Study On Removal Performance And Intensified Strategies Of Typical Antibiotics In Microbial Fuel Cells Integrated With Constructed Wetlands

Antibiotics have been extensively used for treating infectious diseases of humans and animals as prophylactics or therapies,and/or as growth promoters and nutrient replacements for animal production.Therefore,it is widely used by humans to improve human health and promote economic development.However,due to the increasing usage of antibiotics and incomplete metabolism by humans and animals,tremendous quantities of antibiotics have been discharged into the environment as original compounds and/or their metabolites with feces and urine,increasing detection frequencies and detected concentrations.More seriously,the increasing concentrations of antibiotics in the environment are able to accelerate the occurrence of antibiotic resistant bacteria（ARB）and antibiotic resistance genes（ARGs）,which can transfer between pathogenic and non-pathogenic bacteria by both vertical and horizontal gene transfer.The residual antibiotics and emerging antimicrobial resistance（ARGs and ARB）pose a severe threat to the environment and ecosystem,as well as human health.Constructed wetlands integrated with microbial fuel cells（MFC-CWs）are an innovative wastewater treatment technology with low costs associated with establishment and maintenance,which has been applied to the removal of a variety of contaminants removal including inorganic compounds and organic compounds,especially for refractory organic contaminants.Consequently,lab-scale experiments were conducted by microcosm-scale MFC-CWs to explore the removal performance of sulfamethoxazole（SMX）,tetracycline（TC）and co-exsisting contaminants.The effects of carbon source species and concentrations,external resistance and aeration duration on the removal of antibiotics were also evaluated.The strengthening measures for antibiotic removal were then put forward depending on the results of above-mentioned experiments.The main conclusions are listed as follows:（1）Circuit operation mode and plants are the main factors affecting the COD and NH₄⁺-N removal effects of MFC-CWs,respectively.More than 70%of organic matter is mainly removed in the anaerobic zone.The presence plants significantly improves the NH₄⁺-N removal effect and bioelectricity generation performance（voltage output,power density and coulomb efficiency）of MFC-CWs.Therefore,closed-circuit MFC-CWs with plants can efficiently remove COD and nitrogen in wastewater.（2）The presence of plants and circuit connection can synergistically strengthen the SMX and TC removal capacity of MFC-CWs,and the removal efficiencies in 24 h have exceeded 99%.The presence of plants and circuit connection in MFC-CWs promotes the accumulation of SMX and TC in the electrode layers of MFC-CWs,and the residual antibiotics in the anode layer were higher than those in the cathode layer.For coexisting pollutants,plants and circuit operation mode were respectively the dominant influential factors affecting the removal of COD and NH₄⁺-N.Planting plants can significantly improve the voltage output and coulombic efficiency in MFC-CWs.With the increase of influent antibiotic concentrations,NH₄⁺-N removal performance and coulombic efficiency both gradually decreased,while the COD removal was not significantly affected.Therefore,the presence of antibiotics may inhibit the removal of NH₄⁺-N.（3）MFC-CWs utilizing glucose as carbon source with influent concentration of200 mg·L^-1exhibited the best antibiotic removal efficiencies.Best antibiotic removal performance in MFC-CWs were observed when the external resistance（700Ω）was close to internal resistance（600.11Ω）,with the removal efficiencies of 99.4%（SMX）and 97.81%（TC）,respectively.Compared with the non-aeration treatment,the antibiotic removal efficiencies in MFC-CWs were increased by 4.98%（SMX）and4.34%（TC）,respectively,with the aeration duration of 12 h.（4）For bioelectricity generation performance,glucose outperformed sodium acetate,sucrose and starch,with the highest voltages of 386±20 mV,maximum power density（MPD）of 123.43 mW·m^-3,and coulombic efficiency（CE）of 0.273%.Increasing carbon source concentrations from 100 to 400 mg·L^-1,significantly（p<0.05）increased the voltage and MPD,but decreased the internal resistance and CE.The highest MPD was obtained when the external resistance（700Ω）was close to the internal resistance（600.11Ω）.Aeration not only improved the voltage and MPD,but also reduced the internal resistance.（5）Both sponge iron and calcium peroxide can significantly improve the removal efficiencies of SMX and TC in MFC-CWs,and increase the removal efficiencies of antibiotics by 0.83%-1.32%（SMX）and 6.08%-8.75%（TC）,respectively.Both the addition of sponge iron and calcium peroxide can strengthen the removal of organic matter by MFC-CWs,but the strengthening effect of NH₄⁺-N removal is not obvious.The addition of sponge iron to the anode area can significantly improve the voltage output,power density and coulombic efficiency of MFC-CWs,and reduce the internal resistance of the system.The addition of sponge iron to the anaerobic area can increase the relative abundance of Firmicutes and Actinomycetes in the anaerobic area of MFC-CWs,and the addition of CaO₂ to the cathode area can increase the relative abundance of Bacteroides,Chloroflexum and Actinomycetes.In addition,the increase in the relative abundance of Thiomonas and Geobacter in the anode zone may be the dominant reason for the increase in the antibiotic removal performance and electricity generation performance of MFC-CWs.