Effect Of Chlortetracycline On SBR System Operation And Microbial Community Structure

The impact of the extensive use of antibiotics on the ecological environment and human health is a hot spot in the current environmental field.The impact of antibiotics discharged into the sewage treatment system with the sewage on the activated sludge is still lacking in-depth microbiological analysis.Chlortetracycline is mainly added as a veterinary antibiotic in feed to increase production.After human and animal excrement is transferred to the soil and water environment,the frequency of detection is high,which causes serious inconvenience to the biological treatment of sewage treatment plants.Therefore,it is of great significance to study the influence of chlortetracycline on activated sludge in the main process.In response to the above problems,the research content and results are as follows:(1)After two months of operation,the effluent quality is stable,different concentration gradients of chlortetracycline were added to the reactor.The three stages were 0.05 mg/L,0.5 mg/L and 1 mg/L,and each stage was run for 25 days.Studies have shown that as the concentration of chlortetracycline increases,the performance of the activated sludge system is significantly inhibited.The COD removal rate increased slightly when the chlortetracycline concentration was 0.05 mg/L,and then the removal rate dropped sharply at higher concentrations,and finally only 58.0±2.0%.As the concentration of chlortetracycline increases,The removal rate of NH4+-N,TN and TP gradually decrease,indicating that the addition of antibiotic chlortetracycline hydrochloride may affect the microbial community structure in activated sludge,which in turn affect the removal rate of nitrogen and phosphorus.In the four stages,the content of NO2--N did not change much,but the accumulation of NO3--N was basically fluctuating and rising,indicating that the synergistic effect of nitrifying bacteria and denitrifying bacteria was weakened.In addition,the microbiological activity test of activated sludge showed that the sedimentation property became worse and the treatment effect was reduced,which may also be related to the change of the microbial structure by chlortetracycline.The contents of five tetracycline resistance genes(tetA,tetX,tetO,tetC,tetM)at different stages were detected by fluorescence quantitative PCR.It was found that tetA was not detected,and the other four were detected,indicating that there are a certain amount of resistance genes in tap water and the original activated sludge plant,and with the increase of chlortetracycline dosage and time,the content of resistance genes in effluent and activated sludge increases.(2)A total of 24 samples,six samples of activated sludge in four stages were sent to Meiji Biopharmaceutical Company for microbial sequencing and analysis to explore the impact of chlortetracycline on the structure and diversity of microbial communities.The results showed that the number of AS Vs were 244,269,221,and 288,respectively,indicating that the diversity of microbial communities has changed greatly,and the long-term administration of antibiotics also led to the detection of new species.From the perspective of phylum level,the abundance of Actinobacteria decreased,indicating that the bacteria could not adapt to the chlortetracycline environment.On the contrary,the abundance of Bacteroidota and Proteobacteria increased,indicating that these phyla have the ability to tolerate chlortetracycline.Under a more clear classification,the abundance of Propioniciclava belonging to Actinobacteriota decreased,the abundance of norank_f__Pleomorphomonadaceae belonging to Proteobacteria and Chlorobium belonging to Bacteroidota increased.The trend is the same as that of the phylum,indicating that these genera dominate in the phylum.(3)In order to further explore the changes of the microbial molecular ecological network and its key species in the system under the action of different chlortetracycline concentrations,24 samples were used for 16S rRNA highthroughput sequencing data to construct the molecular ecological network,and Cytoscape(3.8.2)software was used to complete the visual analysis.Phase Ⅱ(chlortetracycline is 0.05 mg/L)has the most nodes,the highest network complexity,and the highest transmission efficiency between species.However,high concentrations of chlortetracycline have a negative impact on the interaction between microorganisms,forming a looser and evenly distributed network structure.The two dominant bacteria phyla Bacteroidetes and Proteobacteria in the molecular ecological network,the proportion of which changes significantly with the increase of chlortetracycline concentration.It can also be seen from the network modules and connecting lines that there are significant differences in the interaction between species.Most of the module center nodes belong to the Patescibacteria phylum(37.5%),and most of the key species in the connection nodes come from the Bacteroidota phylum(40%)and Chloroflexi phylum(40%).The MENA obtained from the experiment proves that chlortetracycline has changed the network structure.