Ozone absorption

Ozone has three major absorption bands for solar radiation named the Hartley, Huggins and Chappuis bands. It also has an absorption band at terrestrial infrared wavelengths (not relevant here). The strongest ozone absorption is in the 

The importance of ozone as a shield against damaging short-wave radiation reaching the Earth requires an understanding of its existence and the recently observed stratospheric depletion. 

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It is well known that ozone is quite soluble in water. Therefore, one expects that ozone absorption wi sulfur dioxide would contribute to significant oxidation of sulfur dioxide. Experiments of Penkett have shown that oxidation of sulfur dioxide in air at 7 ppb when absorbed in water droplets with ozone, which is present in surrounding air at 0.05 ppm, can be as large as 13%/h. Thus, foggy or cloudy air mixed with... 

Thome, L., and G. P. Hanson. Species differences in rates of vegetal ozone absorption. Environ. PoUut. 3 303-312, 1972. 

Table 4.3 shows the ozone absorption cross sections (base e) at 298 and at 226 K measured by Molina and Molina (1986), with which recent studies are in agreement, particularly below 240 nm (e.g., see Malicet et al., 1995 DeMore et al., 1997). The cross sections below 275 nm are not very sensitive to temperature over the 226-298 K temperature range, typically < 1%, but the temperature dependence becomes significant above 275 nm. Table 4.4 shows the temperature dependence of these absorption cross sections at longer wavelengths, averaged over the spectral regions shown. 

TABLE 4.3 Ozone Absorption Cross Sections (Base e) ... 

TABLE 4.4 Ozone Absorption Cross Sectionsu,b as a Function of Temperature Averaged over the Spectral Intervals Shown... 

The importance of this high concentration of ozone in the stratosphere resides in its effects on radiation and associated feedbacks. Figure 12.2 shows the ozone absorption spectrum, which was discussed in detail... 

The absorption cross section on the ordinate of the ozone absorption spectrum at the beginning of this chapter is defined by the relation... 

All systems proved capable of reaching the required effluents limits at comparatively low specific ozone absorptions, as low as 0.5 to 1.8 g 03g-1 CODt( in the influent (for further details see Table 3-3). 

Normally, it makes little sense to apply such systems in lab-scale ozonation experiments, since the high mass transfer rates are only achieved at high gas flow rates which because of the typical operation characteristics of EDOGs accordingly means low ozone gas concentrations. An appropriate field of application was, however, presented in the study of Sunder and Hem pel (1996) who operated a tube-reactor for the ozonation of small concentrations of perchloroethylene. An injector nozzle coupled with the highly efficient Aquatector ozone-absorption unit was installed in front of the tube-reactor. Both the gas and liquid were partially recycled in this system. According to the authors more than 90 % of the ozone produced was absorbed in demineralized water and dissolved ozone concentrations ranged up to 100 pmol L-1 (cL = 5 mg L-1, T= 20 °C). 

Where necessary and applicable, the specific ozone dose or the specific ozone absorption (best recorded and computed on-line) is recommended as the measure for analyzing process performance. Since in waste water ozonation, the ozone off-gas concentration often increases during the batch-treatment, the specific ozone absorption will not vary linearly with the treatment time. 

A procedure for conducting a series of batch ozonations with minimum parameter variation is fill the reactor to the desired level, ozonate, withdraw the whole solution, fill again to the same level and repeat the oxidation with a new set of ozonation conditions (preferably varying the oxidation time or the specific ozone absorption) in the next run. 

Due to the complexity of most waste waters and unknown oxidation products, differences in lumped parameters such as COD or preferably DOC are used to quantify treatment success. A model to describe the oxidation process, including physical and chemical processes, based on a lumped parameter has been tried (Beltran et al., 1995). COD was used as a global parameter for all reactions of ozone with organic compounds in the chemical model. The physical model included the Henry s law constant, the kLa, mass transfer enhancement (i. e. the determination of the kinetic regime of ozone absorption) as well as the... 

All experimental results should best be evaluated as a function of the specific ozone dose and related data such as the specific ozone absorption and/or consumption. Additionally the ozone yield coefficient, denoting the ratio of ozone absorbed in the liquid (i. e. transferred from the gas) to the DOC removed by ozonation or the total system (cf. Chapter B 1), is often of interest. 

In the laboratory, this method has been successfully applied to highly loaded tannery waste water (Jochimsen, 1997). Figure 6-4 shows a qualitative example of how such experiments can be evaluated by assessing the remaining concentration of the DOC (or the degree of DOC removal) as a function of the specific ozone absorption. 

For the transmittance due to ozone absorption was adopted Leckner s (2) expression ... 

From 200 to 242 nm, the 02 absorption, which is related to the Herzberg continuum with low absorption cross section, occurs in the stratosphere. In this spectral region, the ozone absorption must be introduced since the 03 Hartley band is characterized by high values of the absorption cross section between 200 and 300 nm. The simultaneous absorption by 02 and 03 must be considered in the stratosphere, whereas the O3 absorption is practically negligible in the mesosphere since the total number of absorbing ozone molecules is small. 

Therefore light of wavelength 11,400 A. or less provides enough energy for the dissociation of ozone. Absorption coefficients in the ultraviolet... 

Fig. 2.—Water vapour, carbon dioxide, and ozone absorption at 14 2°.

The design of ozonation contactors requires knowledge of kinetic information (see later), that is, the rate at which pollutants or matter present in water react with ozone, both directly and/or indirectly, and hence the rate of ozone absorption. Reaction rates can be calculated if rate constants of these reactions are known. Thus, the determination of rate constants represents a... 

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