Removal of manganese from groundwater in the ripened sand filtration: Biological oxidation versus chemical auto-catalytic oxidation

This work is a contribution to understand the interaction of biological and chemical auto-catalytic oxidation processes for the removal of manganese (Mn) (0–1.8 mg/L) using the ripened sand filter. Here, penicillin, sodium chloride (NaCl), autoclave sterilization and sodium hypochlorite (NaClO) were chosen as the four inactivation methods to distinguish biological and chemical oxidation processes on the removal of Mn in the ripened sand filter. The amounts of manganese-oxidizing bacteria (MnOB) in the filters before inactivation, right after inactivation and after 150 days of recuperation were found to be 10⁴ CFU/g, 0 CFU/g and merely 10² CFU/g. The data suggested that autoclave sterilization and NaClO inactivated filters were less effective for 36% removal of Mn compared to penicillin and NaCl inactivated filters for which over 98% was possible to be removed, and the chemical oxidation ratio was 81%. Characterization of manganese oxides (MnOx) was carried out by scanning electron microscopy energy dispersive spectroscopy (SEM-EDS), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that active MnOx present on the ripened media were poorly crystalline and belonged to birnessite. Compared with penicillin and NaCl inactivation, MnOx were oxidized during NaClO and autoclave sterilization inactivation process, which caused a great influence on the crystal structure. The removal of Mn in the ripened sand filter after inactivation was predominantly achieved by chemical auto-catalytic oxidation of active MnOx although biological oxidation also existed overall the process.