In recent years,with the rapid development of aquaculture industry,environmental problems related to eutrophication and antibiotic pollution in the aquatic environment are growing.Constructed wetlands(CWs)is widely used for treating aquaculture wastewater,because of its low treatment cost,easy operation and maintenance.CWs have been proven to be a green technology without secondary pollution.However,the contaminant removal efficiency of CWs are affected by complex factors,including hydraulic flow patterns,type and composition of substrates and plants,hydraulic retention time,strengthening methods,seasonal factors,the removal efficiency of antibiotics or nutrients in different studies or engineering cases are not inconsistent,and the influencing mechanisms are still unclear.Thus,five sets of constructed wetland systems with different substrates,plants and strengthening conditions(CW1,CW2,CW3,CW4 and CW5)were constructed in this study to analyze the removal efficiency and influencing factors of four typical antibiotics(ofloxacin,oxytetracycin,florfenicol and sulfamethoxazole)in vertical subsurface flow constructed wetlands.Then,the effects of antibiotics on nutrient removal in constructed wetlands were identified,and the microscopic mechanism of nutrient removal affected by antibiotics was determined from the perspective of microorganisms.The main conclusions are as follows:(1)Five constructed wetlands under different conditions showed good removal effects on ofloxacin and oxytetracycline.When the hydraulic retention time ranged from 1 to 3 days,the removal rate of florfenicol and sulfamethoxazole significantly increased with the hydraulic retention time increasing,and growth rate were 11.01%and19.57%,respectively.The removal rates of florfenicol,oxytetracycin,ofloxacin and sulfamethoxazole were increased by 2.77%and 19.72%,0.57%and 0.97%,0.51%and 0.55%,6.48%and 32.05%,respectively,by planting Sesuvium portulacastrum and adding biochar.Increasing aeration significantly increased the removal rates of florfenicol and sulfamethoxazole by 8.13%and 31.34%,respectively.The removal rates of oxytetracycin,ofloxacin and sulfamethoxazole were increased by0.65%,4.81%and 32.65%,respectively.(2)The average removal rates of TN decreased by 16.22%and15.33%after antibiotic exposure in spring and autumn,and increased by6.69%in summer.In spring,summer and autumn,the average removal rates of NH4+-N decreased by 11.19%,4.28%and 14.74%,respectively,after antibiotic exposure.In spring and autumn,The average removal rate of NO3--N decreased by 4.84%and 25.12%,respectively,in spring and autumn,and increased by 24.74%in summer.The average removal rates of TP after antibiotic exposure decreased by 19.73%,33.96%and 4.89%,respectively,in spring,summer and autumn.(3)In spring and summer,the addition of four antibiotics decreased bacterial diversity and changed bacterial community structure in CW3and CW5 effluent.In spring,the relative abundance of bacterial communities related to nitrogen conversion,nitrate reduction,nitrate respiration,nitrogen respiration and nitrate denitrification,decreased after the addition of antibiotics.In summer,the relative abundance of bacterial communities related to nitrate reduction,nitrate respiration and nitrogen respiration increased in the system.In spring,the relative abundance of Rho-docyclacae and Aeromonas changed from increasing to decreasing before and after the presence of antibiotics,and the decrease of relative abundance of Bacillus increased,which might be an important reason for the decrease of phosphorus removal rate.In the presence of antibiotics,the relative abundance of Nitrospira decreases,which may be one of the reasons for the declining removal rate of ammonia nitrogen.The presence of antibiotics reduced the relative abundance of Azospira and Hydrogenophaga,which may be an important reason for the decreased nitrate removal rate.In summer,the relative abundance of Rho-docyclacae and Bacillus changed from an increase to a decrease before and after the presence of antibiotics,which might be an important reason for the decrease of phosphorus removal rate.The presence of antibiotics reduces the relative abundance of Nitrospira,which may be an important reason for the declining removal rate of ammonia nitrogen.The presence of antibiotics increases the relative abundance of Hydrogenophaga,which may be an important cause of the increased nitrate removal rate. |