Antimicrobials: ozone


Ozone not only protects the Earth from the harmful effects of sunlight, but it itself is destructive to living organisms, not only for microbes, but also for people.

Today, ozone is used in areas as diverse as bottled water, disinfection in swimming pools, and wastewater treatment.

In 2001, the United States Food and Drug Administration approved the use of ozone as an antimicrobial agent, but only in certain situations where people would not be exposed to its toxic effects. A hundred years ago, ozone was treated much more warmly: then it was known that ozone was capable of killing microbes, so ozone generators were installed in churches, in theaters, in the London Underground. The authorities hoped that the gas would protect people. In those years, it was believed that most pathogens were spread through the air, so it seemed obvious that an oxidizing gas was the best way to deal with the infection.

Doctors proved this theory, citing as an example the excellent health of people living in the mountains and on the ocean, then it was mistakenly believed that in these places ozone is present in the air in high concentrations. Of course, this theory was wrong, and we now know that inhaling ozone only damages the lungs. Despite this, more ozone is being produced today than ever before. Nearly all of it goes into water disinfection, from ultrapure water used in the pharmaceutical industry to water that needs to end up in rivers from wastewater treatment plants.

The ozone of the atmosphere is found in its upper and lower layers. At the top, it forms a protective layer that protects us from the effects of UV rays coming from the sun. Below, at the surface of the Earth, it is a pollutant that has a damaging effect on plants and animals. It used to get into the air mainly with the exhaust gases of cars, this was before the advent of catalytic converters. Although older car engines did not emit ozone per se, they did produce oxides of nitrogen, especially nitrogen dioxide (NO2). Under the action of sunlight, this substance is able to decompose into nitrogen monoxide and an oxygen atom (NO + O), the latter, reacting with an oxygen molecule (O2), forms ozone (O3). As a result, on warm sunny days, nitrogen levels in cities and suburbs could rise to 0.1 parts per million parts of air, the upper limit for ozone concentrations for people who work with this gas. At times, the ozone level in the air could rise to 0.25 parts per million. In nature, the concentration of ozone in the air is only 0.02 parts per million, and this level is safe for humans. Atmospheric dust catalyzes the reverse conversion of ozone to oxygen.

Ozone dissolves in water up to a concentration of 570 parts per million, the resulting solution is not very stable, but despite this, it is a powerful bactericidal agent. Public pool water is often sterilized with ozone, although a small amount of hypochlorite must also be added to the water, as much of the ozone is removed from the water before entering the pool. And in any case, the gas does not stay in the water long enough to be completely safe for swimmers. For this reason, in many pools, ozonation is not used at all: by the time the water is used, all the ozone may have already evaporated from it, and with it the antibacterial protection. But despite this, in a number of countries, such as France, ozonation has been used for more than a hundred years (the first ozonizers were installed in the Netherlands in 1893), and it is the preferred method of disinfecting pool water. Ozone is an even stronger oxidizing agent than hypochlorite, being able to kill pathogens such as Cryptosporidium, which is resistant even to high concentrations of hypochlorite. Now ozonation is becoming more and more popular. This is because people are concerned about the side effects of chlorination. Ozone stations for the disinfection of drinking water were built in California in 1987, over the next ten years the total number of such stations in the state reached 250.

Those who drink bottled water can also thank ozone for the purity of this product. While carbonate water is protected from bacteria due to its acidity, non-carbonate water provides conditions for the growth of microorganisms. The best way to deal with aquatic microbes is ozonation, which keeps the water clean until the moment of packaging. Industrial effluents can be polluted in a variety of ways, and ozone-oxidizer allows you to save them not only from microbes, but also from organic waste. To carry out such purification, ozone is produced directly at the place of its use.

To protect the water of aquariums, fish farms, fish hatcheries and shrimp farms, ozonation is a more successful method than chlorination. Ozone generators are easy to operate, and ozonized water can be easily deozonized by passing through carbon filters before being returned to the fish and shrimp pond. Ozone is used to treat water in wastewater treatment plants, especially if it is then drained near public beaches. This gas not only fights bacteria, but also helps to get rid of unpleasant odors by oxidizing malodorous sulfides to odorless sulfates.

Ozone was discovered in 1840 by the German chemist Christian Friedrich Schönbein, who worked at the University of Basel in Switzerland. The scientist called the resulting gas the Greek word «ozon», which means «smell». This name was chosen due to the fact that the history of ozone goes back to the ancient Greeks, who noticed that immediately after a thunderstorm there was some unusual smell in the air. It is now known that after a thunderstorm, the concentration of ozone in the air increases significantly, and this is due to lightning, due to the energy of which ozone is formed from oxygen. At first, Schonbein believed that he had discovered a new element similar to chlorine, but later he proved that he had obtained a new form of the oxygen molecule, consisting of three oxygen atoms.

Ozone can be obtained in two main ways: the first is to pass oxygen through metal-coated glass tubes, creating in them a constant electric spark under a voltage of 15 kilovolts. The air coming out of such tubes will contain 2% ozone. The performance of such a generator reaches 500 grams of nitrogen per hour, although often the need for ozone does not exceed 1-2 grams per hour. Another way to produce ozone is to expose the air to ultraviolet light, a technique suitable for applications where only small amounts of the gas are needed. Ozone can be condensed from air if the latter is cooled below the boiling point of ozone, which is -112 °C. Liquid ozone is a blue liquid that turns into a dark purple solid at -193°C. Both liquid and solid ozone are explosive.

Source: based on the book by John Emsley «On the benefits and harms of the products we love to buy»

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