Performance of Iron-Carbon-Manganese Ore Composite Substrate Constructed Wetland for Simultaneous Removal of Nitrogen and Tetracycline
Constructed wetlands (CWs) with conventional substrates often exhibit limited removal of nitrogen and antibiotics from secondary effluent. This study developed an iron-carbon-manganese ore (Fe-C-Mn) composite substrate CW to enhance simultaneous removal of nitrogen and tetracycline (TC). Under influent TC of 2 mg·L−1 and total nitrogen (TN) of 15 mg·L−1, the Fe-C-Mn system achieved average TC removal of 91.3%, significantly higher than the gravel control (27.2%). TN and nitrate nitrogen (NO3−-N) removals reached 71.7% and 83.3%, respectively, versus 7.8% and 1.2% in the control. Substrate analysis revealed increased surface roughness and synergistic generation of active components (Fe(II)/Fe(III) and Mn(II)), driving autotrophic denitrification and TC biodegradation/chemical degradation. Microbial community analysis indicated reduced overall diversity but selective enrichment of potential TC degraders (e.g., Trichosporon, Bacillota) and denitrifiers (e.g., unclassified_f_Rhodocyclaceae). TC degradation pathways included demethylation, hydroxylation, and ring-opening, ultimately yielding small metabolites. These findings provide theoretical and technical support for enhanced removal of antibiotics and nitrogen from secondary effluent using CWs.