Ozone oxidizes the transition metals to their higher oxidation state in which they usually form less soluble oxides that are then easy to separate by filtration. Iron, for example, is usually in the ferrous state when dissolved in water. With Ozone it yields ferric iron which is further oxidized in water to Ferric Hydroxide ? a molecule that is very insoluble and precipitates out.

Other metals such as Arsenic (in the presence of Iron), Cadmium, Chromium, Cobalt, Copper, Lead, Manganese, Nickel, and Zinc can be treated in a similar way. At Ozone levels above 4 ppm however, Manganese will form soluble permanganate, showing up as a pink color.