| Sulfonamides(SAs)are widely used in veterinary medicine and human medicine because of their broad-spectrum antibacterial activity for preventing and treating bacterial infection,low cost and easy preparation,but at the same time,the abuse of SAs causes serious environmental pollution problems.Sulfamethoxazole(SMX)and trimethoprim(TMP)are two common SAs,which are often detected in the effluent of sewage treatment plants because of their strong water solubility,strong persistence and difficult degradation by microorganisms.Constructed wetlands have the advantages of low construction cost,convenient operation and maintenance management and beautification of the environment.It has been widely used in advanced treatment process of sewage treatment plants to remove trace organic pollutants in tail water,but it also has some problems such as low efficiency.Iron/manganese oxides have strong performance of ion exchange,adsorption and oxidation,which can realize the iron/manganese valence cycle under the action of iron/manganese redox bacteria.In recent years,iron/manganese ore has become a high-quality choice for constructed wetlands substrate because of its wide variety,easy preparation and low price,but there is no related report on the treatment of wastewater containing SMX and TMP by iron/manganese ore constructed wetlands.In this study,iron/manganese ore up-flow vertical subsurface constructed wetlands were constructed,and their removal efficiency on pollutants such as COD,TP,TN and NH4+-N,SMX and TMP were explored.The impact of SAs addition on the removal of conventional pollutants in wetland systems was investigated,and the compression resistance of iron/manganese ore wetlands to the increase of pollution load and the buffer performance to cope with the impact of SAs addition were investigated,and the removal mechanism of pollutants was further explored.The main conclusions of this study are as follows:(1)The removal efficiency of conventional pollutants such as COD,NH4+-N,NO3--N,TN and TP was significantly improved by adding iron/manganese ore.The addition of limonite significantly improved the removal efficiency of NO3--N.The average removal rate of NO3--N in iron ore group reached 64.27%,which was higher than that in manganese ore group(60.35%)and control group(39.50%).The addition of manganese ore improved the removal efficiency of COD,NH4+-N,TN and TP,and the average removal rates of COD,NH4+-N and TN in manganese ore group were 83.59%,75.53%and 68.50%,which were slightly higher than those in iron ore group(79.76%,72.62%and 66.45%).The removal rate of TP in manganese ore group was 78.15%,which was significantly higher than that in iron ore group(48.71%)and control group(32.56%).In addition,the impact compression efficiency of COD,NH4+-N,TN was slightly higher in manganese ore group than in iron ore group,and higher in iron/manganese group than in control group.(2)The addition of SAs has little effect on the removal efficiency of COD and TP in the three constructed wetlands,but the addition of iron/manganese ore improves the buffering capacity of the systems.The addition of SAs significantly inhibited the removal rate of TN and NH4+-N and significantly improved the removal efficiency of NO3--N.With the influence of SAs addition on NH4+-N removal efficiency,manganese ore group showed stronger buffer performance,while iron ore group showed stronger buffer performance in NO3--N removal efficiency.(3)Iron/manganese ore improves SAs removal efficiency of constructed wetland systems.For SMX removal,the iron ore group(83.72%)and manganese ore group(77.85%)are slightly higher than the control group(71.26%).The removal of TMP in iron ore group(77.45%)and manganese ore group(65.83%)was significantly higher than that in control group(50.44%).In addition,resistance genes sull,sul2 and drfV and an integrase gene intll were detected at different heights of wetland systems.The addition of SAs significantly increased the relative abundance of drug-resistant bacteria.The ecological toxicity of the effluent from the constructed wetlands of iron/manganese ore was evaluated,and no ecological toxicity to luminescent bacteria and Chlorella was observed.(4)The addition of iron/manganese ore promoted the iron/manganese cycle in wetlands(including the formation of iron-manganese film on the root surface),and the cycle process promoted the removal efficiency of nitrogen and SAs in constructed wetlands.Limonite increases microbial diversity,and the addition of iron/manganese ore not only increases the relative abundance of Proteobacteria,but also increases the relative abundance of nitrate-dependent iron/manganese oxidizing bacteria and further strengthens denitrification.The relative abundance of SAs degrading bacteria in limonite layer and manganese ore sand layer of iron/manganese ore group was higher than that of control group,which promoted the microbial degradation process of SAs.The addition of SAs affected the microbial community structure,which increased the abundance of Chloroflexi and gamma-Proteobacteria,while decreased the abundance of Actinobacteria and alpha-Proteobacteria. |
PDF Full Text Request