| Due to the powerful effect of sterilization, fluoroquinolone antibiotics(FQs) has been widely used all over the world. However, the wide use of FQs have led to continuous pollution into the environment in a variety of ways, which results in pseudo persistance phenomenon. The long-term existence of FQs in the environment causes selective pressure on microorganisms, induces the occurance of resistant bacteria and resistance genes(ARGs), and even causes significant risks to human health. The urban sewage treatment system, an important pollution source of FQs and its resistance genes, has attracted attention. Study on the residue and removal of FQs and its pollution situation of ARGs in sewage treatment plant has significant meaning to find out the rules of their generation, migration and evolution, which are of great significance to prevent and reduce such pollution.This study was carried out in the biological aerated filter, and mainly investigated the removal behavior of ciprofloxacin and its influencing factors in biological aerated filter. Also, the effect of ciprofloxacin on the resistance genes pollution characteristics and microbial community structure were studied.The results showed that DO、C/N and trace CIP had a certain role on the operation efficiency of BAF. The decrease of DO led to lower COD removal rate, but the organic matter still got better removal. The concentrations of NH4+-N, NO2- and NO3- in the effluent changed, which showed that the change of DO had a significant inhibitory effect on nitrification. At the same time, the CIP removal rates of the two groups significantly decreased, and the average removal rate s decreased by 7.9% and 9.2% respectively. When the C/N value increased, the COD removal rate increased by 17.69%~18.66%. The increase of C/N value also promoted the nitrification and the removal effect of CIP. When the concentration of CIP was 0~300μg/L, the removal rate of COD in BAFs were relatively stable. When the influent concentration of CIP was 300μg/L, the ammonia oxidation process was inhibited. At the same time, the removal rate of CIP increased slightly with the increase of CIP concentration. In addition, the CIP removal rate of 2#BAF was higher than that of 3#BAF during the whole operation, which showed that the nitrification reaction was beneficial to the biodegradation rate of CIP.By q PCR, qep A, aac, oqx B and par C were detected in the effluent and biofilm, and their law exsists to: aac > par C > oqx B > qep A. When DO decreased, the concentrations of qep A, aac, oqx B and par C in the effluent and biofilm decreased by different degrees. CIP had a selective effect on par C, aac and oqx B, and the effect was more obvious when the influent concentration of CIP was 300μg/L. Relatively, the concentration of qep A was low, and had decreasing trend. Compared with the biofilm, the concentration of CIP-ARGs in the effluent was higher than that in the biofilm. Overall, the response of CIP-ARGs in the effluent and biofilm to DO and CIP was similar, which indicated that there was a correlation between the CIR-ARGs in the effluent and biofilm.Pearson correlation analysis was used to analyzing the relative expression of the relationship between CIP and CIP-ARGs. In the biofilm, oqx B and CIP showed a significant positive correlation(0.959 < R < 0.984, P < 0.05); In the effluent, the correlation between the four CIP-ARGs and CIP were not significant(P > 0.05). It indicated that the existence of CIP has selective pressure on the generation and evolution of oqx B.High throughput sequencing results showed that the dominant species in the BAF were Proteobacteri and Bacteroidetes. In the BAF, Nitrosomonas and Nitrospira were the main species in the nitrification process. The increase of ammonia nitrogen was beneficial to the abundance of Nitrosomonas and Nitrospira. The addition of CIP had effect on the microbial community structure in BAF, and microbial diversity changed with the concentration of CIP. In the BAF, resistant bacteria were mainly Proteobacteria and Bacteroidetes. After adding 50 μg/L CIP, the abundance of the Nitrospirae decreased, but it was not obvious with the increase of the concentration of CIP. The abundance of Cyanobacteria decreased rapidly after the addition of CIP, which showed that Cyanobacteria was sensitive to the presence of CIP. In addition, the high concentration of CIP did not have inhibition on Chlorobi and Chloroflexi, however, made its abundance increase. |
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