Study On Phosphorus Removal Performance Of Constructed Wetland Under The Stress Of AgNPs

Silver nanoparticles(AgNPs)shows a wide application prospect in biomedicine,antibacterial,microelectronics and other fields.Inevitably,its mass production and use make it enter the environment in various ways,which will cause potential environmental risks.The negative effects of AgNPs exposure on plants,soil microbial and treatment of sewage have been confirmed.However,the current research on the effects of AgNPs on constructed wetland ecosystems has not attracted enough attention.Therefore,it is of great practical significance to establish the effect of AgNPs exposure on the performance of phosphorus removal in constructed wetlands,to explore the potential for removing nanosilver from constructed wetland systems,and to construct an integrated wetland that can effectively treat wastewater containing nanoparticles.The vertical flow constructed wetland system under the AgNPs(50,200?g/L)stress was used as the research object,during the 450 d inspection period,to explore the effects of AgNPs exposure on the phosphorus removal efficiency,soil phosphatase activity,phosphorus removal microorganisms and AgNPs migration in the wetland system.The results showed that under the short-term exposure(0~140d)of AgNPs,the exposure of different concentrations of AgNPs inhibited the removal of phosphorus in constructed wetlands,Under the long-term stress of AgNPs,the TP and SOP removal rates of the effluent gradually recovered over time.In the experimental concentration range,the long-term exposure of AgNPs did not significantly inhibit the activity of acid phosphatase,but changed the microbial community structure,the corresponding dominant flora has changed significantly.The migration of pollutants along the wetland shows that the soil layer is the main fate of various pollutants including AgNPs.In the case of different AgNPs exposure concentrations,the wetland can effectively remove AgNPs from the wastewater.With the passage of wetland running time,AgNPs gradually migrates from the soil surface to the bottom layer.The higher the concentration of AgNPs,the stronger the migration ability.However,plants can transfer AgNPs from root to stem and leaf tissues,and long-term exposure of AgNPs inhibits the growth of the Yellow Iris root system.Under the stress of AgNPs(100?g/L),four vertical flow wetland systems(with unplanted,I.pseudacorus,A.donax and C.alternifolius)were studied to explore the effects of phosphorus removal,soil phosphatase activity,and AgNPs removal and migration under different exposure times.The results showed that the short-term exposure(0~140d)of AgNPs significantly inhibited the phosphorus removal performance of constructed wetlands.Under the long-term exposure of AgNPs,the effects of phosphorus removal of wetlands without plants and C.alternifolius were significantly inhibited,but,the effects of phosphorus removal of wetlands with I.pseudacorus and A.donax gradually restored to its original level.It can be seen that effect of AgNPs long-term exposure on phosphorus removal in wetland has a close relationship with plant species.Under the long-term exposure of AgNPs,the phosphorus removal efficiency of the four wetlands was in the following order: A.donax? I.pseudacorus>C.alternifolius > unplanted.In the range of AgNPs concentration(less than 200?g/L),under the long term stress of AgNPs,the constructed wetland can ensure good phosphorus removal effect and have the potential to remove nanoparticles.It is feasible to treat the water treatment system containing AgNPs sewage.