Photo-initiated oxidation, treatment 217

The special features of UV treatment technologies of water and air that are favored by manufacturers, researchers and developers are collected in Tab. 2-1 (cf FIGAWA, 1997, Prengle Jr et al., 1996, Freeman and Harris, 1995, von Sonntag, 1995, Meyer and Fischer, 1994). From this table it is evident that a remarkable difference in the numerical handhng of UV disinfection and photo-initiated oxidation techniques ex-... 

However, it must be stated that the reaction pathways are different during the various treatment routes. This fact manifests itself in the different number and types of intermediate oxidation products that have been identified with identical substrates during different AOPs (cf Rajeshwar, 1996). Further, the optimum conditions for a specific photo-initiated AOP treatment depend mainly on the nature of the waste or model water. For instance, H2O2-O3 treatment (without irradiation) can have advantages in the treatment of waters with high inherent UV ab-... 

When the peroxyl population was quickly destroyed by 2-methyl -2-nitrosopropane treatment, post-y oxidation still occurred (Figure 7). In addition, film which had been pre-oxidized by xenon-arc photo-initiated oxidation showed an identical, slow, thermal oxidation during storage, as well as a rapid embrittlement in the accelerated aging at 60°C (Figure 6). The photo-oxidation of PP is well... 

Photo-initiated AOPs are subdivided into VUV and UV oxidation that are operated in a homogeneous phase, and in photocatalysis (Fig. 5-15). The latter can be conducted in a homogeneous aqueous phase (photo-enhanced Fenton reaction) or in a heterogeneous aqueous or gaseous phase (titanium dioxide and certain other metal oxide catalysts). These techniques apply UV-A lamps or solar UV/VIS radiation and they are in pre-pilot or pilot status. According to Mukhetjee and Ray (1999) the development of a viable and practical reactor system for water treatment with heterogeneous photocatalysis on industrial scales has not yet been successfully achieved. This is mainly related to difficulties with the efficient distribution of electromagnetic radiation (UV/VIS) to the phase of the nominal catalyst. 

UV oxidation of organic water pollutants in the presence of hydrogen peroxide, ozone or both with powerful medium-pressure mercury lamps is performed on industrial scales (Gottschalk et al., 2000). The synergistic combination of ozone and UV is especially suited for water sanitation, i.e. treatment of swimming pool and spa water (Rice, 1997). Many full-scale remediation applications of photo-initiated AOPs using hydrogen peroxide or ozone are already in operation (Chem-viron Carbon, 1997, Freeman and Harris, 1995). 

Tab. 5.2 Current examples of research related to photo-initiated AOPs in aqueous phase. Ox intermediary oxidation products formed, detected during treatment and characterized. Research examples concerning VUV oxidation in aqueous phase and UV oxidation in the gas phase are presented in Chapter 7 (Table 7-2 and Table 7-4, respectively). For O3-UV based AOPs refer to Cottschalk et al. (2000)... 

Tab. 7.4 Examples of research related to homogeneous and heterogeneous photo-initiated AOPs in the gas phase. Examples of applications of incoherent excimer lamps are collected in Table 7-2. Ox intermediary oxidation products formed and detected during treatment... 

The chemical and electrochemical oxidations of triphenylphosphine sulphide and phosphorothioates in acetonitrile have been investigated.In both reactions, triphenylphosphine sulphide initially gives a product formulated as a dimeric di-cation (39), but this rapidly decomposes on removal of the solvent or exposure to air. Triphenylphosphine oxide and sulphide form radical anions on treatment with potassium in ether at low temperature or by one-electron reduction at a Hg cathode in DMF. The photo-oxidation (sensitized by polymer-supported Rose Bengal) of triphenylphosphine selenide to the oxide has been shown to be highly solvent-dependent. 

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