UV Radiation Processes

Beltran FJ, Gonzalez M, Rivas FJ, Acedo B. Aqueous degradation of VOCs in the ozone combined hydrogen peroxide or UV radiation processes. 1. Experimental results. J Environ Sci Health A 1999 34 649-671. 

Chemical oxidation is very effective in destroying free cyanide as well as cadmium, copper, and zinc cyanide complexes. However, nickel cyanide is incompletely destroyed, and iron cyanide complexes are apparently unaffected by chlorine or ozone. The ozone-UV radiation process (i.e., advanced oxidation process) is effective for treatment of complexed cyanide, such an ferric cyanide, copper cyanide, and nickel cyanide. Performance data of oxidation processes from the following industries are presented in the appendixes ... 

The H2O2/UV radiation process is based on the direct homolytic photolysis of hydrogen peroxide to give two hydroxyl radicals ... 

The layer width is taken from the relation d > 1,5 dg, where dg - thickness of a gas discharge gap. The employment of a resistive layer instead of electrode profiling can significantly simplify the device manufacture. The UV radiation is efficiently converted into a visible one by a number of photo-luminophors, e.g. Zn2Si04 Mn. For stroboscopic registration of fast-proceeding processes the luminophors with short period of luminescence are used, e.g anthracene etc. 

B) The multiphoton excitation of electronic levels of atoms and molecules with visible or UV radiation generally leads to ionization. The mechanism is generally a combination of direct, Goeppert-Mayer, and quasi-resonant stepwise processes. Since ionization often requires only two or tln-ee photons, this type of multiphoton excitation is used for spectroscopic purposes in combination with mass-spectrometric detection of ions. 

The oxidation may be carried out with an inert solvent thermally (35), with a sensitizer such as bromine (36), with uv radiation (37), or over a suitable catalyst (38). Principal by-products of all these oxidation processes are the acyl fluoride products derived from oxidative cleavage of the perfluoroaLkene (eq. 

Initiation of radical reactions with uv radiation is widely used in industrial processes (85). In contrast to high energy radiation processes where the energy of the radiation alone is sufficient to initiate reactions, initiation by uv irradiation usually requires the presence of a photoinitiator, ie, a chemical compound or compounds that generate initiating radicals when subjected to uv radiation. There are two types of photoinitiator systems those that produce initiator radicals by intermolecular hydrogen abstraction and those that produce initiator radicals by photocleavage (86—91). 

Fig. 3. Lithographic process using positive- and negative-resist systems. The element (a) is (b), exposed to uv radiation (c), developed and (d), the metal is...

Some limitations are associated with UV radiation for disinfection. These include (1) The process performance is highly dependent on the efficacy of upstream devices that remove suspended solids (2) Another key factor is that the UV lamps must be kept clean in order to maintain their peak radiation output (3) A further drawback is associated with the fact that a thin layer of water (< 0.5 cm) must pass within 5 cm of the lamps. 

One way of implementing the UV disinfection process at existing activated sludge plants involves suspending the UV lights (in the form of low-pressure mercury arc UV lamps with associated reflectors) above the secondary clarifiers. The effluent is exposed to the UV radiation as it rises over the wire in a thin film. 

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