Significant insights of CaO₂ promoting heavy metal complexes removal during a plasma process

Heavy metal-antibiotic complexes pose a serious threat to human health and are difficult to remove by traditional methods. In this study, a novel and green strategy of discharge plasma technology combined with calcium peroxide (CaO₂-DBD) was proposed for the efficient removal of Cu-ciprofloxacin (Cu-CIP) complexes. An obvious synergistic effect on Cu-CIP decomposition was performed between CaO₂ and DBD system, showing kinetically 10 times faster than a single DBD system, and appropriate dosages of CaO₂ favored this process. The removal rates of Cu-CIP were significantly inhibited after the addition of NO₃^-, Cl^-, and SO₄^2-. The formation of ·O₂^-, ·OH, and ¹O₂ was promoted by CaO₂ addition and reacted as the dominant active species contributing to the decomposition of Cu-CIP. The strong oxidation and alkaline environments enhanced the decomposition process. Cu-CIP decomposition processes involved piperazine ring opening and decarboxylation reactions. Besides, the release of Ca(OH)₂ further promoted the formation of Cu precipitations. The main alkali-precipitated products were composed of Ca-based carbonates and Cu-based carbonates. This study revealed the potential mechanism underlying Cu-CIP degradation in the CaO₂-DBD system and provided a promising technique for controlling heavy metal-antibiotic complexes from wastewater.