Versatile Fe₃O₄-impregnated catalytic ceramic membrane for effective atrazine removal: Confined catalytic oxidation processes, reactive oxygen species selectivity and performance in real wastewater

An Fe₃O₄-impregnated catalytic ceramic membrane (CCM) was fabricated through a facile ethylene glycol-gel-assisted wet impregnation method. Ethylene glycol played a dual role, acting as a reducing agent for iron (III) nitrate salt and a chelating agent to disperse catalyst uniformly in the CCM. The resulting 5xFe₃O₄-CCM efficiently activated peroxymonosulfate (PMS) to generate reactive oxygen species (ROS), achieving a 99% removal of atrazine (ATZ) within a short hydraulic retention time (HRT) of 5.7 s. This was facilitated by the spatial confinement effect in CCMs, enhancing the interaction among ATZ, ROS and CCM. The versatile 5xFe₃O₄-CCM could also effectively activate H₂O₂ and peroxydisulfate (PDS). It demonstrated robustness in real wastewater matrices (settled water and RO-reject) collected from local water reclamation and treatment plants. The 5xFe₃O₄-CCM exhibited self-cleaning properties in reducing fouling of CCM by humic acid. ROS scavenging experiments and electron paramagnetic resonance (EPR) spectroscopy revealed the pivotal role of SO₄^•-, ^•OH, and ¹O₂ in ATZ removal. The co-existing anion species HCO₃^- showed a strong inhibitory effect on ATZ degradation compared to other ionic species (NO₃^- and Cl^-), attributed to different scavenging reaction rate of both SO₄^•- and ^•OH by anions in generating less reactive species. Possible degradation pathways of 5xFe₃O₄-CCM/PMS were proposed based on the LC-QTOF analysis, including oxidation, dealkylation, dealkylation-hydroxylation, dechlorination-hydroxylation of both s-triazine ring and side chain. The toxicity of the ATZ by-products was assessed, revealing reduced toxicity after treatment. With optimized operating parameters, Fe₃O₄-CCM can be utilized effectively in different advanced oxidation processes (AOPs) and real wastewater matrices.