Inhibitory Effect Of Oxytetracycline On Nitrogen Removal Efficiency In SBR System

Oxytetracycline(OTC)are widely applied in many fields,such as medicine and Animal Husbandry.Because of that OTC is difficult to be biodegraded,a great quantity of OTC will enter the water environment,especially the wastewater treatment plants(WWTPs).Those that existed in wastewater treatment plant(WWTPs)can seriously affect the microorganisms,such as nitrifying and denitrifying bacteria.Hence it is necessary and meanful to understand the performance of microorganisms after exposure to OTC.The mature activated sludge was taken as the seed sludge in this experiment.After sludge acclimation in the laboratory,the performan is steady and excellent.The efficiency of nitrogen removal in the SBR system was more than 95%,and the removal efficiency of CODcr was significant.This study in terms of the variations of ammonia nitrogen removal efficiency(N-removal),Chemical Oxygen Demand(COD)removal efficiency,extracellular polymeric substance(EPS)concentration,special oxygen utilization rate(SOUR)and the microbial community shift after exposure to oxytetracycline(OTC)were evaluated in this research.Results showed that the ammonia nitrogen removal efficiency(N-removal)declined from 99.0%in control test to 77.2%,47.4%and 0.0%in R2(1 mg L-1),R3(5 mg L-1)and R4(10 mg L-1)respectively.In the recovery phase,R2(1 mg L-1),R3(mg L-1)reactor has good recovery,but R4(10 mg L-1)reactor recovery was poor.The removal efficiency of CODcr decreased from 89.51%to 84.55%(1 mg L-1),to 16.23%(5 mg L-1)and to 2.51%(10 mg L-1),respectively.In the recovery phase,removal effiency appeared different degree of recovery,but could not return to the initial level.In addition,high concentration of oxytetracycline(10 mg L-1)induced EPS and the SOUR of heterotrophic bacteria declined to 44.3%and 41.2%when compare to the control.The high-throughput sequence analysis revealed that the high concentration(above 5 mg L-1)oxytetracycline had seriously affected on the microbial community.Thus the microbial community composition changed significantly with the increase of oxytetracycline concentration.OTC remarkably caused the significant growth inhibition of Proteobacteria whereas promotion to Bacteroidetes,which was beneficial to screen the certain bacteria.Moreover,according to the analysis on genus level,some functional bacteria,such as Nitrospira and Nitrosomonas,were inhibited by oxytetracycline,and the proportion of anoxic heterotrophic bacteria(Candidatus_Competiacter)decreased significantly,which was consistent with the macroscopic data of ammonia nitrogen and CODcr removal efficiency.It was interesting that non filamentous bulking had been acknowledged with the increasing Zoogloea.