Effects Of Two Antibiotics On Decontamination Performance And Rhizosphere Microecology In Bioretention Cell

Bioretention cell（BRC）has significant effects in reducing water quantity and improving water quality,and has the advantages of low cost and high ornamental value.At present,many studies on BRC are limited to conventional water quality analysis,and there is a lack of research on the removal of emerging pollutants such as antibiotics and antibiotic resistance genes（ARGs）.Therefore,studying the removal performance of BRC on antibiotics and ARGs and analyzing the changes of BRC’s own characteristics under the antibiotic load are of positive practical significance for the treatment of antibiotic pollution and the improvement of BRC’s decontamination performance.In this experiment,Ofloxacin（OFLX）and Tetracycline（TC）were selected as the target antibiotics with four concentration gradients and one control group.The decontamination performance and rhizosphere microecological changes of BRC under the stress of combined antibiotics（OFLX,TC）were investigated,and the main findings were as follows.（1）Experiments on the effect of single antibiotic OFLX on the decontamination performance of BRC were carried out.The results showed that under the load of single antibiotic OFLX,COD could maintain more than 90%removal rate,and the OFLX concentration showed a low promotion and high inhibition effect on COD removal;TN removal rate was around 70%,and OFLX had a slight inhibition effect on TN removal;OFLX had a significant promotion effect on NH₄⁺-N removal,and 0.2μg/ml OFLX increased NH₄⁺-N removal rate by 25.98%;The removal rate of TP remained above 95%,and the effect of OFLX on TP removal was not significant;all BRC systems had efficient and stable removal effect on OFLX,and the removal rate was higher than 90%,and it was proportional to the concentration of OFLX itself.（2）Experiments on the effect of the compound antibiotic OFLX+TC on the decontamination performance of BRC were carried out.The inhibition of COD and TN removal by OFLX+TC was more obvious than that by single antibiotic stress conditions,and the combination of the two antibiotics showed synergistic effects in inhibiting organic matter degradation and denitrification;the enhancement of NH₄⁺-N removal rate was not as good as that of single antibiotic,and the enhancement of NH₄⁺-N removal rate by 0.2μg/ml OFLX+0.1μg/ml TC was only 20.36%,the two antibiotics were antagonistic to NH₄⁺-N removal;the effect on TP removal was not significant;each BRC system had stable and efficient removal effect on both OFLX and TC,the removal rate was higher than 90%,and it was proportional to the concentration of OFLX/TC itself.（3）The antibiotic enrichment and organic acid secretion of phalaris arundinacea in each BRC reactor under the compound antibiotic stress were detected.The results showed that the enrichment of OFLX in the roots and stems was significant,with the total amount of OFLX enrichment being 10.57,11.73,10.41 and 3.73μg/g,respectively,and the amount of OFLX enrichment in the stems and leaves showed a significant decreasing trend with the antibiotic concentration;the enrichment of TC by the roots and stems of phalaris arundinacea was low,with total TC enrichment of 0.1507,0.1688,0.1464 and 0.1167μg/g,respectively.The secretion of acetic acid,lactic acid and citric acid in the secretion of the roots of phalaris arundinacea was greater than that of other organic acids,and the secretion of acetic acid showed a significant positive correlation with the concentration of antibiotics（P<0.05）,the secretion of citric acid showed a highly significant positive correlation with the concentration of antibiotics（P<0.01）,and the secretion of lactic acid showed a significant negative correlation with the concentration of antibiotics（P<0.05）.（4）The changes of inter-root microecology of each BRC reactor were analyzed.The results showed that the microbial Richness index and chao1 index decreased significantly under single/compound antibiotic stress,and the microbial species richness and total number of species decreased,and the decline was greater in the compound stage than in the single antibiotic stage,and the compound antibiotic load had a greater inhibitory effect on the microbial community than the single antibiotic.As detected by real-time fluorescence quantitative PCR,the total bacterial 16S r RNA gene copy number in different BRC reactors was maintained at 10⁸～10⁹ copies/g,with a decreasing trend with increasing antibiotic concentration;the gene copy number of ARGs in BRC reactors was more erm B>tet W>qnr S,.The absolute abundance of all three types of resistance genes increased in the low concentration antibiotic reactor,and the low concentration antibiotic stress induced the production of these three types of resistance genes.In the control group R0,the relative abundance of nar G accounted for the highest percentage of 0.712%,and the relative abundance of nir S,nor B and nos Z accounted for 0.158%,0.178%and 0.269%,respectively.The absolute abundance of all four denitrification functional genes decreased in the BRC reactor under the compound antibiotic load,with nos Z decreasing the most,and its absolute abundance decreased to the lowest in R6～R8.The results of the study provide a realistic technical reference for the practical application of BRC for the removal of antibiotic-containing wastewater.