Ultrasound as a basic and auxiliary process for dye remediation: A review

Ultrasonic treatment of recalcitrant contaminants has been of utmost interest recently due to the advantages of the cavitation phenomenon, which enhances the efficiency of Advanced Oxidation Processes (AOPs). The current review summarizes the use of ultrasound with biochemical, electrochemical, ozonation, photolysis, photocatalysis and Fenton processes for the degradation of mostly textile dyes and dyebath. There is a few studies about ultrasonic degradation of textile effluents or wastewater due to highly variable contents. It was found that the most common use of ultrasonic irradiation for dye degradation is the combined with the heterogeneous catalysts/adsorbents. The reaction mechanism of the ultrasonic irradiation in heterogeneous media was well investigated and understood. However, there is still lack of information about the reaction mechanism of ultrasonic irradiation in the homogeneous solutions, especially containing ferrous ions. Fenton reaction is already fast itself and gives effective degradation during the oxidation. Therefore, addition of ultrasonic irradiation to Fenton oxidation was less effective compared to other auxiliary processes. It should also be noted that ultrasonic irradiation had a negative effect on dye degradation during combined with electro-oxidation process. ► Ultrasonic dye degradation provides a safe treatment method with stable products. ► High frequency ultrasonic equipment is more effective than that of low frequency. ► Dye mineralization cannot be completely obtained with high frequency ultrasound. ► Ultrasonic irradiation is quite effective when combined with other AOPs. ► All of the studies have been limited in the laboratory scale.