**Application of Different Advanced Oxidation Processes for the Degradation of Organic Pollutants**

Amilcar Machulek Jr., Silvio C. Oliveira, Marly E. Osugi, Valdir S. Ferreira, Frank H. Quina, Renato F. Dantas, Samuel L. Oliveira, Gleison A. Casagrande, Fauze J. Anaissi, Volnir O. Silva, Rodrigo P. Cavalcante, Fabio Gozzi, Dayana D. Ramos, Ana P.P. da Rosa, Ana P.F. Santos, Douclasse C. de Castro and Jéssica A. Nogueira

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/53188

**1. Introduction**

Water is not only an economic, but also an increasingly important social commodity. Potable water is an essential resource for sustaining economic and social development in all sectors. A safe water supply and appropriate sanitation are the most essential components for a healthy and prosperous life. However, increases in human activities have led to exposure of the aqueous environment to chemical, microbial and biological pollutants as well as to micropollutants. Thus, liquid effluents containing toxic substances are generated by a variety of chemistry-related industrial processes, as well as by a number of common household or agricultural applications.

New, economically viable, more effective methods for pollution control and prevention are required for environmental protection and effluent discharge into the environment must have minimal impact on human health, natural resources and the biosphere.

Research in photochemical and photocatalytic technology is very promising for the develop‐ ment of viable alternatives for the treatment of polluted waters and effluents from various sources, including both industrial and domestic. Currently available chemical and photo‐ chemical technology permits the conversion of organic pollutants with a wide range of

chemical structures into substances that are less toxic and/or more readily biodegradable by employing chemical oxidizing agents in the presence of an appropriate catalyst and/or ultraviolet light to oxidize or degrade the pollutant of interest. These technologies known as advanced oxidation processes (AOP) or advanced oxidation technologies (AOT), have been widely studied for the degradation of diverse types of industrial wastewaters. These processes are particularly interesting for the treatment of effluents containing highly toxic organic compounds, for which biological processes may not be applicable unless bacteria that are adapted to live in toxic media are available. The production of powerful oxidizing agents, such as the hydroxyl radical, is the main objective of most AOP. The hydroxyl radical reacts rapidly and relatively non-selectively with organic compounds by hydrogen abstraction, by addition to unsaturated bonds and aromatic rings, or by electron transfer. In the case of persistent organic pollutants (wastes), complete decontamination may require the sequential application of several different decontamination technologies such as a pretreatment with a photochemical AOP followed by a biological or electrochemical treatment.

The AOP are of two main types: homogeneous and heterogeneous processes, both of which can be conducted with or without the use of UV radiation. Thus, for example, the homogeneous process based on the reaction of Fe2+ with H2O2, known as the thermal-Fenton reaction process typically becomes more efficient for the mineralization of organic material present in the effluent when it is photocatalysed. This latter process (Fe2+/Fe3+, H2O2, UV-Vis) is commonly referred to as the photo-Fenton reaction. Among the heterogeneous AOP, processes using some form of the semiconductor TiO2 stand out because UV irradiation of TiO2 results in the

Application of Different Advanced Oxidation Processes for the Degradation of Organic Pollutants

http://dx.doi.org/10.5772/53188

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AOP and their applications have attracted the attention of both the scientific community and of corporations interested in their commercialization. This can be illustrated by means of searches, in August, 2012, of the Science Finder Scholar database (version 2012). This database covers the complete text of articles/papers indexed from over 15475 international journals and 126 databases with abstracts of documents in all areas, as well as several other important sources of academic information. The results of the searches were organized as histograms to show the evolution of the number of publications (arti‐ cles or patents) related to the different kinds of AOP. Figure 1 shows the results of a search using the keywords "advanced oxidation processes", which yielded approximately 840 publications and which nicely reflects the rapid growth in interest AOP, given the

1988 1992 1996 2000 2004 2008 2012

Year

**Figure 1.** Number of publications per year indexed in the Science Finder Scholar database retrieved using the key‐

generation of hydroxyl radicals, promoting the oxidation of organic species [1,6].

unique characteristics and the versatility of application of AOP.

AOP

0

20

40

60

Publications

words "advanced oxidation processes".

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**2.1. Advances in research on AOP**

This chapter discusses the influence of different AOP on the degradation and mineralization of several different classes of organic pollutants such as pesticides, pharmaceutical formula‐ tions and dyes. The use of the Fenton and photo-Fenton reactions as tools for the treatment of pesticides and antineoplastic agents is presented, as well as examples of the optimization of the important parameters involved in the process such as the source of iron ions (free or complexed), the irradiation source (including the possibility of using sunlight), and the concentrations of iron ions and hydrogen peroxide. The chapter also reports the use of TiO2 nanotubes obtained by electrochemical anodization, nanoparticles prepared by a molten salt technique, and Ag-doped TiO2 nanoparticles as heterogeneous photocatalysts, emphasizing their potential for use in environmental applications. These catalysts were characterized by a combination of techniques, including scanning electron microscopy, elemental analysis, and energy dispersive x-ray spectroscopy.
