Both the cavity expansion and compression ratios increase as the acoustic power
increased, allowing to increase the amount of the trapped water vapor as well as the
bubble temperature at the last stage of the collapse (Merouani et al. 2014b). As a
result, higher amount of free radicals could be produced at higher applied acoustic
intensities leading to higher sonochemical effect within and surrounding the bubble.
Besides, the number of cavitation bubbles increases when higher acoustic intensities
are applied (Brotchie et al. 2009; Merouani et al. 2013; Ferkous et al. 2015a).
Consequently, better sonochemical effects could be achieved with intensity increase.
5.6.3 Liquid Temperature
In general, an increase in the liquid temperature in the range 25–55
C have
conducted to higher degradation rate of several synthetic dyes at different
sonochemical conditions (Ghodbane and Hamdaoui 2009a; Merouani et al. 2010c,
2016; Ferkous et al. 2016; Chadi et al. 2018b). These findings were accompanied
with higher accumulation rates of H 2 O 2 in the solution at higher liquid temperatures
(Merouani et al. 2010b; Chadi et al. 2018b), meaning that higher concentration of
free radicals can be generated at higher liquid temperatures.
The single bubble results showed that there exists an optimal liquid temperature
(~20–30
C) for the production of
Á OH inside a single bubble (Merouani et al. 2015,
2016), but the number of active bubbles was dramatically increased with increasing
liquid temperature (Merouani et al. 2016; Chadi et al. 2018b). The global production
rate of
Á OH radical augmented with augmenting solution temperature in the range of
25–55
C. Based on these findings, Merouani et al. (2016) have concluded that the
predominant factor that controls the effect of liquid temperature on the sonochemical
degradation of dyes is the number of bubbles.
However, a new trend of the bulk liquid temperature has been lately reported by
the same group: the impact of liquid temperature on the sonolytic removal of
toluidine blue is sensitively dependent to the initial dye concentration. At a low
dye concentration, i.e., less than 2 mg/L, the degradation rate was noted to be
affected by the temperature rise in the interval of 25–70
C. However, for higher
dye concentration, the temperature rise for up to 50
C improved significantly the
degradation rate. The authors have attributed this dependence to the displacement of
the reaction zone with the dye concentration. At lower dye loadings, the liquid bulk
is the predominant reaction zone, and increasing the solution temperature in this case
could not influence the dye removal rate as the dye molecules are always far from the
interfacial region where high concentration of
Á OH is suspected. However, the
degradation zone may be moved progressively toward the bubble-solution interface
as the dye concentration in the solution is high. In this case, higher liquid temperatures could promote the degradation rate of the dye through increasing the interfacial concentration of
Á OH radicals.
5 Sonochemical Treatment of Textile Wastewater
171
increased, allowing to increase the amount of the trapped water vapor as well as the
bubble temperature at the last stage of the collapse (Merouani et al. 2014b). As a
result, higher amount of free radicals could be produced at higher applied acoustic
intensities leading to higher sonochemical effect within and surrounding the bubble.
Besides, the number of cavitation bubbles increases when higher acoustic intensities
are applied (Brotchie et al. 2009; Merouani et al. 2013; Ferkous et al. 2015a).
Consequently, better sonochemical effects could be achieved with intensity increase.
5.6.3 Liquid Temperature
In general, an increase in the liquid temperature in the range 25–55
C have
conducted to higher degradation rate of several synthetic dyes at different
sonochemical conditions (Ghodbane and Hamdaoui 2009a; Merouani et al. 2010c,
2016; Ferkous et al. 2016; Chadi et al. 2018b). These findings were accompanied
with higher accumulation rates of H 2 O 2 in the solution at higher liquid temperatures
(Merouani et al. 2010b; Chadi et al. 2018b), meaning that higher concentration of
free radicals can be generated at higher liquid temperatures.
The single bubble results showed that there exists an optimal liquid temperature
(~20–30
C) for the production of
Á OH inside a single bubble (Merouani et al. 2015,
2016), but the number of active bubbles was dramatically increased with increasing
liquid temperature (Merouani et al. 2016; Chadi et al. 2018b). The global production
rate of
Á OH radical augmented with augmenting solution temperature in the range of
25–55
C. Based on these findings, Merouani et al. (2016) have concluded that the
predominant factor that controls the effect of liquid temperature on the sonochemical
degradation of dyes is the number of bubbles.
However, a new trend of the bulk liquid temperature has been lately reported by
the same group: the impact of liquid temperature on the sonolytic removal of
toluidine blue is sensitively dependent to the initial dye concentration. At a low
dye concentration, i.e., less than 2 mg/L, the degradation rate was noted to be
affected by the temperature rise in the interval of 25–70
C. However, for higher
dye concentration, the temperature rise for up to 50
C improved significantly the
degradation rate. The authors have attributed this dependence to the displacement of
the reaction zone with the dye concentration. At lower dye loadings, the liquid bulk
is the predominant reaction zone, and increasing the solution temperature in this case
could not influence the dye removal rate as the dye molecules are always far from the
interfacial region where high concentration of
Á OH is suspected. However, the
degradation zone may be moved progressively toward the bubble-solution interface
as the dye concentration in the solution is high. In this case, higher liquid temperatures could promote the degradation rate of the dye through increasing the interfacial concentration of
Á OH radicals.
5 Sonochemical Treatment of Textile Wastewater
171