Tetracycline degradation for wastewater treatment based on ozone nanobubbles advanced oxidation processes (AOPs) – Focus on nanobubbles formation, degradation kinetics, mechanism and effects of water composition

• Nanobubbles technology gives four-fold increase in ozone mass transfer coefficient. • O 3 NBs increase the degradation by three folds compared to O 3 microbubbles. • Rapid degradation of TC antibiotic at pH 4 and high salinity wastewater conditions. • High applicability for real wastewater under lower concentrations of antibiotic. • Scavenging experiments confirmed radical mechanism of pharmaceutical degradation. Presence of pharmaceuticals, especially antibiotics, in industrial and domestic effluents causes serious damage to the environment. Classic wastewater treatment processes, in particular conventional biological treatment methods, are not sufficient to rapidly eliminate antibiotics. Typically, Advanced Oxidation Processes (AOPs) based on activation of hydrogen peroxide, ozone or persulfate for production of particular type of radical species or singlet oxygen are used. A one of cutting-edge technologies to increase effectiveness of AOPs based on ozone are nanobubbles based processes. Thus, this paper focuses on utilization of ozone in the form of nanobubbles for degradation of tetracycline (TC). The effects of several reaction parameters, such as antibiotic concentration, ozone intake, pH, presence of salts, were investigated. This study revealed that the presence of ozone nanobubbles had a substantial positive impact on the degradation of TC. This improvement may be attributed to the enhanced mass transfer and the production of reactive radicals that occur during the collapse of the nanobubbles. Identification of radical species revealed a significant contribution of hydroxyl radicals in the degradation of the antibiotic. AOP process based on O 3 nanobubbles was most ( • OH) and superoxide (O 2 – ) effective with 100 % degradation efficiency of 100 mg/L TC within 20 min at 8 mg/L concentration of ozone. Based on identified by LC-MS intermediates a degradation mechanism has been described. Degradation of TC and intermediates transformations included methylation, hydroxylation, ring-opening steps as well as cleavage of C-N bonds. This research introduces a novel technique combining nanobubbles with advanced oxidation processes (AOPs), which is anticipated to provide enhanced efficiency and environmental sustainability.