Simultaneous Removal of CODMn and Ammonium from Water by Potassium Ferrate-Enhanced Iron-Manganese Co-Oxide Film

Abstract

Iron-manganese co-oxide film (MeOx) has a high removal efficiency for ammonium (NH4+) and manganese (Mn2+) in our previous studies, but it cannot effectively remove CODMn from water. In this study, the catalytic oxidation ability of MeOx was enhanced by dosage with potassium ferrate (K2FeO4) to achieve the simultaneous removal of CODMn and NH4+ from water in a pilot-scale experimental system. By adding 1.0 mg/L K2FeO4 to enhance the activity of MeOx, the removal efficiencies of CODMn (20.0 mg/L) and NH4+ (1.1 mg/L) were 92.5 ± 1.5% and 60.9 ± 1.4%, respectively, and the pollutants were consistently and efficiently removed for more than 90 days. The effects of the filtration rate, temperature and pH on the removal of CODMn were also explored, and excessive filtration rate (over 11 m/h), lower temperature (below 9.2 °C) and pH (below 6.20) caused a significant decrease in the removal efficiency of CODMn. The removal of CODMn was analyzed at different temperatures, which proved that the kinetics of CODMn oxidation was pseudo-first order. The mature sands (MeOx) from column IV were taken at different times for microscopic characterization. Scanning electron microscope (SEM) showed that some substances were formed on the surface of MeOx and the ratio of C and O elements increased significantly, and the ratio of Mn and Fe elements decreased significantly on the surface of MeOx by electron energy dispersive spectrometer (EDS). However, the elemental composition of MeOx would gradually recover to the initial state after the dosage of Mn2+. According to X-ray photoelectron spectroscopy (XPS) analysis, the substance attached to the surface of MeOx was [(-(CH2)4O-)n], which fell off the surface of MeOx after adding Mn2+. Finally, the mechanism of K2FeO4-enhanced MeOx for CODMn removal was proposed by the analysis of the oxidation process.