5.9 Conclusion
In summary, the sonochemical treatment is a promising technique for the destruction
of textile dyes in aqueous effluents. Textile dyes are nonvolatile compound that
degrade mostly at the bubble-solution interface and in the solution bulk via hydroxyl
radical attack. The degradation rate is affected by sonochemical parameters, i.e.,
frequency and power, and environmental conditions, i.e., liquid temperature, pollutant concentration, physicochemical properties of the solution, presence of salts and
gases, and so forth. In this chapter, the recent researches on sonochemical treatment
of the textile dyes including degradation data, influencing parameters, impact of
water matrix constitutes, and process intensification techniques were presented.
Although the evident development has been attained, the sonochemical process
still faces numerous challenges. More efforts may be focused on the next topics:
(i) To better understand the effective action of the sonochemical treatment, the
degradation of textile dyes should be analyzed in depth and, particularity, in
terms of total organic carbon removal and by-products identification and
quantification because the degradation products may be more toxic than the
initial pollutant.
(ii) Because dyes are nonvolatile, it is important to develop methods that make easy
the accumulation of dyes at the reactive interfacial area of cavitation bubble.
Also, novel techniques to enhance the number of inertial bubbles are
researched. One recent technique for this issue is to combine ultrasound with
catalysts, i.e., sonocatalysis.
(iii) There is a requirement to improve our knowledge on the extent of
sonochemical reactions in industrial-scale ultrasonic reactors. Even though
much data on sonochemical degradation of textile dyes at lab scale have been
accumulated, the application of this technology to large-scale operations was
poorly investigated. The attenuation of the sound wave in big structures is a
principal factor that affects the efficiency of the sonolytic treatment (Kerabchi
et al. 2018). It is of interest to understand the characteristics of the sound field
because the sound propagation in big reactors differs from those in lab-scale
ones (Kerabchi et al. 2018). Thus, there are still lost links between lab-scale and
industrial-scale sonochemical processes. The following topics are also required
for the implementation of the sonochemical treatment for industrial use (Son
2015):
– Reactor design including sonoreactor size/shape/material, transducer location/array, and internal structure
– Studying of the liquid depth on the sonochemical efficiency of the process
– Development of continuous-flow sonochemical reactors
180
S. Merouani and O. Hamdaoui
In summary, the sonochemical treatment is a promising technique for the destruction
of textile dyes in aqueous effluents. Textile dyes are nonvolatile compound that
degrade mostly at the bubble-solution interface and in the solution bulk via hydroxyl
radical attack. The degradation rate is affected by sonochemical parameters, i.e.,
frequency and power, and environmental conditions, i.e., liquid temperature, pollutant concentration, physicochemical properties of the solution, presence of salts and
gases, and so forth. In this chapter, the recent researches on sonochemical treatment
of the textile dyes including degradation data, influencing parameters, impact of
water matrix constitutes, and process intensification techniques were presented.
Although the evident development has been attained, the sonochemical process
still faces numerous challenges. More efforts may be focused on the next topics:
(i) To better understand the effective action of the sonochemical treatment, the
degradation of textile dyes should be analyzed in depth and, particularity, in
terms of total organic carbon removal and by-products identification and
quantification because the degradation products may be more toxic than the
initial pollutant.
(ii) Because dyes are nonvolatile, it is important to develop methods that make easy
the accumulation of dyes at the reactive interfacial area of cavitation bubble.
Also, novel techniques to enhance the number of inertial bubbles are
researched. One recent technique for this issue is to combine ultrasound with
catalysts, i.e., sonocatalysis.
(iii) There is a requirement to improve our knowledge on the extent of
sonochemical reactions in industrial-scale ultrasonic reactors. Even though
much data on sonochemical degradation of textile dyes at lab scale have been
accumulated, the application of this technology to large-scale operations was
poorly investigated. The attenuation of the sound wave in big structures is a
principal factor that affects the efficiency of the sonolytic treatment (Kerabchi
et al. 2018). It is of interest to understand the characteristics of the sound field
because the sound propagation in big reactors differs from those in lab-scale
ones (Kerabchi et al. 2018). Thus, there are still lost links between lab-scale and
industrial-scale sonochemical processes. The following topics are also required
for the implementation of the sonochemical treatment for industrial use (Son
2015):
– Reactor design including sonoreactor size/shape/material, transducer location/array, and internal structure
– Studying of the liquid depth on the sonochemical efficiency of the process
– Development of continuous-flow sonochemical reactors
180
S. Merouani and O. Hamdaoui