Colourants, surfactants and refractory organic substances all share the characteristic of being formed by organic molecules with double bonds.
These complex molecules are attacked and broken up by ozone. When the treatment is followed by a biological phase, simpler molecules are formed which are more easily biodegradable and assimilated by bacteria. The final products of the process are molecules of oxygen and water. This makes ozone an ecofriendly oxidizing agent as it does not produce sludge and concentrates, avoiding disposal of the latter.
In aqueous solution with the presence of hydrogen peroxide, there is a formation of hydroxyl free radicals OH, which are very reactive even against molecules with strong C-H (carbon-hydrogen) bonds.
In this case the following reaction occurs:
RH +-OH = R++ H2
The progression of the reactions involves a chain reaction with more and more radicals being formed. The reactivity of ozone allows degradation of stable resonant molecules including benzene and phenol.
If the water includes special characteristics or in the case of particularly refractory pollutants, it is possible to adopt an “advanced oxidation process” combining ozone with other oxidants such as Hydrogen peroxide (H2O2) or ultraviolet radiation. These act as catalysts reacting with the ozone to form hydroxyl radicals, which have a higher oxidizing potential 2.8 V compared to ozone alone 2.07 V. Ozone however has the highest chemical potential amongst other singular oxidants.
|Oxidising agent||Symbol||Chemical potential (V)|