challenged traditional chemical treatment systems in providing exceptional water clarity with minimum chlorine odor and bather discomfort. Adding fire to this interest is the recent press given to the chlorine resistant, pathogenic parasites (Cryptosporidium parvum) and bacteria (Legionella pneumophila) that exist within many of our communities municipal water systems.
Today, most of the large commercial pool designs include Ozonation system as an integral part of the pool's water treatment system. However, ozone treatment approach can vary widely in design and effectiveness. A good design approach is to model the ozone treatment system after other successful operating systems, keeping in mind your water quality goals and the differences as well as the similarities between your pool and the ozone treated pools you are studying. These differences may include pool location water temperature, water quality and bather load. When an ozone treatment program is properly designed, it should provide some or all of the following benefits:
Reduced Chemical Usage
When ozone is properly applied it can demonstrate chemical savings in two ways. First, if ozone is sized and integrated into the treatment system properly, it will act as the primary oxidizer and disinfectant. This reduces the amount of chemical (chlorine or bromine) needed to maintain the free halogen residual required by state law. Second, when ozone is used in conjunction with sodium bromide, it has the potential to regenerate spent bromine, thus reducing the sodium bromide feed rate. Some facilities that use ozone and sodium bromide in this manner have reported up to a 60 percent reduction in chemical usage.
Ozone has been shown to be a superior disinfectant to chlorine or chlorine-bromine treatments still used in many U.S. pools and spas. Studies conducted under the guidance of Dr. Eugene Rice. USEPA Office of Drinking Water Standards, show that the C.T value [(Disinfectant concentration in mg/L) X (Contact time of disinfectant with water)] of free chlorine for 99 percent inactivation of the Cryptosporidium oocyst is 7,200, while ozone shows a much lower C.T value of 5-10. Ozone's reaction against fecal coliforms is even more dramatic. Strains of E. Coli bacteria exposed to a 0.1 mg/L residual of ozone are destroyed in less than 12 seconds.
To achieve disinfection in a swimming pool application, an applied ozone dosage of 0.8 to 1.6 mg/L is usually sufficient to provide effective ozone residual for inactivation of microbes and conversion of residual disinfectants. The actual dosage and contact time required to generate a disinfecting residual will depend upon the water quality and whether the pool is utilizing chlorine or bromine to provide a residual pool disinfectant. A minimum contact time of two minutes is usually sufficient for microbe inactivation and disinfectant conversion.
Enhanced Bather Comfort
The addition of ozone to a swimming pool treatment system has a dramatic effect on bather comfort. Compared to chlorine treated pools, ozone fed pools are far ahead of chlorine injection and dramatically reduces chemical consumption by destroying many of the organics and microorganisms that react with chlorine. The lower chlorine demand allows the pool operator to achieve disinfection with minimal chlorine residual, thus reducing the strong chlorine odor associated with indoor pools and minimizing the amount of chlorine off-gas-which may cause considerable corrosion in swimming pool environments. When ozone is applied, a free chlorine residual of 0.4 ppm is usually sufficient to maintain water quality. When oxidizing organic material, if dosage and contact time are sufficient, ozone will also break down chloramines- a major cause of pool odors and bather discomfort- into nitrites and chlorides as shown below :
NH2Cl + 3O3 ==> 2H+ + NO3 + Cl-
Today, many pools and spas have turned to bromine as an alternate disinfectant to chlorine because it is less irritating to the bathers' skin and has a longer half-life than chlorine, and can be continually oxidized back to its disinfecting form- hypobromous acid, after it has combined with pool organics. When ozone and sodium bromide are initially placed together in water at a pH above 7.0 the bromide ion is oxidized to form the hypobromite ion, which quickly disassociates in a manner similar to chlorine, forming hypobromous acid in equilibrium with hypobromite ions.
HOBr + H2O ==> (OBr) + (H3O) +
At a typical swimming pool pH of 7.2 - 7.8, this equilibrium is to the left, providing sufficient hypobromous acid to react with microorganisms and contaminants. As hypobromous acid oxidizes the organic pollutants, the bromine is reduced to bromide ions. Ozone continually oxidizes these bromide ions back to by pobromite ions. (OBr), which disassociate to form hypobromous acid. HOBr / (OBr) + Organic pollutants ==> Br-
Br- + O3 ==> (OBr)-
(OBr)- + (H3O) + HOBr + H2O
Another example of ozone's ability to reactivate expended bromine is its oxidation of the monobromamines, which are formed when bromine combines with urea and other nitrogen compounds. The rapid oxidation of these amines into nitrites and bromide ions (Five times the reaction rate of ozone and chloramines) is followed by the further oxidation of the bromide ions to form hypobromous and hypobromite ions (shown below)
NH2Br + O3 ==> NO3 + Br -
Br - + O3 ==> HOBr + (OH)-
This continual oxidation of the reacted bromide ion back to hypobromous acid is one reason a bromine ozone treatment system is considered one of the most cost effective ways to treat large recreational pools.
Exceptional Water Quality
When Ozone is applied to water, a side benefit is an improvement in water clarity. A phenomenon called micro flocculation occurs - a process in which some of the organic contaminants form a pin floc that can easily be removed by an ozone resistant sand filter. Large, commercial pools with high bather loads often rely on the microflocculation, benefit of Ozone to reduce their dependence on chemical filter aids. The exact dosage of ozone required to generate the pin floc will depend on the water quality and the nature of the water's contaminants. If you are considering adding ozone to an existing pool or spa or perhaps adding it to an existing design for a new facility, it is important to realize that ozone, by itself, is not a panacea for a poorly designed system. Good filtration efficiency, adequate pool turnover rates, good pool hydraulics and proper water chemistry are essential to achieve the benefits promised by ozone Though no nationwide standards for ozone have been implemented, there are some basic safety guidelines proposed by the USEPA as noted below :
Ozone Health And Safety
With the increasing regulatory emphasis on safety and environmental friendly water treatment of swimming pool and spa, industry has growing need for exceptional water quality, the use of ozone as an integral part of the water treatment will continue to grow. Keep in mind that the lack of firm guidelines in the United States has resulted in the installation of a variety of ozone treatment systems with varying degrees of success. If you are interested in pursuing an ozone treatment system for your facility, it is always recommended you select a design team as well as an ozone equipment manufacturer from those firms who possess a long history of successful ozone applications. These companies will be able to provide the technical support and service you want today and will be around when you look for service in the years ahead.
Advantages Of Using Ozone For Swimming Pools And Spas