2. Accumulation of iron sludge that must be removed at the end of the treatment;
3. Impossibility of the general mineralization due to the formation of Fe (III)
carboxylic acid complexes, which can’t be destroyed efficiently with the volume
•OH.
5.4.1.2 Photochemical oxidation
Photochemical technologies have the advantages of being simple, clean, relatively
economical and, in general, more efficient than simple chemical oxidative processes.
In addition, they can disinfect water and destroy contaminants. Consequently, UV
radiation has coupled with powerful oxidants such as O 3 and H 2 O 2 , which include,
in some cases, catalysis with Fe
3+ or TiO 2 , which results in several types of
important photochemical oxidative processes. These photochemical processes can
degrade and/or destroy contaminants employing three possible reactions, including
photodecomposition, based on UV radiation, excitation and degradation of contaminating molecules, oxidation by the direct action of O 3 and H 2 O 2 , and oxidation by
photocatalysis (with Fe
3+ or TiO 2 ), inducing the formation of radicals •OH (Oturan
and Aaron 2014).
As an example, there are photochemical oxidation techniques that have shown
good results for the degradation of organic compounds in the aqueous phase, such
as:
1. Photolysis of H 2 O 2 (H 2 O 2 /UV) (Antonaraki et al. 2002; Hernandez et al. 2002)
2. Photolysis of O 3 (O 3 /UV) (Parsons 2004; Zaviska et al. 2009)
3. Heterogeneous photocatalysis (TiO 2 /UV) (Fujishima et al. 2000; Mills and Le
Hunte 1997)
4. Photo-Fenton (H 2 O 2 /Fe
2+ /UV) (Oturan and Aaron 2014; Pera-Titus et al. 2004)
5.4.1.3 Sonochemical Oxidation
Ultrasounds in aqueous media constitute a particular technology that can proceed
through two different types of actions, be it a chemical (indirect) or physical
(direct) mechanism. In the indirect action, generally performed at high frequency,
the water and dioxygen molecules undergo homolytic fragmentation and yield the
radicals • OH, HO 2 • and •O (Trabelsi et al. 1996).
Direct action, called sonication, involves the formation of ultrasonic cavitation
bubbles that grow, then collapse, creating powerful breaking forces at extremely
high temperatures (2000–5000 K) and pressures (approximately 6x10
4 kPa). In these
extreme conditions, a sonolysis of water molecules occurs, which produces very
reactive radicals capable of reacting with organic chemical species present in the
aqueous medium, and / or degradation by pyrolysis of organic compounds (Zaviska
et al. 2009).
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S. M. Sathianesan Vimala et al.
3. Impossibility of the general mineralization due to the formation of Fe (III)
carboxylic acid complexes, which can’t be destroyed efficiently with the volume
•OH.
5.4.1.2 Photochemical oxidation
Photochemical technologies have the advantages of being simple, clean, relatively
economical and, in general, more efficient than simple chemical oxidative processes.
In addition, they can disinfect water and destroy contaminants. Consequently, UV
radiation has coupled with powerful oxidants such as O 3 and H 2 O 2 , which include,
in some cases, catalysis with Fe
3+ or TiO 2 , which results in several types of
important photochemical oxidative processes. These photochemical processes can
degrade and/or destroy contaminants employing three possible reactions, including
photodecomposition, based on UV radiation, excitation and degradation of contaminating molecules, oxidation by the direct action of O 3 and H 2 O 2 , and oxidation by
photocatalysis (with Fe
3+ or TiO 2 ), inducing the formation of radicals •OH (Oturan
and Aaron 2014).
As an example, there are photochemical oxidation techniques that have shown
good results for the degradation of organic compounds in the aqueous phase, such
as:
1. Photolysis of H 2 O 2 (H 2 O 2 /UV) (Antonaraki et al. 2002; Hernandez et al. 2002)
2. Photolysis of O 3 (O 3 /UV) (Parsons 2004; Zaviska et al. 2009)
3. Heterogeneous photocatalysis (TiO 2 /UV) (Fujishima et al. 2000; Mills and Le
Hunte 1997)
4. Photo-Fenton (H 2 O 2 /Fe
2+ /UV) (Oturan and Aaron 2014; Pera-Titus et al. 2004)
5.4.1.3 Sonochemical Oxidation
Ultrasounds in aqueous media constitute a particular technology that can proceed
through two different types of actions, be it a chemical (indirect) or physical
(direct) mechanism. In the indirect action, generally performed at high frequency,
the water and dioxygen molecules undergo homolytic fragmentation and yield the
radicals • OH, HO 2 • and •O (Trabelsi et al. 1996).
Direct action, called sonication, involves the formation of ultrasonic cavitation
bubbles that grow, then collapse, creating powerful breaking forces at extremely
high temperatures (2000–5000 K) and pressures (approximately 6x10
4 kPa). In these
extreme conditions, a sonolysis of water molecules occurs, which produces very
reactive radicals capable of reacting with organic chemical species present in the
aqueous medium, and / or degradation by pyrolysis of organic compounds (Zaviska
et al. 2009).
126
S. M. Sathianesan Vimala et al.