Removing ammonium from underground water by strengthening Mn(III) generation through electrochemical reduction

Abstract

Manganese oxide has been found to be an active catalyst for ammonium oxidation. This work presented an innovative electrochemical system to improve the removal efficiency of ammonium by strengthening the generation of Mn(III). In this system, the manganese oxide coating activated carbon (MnOx/AC) particles were used as the cathode of a fuel cell (MnOx/AC‐Ca). Compared to the conventional method using MnOx in a nonelectrochemical system (MnOx/AC‐Control), the ammonium removal efficiency was doubled in the MnOx/AC‐Ca system. Conversely, when using MnOx as the anode of a fuel cell (MnOx/AC‐An), the ammonium removal efficiency was lower than that in the MnOx/AC‐Control system. XPS results showed that Mn(III) in the MnOx/AC‐Ca system was obviously higher than that in the MnOx/AC‐Control system. Conversely, more Mn(IV), which was less active than Mn(III) for NH4+-N removal, was detected in the MnOx/AC‐An system. The possible pathway for the ammonium removal by MnOx was that Mn(III) reacted with NH4+-N and produced Mn2+. These Mn2+ were then reoxidized into new active MnOx under the self‐catalysis of MnOx, resulting in a continuous ammonium removal. Moreover, nitrite, the intermediate product of ammonium oxidation, can be oxidized by MnOx, thus helping the ammonium oxidation process. Practitioner points Mn(III) was generated by using MnOx as the cathode of fuel cells. Ammonium removal efficiency went up with the content of Mn(III) in MnOx. Mechanism of the NH4+-N removal by MnOx was discussed.