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

Abstract

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.This chapter discusses the influence of different AOP on the degradation and mineralization of several different classes of organic pollutants such as pesticides, pharmaceutical formulations 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 TiO 2 nanotubes obtained by electrochemical anodization, nanoparticles prepared by a molten salt technique, and Ag-doped TiO 2 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. Advanced Oxidation Processes (AOP)AOP are specific chemical reactions characterized by the generation of chemical oxidizing agents capable of oxidizing or degrading the pollutant of interest. The efficiency of the AOP is generally maximized by the use of an appropriate catalyst and/or ultraviolet light [1][2][3].In most AOP, the objective is to use systems that produce the hydroxyl radical (HO • ) or another species of similar reactivity such as sulfate radical anion (SO 4 •-). These radicals react with the majority of organic substances at rates often approaching the diffusion-controlled limit (unit reaction efficiency per encounter). Both of these species are thus highly reactive and only modestly selective in their capacity to degrade toxic organi...

A Review of Pharmaceuticals and Endocrine-Disrupting Compounds: Sources, Effects, Removal, and Detections

“…The hydroxyl radical is highly reactive and non-selective against refractory organic pollutants with subsequent conversion of the pollutants to CO 2 , H 2 O, and mineral acids. In the last couple of years, AOPs have been extensively exploited and reported in the literature for the degradation of different wastewater containing contaminants such as pesticides, pharmaceuticals, endocrine disruptors, and dye molecules (Stasinakis 2008;Saien et al 2011;Machulek Jr et al 2013). AOPs could be generally classified into (1) homogeneous AOPs and (2) heterogeneous AOPs.…”

Assessment of Sulfate Radical-Based Advanced Oxidation Processes for Water and Wastewater Treatment: A Review

“…AOPs occur in two steps: in situ formation of radicals and their reaction with organic or biological pollutants [21]. These technologies are based on the use of a broad range of photocatalysts, TiO 2 being the most used, or the combination of oxidants such as hydrogen peroxide, peroxymonosulfate or persulfate with metal catalysts or ultraviolet (UV) radiation [24]. AOPs based on the generation of hydroxyl radicals are the most deliberated treatments.…”

“…Oxidation potential of commonly used oxidants [26]. One of the most studied AOPs is the Fenton's reagent and its variations, where iron species (mainly Fe 2+ ) is used as catalyst and hydrogen peroxide acts as oxidant [23][24][25][26]. This technology presents some operation problems that have to be addressed [22,23] Restricted pH working range (pH 2-4) 3.…”

Oxidative Photodegradation of Pyrene and Fluoranthene by Fe-Based and Zn-Based Fenton Reagents

“…Flr degradation by the Fe-based Fenton reagent accounted for 25.96, 14.26, 6.25, and 7.76% more degradation than that for the Zn-based Fenton reagent at 0.25, 0.5, 1, and 2 h of UV exposure, respectively. The mode of action of the Zn-based Fenton reagent could be different from that for the Fe-based Fenton reagent, summarized as [36,37] Zn…”