Main Article Content
Ozone (O3) is a bluish-coloured gas with a characteristic odour that forms in the layers of the atmosphere, near electric shocks, sparks or lightning; the extremely high voltages reached during thunderstorms produce ozone from oxygen. The particular fresh, clean odour, the smell of spring rain is the result of the ozone reproduced by nature. Ozone comes from the Greek word ozein, which means to sense the odour of. Ozone is an essential gas for life on Earth, allowing the absorption of ultraviolet light emanating from the Sun; in fact, the ozone layer in the stratosphere protects against the harmful action of UV-B ultraviolet rays. The gas, not being stable over the long term, is therefore not produced in cylinders; it can currently be prepared through special, certified and authorised devices, which use small electric discharges to convert the oxygen into ozone. It is a molecule formed by three oxygen atoms (O3), with a negative electric charge. It has a short half-life, and will therefore decay after a certain time back to its original form: oxygen. Essentially ozone is nothing but oxygen (O2) with an extra oxygen atom, which has a high electrical charge. Ozone works according to the principle of oxidation. The oxidation mechanism follows two paths: i) Direct: contact of the molecule with the contaminant; ii) Indirect: the ozone decomposes into hydroxyl radicals, more powerful but short-lived. Both reactions occur simultaneously. When the static charged ozone molecule (O3) comes into contact with something capable of oxidising, the ozone molecule’s charge flows directly over it. This happens because ozone is very unstable and tends to change back into its original form (O2). Ozone can oxidise with all kinds of materials, but also with odours and microorganisms such as bacteria, viruses and fungi. The supplemental oxygen atom is released from the ozone molecule and binds to the other material. In the end, only the pure and stable oxygen molecule remains. Ozone is one of the strongest oxidation techniques available for oxidising solutes. The supplemental/added oxygen atom will bind (=oxidation) in a second to each component that comes into contact with ozone. It is used for a wide range of purification processes. It can be employed for disinfection in municipal wastewater and in drinking water treatment plants. However, ozone is increasingly used in the industrial sector. In the food industry, for example, it is used for disinfection, and in the textile and paper industry it is used to oxidise wastewater. The main benefit of ozone is its clean nature, because it only oxidises the materials, barely forming any by-products. Since ozone has a strong characteristic distinctive odour, even very low concentrations can be quickly perceived. This generally makes it safe to work with. Since Chlorine is still the best-known oxidising and disinfectant agent, ozone is often compared with chlorine. Unlike chlorine, antibiotics or various chlorine derivatives that have no effect, ozone acts on viruses and spores. In its sterilising action, ozone directly attacks bacteria by inducing a catalytic oxidation process on the mass of bacterial proteins, unlike chlorine which acts only through specific enzymatic poisoning of vital centres, a process which requires a longer time interval and sensitive quantity for its diffusion inside the cytoplasm. Regarding the virucidal action, it is interesting to keep in mind that with a residual ozone rate of 0.6 ppm (parts per million) and with a contact time of 2 minutes, the percentage of inactivation for bacteria and viruses present in the disinfection liquid is total. Ozone’s oxidising power is 120 times greater than that of chlorine.