Combined removal of ammonia-nitrogen from wastewater by ultrasonic cavitation and electrochemical oxidation

This study systematically explored the purification performance of high-strength ammonia nitrogen(NH3-N) removal wastewater using three processes: ultrasonic cavitation (Process One), electrochemical oxidation (Process Two), and their coupling (Process Three). NH3-N removal rates were determined via ultraviolet spectrophotometry under different parameters. Furthermore, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and laser scanning confocal microscopy (LSCM) characterized the surface morphology and composition of ruthenium-iridium coated titanium electrodes before and after combined treatment. For 1200 mg·L-1 NH3-N removal wastewater, the standalone ultrasonic experiment (40 kHz, 150 W, aeration) showed that the removal rate increased sharply as pH rose from 6.5 to 12.5, owing to pH-dependent NH3-N speciation. The optimal parameters for standalone electrochemical oxidation were 1300 mg·L-1 chloride ions, a current density of 133 mA·cm-2, and pH 10.5, verifying the key roles of high current density and suitable pH. Under these optimized conditions, the coupled process achieved a 96.88% NH3-N removal rate in just 30 min, significantly outperforming single technologies.