Comparing Mn-based oxides filters started by KMnO 4 versus K 2 FeO 4 for ammonium and manganese removal: Formation mechanism of active species

A pilot-scale filtration system was adopted to prepare filter media with catalytic activity to remove manganese (Mn ) and ammonium (NH -N). Three different combinations of oxidants (KMnO and K FeO ) and reductants (MnSO and FeCl ) were used during the start-up period. Filter R3 started up by KMnO and FeCl (Mn →MnO ) exhibited excellent catalytic property, and the NH -N and Mn removal efficiency reached over 80% on the 10 and 35 days, respectively. Filter R1 started up by K FeO and MnSO (MnO ←Mn ) exhibited the worst catalytic property. Filter R2 started up by KMnO and MnSO (Mn →MnO ←Mn ) were in between. According to Zeta potential results, the Mn-based oxides (MnO ) formed by Mn →MnO performed the highest pH and pH . The higher the pH and pH , the more unfavorable the cation adsorption. However, it was inconsistent with its excellent Mn and NH -N removal abilities, implying that catalytic oxidation played a key role. Combined with XRD and XPS analysis, the results showed that the MnO produced by the reduction of KMnO showed early formation of buserite crystals, high degree of amorphous, high content of Mn and lattice oxygen with the higher activity to form defects. The above results showed that MnO produced by the reduction of KMnO was more conducive to the formation of active species for catalytic oxidation of NH -N and Mn removal. This study provides new insights on the formation mechanisms of the active MnO that could catalytic oxidation of NH -N and Mn .