Study On Decontamination Capability Of Constructed Wetland Ecosystem Under The Stress Of AgNPs

The increasing utilization of silver nanoparticles(AgNPs)raises the release into ecosystem.The negative effects of AgNPs on nutrient removal in wastewater treatment,microbial community structure,enzymatic activity and plant have been confirmed.However,the presence of AgNPs in sewage and effluent from wastewater treatment plant(WWTP)means that the performance of constructed wetlands(CWs)must challenge more risks when CWs are exposed to AgNPs.Therefore,to provide technical support for nanonoparticles removal in CWs and evaluate ecological effect of nanonoparticles,it's essential to investigate the impact of AgNPs on the CWs performance for wastewater treatment.In the present study,the performance of CWs(Iris pseudacorus,Arundo donax,Cyperus alternifolius)exposure to AgNPs(0,50,100,200 ug/L),AgNPs removal and fate were examined.In three lab-scale CWs with I.pseudacorus exposure to AgNPs(0,50,200ug/L),the lower AgNPs level showed actue toxicity on NH4+-N and TN removal while the higher AgNPs level(200ug/L)showed obviously actue toxicity on all pollutant removal(COD?NH4+-N?TN?TP).It revealed that the higher AgNPs level had more obvious impacts than the lower AgNPs level.The COD,NH4+-N,TN and TP removal with time was impoved,sugeesting that CWs could weaken exposure toxicity of AgNPs.Nnitrogen and phosphrous removal efficiencies were still lower compared with control group.In addition,the removal efficiencies of different level AgNPs were all over 94%.The I.pseudacorus showed the excellent ability to accumulate and transport to the lower AgNPs level,and above ground biomass removed more AgNPs than below ground biomass,the phenomenon was opposite to the higher AgNPs level.In four lab-scale CWs with unplanted,I.pseudacorus,A.donax and C.alternifolius exposure to AgNPs(100 ug/L),AgNPs exposure inhibited nitrogen and pollutant removal in all CWs.The stress resistance to AgNPs exposure from high to low was I.pseudacorus,C.alternifolius,A.donax and unplanted which revealed that the presence of plants significantly improved stress resistance of CWs.Before and after AgNPs exposure,I.pseudacorus had the highest nitrogen and phosphorus removal efficiencies.For AgNPs removal,All CWs were quite efficient in AgNPs removal,with mean removal efficiencies exceeding 95%.AgNPs was mainly trapped in soil layer.However,there were obvious differences in plant uptake for AgNPs.The higher accumulation and transimission capacity for AgNPs was found in C.alternifolius.For accumulation concent of AgNPs in C.alternifolius,above ground was much higher than below ground in all CWs.In lab-scale CWs with I.pseudacorus exposure to AgNPs(20ug/L)for advanced wastewater treatment,the effluent could reach the first level A of Discharge standard of pollutants for municipal wastewater treatment plant(GB18918-2002).AgNPs showed acute toxicity effects on nitrogen and phosphorus removal,while no changes of chemical oxygen demand(COD)removal were found.The nitrogen and phosphorus removal effect was improved with time due to the function on CWs.AgNPs removal demonstrated that CWs had the potential to futher remove nanoparticles from wastewater.