Ozone inorganic compounds oxidation

Advanced oxidation processes (AOPs) are a range of water treatments which involve the in situ formation of radicals, particularly hydroxyl radicals, in sufficient quantity to affect chemical or biological contaminants. These include ultrasonic and ultraviolet irradiation but they are sometimes ineffective for the remediation of water which contains a mixture of organic and inorganic compounds. Chemical oxidants can be used to add additional oxidising power to such processes and ozone in conjunction with ultrasound is one such option [31]. 

Table 3-1 Oxidation of inorganic compounds by ozonation (Langlais etal., 1991 Hoign6 and Bader, 1985).

Of all the reactions studied, only the synthesis of nitrogen oxides and acetylene in arcs or plasma torches and that of ozone in glow and corona discharges are of major importance. In addition, a few small-scale preparations of inorganic compounds have been developed, e.g. synthesis of hydrazine and of hydrides and halides of silicon, germanium, tin, lead, phosphorus or arsenic 3> ... 

Indirect reactions are due to the oxidizing action of free radicals that are formed from the decomposition of aqueous hydrogen peroxide when it reacts with other inorganic compounds, such as ozone or Fe2+, or when it is photolyzed. 

Examples of direct reactions are mainly with inorganic compounds such as cyanides and sulfides or ozone and Fe2+. Both reactions of ozone and Fe2+ with hydrogen peroxide represent the initiating steps of advanced oxidation processes 03/H202, treated later in this chapter, and the Fenton oxidation, presented in another chapter, respectively. Hydrogen peroxide, on the other hand, does not significantly react with most organic compounds, at least at appreciable rates for water treatment [6],... 

Hydroxyl radical, OH, is the principal atmospheric oxidant for a vast array of organic and inorganic compounds in the atmosphere. In addition to being the primary oxidant of non-methane hydrocarbons (representative examples of these secondary reactions are given in Table 6), OH radical controls the rate of CO and CH4 oxidation. Furthermore, the OH reaction with ozone also limits the destruction of O3 in the troposphere, it also determines the lifetime of CH3CI, CHsBr, and a wide range of HCFC s, and it controls the rate of NO to HNO3 conversion. Concentration profiles for hydroxyl radical in the atmosphere are shown in Fig. 2. 

In chemical oxidation, chemicals with high positive oxidation potential, such as ozone (2.1 V) and hydrogen peroxide (1.8 V), are used to destroy a wide variety of organic and inorganic compounds such as chlorinated VOCs, mercaptans, phenols, and cyanide (NaCN). 

Generally speaking, the direct ozonation is important if the radical reactions are inhibited. That means that the water either does not contain compounds that initiate the chain reaction (initiators) or it contains many that terminate the chain reaction very quickly (scavengers). With increasing concentrations of scavengers the mechanism of oxidation tends to the direct pathway. Therefore, both inorganic carbon as well as the organic compounds play an important role. 

This comparison is only theoretical. In reality a high production of OH° can lead to a low reaction rate because the radicals recombine and are not useful for the oxidation process. Also not considerd are the effects of different inorganic and/or organic compounds in the water. Various models to calculate the actual OH-radical concentration can be found in the literature, some are described in Chapter B 5, Further information concerning the parameters which influence the concentration of hydroxyl radicals is given in Section B 4.4, as well as a short overview about the application of ozone in AOPs in Section B 6.2. 

Bromine containing species, introduced from Man s release of halons, are also believed to play a significant role in the polar ozone depletion, despite the fact that the total inorganic bromine concentration in the stratosphere is typically two orders of magnitude lower than the inorganic chlorine. This is manifested in the presence of Br0N02 and HOBr, which however are less stable than the chlorine reservoirs, so that relatively more BrO, is in the active fotm [36,37]. There is a synergism between the chlorine and bromine species the oxides radicals GO and BrO react with each other to produce a series of products, G, Br, BrCl and OCIO. The latter compound is an indicator of the elevated levels of both BrO and GO [38]. 

Chemical/physical treatment processes are those in which a chemical reaction is used to alter or destroy a hazardous waste component. Chemical treatment techniques can be applied to both organic and inorganic wastes, and may be formulated to address specific target compounds in a mixed waste. Typical chemical treatment processes include oxidation-reduction reactions such as ozonation, alkaline chlorination, electrolytic oxidation and chemical dechlorination. Physical treatment processes separate waste component by either applying physical force or changing the physical form of the waste. Various physical processes include adsorption, distillation, or filtration. Physical treatment is applicable to a wide variety of waste streams but further treatment is usually required. 

When the waste contains more complex molecules such as compounds refractory to oxidation with OH radicals, as well as in the presence of inorganic ions which can be precursor of long-life oxidants, the Faradic yield cannot be calculated by (8.3) and different alternatives have been proposed. Faouzi and co-worker (Faouzi et al. 2006) proposed a comparison between electrochemical oxidation at BDD anodes and Fenton and Ozone treatments for the removal of dyes a specific parameter OCC (oxygen-equivalent chemical-oxidation capacity) was proposed which is defined as the kg of 02 equivalent to the quantity of oxidant used in each AOP to treat 1 m3 of wastewater. As highlighted by the authors, the parameter OCC may only give information on the chemical efficiency of the oxidants, but it does not give any information related to the real cost of the treatment, as the oxidants can... 

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