CCl 4 !
Á CCl 3 þ
Á Cl
ð5:11Þ
CCl 4 !: CCl 2 þ Cl 2
ð5:12Þ
Á CCl 3 !: CCl 2 þ
Á Cl
ð5:13Þ
Á CCl 3 þ
Á CCl 3 ! CCl 4 þ : CCl 2
ð5:14Þ
Á CCl 3 þ
Á CCl 3 ! C 2 Cl 6
ð5:15Þ
: CCl 2 þ : CCl 2 ! C 2 Cl 4
ð5:16Þ
Á Clþ
Á Cl ! Cl 2
ð5:17Þ
The main advantage of the US/CCl 4 process is that both pollutants, the target dye
and CCl 4 , could be eliminated simultaneously. However, the degradation
by-products should be analyzed in depth because of the possible formation of
toxic trihalomethanes in the solution.
5.8.2 Iron (Fe
2+ )
Assistance of the sonolytic treatment with Fe
2+ at low concentration may enhance
the degradation of nonvolatile compounds (Merouani et al. 2010c). The process
should be operated at acidic conditions to avoid iron precipitation as hydroxide. In
this system, the acoustically formed H 2 O 2 can react with iron via Fenton process
(Eqs. 5.18, 5.19 and 5.20) to produce an excess of hydroxyl radical in the contaminated solution (Torres et al. 2007). However, excess of iron is to be avoided because
it may cause a detrimental effect through radical scavenging (Eq. 5.21):
Fe
2þ
þ H 2 O 2 ! Fe
3þ
þ OH
À
þ
Á OH
ð5:18Þ
Fe
3þ
þ H 2 O 2 Ð Fe‐OOH
2þ
þ H
þ
ð5:19Þ
Fe‐OOH
2þ
! Fe
2þ
þ HO 2
Á
ð5:20Þ
Fe
3þ
þ HO 2
Á
! Fe
2þ
þ O 2 þ H
þ
ð5:21Þ
This technique has been successfully applied for intensifying the sonochemical
degradation of several dyes. The presence of Fe
2+ in sonicated solution of Acid Blue
25 at 1700 kHz and pH 3 have resulted in 2.1-fold increase in the initial degradation
rate, but lower enhancement factor of 1.7 was recorded with 50 mg/L of Fe
2+
(Ghodbane and Hamdaoui 2009a). At 300 kHz, rate enhancements were also
reported for the degradation of rhodamine B, Basic Red 29, and malachite green
in the presence of low concentrations of Fe
2+ at pH 3 (Merouani et al. 2010c;
Moumeni et al. 2012; Boutamine et al. 2017). Additionally, the total organic carbon
removal during Basic Red 29 treatment augmented from 2.5% to 35% after 30 min
5 Sonochemical Treatment of Textile Wastewater
177
Á CCl 3 þ
Á Cl
ð5:11Þ
CCl 4 !: CCl 2 þ Cl 2
ð5:12Þ
Á CCl 3 !: CCl 2 þ
Á Cl
ð5:13Þ
Á CCl 3 þ
Á CCl 3 ! CCl 4 þ : CCl 2
ð5:14Þ
Á CCl 3 þ
Á CCl 3 ! C 2 Cl 6
ð5:15Þ
: CCl 2 þ : CCl 2 ! C 2 Cl 4
ð5:16Þ
Á Clþ
Á Cl ! Cl 2
ð5:17Þ
The main advantage of the US/CCl 4 process is that both pollutants, the target dye
and CCl 4 , could be eliminated simultaneously. However, the degradation
by-products should be analyzed in depth because of the possible formation of
toxic trihalomethanes in the solution.
5.8.2 Iron (Fe
2+ )
Assistance of the sonolytic treatment with Fe
2+ at low concentration may enhance
the degradation of nonvolatile compounds (Merouani et al. 2010c). The process
should be operated at acidic conditions to avoid iron precipitation as hydroxide. In
this system, the acoustically formed H 2 O 2 can react with iron via Fenton process
(Eqs. 5.18, 5.19 and 5.20) to produce an excess of hydroxyl radical in the contaminated solution (Torres et al. 2007). However, excess of iron is to be avoided because
it may cause a detrimental effect through radical scavenging (Eq. 5.21):
Fe
2þ
þ H 2 O 2 ! Fe
3þ
þ OH
À
þ
Á OH
ð5:18Þ
Fe
3þ
þ H 2 O 2 Ð Fe‐OOH
2þ
þ H
þ
ð5:19Þ
Fe‐OOH
2þ
! Fe
2þ
þ HO 2
Á
ð5:20Þ
Fe
3þ
þ HO 2
Á
! Fe
2þ
þ O 2 þ H
þ
ð5:21Þ
This technique has been successfully applied for intensifying the sonochemical
degradation of several dyes. The presence of Fe
2+ in sonicated solution of Acid Blue
25 at 1700 kHz and pH 3 have resulted in 2.1-fold increase in the initial degradation
rate, but lower enhancement factor of 1.7 was recorded with 50 mg/L of Fe
2+
(Ghodbane and Hamdaoui 2009a). At 300 kHz, rate enhancements were also
reported for the degradation of rhodamine B, Basic Red 29, and malachite green
in the presence of low concentrations of Fe
2+ at pH 3 (Merouani et al. 2010c;
Moumeni et al. 2012; Boutamine et al. 2017). Additionally, the total organic carbon
removal during Basic Red 29 treatment augmented from 2.5% to 35% after 30 min
5 Sonochemical Treatment of Textile Wastewater
177