Ozone
When used systematically, ozone has also proven effective in recreational water treatment. Its effectiveness against chlorine-resistant organisms and ability to remove chlorinated disinfection byproducts makes it an attractive choice for supplemental sanitation and oxidation. It is commonly used in wastewater and drinking water treatment applications, as well as disinfection in commercial aquariums. Much like UV, when used as a supplemental sanitizer for recreational water, it is effective against chlorine-resistant organisms such as Cryptosporidium and Giardia.
Ozone is comprised of three oxygen atoms (O3) as illustrated in Figure 1. It is produced onsite through the use of UV energy or, more commonly, corona discharge (CD). Corona discharge is a method whereby oxygen is exposed to electrical energy causing the oxygen molecules (O2) to split. The single oxygen atoms then combine with other oxygen molecules as follows:
O2 + energy → O + O
O + O2 → O3
How it works
Ozone is a gas that is dissolved in water using a venturi injector. Once in the water, ozone decomposes to form free radicals (HO2 and OH). These species are highly reactive and can oxidize impurities such as metal salts and organic matter. It is generally believed micro-organisms are destroyed through a process called cell lysis (oxidation of the cell protoplasm resulting in disintegration of the cell wall). In addition, ozone has been found to be beneficial for the reduction of chloramines, as it reacts directly with monochloramine.
It is important to note that only the water passing through the ozone contact tank is exposed to the disinfectant. Ozone does not hold a residual in a pool; therefore, the only contaminants destroyed are those passing through the tank. In reality, it will take days (depending on flow rate) for all the water to pass through the contact tank. Therefore, ozone must be used for supplemental sanitation only; an appropriate residual of a registered sanitizer must be maintained in the pool at all times.
Ozone can be used in conjunction with bromine systems, as it will regenerate hypobromous acid from the inactive bromide ion as follows:
Br – + O3 + H+ → HOBr + O2
There are a number of ozone manufacturers and installers. Basic installation is very similar—all systems require an ozone generator, injector and air management system. Operators should follow manufacturer’s guidelines for installation, operation and maintenance.
When ozone is used for indoor installations, air monitoring is required, as ozone is considered a ground level air pollutant. The U.S. Occupational Safety and Health Administration (OSHA) has set permissible exposure limits for air contaminants. One such measure of exposure is the time weighted average (TWA). OSHA has set ozone’s TWA at 0.1 parts per million (ppm) over a period of eight hours. Specifically, the ozone concentration in air shall not exceed the eight-hour TWA in any eight-hour work shift of a 40-hour workweek.
