found that when UV and Ozone are reacted together with E. coli, they achieve a 3-log reduction or 99.9 percent inactivation — far more than the sum of the contributions of each disinfectant.

A 2008 study by Cho et al. looked at the effect of hydroxyl radicals against cryptosporidium. It was found that the hydroxyl radical is 104 to 107 more effective against crypto than other popular disinfectants such as ozone, chlorine dioxide, or free chlorine.

Advanced Oxidation Processes are not only superior when it comes to disinfection and sanitation but also in terms of oxidation. Not only do hydroxyl radicals react quickly with natural organic matter, they have also been shown to reduce chlorine’s disinfection byproducts such as trihalomethane and haloacetic acid.

A 2005 study called “Removal of Disinfection By-products Precursors with Ozone-UV Advanced Oxidation Process” reported that the process was able to remove 50 percent of the total organic carbon at typical ozone/UV doses. The same doses were shown to reduce trihalomethane formation by 80 percent and haloacetic acid formation by 70 percent.

These effects are still being studied. The end products of complete oxidation of AOP are carbon dioxide and water.

But oxidation does not always go to completion, and the process can itself lead to disinfection byproducts, depending on the contaminant in the water.

AOP are referred to in the plural form because there are several ways to achieve hydroxyl radicals. The most common ways are to mix UV with ozone, UV with hydrogen peroxide, or hydrogen peroxide with ozone.

Many of the manufacturers for pool and spa units use the ozone/ UV process. However, the way that each manufacturer produces the ozone also varies from company to company.