Performance evaluation of Cu-EDTA decomposition by pulsed streamer discharge in contact with liquid*

Ethylenediaminetetraacetic acid (EDTA) is a complexing agent used in the electroplating, printing, and dyeing industries to enhance the solubility and stability of heavy metal ions. EDTA reacts with heavy metal ions to form stable metal complexes that pose a significant threat to the human body and the environment. In this study, we investigated the decomposition performance of Cu-EDTA in aqueous solution by pulsed streamer discharge in contact with liquid under various experimental conditions. Although Cu-EDTA is decomposed by ozone with low reaction rate, OH radicals have much higher reactivity against Cu-EDTA, and it is worthy to evaluate the ability of gas discharges to directly supply of OH radicals as an alternative to ozonation. Experiments were performed with single-needle or multiple needle electrodes, in air or Ar. Magnetic stirrer is used to enhance the reaction between Cu-EDTA and OH at liquid surface. The change in Cu-EDTA concentration was characterized using HPLC. H₂O₂, NO₂^-, NO₃^-, and O₃ were detected using water inspection test kits and an ultraviolet-visual spectrophotometer. The OH yield was estimated using a colorimetric method with disodium terephthalate. We confirmed that the energy efficiency of Cu-EDTA decomposition using streamer discharges were comparable or even better than those by ozonation, and OH was identified to be dominant species for Cu-EDTA decomposition although most of OH radical were changed into H₂O₂. A combined effect of O₃ and OH was observed during air discharge.