Ozone decomposition in water

Mechanism of ozone decomposition in water depends on the presence of chemical species that can initiate, promote and/or inhibit its decomposition. The most accepted ozone decomposition mechanism is given in Figrtre 3. 

Biihler R E, Staehelin J, Hoigne J (1984) Ozone Decomposition in Water Studies by Pulse Radiolysis. 1. H02/02 and H03/03 as Intermediates, Journal of Physical Chemistry 88 2560-2564. 

Sotelo J L, Beltran F J, Benitez F J, Beltran-Heredia J (1987) Ozone Decomposition in Water - Kinetic Study, Industrial Engineering and Chemical Research 26 39-43. 

On the other hand, the indirect type of ozonation is due to the reactions of free radical species, especially the hydroxyl radical, with the organic matter present in water. These free radicals come from reaction mechanisms of ozone decomposition in water that can be initiated by the hydroxyl ion or, to be more precise, by the hydroperoxide ion as shown in reactions (4) and (5). Ozone reacts very selectively through direct reactions with compounds with specific functional groups in their molecules. Examples are unsaturated and aromatic hydrocarbons with substituents such as hydroxyl, methyl, amine groups, etc. [45,46],... 

Sotelo JL, Beltran FJ, Benitez J, Beltran-Heredia J. Ozone decomposition in water kinetic study. Ind Eng Chem Res 1987 26 39-43. 

J Staehelin, RE Buhler, 1 Hoigne. Ozone decomposition in water studied by pulse radiolysis. 2. OH and HO4 as chain intermediates. J Phys Chem 88 5999-6004, 1984. 

Figure 6. Ozone decomposition in water with different content of total organic matter as TOC (Parketal, 1998).

Staehelin, J. and I Hoigne (1982) Decomposition of ozone in water rate of initiation by hydroxide ions and hydrogen peroxide. Environmental Science and Technology 16, 676-681 Staehelin, I, R. E. Biihler and I Hoigne (1984) Ozone decomposition in water studied by pulse radiolysis - 2. OH and SO4 as chain intermediates. Journal of Physical Chemistry 88, 5999-6004... 

TABLE 1.1 The Temperature Dependence of the Rate Constants k, of Ozone Decomposition in Water... 

The mechanism of decomposition of ozone in water has been the subject of numerous studies, starting from the work of Weiss [47], Among more recent studies, the mechanisms of Hoigne et al. [48] and Tomiyashu et al. [49] are the most accepted in ozone water chemistry. The main conclusion that can be drawn is that ozone stability in water is highly dependent on the presence of substances that initiate, promote, and/or inhibit its decomposition. The ozone decomposition mechanism usually assumed is given in Fig. 4 [50]. 

The indirect pathway is less selective, because the species formed in the process have a higher oxidant ability than the ozone itself, especially HO. The route can be initiated in different ways, by H02 , HCOO , Fe2+, humic substances or principally by HO . This is why, in principle, ozonation is more efficient in alkaline media, presenting an optimum around pH 9. Figure 4 shows a scheme of the main species of ozone decomposition in pure water initiated by hydroxide ions [7]. 

Fig.4 Scheme of the main species of ozone decomposition in pure water initiated by hydroxide ions [7]... 

Determination of ozone residuals in water is quite difficult because of its rapid decomposition, volatility and reactivity. Most test methods available are variations of existing chlorine residual methods that are not specific for ozone. 

FIGURE 1.1 The kinetic curve of ozone decomposition in double distilled water and its semUogarithmic anamorphosis 32°C. 

It is slightly soluble in water, giving a neutral solution. It is chemically unreactive and is not easily oxidised or reduced and at room temperature it does not react with hydrogen, halogens, ozone or alkali metals. However, it decomposes into its elements on heating, the decomposition being exothermic ... 

Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

In 1899, the Curies first reported the coloration of glass and porcelain and the formation of ozone from oxygen by radioactive radiation. Giesel (1900) noted that the coloration of alkali halides under these radiations was similar to the effect of cathode rays he also observed the decomposition of water. R Curie and Debierne (1901) observed continuous evolution of hydrogen and oxygen... 

The diffusivities of ozone in mucus, tissue, and water are unknown. As an approximation, the diffusivity of oxygen in water (2.5 x 10 cm /s) may be used for the diffusivity of ozone in water and in the mucus layer. Although reactivities of ozone in mucus and tissue are unknown, the results of Alder and Hill and Hoigne and Bader, which describe the decomposition of ozone in aqueous solutions, may be used as a first approximation. 

Rice, C.P., Sikka, H.C.,and Lynch, R.S. Persistence ofdichlobenil in a farm pond, / Agric. FoodChem., 22(3) 533-535,1974. Rice, F.O. and Murphy, M.T. The thermal decomposition of five-membered rings, / Am. Chem. Soc., 64(4) 896-899,1942. Richard. Y. and Brener. L. Removal of pesticides from drinking water by ozone, in Handbook of Ozone Technology and Applications, Volume II. Ozone for Drinking Water Treatment, Rice, A.G. and Netzer, A.. Eds. (Montvale, M A Butterworth Publishers, 1984), pp. 77-97. 

H2O2 [86], UV/O3 proeess is based on the faet that by the decomposition of ozone under UV radiation two OH radicals are generated which rather form H2O2 than react with organic matter present in water, shown by equation (18) ... 

Figure 3. Scheme of ozone decomposition mechanism in water. P = promoter (e.g. ozone, methanol), S = scavenger or inhibitor (e.g. /-butanol, carbonate ion), I = initiator (e.g. hydroxyl ion, perhydroxyl ion) (adapted by Beltran [35]). 

Hexylene Ozonide. C6H1203 mwl32.18 mobile oil, bp 60° at 12mm, d 0.994 at 23°, np 1.4059 at 25°. SI sol in water with slow decomposition si sol in pet eth. Explodes if heated strongly above 60° Prepd by reacting hexylene (in hexane or EtCl2) with 15% ozone mixture Refs 1) Beil 1, (90) 2) C. Harries K. 

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