Mechanism of the hybrid ozonation-coagulation (HOC) process: Comparison of preformed Al13 polymer and in situ formed Al species

Abstract

Because of the influence of hydrolysed species from Al-based coagulants on coagulation performance, the performance and mechanism of the developed hybrid ozonation-coagulation (HOC) process using AlCl3·6H2O and preformed Al13 as coagulants were investigated in this study, in which ozonation and coagulation occurred simultaneously within a single unit. It was found that the HOC process exhibited higher organic matter removal performance compared with coagulation and the pre-ozonation-coagulation process. It was found that the high ibuprofen (IBP) removal efficiency in the HOC process was mainly attributed to OH oxidation promoted by in situ formed hydrolysed aluminium species from AlCl3·6H2O and preformed Al13. Furthermore, the surface hydroxyl groups were determined to be the active reaction sites for the HOC process. Due to the higher proportion of surface hydroxyl groups for Al13, the HOC process with preformed Al13 as coagulants (Al13-HOC) exhibited a higher removal performance than that with AlCl3·6H2O as the coagulant (AlCl3-HOC). It was revealed that most of the generated O2− in the Al13-HOC was adsorbed on the surface of Al13 at different pH values, while a considerably lower proportion of adsorbed O2− was observed on the surface of in situ formed Al species from AlCl3·6H2O. Nevertheless, low proportions of adsorbed OH were found on the surfaces of both preformed Al13 and in situ formed Al species, indicating that the OH oxidation for the removal of organic pollutants occurred primarily in the aqueous phase.