Comparing Mn-based oxides filters started by KMnO4 versus K2FeO4 for ammonium and manganese removal: Formation mechanism of active species.

• The start-up of filters for NH 4 + and Mn2+ removal by catalytic oxidation was studied. • Different combinations of oxidants and reductants were introduced during the start-up period. • Comparison of catalytic oxidation activity of MnOx follows: Mn7+→MnO x ˃Mn7+→MnO x ←Mn2+ ˃ Mn2+→MnO x. • Potassium permanganate was more conducive to the formation of active species. A pilot-scale filtration system was adopted to prepare filter media with catalytic activity to remove manganese (Mn2+) and ammonium (NH 4 +-N). Three different combinations of oxidants (KMnO 4 and K 2 FeO 4) and reductants (MnSO 4 and FeCl 2) were used during the start-up period. Filter R3 started up by KMnO 4 and FeCl 2 (Mn7+→MnO x) exhibited excellent catalytic property, and the NH 4 +-N and Mn2+ removal efficiency reached over 80% on the 10th and 35th days, respectively. Filter R1 started up by K 2 FeO 4 and MnSO 4 (MnO x ←Mn2+) exhibited the worst catalytic property. Filter R2 started up by KMnO 4 and MnSO 4 (Mn7+→MnO x ←Mn2+) were in between. According to Zeta potential results, the Mn-based oxides (MnO x) formed by Mn7+→MnO x performed the highest pH IEP and pH PZC. The higher the pH IEP and pH PZC , the more unfavorable the cation adsorption. However, it was inconsistent with its excellent Mn2+ and NH 4 +-N removal abilities, implying that catalytic oxidation played a key role. Combined with XRD and XPS analysis, the results showed that the MnO x produced by the reduction of KMnO 4 showed early formation of buserite crystals, high degree of amorphous, high content of Mn3+ and lattice oxygen with the higher activity to form defects. The above results showed that MnO x produced by the reduction of KMnO 4 was more conducive to the formation of active species for catalytic oxidation of NH 4 +-N and Mn2+ removal. This study provides new insights on the formation mechanisms of the active MnO x that could catalytic oxidation of NH 4 +-N and Mn2+. [Display omitted] [ABSTRACT FROM AUTHOR]