Performance and microbial responses of vertical flow constructed wetlands intensified by electric and magnetic fields for domestic wastewater purification

This study constructed two types of enhanced vertical flow constructed wetlands: the electric field enhanced and the magnetic field enhanced vertical flow constructed wetland. The aim was to investigate the performance and microbial mechanisms of the electric and magnetic fields in treating domestic wastewater by the vertical flow constructed wetland. Results showed that M_VFCW achieved optimal COD (67.79%) and NH₄⁺-N (88.76%) removal at hydraulic retention time (HRT) of 72 h, whereas E_VFCW excelled in TP removal (61.84%). Mechanistically, the electric field directly increased dissolved oxygen concentration through anodic oxygen evolution, while OH - generated at the cathode elevated the local pH, creating a favorable alkaline microenvironment for phosphate immobilization. In addition, this electrochemical perturbation selectively enriched electroactive microorganisms, thereby enhancing extracellular electron transfer and organic pollutant degradation. Conversely, the magnetic field activated phosphatase, urease, and dehydrogenase, enriching Proteobacteria , including key denitrifying genera, while inducing a mild plant antioxidant response. KEGG prediction indicated up-regulated pathways in carbon, energy metabolism, and membrane transport under external fields. Redundancy analysis revealed environmental factors explained 60.77% of community variation. Neither strategy caused plant oxidative stress, confirming excellent biosafety. Preliminary economic assessment showed that E_VFCW and M_VFCW annual energy costs are approximately 3.3 and 0.7 USD, with capital investments of 291 and 247 USD, respectively, though electrode corrosion, demagnetization, and scale-up costs remain practical challenges. The electric field and magnetic field enhance the vertical flow constructed wetland, exerting their respective strengthening advantages for different pollutants, thus providing a theoretical basis for the enhanced wastewater treatment measures.