The Study Of Cefalexin Production Wastewater Treatment Process And Microbial Community Succession Law

Antibiotic production wastewater contains high concentrations of conventional pollutants such as COD and ammonia nitrogen,also contains high concentrations of antibiotics and intermediates,meanwhile contains antibiotics resistance genes.If these pollutants have not been effectively removed from the wastewater,that will cause serious environmental pollution once they was discharged into the receiving water bodies.Therefore,it was necessary to explore the mechanism of the removal of these pollutants in the antibiotic wastewater treatment process and further strengthen its removal to provide guidance for engineering practice.In addition,high levels of residual antibiotics in the wastewater and fluctuations in the water quality of the wastewater might had an negative impact on the steady operation of the process.Therefore,the EGSB coupled A/O-MBR process was used to treat the cephalexin production wastewater,and the impact of cephalexin in wastewater and the volume load on operation of the process was investigatived,and the main pollutants degradation mechanism also was analyzed under the molecular level.Based on the above background,this study run two EGSB reactors in parallel,which were denoted as E1 and E2,respectively.Studies had shown that cefalexin（200 mg/L）in wastewater interferes with the stable operation of the EGSB reactor,resulting in an increase in effluent COD concentration and a decrease in COD removal.However,with the acclimation of microorganisms in the reactor,the removal rate of COD gradually increased and the operation of the EGSB reactor stabilized after 32 days.In addition,cephalexin in wastewater caused the accumulation of genes ampC,bla CTX-M,bla OXA-1,bla OXA-2 and bla OXA-1 in the effluent of EGSB reactor and also increased the int I1 recombinant antibiotic resistance gene in sludge,and more bacteria carrying beta-lactam resistance genes were induced in the sludge.The removal rate of cefalexin researched to 99%,of which biodegradation was the main way to remove in the EGSB reactor.Three cefalexin biodegradable products could be detected in the effluent of EGSB reactor.Among them,the only confirmed biodegradation product D-1 was2-hydroxy-3-phenyl-6-methylpyrazine.The statistical analysis showed that the accumulation of these three degradation products in the effluent might be the main reason,leading to the instability of the initial operation of the EGSB reactor.Stable operation of the EGSB system had formed a unique microbial flora structure as follows:（1）Proteobacteria Proteobacteria,Spirochaetae,Spirochaetae,Firmicutes and Bacteroidetes Bacteroidetes were the core bacterial flora.（2）Methanobacterium and Methanosaeta were the dominant archaea;（3）Ascomycota were the dominant fungal flora.Although EGSB reactors had a high removal efficiency of pollutants in cephalexin production wastewater,COD,NH₃-N,TN,cephalexin,cefalexin degradation products and resistance genes still remained in the effluents,so further treatment was needed.Therefore,this study next investigated the performance of EGSB+A/O-MBR combination process treating cefalexin production wastewater,as well as the key control parameter of the process-the impact of volume load.The results showed that,when volume loading was 1.56 g/L/d,the removal efficiencies of COD and ammonia nitrogen were 97%and 99%,,and the effluent concentrations of COD and NH₃-N was 200 mg/L and 3 mg/L,respectively;the removal efficiency of cephalexin was as high as 99.9%,and the concentration of cephalexin in the effluent was only about 2.0μg/L.The removal efficiency of theβ-lactamase resistance gene and int I1 were higher in the EGSB+A/O-MBR,except the amp C gene,the otherβ-lactam genes and int I1 were mainly removed in the A/O-MBR reactor.When volumetric load increased to 4.17 g/L/d,not only the removal efficiency of COD and NH₃-N by EGSB+A/O-MBR process was affected,but also the cephalexin and its degradation products was accumulated in the effluent.In addition,the increase of volume load affected the removal ofβ-lactam resistance genes and int Il in the EGSB reactor and also affected the removal of bla OXA gene and int I1 in the A/O-MBR reactor.Meanwhile,in the EGSB reactor sludge,the increase of volume load promoted the accumulation of int I1,bla TEM-1,bla CTX-M,bla OXA-1 and bla OXA-10,while in the A/O-MBR reactor sludge,only bla OXA-1 a small amount of accumulation.The increase of volume load affected the growth of bacteria genus Gelria,Lutispora,Syntrophomonas and vadinBC27 and fungi Sordariomycetes in EGSB system,and inhibited the activity of Methanosaeta.Proteobacteria,Bacteroidetes,Chlorobi and Chloroflexi in the A/O-MBR reactor are the major bacterial flora,and Ascomycota was the predominant Of the fungal community.Thauera and vadin BC27 were the dominant bacteria that degrade COD,while Pseudomonas sp.played a key role in the degradation of cephalexin in the system.When the volumetric load was increased to 4.71 g/L/d,the growth and activity of the aerobic ammonia-oxidizing bacteria were inhibited,which impeded the nitrification process and reduced the removal rates of NH3-N and TN.In addition,with the increases of volume load,the mechanism of transfer ofβ-lactam-resistant genes in EGSB reactor sludge was the horizontal transfer depending on int I1,while the vertical transfer depending bacterial growth was declined,especially the bla TEM-1 gene;transfer mechanism ofβ-lactamase gene in A/O-MBR reactor sludge is mainly vertical transfer,but the horizontal transfer of int I1 had been hindered.The results of this study showed that the EGSB+A/O-MBR process could effectively remove the pollution of cefalexin wastewater when the volume load was1.56 g/L/d.