Fate of Antibiotics and Their Corresponding Resistance Genes in Bioelectrochemical Electrochemical-assisted Constucted Wetland System

Author:Zhang Shuai

Supervisor:li xian ning song hai liang


Degree Year:2018





Antibiotics in the natural environment can induce the growth of antibiotic resistance bacteria(ARB)and antibiotic resistance genes(ARGs).This growth normally accelerates the spread of ARGs and cause chemical pollutions.Metabolites from the antibiotics and its inductive effect can also threaten human health.Microbial fuel cells(MFC)converts the chemical energy organics possess to electrical energy,which represents interesting opportunities in wastewater treatment.This project proposes the combined utilization of constructed wetland(CW)and MFC for enhanced production of electrical energy,which can potentially be used on-site for the removal of antibiotics.This proposal can significantly enhance removal efficiency of antibiotics and maximize resource recovery from waste.BER has the advantage of low electrical energy demands and capable of using direct current at low voltages.Application of CW-MFC can offer significantly enhance the electrical energy BER requires and maximize the individual advantages of CW,MFC,and BER.This project can significantly reinforce the removal of antibiotics and minimize its spread into the water environment by strategically utilizing combined ecological,microbial and electro-chemical methods.SMX and TC were selected as model antibiotics in this project.The operating conditions of 3D-BER were studied,as well as its effects on the degradation pathways and microbial communities.The capacity of electrical energy production from CW-MFC was investigated,and the combined system of BER-CW-MFC was then established.Key findings from the project are as follows:1.Good removal rates of TC and SMX were observed at low voltages.At antibiotics concentration of 1600 μg/L,removal rates greater than 82.6% and 72.2% were observed for TC and SMX,respectively.The improved removal efficiency was likely due to the additional electro-chemistry capacity and accelerated microbial degradation and activated carbon adsorption.The low voltages used in the experiment increased microbial population and active enzymes.Increased abundance of ARGs on the electrodes was also observed.The relatively high concentrations of antibiotics increased the amounts of tet and sul on the cathode.Whereas low voltages had very little impact of the amount of tet or sul on the 3D-BER cathode.15 predominant microbial species were detected with the most predominant one being Proteobacteria followed by Bacteroidetes,Chloroflexi,Firmicutes,and Verrucomicrobia.2.High removal rates of TC and SMX were observed in the CW-MFC,and greater than CW.Adsorption of TC and SMX was observed higher on the CW-MFC cathode,with greater adsorption efficiency of TC greater than SMX.High concentrations of TC and SMX reduced the current density of CW-MFC.At the layer of CW-MFC anode,the absolute abundance of sul and tet genes was observed high,which was likely related to the antibiotics concentrations.The relative abundance of sul and tet increased with treatment time and stabilized towards the later phase of treatment.3.BER showed strong capability for removal of SMX and this removal efficiency was further enhanced with increased voltages.Increased operation period of the BER system also improved the removal rate of SMX.In addition,this experiment modelled the degradation processes of SMX and BER,analyzed the degradation pathways of SMX,and found the significance of microbial community in the degradation process.Reliable electricity could be supplied to BER from the CW-MFC system and had a positive impact on the removal rate of SMX.Low voltages improved SMX removal rate but had no impact on the degradation by-products from it.The predominant bacterial species from the BER system were Proteobacteria,Bacteroidetes,Chloroflexi,Spirochaetes,Firmicutes,and Actinobacteria.The predominant archae species were Euryarchaeota and Parvarchaeota.Low voltages were also found to have an impact on the community structure and morphology.4.High SMX removal efficiency greater than 99.3% was observed in the coupling system.More than 85.7% of SMX was successfully removed in the BER system and the residual SMR was further removed in the CW-MFC system.Reducing HRT had a negative impact on the removal of SMX in individual treatment units but removal remained high in the coupling system.The relative abundance of sul increased when the SMX in the influent increased,and this was not observed for the coupling CW-MFC system.There was no significant difference in the relative abundance of sul with the combined electrical currents.The relative abundance of sul in the BER effluent was observed higher than in the CW-MFC effluent,and this increased with reduced HRT(also for the BER effluent).At different HRTs,the relative abundance of sul was observed higher in the BER effluent than in the CW-MFC effluent.