Research On Treatment Of Sulfamethoxazole Wastewater By Constructed Wetland-Microbial Fuel Cell System

As a new pollutant with broad antimicrobial spectrum and strong antimicrobial activity,sulfonamides have been widely used in the prevention and treatment of diseases.Sulfamethoxazole（SMX）is a common sulfonamide.It is discharged into the water environment will seriously affect the growth of algae and plants in the water,and prone to antibiotic resistance,which threatens human health.Therefore,this study used constructed wetland-microbial fuel cell system to treat SMX wastewater,and systematically evaluated the difference of SMX removal between open-circuit constructed wetland-microbial fuel cell and constructed wetland-microbial fuel cell.Including（1）the electricity generation analysis of CW-MFC,（2）the removal efficiency of SMX and other common pollutants,（3）the difference of extracellular polymeric substances（EPS）produced by microorganisms in the two devices,（4）the changes of microbial communities caused by SMX stress were evaluated,（5）the abundance of SMX resistance gene Sul1 in the two devices was compared.The results were as follows:（1）Power generation performance of CW-MFCIn the early stage of operation,the voltage of CW-MFC increased rapidly,the maximum voltage reached 505.92 mV,and the average power output was 421.28±19.76 mV.During 20-40days,the microbial community was not stable enough because the device did not adapt to the stress of SMX,resulting in a decrease in voltage.After 45 days,the microbial community gradually stabilized and the voltage began to rise.The polarization curve was obtained by changing the resistance from large to small.After calculation,the internal resistance of CW-MFC device was 176.03Ω,the maximum power density was 7.428 m W/m²,and the current density was 37.18 m A/m².The electrical performance was good.That is why it creates conditions for high removal rate of pollutants.（2）Pollutants removalThe removal of major pollutants by two devices entered a stable period around 25 days.During the stable period,the removal efficiency of TN,NH₄⁺-N and SMX in CW-MFC were significantly higher than those in CW（P<0.05）.The removal efficiency of total phosphorus（TP）and COD were above 98%and 85%,respectively.There was no significant difference between the two devices（P>0.05）.The results showed that the complete current pathway formed in CW-MFC promoted the metabolism and growth of microorganisms degrading TN,NH₄⁺-N and SMX,resulting in positive effects and significant differences in removal efficiency.The removal of TP and COD does not require additional current.In summary,compared with CW,CW-MFC has higher pollutant removal efficiency and less fluctuation.（3）Extracellular polymer analysisThe analysis of EPS detection results showed that more EPS was secreted on the last day of the experiment than on the first day due to the addition of sulfamethoxazole,indicating that microorganisms used the secretion of EPS to protect cells.The components of EPS were qualitatively analyzed and three peaks were identified.The main components were fulvic acid-like compounds,soluble microbial by-products and tyrosine-like substances.The fluorescence intensity of fulvic acid-like compounds is the highest,and tyrosine-like substances represent one of the protein substances.The fluorescence peak intensity of fulvic acid-like compounds in CW-MFC is lower than that of CW.It’s indicating that in CW-MFC,SMX residual is less,so the amount of EPS is relatively less,which is consistent with the high pollutant removal rate of CW-MFC.（4）Microbial community and resistance genesAfter adding SMX,the microbial diversity including Alpha and Beta diversity of CW anode was lower than that of CW-MFC anode.The study on microbial community evolution showed that Proteobacteria was the dominant phylum with the largest proportion.Methylotenera is the dominant genus of CW-MFC,and its relative abundance is greater than CW.As a kind of denitrifying bacteria,Methylotenera mainly exists in the anode for denitrification.Through quantitative analysis of Sul 1 resistance genes,the copy number of Sul 1 resistance genes in CW is higher,which proves that antibiotic resistance is easy to accumulate in CW and has a greater risk of drug resistance gene transmission.At the four levels of phylum,class,family and genus,the sludge composition of CW-MFC anode is similar to that of the initial sludge.In other words,after the addition of SMX,the overall device performance and electrical performance of CW-MFC are almost unaffected,which proves that its stability is good.