Corona vs. UV Ozone

Many users of ozone are made to believe that it will help in every scenario. Ozone chemistry is often totally ignored. UV Ozone, in India, is often recommended for water disinfection, when in reality, ozone offers no benefits in water treatment. Benefits, not the cost, should be the only criteria for selection.

Ozone is a very good disinfectant and many people know it by that. However, the benefits and effectiveness of ozone will depend on the method of ozone generation.

Primarily, there are two ways of producing ozone:

-Ozone using UV lamps

-Ozone by the Corona discharge method

Role of Ozonation

The purpose of ozone is both to perform oxidation, as well as disinfection (oxidation to remove organic and inorganic contaminants, and disinfection to kill bacteria, etc).

Regardless of how much ozone is generated per hour, a minimum concentration of at least 1% is required for both oxidation and disinfection. UV ozone generators cannot perform oxidation and disinfection at the same time at this concentration.

Concentration of Ozone

CD ozone generators can produce ozone at a concentration ranging from 1-16% w/w, compared to 0.1-0.001% w/w by UV ozone. This means that CD ozone generators can produce at concentration from 10 to 1000 times higher than that of UV ozone. The amount of air needed for UV ozone generators is 10 times more than what is needed for a CD ozone generator.

UV Lamps Used

A majority of UV ozone generators will use 454 manometers (nm) radiation. 89% of relative spectral energy of UV lamps are at 254 nm, and low of 218 nm. The maximum production of UV ozone happens at 260-265 nm. Therefore, by using 254 nm UV bulbs, it is impossible to produce more than just traces of ozone.

Mechanism of Action

That is the most important difference between UV ozone generation and CD ozone generation. Ozone generated by UV ozone is immediately decomposed by the UV radiation, which then forms free hydroxyl radicals. In aqueous ozone solutions, these free radicals (OH+) can be very powerful oxidizing agents. However, the disadvantage to these free radicals is that their half-life is around microseconds, and compared to 22 minutes of ozone. Because of this, ozone that is generated by the UV method, cannot be expected to remain in the solution for a sufficient period of time that allows adequate disinfection, even though chemical oxidation can occur.

Recently, UV ozone has started using 172 nm bulbs. These bulbs produce a higher concentration of ozone, but the bulbs themselves have not been commercially available or tested yet.

Why Concentration of Ozone is Significant?

There is only a partial solubility of ozone in water that is governed by Henry’s Law (the solubility of the gas in water is directly proportional to its partial pressure in the gas phase). Because of Henry’s Law, the higher the ozone concentration means the greater the solubility into water. The more ozone that is dissolved into water, the more effective it can be as a disinfectant. Through research and studies, it is clear that through UV radiation, there is not much ozone available in the water for both oxidation and disinfection.

Chicks Law Factor

The process in which ozone disinfects is governed by Chick’s Law. This law follows the Contact Time factor. For each strain of bacteria/virus, ozone has different contact times needed to kill that strain. Contact time needs to be controlled or maintained in order for the full benefits of ozone disinfecting to work. Just like antibiotics, each particular antibiotic needs a certain amount of time for it to work effectively. For ozone disinfecting to work, there needs to be enough contact time for it to do its job properly. The most important factors in ozone disinfection are concentration and time, both are not achievable with UV ozone generation.

Ozone can more easily destroy air-borne bacteria and viruses rather than water borne organisms. That is why the ozone requirement for air treatment is so low. That is another reason that UV ozone is only used in air treatment – high concentrations of ozone are not required for disinfecting. Ozone only has to spread in the air in order to work effectively, whereas in water ozone needs to first be dissolved in order to work.

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