Study On The Effect Of Typical Antibiotics On Biological Nitrification And The Potential Biological Safety Risk

The wastewater generated during the production of antibiotics contains residual antibiotics,and often high content of nitrogen.At present,biological nitrogen removal process is widely used.The nitrifying bacteria involved in the nitrification process are autotrophic bacteria,which are very sensitive to toxic and harmful substances.Thus,nitrification performance is easily inhibited by antibiotics.In addition,under the continuous selective pressure of antibiotics,it is easy for the microorganisms to proliferate antibiotic resistance genes(ARGs),which can be spreaded in the biological treatment system.ARGs will pose potential risks to human health and ecological environment after being discharged into the environment via sludge and effluent.There are many kinds of antibiotics.And different antibiotics have different inhibition mechanisms on the nitrifying bacteria.In this study,benzylpenicillin G sodium,oxytetracycline and streptomycin sulfate,which have different antibacterial mechanisms,were selected to investigate the short-term effects of the antibiotics on the biological nitrification by the batch experiments.The activated sludge was acclimated with the antibiotics by gradually increasing the concentration of the antibiotics.And the effects of benzylpenicillin G sodium,oxytetracycline and streptomycin sulfate on the nitrification performance were studied respectively.And the ARGs and bacterial community structure were analyzed during the period of acclimation.Furthermore,the contents of ARGs and class I integron(intI1)in the effluent and the content of intI1 in the domesticated sludge were analyzed.And the potential risks of sludge and effluent discharged into the environment were discussed.The main results were as follows:(1)The half maximal inhibitory concentration(IC50)values of benzylpenicillin G sodium for ammonium oxidizing bacteria(AOB)and nitrite-oxidizing bacteria(NOB)were 81.4 mg/L and 71.2 mg/L,respectively.During the long-term acclimation period,the nitrification performance decreased gradually with the increase of the content of benzylpenicillin G sodium.When the concentration of benzylpenicillin G sodium was 20mg/L,the specific ammonia oxidation rate(SAOR)and specific nitrate production rate(SNPR)were 7.22±0.87 mg N/(g MLSS·h)and 2.36±0.72 mg N/(g MLSS·h),respectively.And the relative abundance and blaVEB increased by 2.28 orders of magnitude,respectively.(2)The IC50 values of oxytetracycline for AOB and NOB were 92.1 mg/L and 87.3mg/L,respectively.During the long-term acclimation period,the nitrification performance decreased slowly with the increase of oxytetracycline concentration.When the oxytetracycline concentration was 50 mg/L,SAOR and SNPR were 14.46±0.63 mg N/(g MLSS·h)and 3.79±0.59 mg N/(g MLSS·h),respectively.The relative abundance of tetA in the activated sludge increased by 3.50 orders of magnitude.(3)The IC50 values of streptomycin sulfate for AOB and NOB were 75.4 mg/L and66.1 mg/L,respectively.After long-term acclimation,the nitrification performance decreased rapidly with the increase of streptomycin sulfate concentration.When the concentration of streptomycin sulfate was 10 mg/L,SAOR and SNPR were 3.43±0.52 mg N/(g MLSS·h)and 0.24±0.03 mg N/(g MLSS·h),respectively.The relative abundance of aadA1 in the sludge increased by 0.99 orders of magnitude.(4)The inhibition effect of streptomycin sulfate on the nitrifying bacteria was the strongest,followed by benzylpenicillin G sodium and oxytetracycline.In the sludge acclimated with the antibiotics,the protein content in the extracellular polymer substances of sludge increased significantly.While the polysaccharide content changed slightly.Proteobacteria and Bacteroidetes were the predominant phyla.And Nitrosomonas was the most abundant genera.(5)High abundance of ARGs and intI1 were detected in the effluent and sludge of the biological treatment system.ARGs and intI1,which were discharged into the environment via the effluent and the sludge,will threaten human health and ecological environment.