A dual-oxidant advanced oxidation process system containing CaO2 and peroxymonosulfate for organic pollutant degradation: High adaptability and synergistic effect

In this study, a dual-oxidant advanced oxidation process (AOP) system containing calcium peroxide (CaO2) and peroxymonosulfate (PMS) was developed for the first time to efficiently degrade refractory organic pollutants. It was found that the system with 0.1 g/L CaO2 and 0.3 g/L PMS could degrade more than 91% of 50 mg/L tetracycline (TC) within 4 min at room temperature, and the degradation process much followed the pseudo second-order kinetic model. The presented AOP system exhibited strong anti-interference capabilities towards coexisting inorganic anions (Cl−, SO42–, NO3–, HCO3– and HPO42–) and humic acid (HA), even at high concentrations. Moreover, the system could efficiently work in a wide pH (3−12) range, suitable for natural waterbodies and various organic pollutants. The results of quenching experiments and electron paramagnetic resonance (EPR) tests demonstrated that singlet oxygen (1O2) was the dominate reactive oxygen species (ROS) responsible for organics degradation. A synergistic mechanism of the dual-oxidant system was confirmed by a series of comparative experiments, where CaO2 continuously provided OH− and H2O2, and then combined with PMS to produce predominant 1O2 and inferior O2•–, respectively. Further, the possible pathways of TC degradation were deduced based on analyses of the intermediates.