Effect Of Sulfamethoxazole On Nitrogen Removal Performance In Constructed Wetland

Due to the impact of human production and life and the lack of purification system,more and more low-polluted water of sewage treatment plant tail water,rainwater runoff and agricultural runoff was discharged into water bodies and is one of the main sources of nitrogen pollution for the lake water body,and further cause the eutrophication of the water body.Constructed wetlands(CWs)are widely used to reduce nitrogen pollution load for low-polluted water due to their low cost and good removal effect.Sulfamethoxazole(SMX),as one of the common antibiotics,is widely used and discharged into the environment.SMX has been detected in low-polluted water.Finally,SMX has been discharged into CWs and it disturb nitrogen removal.Hence,Research on the effect of SMX stress on the nitrogen removal process in CWs is of great significance for improving the nitrogen removal effect of low-polluted water and preventing further eutrophication.In this work,three CWs planted with Cyperus alternifolius and Thalia dealbata and Acorus calamus respectively were constructed.The effects of different concentrations(0.1 mg/L,0.5 mg/L and 1 mg/L)of SMX on nitrogen removal process were studied from three aspects of nitrogen removal effect,plant physiological response and microbial community structure change.(1)The plant species and SMX concentration had influence on the nitrogen removal efficiency.With the increase of SMX stress concentration,the removal of NO3--N and TN in the three CWs were significantly inhibited.Although the removal of NH4+-N was inhibited,the removal rate was more than 95%.Compared with CWs with Cyperus alternifolius and Acorus calamus,the nitrogen removal effect of Thalia dealbata system was the best under SMX stress.(2)SMX can affect the physiological activity of wetland plants.Compared with the initial concentration of SMX(0.1 mg/L),high concentration of SMX(1 mg/L)inhibited the synthesis of chlorophyll and root activity,increased the content of malondialdehyde(MDA),and promoted the activities of superoxide dismutase(SOD)and peroxidase(POD).With the increase of SMX concentration,the stress resistance and antioxidant capacity of Thalia dealbata were relatively strong.Correlation analysis showed that root activity was positively correlated with chlorophyll content,and negatively correlated with MDA content,SOD and POD activity.(3)Plant species and SMX concentration affected the composition and structure of microbial community.High concentration of SMX reduced the microbial diversity of the Cyperus alternifolius system,and increased the microbial diversity of the Thalia dealbata and Acorus calamus systems.SMX concentration was the most important factor causing the difference of microbial community structure.Actinobacteria and Proteobacteria were the main contributing species to the difference of microbial community structure among different concentrations of SMX.Under high concentration of SMX stress,the relative abundance of Proteobacteria decreased and that of Actinobacteriata increased.The decrease of relative abundance of major denitrifying bacteria,such as hypomicrobium and hydrogenophaga,might contribute to the deterioration of nitrogen removal efficiency.Plant species was the secondary factors causing the difference of microbial community structure.Chloroflexi,Proteobacteria and Bacteroidota are the main contributing species to the difference of microbial community structure among different plant systems.Comprehensive analysis showed that compared with the Cyperus alternifolius and Acorus calamus system,the Thalia dealbata system was more conducive to the growth of nitrogen removal functional bacteria and nitrogen removal under SMX stress.Combined with nitrogen removal,the stress resistance and antioxidant capacity of plants and the abundance changes of nitrogen-related microorganisms,it is concluded that the CWs with Thalia dealbata was more conducive to nitrogen removal.Therefore,the effects of different concentrations(0 mg/L,0.1 mg/L and 1 mg/L)of SMX on the functional genes(anammox,amoA,nxrA,narG,nirK,nirS and nosZ)in the nitrogen removal process were studied,and the mechanism of SMX on the nitrogen removal process was further analyzed.