Nutrient removal performance and mechanisms of a coupled resin–duckweed system for aquaculture wastewater treatment

The rapid growth of intensive aquaculture has led to a large volume of wastewater discharge, exacerbating global eutrophication. In this study, a coupled anion exchange resin–duckweed system was developed. This system achieved spatiotemporal synergy between resin adsorption and phytoremediation through a fully mixed reactor design. The results showed that the resin modified with hydrated lanthanum oxide achieved 100% removal of total phosphorus (TP) through stable phosphate complexation, and the MIEX resin improved kinetics compared with conventional resins. Duckweed maintained stable ammonium–nitrogen (NH4+–N) removal rates exceeding 88% at a salinity of ≤ 5000 mg/L. The coupled MIEX–duckweed system enhanced TP and soluble reactive phosphorus removal rates to 84.7% and 99.4%, respectively, which was approximately 30% higher than those achieved by a single MIEX system. Mechanistic analysis revealed a cascade purification chain: resins rapidly sequestered pollutants through ion exchange/coordination, while duckweed enabled long-term nutrient assimilation and salinity buffering through osmoregulation. Moreover, the salt tolerance of duckweed mitigated salinity accumulation resulting from resin regeneration, thereby overcoming a key operational constraint in the long-term operation. This study presents a low-carbon solution for efficient aquaculture wastewater treatment, integrating rapid purification with resource recovery potential. Additionally, it establishes a theoretical foundation for engineering applications.