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Page 1 of 4 Disinfection and Oxidation with Ozone by P. M. Menon
OZONECARBON TECHNOLOGIES PTE LTD.
70 Anson Road, #26-03, Apex Tower, Singapore 079905
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Abstract
This paper examines the use of ozone technology, often called a "green" technology, for oxidation and disinfection of air, water and environmental surfaces.
Based on the review of the available literature and the extensive industry experience gained by the author, it is concluded that if ozone treatment is used properly, it can serve as an environmental friendly and cost effective method for disinfection and oxidation of objectionable compounds.
Introduction
Ozone has received much attention in the last few decades among the environmental health professionals, as its by-products do not cause pollution problems unlike other disinfectants such as chlorine.
The use of ozone in the air, water and hygiene industry is however limited presently, due to the lack of awareness among the users. In certain projects, ozone systems are installed initially, as the consultants recommend the use of a clean technology. However, subsequently the ozone systems are not used at their potential and the end user may have to switch to the traditional technology.
Unfortunately, such incidents are not due to the inability of ozone to disinfect or oxidise objectionable compounds, but because of failure to understand the chemistry of ozone, its applications and the underlying process engineering.
(Some industry experts also highlight reasons such as - poorly designed systems, which are either under/over sized; concerns regarding safety; and failure to service the systems since the systems are sometimes installed by "traders" who lack the knowledge and expertise to maintain them.) In order to understand how ozone works, it is necessary to take a look at its properties and the way it performs disinfection and oxidation.
What is ozone? Ozone is an allotropic form of oxygen having three atoms of oxygen. Two of the atoms are with double bonds whereas the third atom is loosely held by a single bond. The third, loosely held atom tends to break away and attach itself to a host oxidizing it with the original ozone molecule reverting back to oxygen. It is this property of ozone which makes it a very powerful oxidizing and disinfecting agent for both the air and water applications.
O3 <=> O2 + O………..Eq. (1)
Ozone is the most powerful oxidizing agent next only to fluorine. It is present in small proportions in the atmosphere, which can increase up to 0.3 to 0.5 PPM after a thunderstorm. It is present in the earth’s stratosphere filtering the UV rays from the sun, having a wavelength of 200 to 300 nm.
Table. 1: Comparison of ozone with other oxidizing agents
| Oxidizing Agent | Oxidation potential in V (ORP) | ORP, relative to chlorine | | Fluorine | 3.06 | 2.25 | | Hydroxyl-radical | 2.80 | 2.05
| | Atomic Oxygen | 2.42 | 1.78
| | Ozone | 2.08 | 1.52
| | Hydrogen peroxide | 1.78 | 1.30 | | Hypochlorite | 1.49 | 1.10
| | Chlorine | 1.36 | 1.00
| | Chlorine dioxide | 1.27 | 0.93
| | Molecular Oxygen | 1.23 | 0.90 |
The Table 1 above compares the electro-chemical oxidation potential of ozone with other oxidizing agents.
Although ozone is a very powerful oxidizing agent, it is an unstable gas that breaks down to oxygen within minutes. It must therefore be produced at site for immediate use. It cannot be produced at some other site, bottled and transported to the point of use. The other important point about ozone is that it is only partially soluble in water. As a result, great importance is paid in the mixing and mass transfer of ozone from the gas phase to the liquid phase.
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