Peroxymonosulfate-based cleaning technology for metal oxide-coated ceramic ultrafiltration membrane polluted by Alcian Blue 8GX dye: Radical and non-radical oxidation cleaning mechanism

Cleaning effect and mechanism of peroxymonosulfate (PMS)-based oxidation technology were systematically studied in metal oxide-coated ceramic membrane (CM) cleaning process. Metal oxides (MnO2, Fe2O3, Co3O4, CuO and Mn3O4) were evenly coated on CM surfaces via silane modification and dip-coating followed by calcination. The performance of prepared CMs was investigated by filtrating Alcian Blue 8GX dye. Flux decline extents of different metal oxide-coated CMs were greatly influenced by metal oxide hydrophilicity, and their rejection rates for dye increased by 10.2-47.6%, probably due to the enhanced adsorption or electrostatic repulsion of pollutants. PMS had better cleaning effects on metal oxide-coated CMs than virgin CM (64.0%) following the order: MnO2-coated CM (75.3%) > Co3O4-coated CM (73.8%) > Fe2O3-coated CM (71.2%) > Mn3O4-coated CM (70.5%) > CuO-coated CM (70.2%). This was well consistent with order of dye degradation efficiency oxidized by PMS activated with those metal oxides, indicating that degradation efficiency of foulant largely determined cleaning effect. The mechanisms were proposed and then verified that radical (O-2(center dot-)), and non-radical (O-1(2) and PMS direct oxidation) pathways simultaneously occurred, and metal oxides coated on CMs surfaces mainly promoted non-radical oxidation process. This study provides insight to better utilize metal oxides activated PMS oxidation technology for membrane cleaning and improve its cleaning efficiency for dye wastewater treatment.