Catalytic Ozonation of Ammonia Nitrogen to Nitrogen by Manganese-Loaded Powdered Activated Coke

Activated carbon has shown good catalytic performance in water treatment, but its wide application is limited by its high price. Activated coke exhibits functional groups and is low-cost. However, there is limited research on activated coke as a catalyst. In our previous study, powdered activated coke (PAC) exhibited good catalytic performance in NH3-N treatment with ozonation. Increasing nitrogen selectivity is the key to harmless degradation of NH3-N, which has received little attention. In this paper, manganese-loaded powdered coke (Mn–PAC) was prepared, aiming to further improve the nitrogen selectivity. Under the same conditions, the PAC/O3 system achieved 92.16% NH3-N removal and 49.46% nitrogen selectivity, while the Mn–PAC/O3 system achieved almost 100% NH3-N removal and 79.31% N2 selectivity. When Mn–PAC was reused for the sixth time, the system achieved about 70% and 46% NH3-N removal and N2 selectivity, both of which were about 10% higher than those of PAC. Complex redox and synergistic interactions existed in the Mn–PAC/O3 system. The Mn–PAC surface contains reactive sites such as C=C, C=O, π–π bonds, ArOH, and various MnOx. These components collectively facilitate ozone decomposition into ·OH, ·O2−, and 1O2. The 1O2 may play a significant role in converting NH3-N to N2.