The treatment performance and the removal mechanism of pollutants in vertical flow constructed wetlands combined with magnetic field

Low and irregular pollutant removal has been considered as a challenging problem in constructed wetlands (CWs) for the treatment of waste water. In this study, a novel CW with magnetic field (MF) coupling was developed for treating domestic wastewater with high pollutant removal. The results showed that the removal efficiencies of NH4+-N, TP and COD in MF exposed CWs (MF-CWs) were 23.61 %, 47.59 % and 68.68 % higher than those in control CWs (C-CWs). The TP and N concentrations of plants were significantly higher than those in C-CWs (P < 0.05). The MF significantly affected the diversity and composition of the bacterial community (P < 0.05). Bacterial community richness (Chao1 index) was significantly positively correlated with NH4+-N removal. Phylum-level bacterial communities were dominated by Pseudomonadota, Chloroflexota, Bacteroidota and Thermodesulfobacteriota. The dominant bacteria represented by Thermodesulfobacteriota were significantly positively correlated with COD, NH4+-N and TP removal efficiencies. In conclusion, bacterial diversity was the most important variable affecting NH4+-N and TP removal, followed by dominant bacteria, and plant uptake mainly affected them indirectly by altering the bacterial diversity. Decomposition by microorganisms could be the main cause of COD removal. The above results would be a contribution to a better understanding of the mechanism of the magnetic coupling.