Disinfection by ozone takes place by rupture of the cell wall of a microorganism. This is a more effective method than chlorine which diffuses into the cell protoplasm and inactivates the enzymes. Ozone level of 0.4 ppm for 4 minutes has been shown to kill any bacteria, virus, mold and fungi. Ozone inactivates viruses on contact even at very low residual concentrations. In case of polio only 0.012 ppm removes all viruses in less than 10 seconds.
Mold and mildew are very easily controlled by ozone in air and in water. Giardia and Cryptosporidium cysts are susceptible to ozone but not affected by normal levels of chlorine.