A comparison study of the start-up of a MnO_x filter for catalytic oxidative removal of ammonium from groundwater and surface water

As an efficient method for ammonium (NH₄ ⁺) removal, contact catalytic oxidation technology has drawn much attention recently, due to its good low temperature resistance and short start-up period. Two identical filters were employed to compare the process for ammonium removal during the start-up period for ammonium removal in groundwater (Filter-N) and surface water (Filter-S) treatment. Two types of source water (groundwater and surface water) were used as the feed waters for the filtration trials. Although the same initiating method was used, Filter-N exhibited much better ammonium removal performance than Filter-S. The differences in catalytic activity among these two filters were probed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and compositional analysis. XRD results indicated that different manganese oxide species were formed in Filter-N and Filter-S. Furthermore, the Mn3p XPS spectra taken on the surface of the filter films revealed that the average manganese valence of the inactive manganese oxide film collected from Filter-S (FS-MnO_x) was higher than in the film collected from Filter-N (FN-MnO_x). Mn(IV) was identified as the predominant oxidation state in FS-MnO_x and Mn(III) was identified as the predominant oxidation state in FN-MnO_x. The results of compositional analyses suggested that polyaluminum ferric chloride (PAFC) used during the surface water treatment was an important factor in the mineralogy and reactivity of MnO_x. This study provides the theoretical basis for promoting the wide application of the technology and has great practical significance.