Application of iron-carbon constructed wetlands for treating complex agricultural wastewater under pesticide and antibiotic stress: Performance and mechanisms.

Agricultural non-point source pollution often causes combined pesticide-antibiotic threat, such as atrazine (ATZ) and tetracycline (TC), originating from farmland drainage, livestock wastewater, and aquaculture effluents. Although iron-carbon constructed wetlands (CWs) show potential for pollution control, their performance and underlying mechanisms under the co-stress of ATZ and TC remain poorly understood. This study compared the purification mechanisms of complex agricultural wastewater in iron-carbon CWs modified with differently activated biochar. The acid-activated group (CW-FeC-Ac) achieved peak removal efficiencies of 96.64% for ATZ and 44.03% for TC, significantly outperforming the control (< 19%, p < 0.05). Despite dual emerging contaminant stress, conventional nitrogen, phosphorus, and COD removal was substantially enhanced across all iron-carbon groups. Mechanistically, iron-carbon micro-electrolysis synergized biochar's high specific surface area and porosity with iron filings' rapid electron transfer, optimizing both physicochemical adsorption and microbial niches. Increased protein and chlorophyll content in plants, as well as well-regulated antioxidant enzyme systems, demonstrate that the iron-carbon microenvironment alters plant growth. Concurrently, Actinomycetota and Bacillota were enriched in activated biochar groups. KEGG profiling confirmed the upregulation of key microorganisms (genes) driving nitrogen/phosphorus removal and ATZ/TC biodegradation. These findings provide valuable guidelines for optimizing iron-carbon CWs in agricultural pollution control.