The role of synergistic effects between ozone and coagulants (SOC) in the electro-hybrid ozonation-coagulation process

Abstract

In order to improve the dissolved organic matter removal efficiency, an electro-hybrid ozonation-coagulation (E-HOC) system was developed in this study, in which the electro-coagulation (EC) and ozonation occurred simultaneously in one integrated unit. Higher removal efficiency was observed for the E-HOC process compared with those of EC, ozonation and pre-ozonation-EC process for the treatment of wastewater treatment plant (WWTP) effluent and ibuprofen (IBP). 58.6% dissolved organic carbon (DOC) removal efficiency was achieved in the E-HOC process for the treatment of WWTP effluent at optimal operational condition (current density 15 mA/cm2, initial pH 5 and ozone dosage 1.5 mg O3/mg DOC). Based on the reactive oxygen species (ROS) detection and reactions on the electrodes, the synergistic effects between ozone and coagulants (SOC) were found to be involved in the E-HOC process. According to pseudo-first-order rate constant analyses, the contribution of five possible organic removal pathways was quantified. It was revealed that the peroxone and SOC effects exhibited almost equal contribution to IBP removal at initial pH 5 under different current densities, both of which played the dominant role in the E-HOC process. However, the contribution of the SOC effects decreased significantly when the initial pH increased to 7 and 9. As an important pathway for organic removal in the E-HOC process at initial pH 5, the mechanism of the SOC effects was analysed at initial pH 5. It was revealed the SOC effects can further improve hydroxyl radicals (•OH) generation, and the surface hydroxyl groups of the hydrolysed Al species generated from anode electrolysis were determined to be the active sites to generate ROS in the SOC effects.