Advanced Oxidation Processes in Water Treatment

The use of advanced oxidation processes (AOPs) to remove pollutants in water treatment applications has been widely studied and applied industrially, but it is still an area of active development. New problems derive from toxic, refractory and xenobiotic micropollutants and the increasing requirements in terms of energy efficiency and quality of water in several industrial wastewater streams. This chapter introduces the AOP technologies and discusses the possibilities offered by using catalysts in these methods, with selected examples regarding the industrial applicability of these AOPs and open questions about their further development. 

Water is an essential compound for life on Earth and its quality is crucial for the future of humanity. Human alterations to the water cycle combined with direct and indirect pollution have a profound effect on water availability and quality. Consequently, not only is the availability of water resources decreasing, but the quality is also worsening. Only a small fraction of the available surface water meets the quaUty necessary for human and industrial use of water, and there is an increasing need for improved technologies to treat wastewater, remediate polluted water resources and eliminate micropollutants from water. 

In addition to the treatment of wastewaters and raw waters for human consumption and industrial uses, remediation of contaminated sites is another relevant area 

UV radiation is used to produce hydroxyl radicals (for example, by homolytic splitting of hydrogen peroxide) and in some cases for the degradation of compounds sensitive to UV radiation. When colored chemicals are present (dyes, for example) solar light could be used, with the dye also acting as photosensitizer. The costs of UV radiation treatment processes are largely dependent on the absorption properties 

Electrochemical oxidation Anodic oxidation Electro-Fenton 

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Litter MI (2005) Introduction to photochemical advanced oxidation processes for water treatment. In Boule P, Bahnemann DW, Robertson PKJ (eds) Environmental Photochemistry Part II, vol 2. Springer, Berlin/Heidelberg, pp 325-366... 

Lafi, W.K., Al-Anber, M., Al-Anber, Z.A., Al-Shannag, M., and Khalil, A. 2010. Coagulation and advanced oxidation processes in the treatment of ohve mill wastewater (OMW). Desalin Water Treat. 24 251-256. 

Parsons, SA Williams, M. Introduction. In Parsons SA, editor. Advanced oxidation processes for water and wastewater treatment. London IWA Publishing 2004 1-6. 

Hoigne J (1998) Chemistry of Aqueous Ozone and Transformation of Pollutants by Ozonation and Advanced Oxidation Processes, in The Handbook of Environmental Chemistry Vol. 5 Part C, Quality and Treatment of Drinking Water II, ed. by J Hrubec, Springer- Verlag, Berlin, Heidelberg. 

All of the facts mentioned above and the observation that several photochemical AOTs for water and air remediation have been successfully commercialized during recent years, justify a comprehensive description of photochemically driven advanced oxidation processes for water and air treatment in this book, which includes a brief description of UV disinfection techniques. 

Muller )-P, Gottschalk C, )ekel M (2000) Comparison of Advanced Oxidation Processes in Flow-Through Pilot Plants, Proceedings of the 2 International Conference on Oxidation Technologies for Water and Wastewater Treatment, Clausthal-Zel-lerfeld, Germany, 28-31 May 2000, electronic release. 

This entry introduces applications of ozone technology in various areas water and wastewater treatment control of the microbial safety of food decontamination of soils polymer surface modification and bleaching paper pulps. For water and wastewater treatment, in addition to being used alone, ozone is increasingly used in combination with heterogenous catalysts, UV/H2O2 (advanced oxidation process), and biological treatment to enhance ozonation efficiency. The discussion that follows mainly introduces the applications of ozone in water and wastewater treatment because ozone has been both extensively and intensively used in this area however, it does briefly describe other applications. 

Hoign4 J (1998) Chemistry of aqueous ozone and transformation of pollutants by ozonation and advanced oxidation processes. In Hrubec J (ed) The Handbook of Environmental Chemistry, vol 5. part C. Quality and Treatment of Drinking Water 11. Springer, Berlin Heidelberg New York... 

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. 

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]. 

Powerful oxidant treatments are also necessary to remove multi-dmg-resistant bacteria [122] and residues of medicaments with ecotoxicological effects from hospital effluent, in order to reduce their impact on the final receiving water bodies. Advanced oxidation processes, including the Fenton reaction, are likely candidates [123]. 

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