In this study, ultrasonic treatment was used to remove the passive film that formed on electrode surface during electrocoagulation (EC). The variation of electrode impendence was examined to evaluate the effect of passivation on EC and the ultrasound-electrocoagulation (sono-EC) process. The effects of operating parameters current density, pH and ultrasonic power on the removing efficiency in sono-EC were studied. A synthetic wastewater that contained Reactive Blue 19 dye was used in all experiments. The results demonstrated that the electrode impedance increased during the EC process but decreased during the sono-EC process, indicating that the passive film can be removed from the sacrificial electrode using ultrasound, causing the sacrificial electrode to generate more coagulant metal. Additionally, the ultrasound reduces the size of the metal hydroxide which in turn adsorb more contamination in synthetic wastewater. The SEM results show that ultrasound process could successfully remove the passive film on the plates. An intermittent ultrasonic process and double-type reactor were utilized to reduce the breaking of flocs in the system. A total of 97% of the RB19 was removed by intermittent sono-EC treatment at a current density of 18 mA/cm2, a pH of 5, an electrolysis time of 60 min and an ultrasound power of 150 W. Furthermore, the remove of the RB19 in the sono-EC process can be well expressed by a variable-order-kinetic model in the sono-EC system. In conclusion, ultrasonic equipment improves EC performance by removing the passive film.
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