Removal Rates And Mechanism Of Antibiotics And Nitrogen In Subsurface Flow Constructed Wetlands With Different Substrates

The abuse of antibiotics in medical treatment,livestock breeding and other industries leads to the direct or indirect release of antibiotics in the environment,which poses a potential threat to the ecological environment and human health.At present,the conventional wastewater treatment process can not remove antibiotics effectively,andthe sewage discharged from some water treatment plants has become a primary source of antibiotics and antibiotic resistance genes（ARGs）in natural water.In addition,the removal of high concentration nitrogen in domestic sewage has been widely studied.As an efficient and economical wastewater treatment system,constructed wetland has been applied in water treatment throughout the world.However,the removal efficiency of different constructed wetlands varied greatly with the matrix in the constructed wetlands.Thus,the exploitation of low cost-high efficiency constructed wetlands and the removal machanisms have been focused on at present.In this study,we explored the effect of antibiotic on nitrogen removal in VFCWs,and investigated the effect of substrates on the simultaneously removal of antibiotics and nitrogen.Besides,we studied the microbial mechanism of pollutant removal in constructed wetland based on microbial community,functional genes and soil enzyme activity.The main results and conclustions are as follows:（1）The experiment was carried out in two vertical flow constructed wetlands（VFCWs）models with the addition of ciprofloxacin hydrochloride（CIPH）and sulfamethazine（SMZ）at a high level of concentrations（50μg/L for each antibiotic）.During the whole operational period（120 days）,the results showed that the removal efficiencies of TN and NH₄⁺-N were significantly decreased（from 66.57%to 60.08%,and 93.81%to 85.76%）,and the abundance of gene amo A was also significantly reduced in response to antibiotics.Despite removal rate of NO₃^–-N has no significant differences,real-time quantitative polymerase chain reaction（RT-PCR）results indicated that significant low gene copy number involved in denitrification process were obtained in the addition of CIPH and SMZ.Further,CIPH and SMZ altered the overall bacterial community structure and reduced the bacterial diversity.This study indicated CIPH and SMZ affected the removal of nitrogen and the microorganism functions were inhibited.Furthermore,the effects of CIPH and SMZ on functional micoorganisms were different during the operation of VFCWs.（2）A vertical flow constructed wetland（VFCW）packed with the different substrates was designed to treat antibiotic wastewater.Manganese（Mn）ore（CW-M）parallel with biochar（CW-C）and solo zeolite（CW-Z）were used to enhance synchronous removal of ciprofloxacin hydrochloride（CIPH）,sulfamethazine（SMZ）and nitrogen（N）from the wastewater.The results indicated that CW-M demonstrated a significant potential to remove CIPH（93%）,SMZ（69%）,TN（71%）,NH₄⁺-N（94%）and NO₃^–-N（94%）respectively,across all the treatments.The abundances of amo A,nir K and nir S genes were markedly higher in CW-M and CW-C,while CW-C inhibited the production of quinolone resistance genes.Results showed that different substrate could affect the microbial diversity and structure.The increase of the abundance of nitrogen-related phyla were associated with the addition of Mn ore.Overall,Mn ore has a considerably potential to enhance the treatment performance of antibiotics and nitrogen in VFCWs.（3）The rhizosphere soil physicochemical properties and the activities of soil nitrogen transformation enzymes of four VFCWs were measured after 120 d operation.Results showed that manganese ore and biochar significantly increased the soil microbial biomass and enhanced pollutants removal rates.CIPH and SMZ stress reduced nitrogen transform in the rhizosphere soil,and resulted in increases of TN,NH₄⁺-N and NO₃^–-N.Antibiotics had significant inhibitory effects on urease（UR）,nitrate reductase（Na R）,nitrite reductase（Ni R）and nitrification potential（PNR）,while denitrification potential（PDR）was less affected by antibiotic stress.The activities of UR and PNR were significantly increased by manganese ore and biochar.Manganese ore was more conducive to the growth of most nitrogen transforming microorganism,and could better eliminate the influence of antibiotics.Soil enzyme activity is the most important factor that directly determines nitrogen removal efficiency,and enzyme activity is more significantly affected by the substrate type.