Towards a comparison between the hybrid ozonation-coagulation (HOC) process using Al- and Fe-based coagulants: Performance and mechanism

In this study, the removal performance of a hybrid ozonation-coagulation (HOC) process using AlCl₃[rad]6H₂O (Al–HOC) and FeCl₃[rad]6H₂O (Fe–HOC) as coagulants for the treatment of wastewater treatment plant (WWTP) effluent and ibuprofen (IBP) was investigated. Compared with the conventional coagulation process and pre-ozonation-coagulation process, much better organic matter removal performance can be achieved for both the Al–HOC and Fe–HOC processes. The Fe–HOC process showed an obviously higher dissolved organic carbon (DOC) removal efficiency than that of the Al–HOC process. Surface hydroxyl groups were determined to be the active sites in generating [rad]OH in the HOC process, and the hydrolysed Fe species possessed a higher content of surface hydroxyl groups than the hydrolysed Al species according to fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectra (XPS) analyses. In addition, the hydrolysed Fe species contained a higher portion of tetrahedral sites that were more likely to be stronger Lewis acid sites to react with ozone to generate [rad]OH. Furthermore, peroxone reactions in the HOC process were other possible way to enhance the [rad]OH generation, and higher H₂O₂ generation was observed in the Fe–HOC process due to higher [rad]O₂⁻ generation. Therefore, better removal performance of the Fe–HOC process can be obtained due to the increased [rad]OH generation in the Fe–HOC process.