Previous studies have shown that ammonium and manganese could be removed from water by biofilm in a trickling filter. However, it always takes several months to start up a biofilm filter. In this study, by oxidizing manganese and ferrous ion from raw water using potassium permanganate continuously, an iron manganese co-oxide filter film (MeOx) was formed quicldy on the surface of virgin quartz sand in a pilot scale filter, and the start-up period was less than 30 days. Interestingly, 90% ammonium and manganese could be removed by the filter film even after the bacteria were inactivated completely in both the filter film and raw water (by aerating ozone and injecting hydrogen peroxide), suggesting that microorganisms may play a negligible role in our system. Additionally, the filter film exhibited high oxidation activity when the temperature was down to 6.6 degrees C. The filter film was characterized by scanning electron microscopy, X-ray fluorescence spectroscopy and X-ray photoelectron spectroscopy methods. Finally, a chemical catalytic oxidation mechanism for ammonium removal was proposed by the analysis of the oxidation process. Ammonium was oxidized to nitrate through the process of catalytic oxidation, generating hydrogen ions. MeOx plays as a catalyst, and the intermediates O-center dot can potentially serve as both oxidant and reductant in one-electron-transfer reactions with NH4+ and O-2. (C) 2016 Elsevier B.V. All rights reserved.