Advanced oxidation process application

The oxidative degradation of organic pollutants in water and air streams is considered as one of the so-called advanced oxidation processes. Photocatalytic decomposition of organics found widespread industrial interest for air purification (e.g., decomposition of aldehydes, removal of NO , ), deodorization, sterilization, and disinfection. Domestic applications based on Ti02 photocatalysts such as window self-cleaning, bathroom paints that work under illumination with room light, or filters for air conditioners operating under UV lamp illumination have already been commercialized. Literature-based information on the multidisciplinary field of photocatalytic anti-pollutant systems can be found in a number of publications, such as Bahnemann s [237, 238] (and references therein). 

Bioprocesses for the removal of nitrogen oxides from polluted air are an interesting alternative [58], but current reaction rates are still too low for large-scale applications. Advanced biological processes for the removal of NO from flue gases are based on the catalytic activity of either eukaryotes or prokaryotes, e.g. nitrification, denitrification, the use of microalgae and a combined physicochemical and biological process (BioDeNO ). 

Intensification can be achieved using this approach of combination of cavitation and advanced oxidation process such as use of hydrogen peroxide, ozone and photocatalytic oxidation, only for chemical synthesis applications where free radical attack is the governing mechanism. For reactions governed by pyrolysis type mechanism, use of process intensifying parameters which result in overall increase in the cavitational intensity such as solid particles, sparging of gases etc. is recommended. 

The similarity between the mechanism of destruction and some of the common optimum operating conditions in the case of different advanced oxidation techniques point towards the synergism between these methods and fact that combination of these advanced oxidation processes should give better results as compared to individual techniques [70]. This indeed is applicable to hydrodynamic cavitation as well and there have been reports where hydrodynamic cavitation has been combined with other advanced oxidation processes with great success. 

It is expected that in the very near future, the application of closed water loops will show an intensive growth, strongly supported by the further development of separate treatment technologies such as anaerobic treatment, membrane bioreactors, advanced biofilm processes, membrane separation processes, advanced precipitation processes for recovery of nutrients, selective separation processes for recovery of heavy metals, advanced oxidation processes, selective adsorption processes, advanced processes for demineralisation, and physical/chemical processes which can be applied at elevated temperature. 

During the last two decades an increasing interest in the application of Advanced Oxidation Processes (AOPs) is observed. These processes are applied for the oxidation of toxic organic pollutants present in wastewater or in surface water that is used for the production of drinking water. The process of oxidation is mainly based on the oxidative destruction by radicals of which the hydroxyl radical (OH ) is the most powerful one. Most important AOPs are ... 

The advanced oxidation processes offer the possibility for destruction of recalcitrant biodegradable and toxic organic pollutants. The field of applications regarding wastewater treatment varies. AOPs can be applied as ... 

Suty, H., De Traversay, C., and Cost, M. (2004). Applications of advanced oxidation processes Present and future. Water Sci. Technol. 49, 227-233. 

The detection of new kinds of microorganisms, such as the cysts and oocysts of parasites (Giardia, Cryptosporidium), the identification of more and more chemical pollutants in waters and increasing quality levels required for drinking and waste waters has induced new interest in ozonation and ozone-based advanced oxidation processes. However, care has to be taken in the application of ozonation, since recent research has indicated that presumably hazardous by-products can be formed, e. g. bromate in the ozonation of waters containing bromide. 

Bigot V, Luck F, Paillard H, Wagner A (1994) Evaluation of advanced oxidation processes for landfill leachate treatment, in Proceedings of the international ozone symposium Application of ozone in water and wastewater treatment , Bln A K (ed.) Warsaw Poland May 26-27 330-343. 

An example where all four areas are utilized in combination with production processes is found in ozone applications in the semiconductor industry (Section B 6.1). Part of ozone s effectiveness in these four areas is derived from its production of OH-radicals. Combined processes, i. e. advanced oxidation processes, represent alternative techniques for catalyzing the production of these radicals and expands the range of compounds treatable with ozone (Section B 6.2). 

Any oxidation process in which hydroxyl radical is the dominant species is defined as an advanced oxidation process (AOP). For any oxidation reaction, two factors determine the rate of reaction. First, if a reaction has a high free energy or high electrical potential, the reaction is very likely to occur and it is considered to be thermodynamically favorable. The oxidation potentials for common oxidants suitable for environmental applications are listed in Table 4.1. 

Orlando M. Alfano and Alberto E. Cassano, Scaling-Up of Photoreactors Applications to Advanced Oxidation Processes... 

Beltran FJ, Rivas FJ, Alvarez P, Alonso MA, Acedo B. A kinetic model for advanced oxidation processes of aromatic hydrocarbons in water application to phenanthrene and nitrobenzene. Ind Eng Chem Res 1999 38 4189-4-199. 

Pedit JA, Iwamasa KJ, Miller CT, Glaze WH. Development and application of a gas-liquid contactor model simulating advanced oxidation processes. Environ Sci Technol 1997 31 2791-2796. 

Bolton JR, Bircher KG, Tumas W, Toldman CA. Figures-of-merit for the technical development and application of advanced oxidation processes. J Adv Oxid Technol 1996 1 13-17. 

Bergmann, H. and Rollin, J. (2006c) Product and by-product formation using doped diamond anodes in disinfection electrolysis of drinking water. 1. European Conference on Environmental Application of Advanced Oxidation Processes (EAAOP), Chania/Greece, Conference Materials Full text version P198, pp. 1-6 and Book of Abstracts, p. 218. 

Figures 1 and 2 have been reproduced from Int. J. Chem. React. Eng. Reference Alfano, O.M., Cassano, A.E., 2008, Photoreactor modeling. Applications to advanced oxidation processes, figures 1 and 2, Copyright 2008, with permission from The Berkeley Electronic Press.

---