Key factors maintaining catalytic ammonium oxidation activity of manganese oxide active filter media: The role of bicarbonate

Abstract

The removal of ammonium (NH4+-N) via the catalytic oxidation of manganese oxide (MnOx) active filter media is a new technology. In this study, three different types of water (groundwater, surface water, and deionized water) were used to investigate the key factors affecting the sustainability of the catalytic activity of active MnOx filter media. The NH4+-N removal performance of the MnOx active filter media differed in different water environments, especially in deionized water, and the removal ability of NH4+-N was gradually decreased with increasing the running time. The continuous NH4+-N removal kinetics in different water environments were investigated. The rate constant k of the NH4+-N removal kinetics gradually decreased with NH4+-N removal, even in the groundwater environment, and the rate constant k decreased from 1.18 to 0.97 to 0.19. The addition of bicarbonate enhanced the ability to remove NH4+-N again, which confirmed that bicarbonate was the driving force for the continuous catalytic oxidation of NH4+-N. Based on the FTIR and XPS analysis results, the bicarbonate structure was consumed during the continuous removal of NH4+-N. Moreover, bicarbonate could affect the structure of MnOx, and then affected the electron transfer process of different valence manganese ions during the catalytic oxidation of NH4+-N, especially the conversion of Mn3+ to Mn2+. This study provides new insights into the theory of continuous catalytic oxidation by MnOx for NH4+-N removal.