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Manganese and ammonium pollution in surface water sources has become a serious issue.In this study,a pilot-scale filtration system was used to investigate the effect of ammonium on manganese removal during the simultaneous removal of ammonium and manganese from surface water using a manganese co-oxide filter film (MeOw).The results showed that the manganese removal efficiency of MeOx in the absence of ammonium was high and stable,and the removal efficiency could reach 70％ even at 5.5 ℃.When the influent ammonium concentration was lower than 0.7 mg/L,ammonium and manganese could be removed simultaneously.However,at an ammonium concentration of 1.5 mg/L,the manganese removal efficiency of the filter gradually decreased with time (from 96％ to 46.20％).Nevertheless,there was no impact of manganese on ammonium removal.The mechanism by which ammonium negatively affected manganese removal was investigated,demonstrating that ammonium affected manganese removal mainly through two possible mechanisms.On one hand,the decreased pH caused by ammonium oxidation was unfavorable for the oxidation of manganese by MeOx;on the other hand,the presence of ammonium slowed the growth of new MeOx and retarded the increase in the specific surface area of the MeOx-coated sand,and induced changes in the morphology and crystal structure of MeOx.Consequently,the manganese removal efficiency of the filter decreased when ammonium was present in the inlet water.