7.3 Environmental Applications in Advanced Oxidation
Processes
7.3.1 Introduction and Overview
Recently, environmental quality demands have increased with one of the most
challenging issues being the presence of recalcitrant compounds in wastewater,
due to their potential toxicity. Persistent organic compounds in wastewater can be
hazardous or toxic and may cause several problems both in the environment and on
human health. Although, the conventional processes such as physical, chemical, or
biological are usually efficient for the degradation of pollutants occurring in wastewaters, most of these compounds are, however, not effectively removed. In this
context, advanced oxidation processes (AOPs), which are oxidation methods based
on the presence of highly reactive species such as hydroxyl radicals, are raising great
interest for the removal of those organic pollutants not remediable by conventional
methods due to their lack of ability for biodegradation and high chemical stability
(Wu et al. 1999; Neyens and Baeyens 2003; Tian et al. 2011).
Over the past decades, AOPs for wastewater treatment has drawn the attention of
researchers, as they are one of the most promising advanced technologies to eliminate the total organic content, toxic pollutants, and even microbiological contamination from wastewaters (Bethi et al. 2016). Depending on the chemical structure of
the pollutant molecules, AOPs can mineralize some of them into ultimately harmless
substances like CO 2 and H 2 O, avoiding, therefore, the issue of pollution shifting
(Micó et al. 2010).
AOPs have been proposed as alternative methods for the elimination of many
toxic organic compounds in wastewater because they can generate less toxic intermediate products during the degradation of organic pollutants. As compared to the
conventional treatment techniques, AOPs are more efficient and capable of
degrading recalcitrant organic pollutants (Klamerth et al. 2012; Benotti et al. 2009;
Babuponnusami and Muthukumar 2014).
In addition, the conventional methods such as biodegradation, chlorination,
adsorption, coagulation, etc. cannot remove emergent pollutants such as oxytetracyclines (OTC, Fig. 7.4, a broad-spectrum antibiotic) efficiently due to its
bio-resistant property and chemical stability (Liu et al. 2016).
The particular importance of these technologies appears to be in destroying
biologically nondegradable chemical structures, as well as ozone-resistant substances such as organic pesticides, dyes, (Cheng et al. 2015; Agustina 2012; Chen
and Zhu 2011) aromatic structures, (Karci et al. 2012, 2014) and petroleum constituents (Diya’uddeen et al. 2011) present in the wastewaters. However, the use of
AOPs is not cost-effective if mineralizing toxic and recalcitrant compounds in
wastewater is intended (Oller et al. 2011).
7 Titanium Oxide-Based Nanomaterials with Photocatalytic Applications. . .
223
Processes
7.3.1 Introduction and Overview
Recently, environmental quality demands have increased with one of the most
challenging issues being the presence of recalcitrant compounds in wastewater,
due to their potential toxicity. Persistent organic compounds in wastewater can be
hazardous or toxic and may cause several problems both in the environment and on
human health. Although, the conventional processes such as physical, chemical, or
biological are usually efficient for the degradation of pollutants occurring in wastewaters, most of these compounds are, however, not effectively removed. In this
context, advanced oxidation processes (AOPs), which are oxidation methods based
on the presence of highly reactive species such as hydroxyl radicals, are raising great
interest for the removal of those organic pollutants not remediable by conventional
methods due to their lack of ability for biodegradation and high chemical stability
(Wu et al. 1999; Neyens and Baeyens 2003; Tian et al. 2011).
Over the past decades, AOPs for wastewater treatment has drawn the attention of
researchers, as they are one of the most promising advanced technologies to eliminate the total organic content, toxic pollutants, and even microbiological contamination from wastewaters (Bethi et al. 2016). Depending on the chemical structure of
the pollutant molecules, AOPs can mineralize some of them into ultimately harmless
substances like CO 2 and H 2 O, avoiding, therefore, the issue of pollution shifting
(Micó et al. 2010).
AOPs have been proposed as alternative methods for the elimination of many
toxic organic compounds in wastewater because they can generate less toxic intermediate products during the degradation of organic pollutants. As compared to the
conventional treatment techniques, AOPs are more efficient and capable of
degrading recalcitrant organic pollutants (Klamerth et al. 2012; Benotti et al. 2009;
Babuponnusami and Muthukumar 2014).
In addition, the conventional methods such as biodegradation, chlorination,
adsorption, coagulation, etc. cannot remove emergent pollutants such as oxytetracyclines (OTC, Fig. 7.4, a broad-spectrum antibiotic) efficiently due to its
bio-resistant property and chemical stability (Liu et al. 2016).
The particular importance of these technologies appears to be in destroying
biologically nondegradable chemical structures, as well as ozone-resistant substances such as organic pesticides, dyes, (Cheng et al. 2015; Agustina 2012; Chen
and Zhu 2011) aromatic structures, (Karci et al. 2012, 2014) and petroleum constituents (Diya’uddeen et al. 2011) present in the wastewaters. However, the use of
AOPs is not cost-effective if mineralizing toxic and recalcitrant compounds in
wastewater is intended (Oller et al. 2011).
7 Titanium Oxide-Based Nanomaterials with Photocatalytic Applications. . .
223