A few words about Ozone
Here we would like to shed light on a worthy alternative to chlorine. Chlorination, just as any water treatment technique, has its advantages and disadvantages. Hence, considering an alternative seems rather sensible. Chlorine’s main and mightiest “competitor” is Ozone. However, it would be exaggerating to say they are indeed competitors, as they work best as a team.
What if a person finds the smell of chlorine simply repellant? Or, to make matters worse, has chlorine sensitivity? Or is reluctant to exposing their children to insidious effects of chloramines? Or feels uneasy at the very mention of “chlorine”? The thing is, water treatment is crucial! So, what could be a way out? The main and most advanced alternative to chlorine-based swimming pool water disinfectants is ozone. Nonetheless, it is worth mentioning that these two are not competitors but rather allies and partners. They do work better as a team than if applied separately. We are to give an overview of the valuable properties of ozone further in this article, but, before we proceed, let us lead you in a brief guided tour into its history. So, what do we know about ozone? Back in the 17th century the characteristic smell appearing around electrifiers, such as lightenings and electric machines, was identified. In 1785 a Dutch physicist M. van Marum attributed the smell to a substance with oxidising properties. In 1801 G. Devi detected its presence in the air. But it was only in 1840 that C. F. Schönbein actually discovered the substance by isolating it. He named the isolated gas “ozone” (from the Greek word ozein meaning “to smell”). Even so, many decades later its definitions in dictionaries read as follows: “ozone is an unknown body, derived in the process of atmospheric air electrifying”. The definition that reflects our modern understanding of the substance was only elaborated at the beginning of the 19th century. Ozone is an allotrope of oxygen (O2 -> O3); in its pure form it is a blue explosive gas. It is rather unstable and easily transforms into oxygen. It is 1,5 times heavier than air, and its solubility is 10 times that of oxygen. At –112°С ozone condenses to a dark blue liquid, and at –119°С it forms a violet-black solid of crystalline structure. At low concentrations most people find its smell pleasant and refreshing. While many tend to describe the smell as “metallic”, D. Mendeleev thought it resembled the smell of crawfish. However, when its concentration is as low as only 1%, its odour is already pungent and sharp. It is impossible to breathe in the air if this smell is present. (By the way, though it had been believed to be beneficial to breathe in a small dosage of ozone, the myth was lately debunked. The pleasant smell we feel in the forest after a thunderstorm, in fact, is not created by ozone, but rather by oxidation products of natural resin and essential oils contained in conifers and other plants. In addition, it is extremely poisonous, even more than CO, so the highest acceptable concentration of ozone in the air is 0,00001%. The smell can be detected at a concentration that is 10 times lower, which means its presence Is detectable long before its concentration reaches the highest acceptable level). In nature ozone is produced in the second major layer of Earth’s atmosphere (at a height of about 15-30 km) as a result of UV transforming oxygen. It is also produced in the process of arc welding or when current transformers, photocopiers, laser printers are working, or when a lightning strikes. As an essential component of the atmosphere it defines radiation absorption, which means that the main portion of biologically active UV radiation does not reach the surface of our planet. Its’ concentration is generally diminutive, with its layer not exceeding 2,5-3 mm on the average. Its maximum concentration is found 20-25 km above Earth. There a few well known methods of ozone production, among them electrolytic, photochemical and cold plasma methods. In electrolytic (also known as “dirty”) method ozone is synthesised in special electrolytic cells, while acid and salt solutions perform as electrolytes (H2SO4, HCLO4, NaCLO4, KCLO4). Ozone is produced as a result of electrolytic dissociation of water when resulting atomic oxygen binds with molecules of Oxygen, thus forming ozone and molecules of hydrogen. This method allows to achieve a higher concentration of ozone in the solution, but is considered to be unfavourable due to high power input and impurity. Photochemical method of ozone production is based on oxygen molecule dissociation by means of narrow-band UV light. This method does not allow to produce high concentration of ozone. Still, it has found practical use in medicine, food manufacture and electronics. It allows efficient air disinfection on the premises where requirements to cleanliness are particularly high. In the cold plasma (also known as “clean”) method different kinds of discharge in gas are typically applied, namely, dielectric barrier, surface and pulsed discharge. This method allows to obtain high concentration of the substance while maintaining the power input and operating costs low. Main advantages of ozone water treatment reside, first and foremost, in its chemical properties. It is one of the most powerful oxidising agents and has a much higher potential when compared with chlorine, preconditioned by the very mechanism of its interaction with microorganisms. What it does is it inactivates bacterial proteins by means of diffusion through a cell membrane into the cytoplasm and targeting its “vital centre”, followed by further oxidation and destruction of organic material. Ozone “finely chops” bacteria into a “salsa”, whereas chlorine reduces its activity to vaguely and selectively poisoning bacteria “vital centres” due to the time it needs to diffuse in the cytoplasm. Apart from its unique ability to eliminate bacteria, ozone is highly efficient in destroying viruses, spores and cysts (thick membranes protecting single-cell organisms, such as mastigophores and rhizopods during reproduction or in adverse environment) and many other pathogenic microbes. Still, as we have previously mentioned, ozone is poisonous, which means that maximum allowable concentration requirements are strict. It should not be detectable in the water of a pool. Especially if we take into account that it is much heavier than air, and tends to condensate on the surface of the water as it evaporates. This exactly where a swimmer will inhale, and where a high concentration of ozone is most likely to occur. This means that if we decide to apply ozone treatment technology without having conducted a rigorous research of the right technology, we are likely to see ourselves on a slippery slope. It would be right to heed warnings and ask your provider how such safety issues are handled. Generally, deactivation process takes place in a reaction tank, through which the treated water goes in just about 2 or 3 minutes, which is more than enough for achieving a desired level of cleanness. The remaining ozone is discharged thanks to a carbon filter, where it partially transforms into oxygen and carbon dioxide. The resulting purified water then is returned when the ozone has been removed. Another safety issue to take into account is the use of a gas sensor on the premises that is connected to alarm system and is able to deactivate the generator if a gas leak is detected. Some other methods of achieving the same effect are available as well. For instance, Dinotec patented a method of partial ozone treatment, which consists of partial (10-20%) swimming pool water ozonation. Can that be effective? Surprisingly, the technology offers a significant advantage, as only a part of the general circulating water flow undergoes ozonation, while a carbon destructor eliminates the excess gas (in other words, the undissolved gas). The water that has been treated then is returned into the circulating flow and is thus diluted from five to ten-fold. That means that the ozone penetrates into the pool with the treated water, and does its job with the remaining amount of water in the pool, while at the same time a part of the ozone has time to decompose and the other part oxidises pollutants that the general circulating water flow contains. In theory, certain amount of ozone is to be present in the pool, however, its amount is too low to be detectable. At the same time, the desired result is achieved, ozone is not found in the water of the pool, while the amount of ozone actually used (and, therefore, produced) is from 5 to 10 times smaller. In monetary terms, the technology allows to substantially reduce power and equipment cost, but ensures a higher level of safety. Another technology of water ozonation allows us to remove reactor tank, which means that the produced ozone is directed straight into the circulating flow, the water that is about to fill up the pool. It is worth mentioning though that the system is only to be used in outdoor pools. Presumably, once ozone is used in the open air, it is multiply diluted and undergoes decomposition. Consequently, the risk for those using the pool is minimised. The technology is mainly “abused” by the US manufacturers. And if you’ll pardon the expression, here I would like to express my subjective opinion of an expert. While I do personally believe that there have not been any lethal or severe illness cases directly linked to the aforementioned technology application, it is rather hard to believe that a “slightly above the standard” ozone consumption has not had any impact on consumers’ health. While it is a strictly personal opinion, I do consider it important to be shared.
And last but not least, it is worth mentioning that since ozone is not present in the water after it has been treated, the use of a disinfectant is essential, even if its amount is kept to a minimum sufficient. It prevents the growth of the microbial flora that comes from the outside of the system. Provided that chlorine has been chosen to fulfil the task, ozone performs yet another valuable function by additionally oxidising and disintegrating the resulting organic material (trihalomethane, chloroform, etc.). As a result, ozone helps to prevent any odour and ensures that hazardous carcinogens are not accumulated in the water.
Forasmuch ozone is capable of entering into a reaction with most inorganic substances, inorganic pollutants that may be found in the water, as they can penetrate from the outside, are also “processed”. Eventually, most soluble salts are transformed into insoluble compounds that sediment on the filters. This helps to brighten the water, eliminate colouring, odour and taste. On top of that, if we think about ozone’s ability to create a powerful electric potential, then charged colloid particles (suspended solids) will end up on the surface of the filters. Further ozone decomposition results in oxygen production, which adds freshness to the water and gives it a “spring water” feel. To sum up, apart from its main function, which is disinfection, ozone does a humongous amount of important work that improves water properties. Among its downsides, perhaps, we should only mention that the price of ozonation equipment can be considerably high (as long as it is safe, effective and reliable), that the need for the use of a disinfectant remains as well as remains the need to use more carbon filters (in systems with full ozonation technology) which due to their sorption properties can become a source of secondary pollution of the water. Nevertheless, there’s nothing like the feel of ozonated water, and not a single method of water treatment is able to provide us with the same benefits.