Removal of humic acid by peroxymonosulfate active with MnOx from the backwashing sludge of a filter for manganese removal

Finding a low-cost and high effective catalyst is an important problem in advanced oxidation processes (AOPs) based on PMS for organic matter removal. In this study, manganese oxide (MnOx) was extracted from the backwashing sludge of a filter for manganese removal and used to activate peroxymonosulfate (PMS) to remove humic acid from water. It was found that thermal treatment had significant effects on the structure and catalytic activity of MnOx. When MnOx was treated at 500 °C, it showed excellent catalytic activity and the removal rate of HA was up to 81.0%. Characterization indicated that the MnOx was converted from buserite and birnessite to α-MnOx after treated at 500 °C, and the specific surface area and the percentage of Mn (III) and Olatt on the surface increased significantly. The repeated utilization experiments indicated that the extracted MnOx still had high activity after reusing for 5 cycles. Quenching experiments showed that 1O2 was the dominant reactive oxygen species to oxidize HA in water. Finally, combining the results of FTIR and XPS spectra of MnOx before and after the catalytic reaction, the reaction mechanism was proposed: PMS was activated to be 1O2 by Mn (III) and Olatt in MnOx with a valence transformation between Mn (II), Mn (III) and Mn (IV) and HA was mainly oxidized by the non-radical pathway through 1O2. The experiments will provide a new strategy for recycling MnOx from backwashing sludge of the filter for Mn2+ removal to remove natural organic matter from water.