Study On The Mechanism Of Enhanced Removal Of ?-lactam Antibiotics From Nitrification Sludge

At present,the abuse of antibiotics has seriously polluted the environment ecosystem.A variety of types of antibiotics could be effectively removed by nitrification system.However,the nitrification antibiotics removal mechanism in the system was not enough in-depth research,understanding the functional genes involved in antibiotics removal process and the changing rule of the microbial community structure will be helpful to reveal the nitrifying removal mechanism of the antibiotics in the system.Meanwhile,the long-term existence of antibiotics can also promote the proliferation of antibiotic resistant bacteria and antibiotic resistance genes(ARGs),which will seriously threaten the security of the ecosystem and human health when discharged into the natural environment.The mechanism of ARGs in the process of nitrification removal of antibiotics was rarely reported.Therefore,this thesis investigated the influence of key factors(antibiotic concentration,p H)on the operation performance of nitrification system and the removal of CFX,taking the ?-lactam antibiotic cephalexin(CFX)as the object.In order to clarify the removal mechanism of ?-lactam antibiotics enhanced by nitrification system,the role of ammonia oxidizing bacterias(AOB)and ammonia oxidizing archaeas(AOA)in the process of antibiotic removal were elucidated by molecular biology technology and high-throughput sequencing technology.In addition,real-time quantitative PCR and high-throughput sequencing were used to reveal the direction,transfer mechanism and changes of potential host bacteria of ARGs to investigate the role of ARGs in antibiotic removal.This thesis aims to provide theoretical basis for effective removal of antibiotics and control of the spread of ARGs.The main conclusions are obtained:(1)The removal efficiency of ?-lactam antibiotic wastewater by nitrification system:Under different concentrations of CFX(1 mg/L,5 mg/L,10 mg/L),the removal rate of CFX could reach above 90%,and the removal rate of CFX was the highest under 5 mg/L CFX,reaching 94.91%.The effluent of low concentration CFX(1 mg/L)nitrification system basically had no biotoxicity,while the effluent of high concentration CFX(5 mg/L,10 mg/L)nitrification system still had a certain biotoxicity,and the residual CFX in the effluent still needed further treatment.The higher the CFX concentration was,the greater the influence was on COD and the ammoina nitrogen removal performance of nitrification system.With the increase of CFX concentration,the COD removal rate gradually decreased from 95% to 89%,and when the CFX concentration reached 10 mg/L,the ammonia removal rate decreased to90%.Under different p H(p H 9,p H 8,p H 7)conditions,the removal ability of CFX increased gradually with the decrease of p H,and the removal rate of CFX increased from about 70% to about 90%.The removal rates of COD and ammonia nitrogen could reach over 90% under different p H conditions.(2)Mechanism of enhanced removal of ?-lactam antibiotics by nitrification system:Under the condition of 5 mg/L CFX,the expression level of amo A-AOB and the relative abundance of AOB(Nitrosomonas)were the highest,and the presence of more Nitrosomonas promoted the co-metabolic degradation of CFX.In addition,the host bacterias of Tolumonas and Hygrogenophaga could avoid the toxicity of CFX,and their enrichment under such conditions also promoted the efficient removal of CFX.Under the condition of 10 mg/L CFX,the expression level of amo A-AOA was the highest,and AOA(Candidatus-methanomethylicus)promoted the co-metabolic degradation of CFX at this stage.Heterotrophic bacteria(Pseudofulvimonas)also participated in CFX removal at this stage,but the expression level of amo A-AOB and the relative abundance of Nitrosomonas were both lower than that of 5 mg/L CFX.Therefore,the removal rate of CFX decreased under the condition of 10 mg/L CFX.Under the condition of p H 7,heterotrophic bacterias(Pseudofulvimonas,Novispirillum)with CFX degradation ability were enriched,and the expression level of amo A-AOB was the highest,which together led to the effective removal of CFX.Under the condition of p H 7,the expression level of amo A-AOA was the highest,and the enrichment of AOA(CandidatusMethanomethylicus)and heterotrophic bacterias(Thauera,Azoarcus,Dokdonella)promoted the removal of CFX at this stage.However,because the expression level of amo A-AOB was the lowest,the removal rate of CFX was the lowest under this condition.