Plasma-based advanced oxidation process for the degradation of metal-EDTA complexes in water: A mechanistic study

Ethylenediaminetetraacetic acid (EDTA) is a chelating agent extensively used in industrial applications. Despite their effectiveness in stabilizing metal ions, metal–EDTA complexes are environmental contaminants that resist biodegradation and are difficult to remove by conventional water treatment. In this study, we developed a plasma-based advanced oxidation processes (AOPs) system using non-thermal plasma that uses pure oxygen gas to degrade Cu–EDTA and Fe–EDTA complexes. The system was optimized by adjusting the input power, and UV–Vis spectroscopy, high-performance liquid chromatography, and liquid chromatography–mass spectrometry were used to evaluate degradation performance and identify the degradation products and pathways. Field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy were used to trace metal ions. High-performance liquid chromatography analysis results showed that Cu-EDTA (40 ppm and 200 ppm) and Fe-EDTA (40 ppm) were degraded over 99 % within 30 min, while Fe-EDTA (200 ppm) took approximately 100 min to reach 99 % degradation. Degradation involved the dissociation and oxidation of metal–ligand bonds, followed by the precipitation of metal ions, reducing their environmental risk. This study highlights the potential of plasma-based AOP as an environmentally sustainable, energy-efficient, and reagent-free solution for treating wastewater containing persistent metal–EDTA complexes, including wastewater from radioactive materials and industrial contaminants.