Novel magnetic coupling constructed wetland for nitrogen removal: Enhancing performance and responses of plants and microbial communities

Vertical flow constructed wetlands (VFCWs) have been widely applied worldwide due to their small footprint and large hydraulic load, however, its sustainable operation and application is still challenging because of the unsatisfactory nitrogen removal. This study developed a novel CW coupled with a magnetic field for treating simulated wastewater, and investigated the effects of magnetic field on enhancing treatment performance and responses of wetland plants and microbial community. The results showed that the magnetic field (average 110 mT) had a significantly intensifying effect on organics and nitrogen removal. The removal efficiencies of NH4+-N and TN in CW exposed to magnetic field (MF-CW) were 10.14% and 9.16% higher than those in control CW (C-CW), and an increased COD removal was also found in MF-CW. Biochemical characteristics of plants indicated that the MF did not cause a severe stress for wetland plants, while MF application shifted significantly the microbial community in CWs. Relative abundances of nitrifying bacteria such as Nitrospira (2.36%), Dokdonella (0.27%) and Nitrosomonas (0.17%) had been significantly promoted due to MF exposure, and nitrification-related microbial enzyme (AMO) activity was also increased by 63%. It can be concluded that introducing MF into CWs could intensify organics and nitrogen removal via the biological process, which would contribute to a better understanding of magnetic coupling mechanism.