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...

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The mineralization of bio-recalcitrant humic acids (HAs) by a solar photo-Fenton (SPF) process was investigated in aqueous system, in order to understand its abatement in real high-HA content matrices, such as sanitary landfill leachates. SPF reactions were performed in tubular photoreactors with CPCs at lab-scale (simulated solar light) and pilot-scale (natural sunlight). Considering the experimental conditions selected for this work, the formation of insoluble HA-Fe complexes was observed. Thus, to avoid HA precipitation, oxalic acid (Ox) was added, since Fe-Ox complexes present a higher stability constant. The effect of different process variables on the performance of SPF reaction mediated by ferrioxalate complexes (SPFF) was assessed with excess of HO (50-250 mg L), at lab-scale: (i) pH (2.8-4.0); (ii) initial iron concentration (20-60 mg Fe L); (iii) iron-oxalate molar ratio (Fe-Ox of 1:3 and 1:6); (iv) temperature (20-40 °C); (v) UV irradiance (21-58 W m); and (vi) commercial-HA concentration (50-200 mg C L). At the best lab conditions (40 mg Fe L, pH 2.8, 30 °C, 1.6 Fe-Ox molar ratio, 41 W m), commercial HAs' mineralization profile was also compared with HAs extracted from a sanitary landfill leachate, achieving 88 and 91% of dissolved organic carbon removal, respectively, after 3-h irradiation (8.7 kJ L). Both reactions followed the same trend, although a 2.1-fold increase in the reaction rate was observed for the leachate-HA experiment, due to its lower humification degree. At pilot-scale, under natural sunlight, 95% HA mineralization was obtained, consuming 42 mM of HO and 5.9 kJ L of accumulated UV energy. However, a pre-oxidation during 2.8 kJ L (12 mM HO) was enough to obtain a biodegradability index of 89%, showing the strong feasibility to couple the SPFF process to a downstream biological oxidation, with low chemicals and energetic demands. Graphical abstract ᅟ.