Development of ozonation and reactive electrochemical membrane coupled process: Enhanced tetracycline mineralization and toxicity reduction

Abstract

The ozone-reactive electrochemical membrane (O3-REM) coupled process for tetracycline (TC) removal was developed by coupling ozonation and electrochemical oxidation in a substoichiometric titanium dioxide (Ti4O7) REM reactor. To achieve concurrent and efficient degradation-mineralization, TC was treated by ozonation and electrochemical oxidation over the Ti4O7 REM anode in a sequent manner. TC was nearly completely removed within 20 min, while the total organic carbon (TOC) removal efficiency attained 9.1% in 20 min, and then reached 77.1% in 80 min under optimal conditions of 2 mg/min ozone dosage and 2 mA/cm2 current density. TC was suspected to be oxidized into some four- and three-ring intermediates within 20 min, some two- and one-ring intermediates within 80 min, and eventually carboxylic acids, CO2 and H2O. The concentrations of NO3−, NO2− and NH4+ increased slightly in the first 20 min and then elevated significantly from 20 to 80 min, indicating an enhanced denitrification rate via electrochemical oxidation. Besides, the bioluminescence inhibition ratio exhibited a slight decrease from 54.5% to 50.6% in the first 20 min and then significantly decreased to 14.5% in 80 min, suggesting an augmented toxicity reduction simultaneously by the coupled technology. Overall, the O3-REM coupled process demonstrated higher TC degradation and TOC removal efficiencies, enhanced toxicity-reduction capability, and lower energy consumption for TC removal compared to individual O3 or Ti4O7 REM processes. By comprehensively analyzing the performance, mechanism and energy consumption of TC removal by the O3-REM coupled process, our research provides insights into the application potential of the coupled process to efficiently eliminate the amount and toxicity of various pharmaceuticals from wastewater.