Application of low frequency ultrasonic waves for Calcon azo dye removal from wastewater: influence of operational parameters and mineral ions, kinetic study and analysis of by-products

In this paper, the degradation of an azo dye (Calcon) in aqueous medium by low frequency ultrasound (26 kHz) was carried out by studying primarily the effect of different parameters on the pollutant elimination such as the applied ultrasonic power, the sonication time, the initial pH of irradiated solution, the colorant concentration, as well as the sonotrode immersion depth of the ultrasonic processor. Moreover, the influence of various mineral salts on the oxidation process was examined . In addition to that, experiments aimed at mineralizing the dye were performed. The results obtained indicated that the best removal efficiencies of the azo compound were achieved with acoustic powers ranging from 90 to 100 W, acidic pH, lower dye concentration (5 mg/L), and a sonotrode immersion depth of 5 cm. Additionally, the sonodegradation was found to be more effective in a salt-free environment. The kinetic studies showed that the ultrasound treatment followed the first order kinetics (R² = 0.98). On the other hand, based on the ion chromatography analysis, it was found that the sonotreatment of the Calcon dye solution was able to successfully mineralize the azo compound forming nitrate and sulfate ions as end products. Furthermore, through High-performance liquid chromatography Mass spectroscopy (LC/MS) analysis, a possible mechanism of Calcon dye degradation was proposed and discussed.