Effects Of Oxvtetracvcline On Strain ZY-2and Wastewater Treatment Performance Of SBR As Well As Its Microbiological Mechanisms

Wastewater from livestock and aquiculture is an important source of tetracyclines, and the wide spread of antibiotic resistant genes has led to an increasing concern about the potential risks to the human beings and environment. The response of one heterotrophic nitrifiers to tetracyclines (TC and OTC), and the impacts of OTC on the performance of SBR treating the high ammonia nitrogen, high COD wastewater were investigated in this study. The main results were as follows:(1) The toxicity effect of low concentration tetracyclines on a nitrifying bacterium ZY-2at stationary phase.Treated with100μg L-1TC/OTC, the growth of ZY-2was inhibited at a certain extent accompanied with the decline of ammonia nitrogen and total nitrogen removal rates. It illustrated that strain ZY-2was sensitive to the antibiotics, and more sensitive to TC compared with OTC at the same concentration. Also, ZY-2treated by TC/OTC had higher activity of SOD and CAT, which can strengthen the elimination of free oxygen radicals. The results indicated that the strain could adjust the antioxidant enzyme activity to protect itself when exposing to100μg L-1TC/OTC.(2) The effect of OTC on the performance of SBR treating the high concentration of ammonia nitrogen and high COD wastewaterThe simulation wastewater was spiked with different OTC doses (0,0.1,5,20,60mg L-1) prior to adding into the SBR reactors (designated as R1-R5), respectively. The reactors were operated for88d, and the running period was grouped into four stages:A (1-22d), B (23-46d), C (47-68d), D (69-88d). When the reactors run to stage B, the pH, nitrogen and COD in the effluent from the reactors with concentration of OTC (OTC≥5mg L-1) have shown some differences with that from the reactors with lower concentration of OTC (OTC≤O.lmg L-1). However, with the continuous running of reactors, the low concentration treatment group started to show some differences with R1, while the treatment efficiency of the high concentration treatment group gradually began to recover. This not only illustrated that accumulation of low concentration of OTC could enhance its impact on the activated sludge (AS), but also showed that the AS could adapt to the high concentration of OTC after a long-term running with OTC. The microbial community structures of reactors during the operation process were investigated using denaturing gradient gel electrophoresis (DGGE) and454pyrosequencing.It was found that the microbial diversities in R3-5at stage B were quite different from those of reactors R1-2, which was coincident with the changes of effluent indexes. Most of the species from all the reactors during the operational processes belonged to two phylums:Proteobacteria and Bacteroidetes, yet the classes in each phylum changed a lot and showed quite different resistance to OTC. Besides, ammonium oxidation bacteria (AOB) and Nitrite oxidation bacteria (NOB) also showed certain resistance to OTC but significantly inhibited by60mg L-1OTC. The potential denitrifying bacterium had a wide diversity and each showed different sensitivity to OTC. The results of real-time qPCR indicated that the antibiotic resistant genes (ARGs) exhibited a certain decline within the operational process, which may be caused by the toxicity from long-term impacts of high ammonia nitrogen and high COD wastewater. Nonetheless, the high concentration of OTC can help maintain the stability of ARGs at a certain extent. For the N-cycle related genes, nirS and nosZ were more stable than amoA under the operation condition. In adition, the expression levels of the three genes were enhanced by different OTC concentrations, suggesting that the carriers of these genes had different resistance to OTC. According to the fingerprint profiles of DGGE of these N-cycle related genes, it was noticed that the band numbers of these genes didn’t decrease with long-term OTC addition, while the changes of dominant genes indicated that the main carriers of these genes varied in the reactors. As a whole, it can be concluded that flexibility of the bacterial community with more adaptive species may lead to the recovery of wastewater treatment efficiency, however, high concentration of OTC can help maintain the stability of ARGs at a certain extent, which were potentially harmful to human and environmental safety.