Optimization of operational parameters and synergistic mechanisms for micro-electric field constructed wetlands in mine wastewater treatment

To investigate the enhancement mechanism of micro-electric fields in constructed wetlands, this study simultaneously established three electro-enhanced wetland (E-CW) systems and three conventional wetland (CW) systems for comparative experiments. Experiments were conducted under voltage gradients of 0–8 V, salinity gradients of 700–1600 mg/L, and hydraulic retention time (HRT) gradients of 1–4 days. This study innovatively proposes a novel dual-electrode layered structure: the anode layer is filled with suspended media serving as a microbial enrichment carrier, while the cathode layer is filled with manganese sand to enhance redox potential and promote electron transfer within the wetland matrix. This coupling of biological enrichment with electrochemical redox processes constitutes a multi-level synergistic model rarely explored in existing wetland research. Key findings are as follows: ① E-CW systems outperformed CW systems overall: Higher removal rates for chemical oxygen demand (COD Mn ), total nitrogen (TN), total phosphorus (TP), and salinity were achieved, peaking at 4 V. ② Removal rates increased with longer HRT but decreased with higher salinity. Pollutant removal became more thorough when HRT >2 days; removal rates began to be significantly inhibited when influent salinity exceeded 1200 mg/L. ③ Micro-electric fields modulated extracellular polymer secretion patterns: inhibiting protein-polysaccharide formation, enhancing microbial structural stability, and directing the enrichment of functional microbial communities. ④ Micro-electric field intervention simultaneously remodels the physical morphology and surface chemistry of the packing material: mesopore volume and specific surface area increase, the material transitions from amorphous to crystalline, and functional group transformations further promote the coupling of pollutant adsorption and degradation. This integrated insight provides both theoretical and engineering significance by revealing coupled biological-electrochemical-material mechanisms, thus offering a scalable and energy-efficient pathway for saline mine wastewater purification.