Chlorine generators and supplemental sanitizers

The recreational water industry is presently observing an expansion of the number of automated biocide delivery systems as well as an increase in the number of biocides that provide supplemental sanitizer capacity. This expansion is not globally uniform. Similarly, the regulatory status of these biocides and treatments is not uniform. Below is a short summary of several systems that are widely available. 

2 Ozone. Ozone is a strong oxidizer formed by the excitation of molecular oxygen into atomic oxygen in an environment that allows it to recombine into O3. Ozone is used as an oxidant and supplemental sanitizer in both pools and especially in spas. The half-life of ozone is on the order of a few seconds (Haas, 1991). Because of the instability, it is not possible to maintain an ozone residual in the entire water column. Ozone must be used in conjunction with a primary sanitizer. Hypochlorous acid, hypobromous acid and PHMB are suitable as primary sanitizers for ozone system, although the consumption of PHMB will be increased by 25 to 50 percent (Unhoch and Vore, unpublished data). 

Ozone is an unstable pungent smelling gas. It must be generated on-site. It is water soluble at 570mg/L at 20° C. This is well above the use levels required for treating pools and spas. 

The free radicals that form upon decomposition also possess great oxidizing power and are very reactive with organics present in the pool or spa environment. Ozone will oxidize bromide ion to bromine and bromate, chloride ion to chlorine and hydrogen peroxide forming hydroxyl radicals. 

Determination of ozone residuals in water is quite difficult because of its rapid decomposition, volatility and reactivity. Most test methods available are variations of existing chlorine residual methods that are not specific for ozone. 

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