Efficacy of <italic>Sesuvium portulacastrum </italic>ecological floating beds on the treatment of seawater recirculating aquaculture wastewater

[Objective] Significant environmental issues have arisen due to the growth of traditional aquaculture.Recirculating aquaculture systems(RAS)are a sustainable approach to fish farming that can help meet the world's growing seafood demand.However, high material costs and complex maintenance requirements are impeding their widespread adoption.Sesuvium portulacastrum Linn., recognized for its economic efficiency and simple management, is an ideal restoration plant for alleviating eutrophication problems in coastal mariculture areas.This study investigated the effectiveness of S.portulacastrum ecological floating beds in treating wastewater from seawater recirculating aquaculture systems.[Methods] To achieve purification and recycling of aquaculture wastewater, an S-shaped racetrack style water treatment system was established, comprising modules such as a sedimentation pond, plant purification pond, aeration pond, and sand filter sump.Monthly inspections were carried out over a six-month period to verify the system's efficiency.[Results] The results showed that environmental factors, including temperature, salinity, pH, and dissolved oxygen, were maintained stably with appropriate ranges within the system.Throughout the process, low concentrations of chemical oxygen demand(COD), dissolved phosphorus, and nitrogen were maintained, with dissolved inorganic nitrogen(DIN)predominantly present as NO3--N to ensure the welfare of cultured organisms.The plant purification pond, featuring S.portulacastrum, played a crucial role in the entire water treatment process, significantly influencing its purification efficiency.The removal rates for COD, NO2--N, NO3--N, NH4+-N, DIN and PO43--P were in the ranges of -9.2%-52.9%, 7.4%-46.1%, 4.0%-27.1%, 33.7%-51.4%, 19.9%-38.7%, and 3.7%-46.9%, respectively.The denitrification process, mediated by microorganisms in the rhizosphere of these plants, emerged as the primary mechanism for nitrogen removal.This biologically driven process not only effectively mitigated nitrogen-induced eutrophication but also significantly improved the chemical composition of DIN, thereby creating a more favorable environment for the health and growth of fish species in aquaculture systems.[Conclusion] This study demonstrates that the integration of S.portulacastrum ecological floating beds into RAS is an advantageous innovation for the sustainable development of cost-effective, high-yield, eco-friendly, and safe mariculture.With its recognized health benefits and medicinal properties, S.portulacastrum is emerging as a promising "marine vegetable" with significant development potential.Through further research and development, S.portulacastrum floating beds are anticipated to become an integral part of sustainable agriculture and the utilization of marine resources in the future.