processes are based on the in situ production and use of hydroxyl radical, i.e.,
● OH,
as a powerful and nonselective oxidant (E
0
¼ 2.8 V) that reacts with most organics
with high rate constant, i.e., 10
6
–10
9 M
À1 s
À1 (Stefan 2017). Advanced oxidation
processes like Fenton process, electro-Fenton, UV/H 2 O 2 , UV/ozone, H 2 O 2 /O 3 , and
UV/TiO 2 can mineralize partially or completely almost organic pollutants (Parsons
2004; Pignatello et al. 2006; Von Sonntag 2008).
Due to the ability of ultrasound (20–1000 kHz) to generate hydroxyl radicals, this
technique has been classified as an alternative advanced oxidation process for water
and wastewater treatment (Thompson and Doraiswamy 1999; Pétrier 2015). The
sonochemical treatment presents several advantages like no addition of reagents,
simple to handling and selective degradation depending to the nature of pollutants
(Adewuyi 2001; Torres-Palma and Serna-Galvis 2018).
This chapter reviewed fundamental and application aspects of textile effluent
treatment by ultrasound. The scope is restricted to efforts made in the last two
decades, which one part to the literature available data and the other part on the
process performance in different matrices, influencing factors and process intensification techniques. The work was then ended by a conclusion in which some
interesting perspectives were highlighted.
5.2 Basic Principles of Sonochemistry and Sonochemical
Treatment
Since the 1950s, it has been recognized that the passage of ultrasound in the
frequency range of 20 kHz–1 MHz through aqueous solution containing solutes
can produce oxidation reactions, which was called sonochemistry (Weissler et al.
1950). The simplest system evidencing the occurrence of chemical reactions is the
oxidation of KI. When a solution of KI was exposed to ultrasound, the colorless
solution changed to yellow, indicating the oxidation of iodide ions into triiodide ions
I 3
À (Weissler et al. 1950; Hart and Henglein 1985, 1987; Gutiérrez et al. 1987).
Besides, it has been well recognized that the main products of water sonolysis are
hydrogen peroxide and hydrogen (Anbar and Pecht 1964; Fischer et al. 1986; Hart
and Henglein 1987), while nitrite and nitrate ions can also be formed for the case of
air-saturated solution (Mead et al. 1976; Hart et al. 1986).
The sonochemical effect arises from the so-called acoustic cavitation, which is
described as the nucleation, growth, and collapse of transient cavities during ultrasonic irradiation of liquids (Leighton 1994; Mason and Peters 2002). The principle
of this event and their subsequent chemical effects is illustrated in Fig. 5.1. The
microbubbles can be either stable, oscillating about their average or equilibrium size
for many acoustic cycles, or transient when they grow to a certain size in one or at
most a few acoustic cycles and violently collapse during the compression part of the
wave (Yasui 2011). The fast collapse of these bubbles is nearly adiabatic, yielding
5 Sonochemical Treatment of Textile Wastewater
149
● OH,
as a powerful and nonselective oxidant (E
0
¼ 2.8 V) that reacts with most organics
with high rate constant, i.e., 10
6
–10
9 M
À1 s
À1 (Stefan 2017). Advanced oxidation
processes like Fenton process, electro-Fenton, UV/H 2 O 2 , UV/ozone, H 2 O 2 /O 3 , and
UV/TiO 2 can mineralize partially or completely almost organic pollutants (Parsons
2004; Pignatello et al. 2006; Von Sonntag 2008).
Due to the ability of ultrasound (20–1000 kHz) to generate hydroxyl radicals, this
technique has been classified as an alternative advanced oxidation process for water
and wastewater treatment (Thompson and Doraiswamy 1999; Pétrier 2015). The
sonochemical treatment presents several advantages like no addition of reagents,
simple to handling and selective degradation depending to the nature of pollutants
(Adewuyi 2001; Torres-Palma and Serna-Galvis 2018).
This chapter reviewed fundamental and application aspects of textile effluent
treatment by ultrasound. The scope is restricted to efforts made in the last two
decades, which one part to the literature available data and the other part on the
process performance in different matrices, influencing factors and process intensification techniques. The work was then ended by a conclusion in which some
interesting perspectives were highlighted.
5.2 Basic Principles of Sonochemistry and Sonochemical
Treatment
Since the 1950s, it has been recognized that the passage of ultrasound in the
frequency range of 20 kHz–1 MHz through aqueous solution containing solutes
can produce oxidation reactions, which was called sonochemistry (Weissler et al.
1950). The simplest system evidencing the occurrence of chemical reactions is the
oxidation of KI. When a solution of KI was exposed to ultrasound, the colorless
solution changed to yellow, indicating the oxidation of iodide ions into triiodide ions
I 3
À (Weissler et al. 1950; Hart and Henglein 1985, 1987; Gutiérrez et al. 1987).
Besides, it has been well recognized that the main products of water sonolysis are
hydrogen peroxide and hydrogen (Anbar and Pecht 1964; Fischer et al. 1986; Hart
and Henglein 1987), while nitrite and nitrate ions can also be formed for the case of
air-saturated solution (Mead et al. 1976; Hart et al. 1986).
The sonochemical effect arises from the so-called acoustic cavitation, which is
described as the nucleation, growth, and collapse of transient cavities during ultrasonic irradiation of liquids (Leighton 1994; Mason and Peters 2002). The principle
of this event and their subsequent chemical effects is illustrated in Fig. 5.1. The
microbubbles can be either stable, oscillating about their average or equilibrium size
for many acoustic cycles, or transient when they grow to a certain size in one or at
most a few acoustic cycles and violently collapse during the compression part of the
wave (Yasui 2011). The fast collapse of these bubbles is nearly adiabatic, yielding
5 Sonochemical Treatment of Textile Wastewater
149