Ozone oxidises most organics to their lower molecular states into simpler compounds. Ozone reacts rapidly with most simple aromatic compounds and unsaturated aliphatics, such as vinyl chloride, 1,1-dichloroethylene, trichloroethylene, p-dichlorobenzene, benzene, etc., but reacts slowly with complex aromatics and saturated aliphatics. Ozone will degrade many organic compounds, such as sugars, phenols, alcohols, and as it degrades these organics, reduces itself to oxygen.
Heavy metals in water are also oxidised with ozone. Ozone oxidises transition metals to higher oxidation state where they form less soluble oxides and can be removed by filtration. Iron, for example, exists in its ferrous state when in dissolved state in water. Ozone oxidises ferrous to ferric iron, which, with water forms ferric hydroxide that is insoluble in water and precipitates. Similarly, other metals like arsenic (in presence of iron), cadmium, chromium, cobalt, copper, lead, manganese, nickel, zinc - can be ozonised to their oxides. However, manganese, at ozone levels above 4, will form soluble permanganate giving pink colour to water.
In advanced oxidation system, ozone is combined with hydrogen peroxide (peroxozone reactions) or with UV irradiation (uvazone reactions) to form very active hydroxyl ions. These hydroxyl ions cause a nucleophilic reaction on organic compounds. This results in displacement of halogens and other functional groups such as amines and sulphides. This way more complex organics can also be reduced further.