Synergistic mechanisms, enhanced pathways, and pollution reduction and carbon mitigation strategies for nitrogen and phosphorus removal in surface flow constructed wetlands

Surface flow constructed wetlands (SFCWs) are an efficient ecological treatment technology and play an important role in controlling nitrogen and phosphorus pollution in aquatic environments. This paper systematically reviewed the mechanisms of nitrogen (N) and phosphorus (P) removal in SFCWs, the key factors influencing their performance, pathways for performance enhancement, and strategies for sustainable management. Mechanistically, SFCWs remove N and P through the coupled effects of plant uptake, microbial transformation, and substrate-mediated adsorption and precipitation. Treatment performance is mainly governed by plant traits, temperature, hydraulic retention time(HRT), and substrate type. Performance can be significantly improved through intensification measures such as biotic enhancement, artificial aeration, external carbon supplementation, and substrate functionalization. For sustainable operation, plant harvesting, resource-oriented utilization of harvested biomass, and operational optimization can deliver co-benefits in both pollution reduction and carbon mitigation. Future research should focus on elucidating multi-factor coupling mechanisms, developing durable functional materials, and advancing intelligent control technologies. Overall, this review provided a theoretical basis and an important reference for the precise management of SFCWs and their innovative application in water pollution control under the carbon-neutrality framework.