| The wide application,bioaccumulation and low absorptivity of antibiotics have made antibiotic wastewater a serious problem facing the whole world.As an important receptor for the transmission of antibiotic resistance genes,wastewater treatment plants pool a large number of antibiotics,while the influence of antibiotics on the wastewater treatment process is still unclear.In this paper,anaerobic/oxic/anoxic sequential batch reactors were constructed to investigate the influence of chlortetracycline（CTC）at different concentration（0.1,1 and 10 mg/L）on biological nitrogen removal and nitrous oxide（N2O）emissions.Combining with the transformation of CTC and nitrogen（including ammonia,nitrite,nitrate,gaseous and dissolved N2O）in typical cycles and the changes of extracellular polymeric substances（EPS）and microbial metabolic pathways,the influence mechanism of CTC on biological nitrogen removal and N2O emissions was investigated.The results showed that CTC inhibited the performance of biological nitrogen removal and exacerbated N2O emissions.In the presence of 10 mg/L CTC,the removal capacity of ammonia nitrogen and total nitrogen in the system decreased from 62.1±0.26 and 60.8±0.47 mg-N/g-VSS to 45.9±0.66 and 43.7±0.88 mg-N/g-VSS respectively.Accordingly,the reduction rates were 26.1±0.77 and 28.1±0.91%respectively.However,10 mg/L CTC increased the N2O emission factor from 4.96±0.06 to 7.14±0.45%with an increase rate of 43.9±7.33%.The 0.1 mg/L of CTC inhibited denitrification process,while 1 and 10 mg/L of CTC inhibited both nitrification and denitrification processes.With the increase of CTC concentration,the main emission pathways of N2O during the oxic stage slid from incomplete oxidation of hydroxylamine to nitrifier denitrification,ultimately increasing the total N2O emissions.In addition,the mechanism study showed that the presence of CTC not only reduces the p H of the system environment,increasing the concentration of free nitrite and inhibiting microbial activity,but also stimulates microorganisms to secrete EPS and combines with it to form EPS-CTC conjugates,hindering mass transfer and intensifying the electron competition among oxidoreductases.Therefore,the ratio of the activity of ammonia monooxygenase to nitrite oxidase and the ratio of the activity of nitrate reductase to nitrite reductase were greater than 1,leading to the nitrite accumulation,thereby increasing the N2O emissions.This paper investigated the influence of CTC on biological nitrogen removal and N2O emissions,attempted to explain the interaction influence mechanism between CTC and microbial metabolism from the perspective of EPS,which provides a new insight for in-depth understanding the environmental behavior of antibiotics in wastewater treatment plants and provides basic data for treatment of antibiotics in wastewater treatment plants. |
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