Catalytic ozonation of NH4+-N in wastewater over composite metal oxide catalyst

Large amounts of water containing-ammonium nitrogen (NH4+-N) have attracted increasing attention. Catalytic ozonation technology, involving the generation of hydroxyl radical (center dot OH) with strong oxidation ability, was originally utilized to degrade organic-containing wastewater. In this paper, Ce/MnOx composite metal oxide catalysts prepared with different preparation conditions were used to degrade wastewater containing inorganic pollutant (NH4+-N). The as-prepared catalyst features were characterized using X-ray diffraction (XRD), Brunauer-Emmett-Teller method (BET), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and H-2-temperature programmed reduction (H-2-TPR) techniques. The results show that the catalyst, prepared by conditions with precipitant Na2CO3 and Ce/Mn molar ratio 1:2 calcined at 400 degrees C for 3 h in pH 11.0, displays the optimal performance, with the removal rate of NH4+-N and selectivity to gaseous nitrogen, 88.14 wt% and 53.67 wt%, respectively. The effects of several operating factors including solution pH, initial NH4+-N concentrations and scavengers were evaluated. In addition, XRD patterns of catalyst with the best performance and the comparative study on decontamination of NH4+-N by various processes (O-3, catalyst and catalyst/O-3) show that the primary metal oxides are CeO2 and MnO2 in Ce/MnOx composite metal oxide catalysts, which have a synergistic effect on the catalytic ozonation of NH4+-N, and the new phase MnO2 plays a great role. After 5 consecutive use cycles, the degradation efficiency is declined slightly, and can still achieve better than 70 wt% over 1 h reaction. Additionally, the application of catalytic ozonation for actual wastewater on the removal rate of NH4+-N was investigated. Possible mechanism and degradation pathway of NH4+-N were also proposed. In a word, the application of CeO2-MnO2 composite metal oxide catalysts in catalytic ozonation can be regarded as an effective, feasible and promising method for the treatment of NH4+-N. (C) 2020 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.

Automated summary

The study investigates the degradation of NH4+-N in wastewater using Ce/MnOx composite metal oxide catalysts prepared under different conditions. The optimal catalyst was found to be prepared with Na2CO3 precipitant and a Ce/Mn molar ratio of 1:2, calcined at 400 degrees C for 3 hours at pH 11.0, showing high removal rates of NH4+-N and selectivity to gaseous nitrogen. The study also explores the effects of various operating factors, catalyst performance, and the application of catalytic ozonation for actual wastewater treatment, suggesting that CeO2-MnO2 composite metal oxide catalysts are effective for NH4+-N treatment.