Photooxidation
UV-Technology - Photooxidation
Advantages of Photooxidation
- irreversible remove of organic pollution
- process free from residues
- no use of chemistry no increase of salinity
- treatment of difficult degradable pollutions
- easy process control, high operational safety
- also usable for batch reactions
- easy combination with biological processes
- effective use of oxidation agent caused in the use of special vacuum-uv-lamps.
Photooxidation - How it works
With Photooxidation, sometimes also called advanced oxidation (AOP) or uv catalyzed wet oxidation, you may destroy organic components inside the air or the water under the help of strong oxidizing agents, like Hydrogenperoxide or Ozone. It is possible to have a complete oxidation down to carbon dioxide, water and if existing other chemicals.
The effectiveness of the process depends on the oxidation potential of the used oxidizing agent.
In the following table you'll find the oxidation potentials of some important oxidizing agents.
| Oxidizing agent | Symbol | el.-chem. Potential (V) | potential rel. to Chlorine (%) |
|---|---|---|---|
| Fluor | F2 | 3,06 | 2,25 |
| Hydroxyl radikal | *OH | 2,80 | 2,05 |
| Atomic oxygen | *O | 2,42 | 1,78 |
| Ozone | O3 | 2,08 | 1,52 |
| Hydrogenperoxide | H2O2 | 1,78 | 1,30 |
| Hypochlorous acid | HClO | 1,49 | 1,10 |
| Chlorine | Cl2 | 1,36 | 1,00 |
| Chlor dioxide | ClO2 | 1,27 | 0,93 |
| Oxygene | O2 | 1,23 | 0,90 |
You can see in the table, that the free hydroxyl radical has the highes oxidzing potential and will be the best for use in oxidation processes. UV radiation in a wave length range between 190 nm and 280 nm causes the breakdown of the hydrogenperoxide to hydroxyl radicals. For this reaction the hydrogenperoxide molecule must adsorb a photon.
Also in the case of using Ozone it is possible to generate hydroxyl radicals. However in this case we have a two step reaction and two photons are needed to produce one radical.
Parallel to the production of hydroxyl radicals direct reactions of the organic compounds may be activated by the photons. Further may be occur recombination reactions.
Photochemical indicated oxidizing processes are under the influence of different factors. These factors may be interference among each other. The substantially factors of influence are:
- Type and concentration of used oxidizing agent
- Concentration of pollution which is to be oxidise
- Wavelength and intensity of the uv radiation
- Concentration of active oxidizing radicals (e.g. Hydroxyl radicals)
The result of the reaction isn't depending from one of this facts or parameters. In each case of using the Photooxidation process a parameter field must be determined to became an optimum result. Thats causes, that a succesful use of Photooxidation processes is only possible after laboratory and pilot tests. In these tests specialists find out the necessary parameter field for the process.