| Solid-phase denitrification(SPD)with plant as carbon source is a low-cost and promising technology for enhanced denitrification of the wastewater treatment plant effluent i.e.tail water.Antibiotics inevitably coexist in the tail water.Because of the antibacterial properties of antibiotics,it is not clear whether the existence of antibiotics would affect the nitrogen removal effect of plant carbon source SPD and how to affect it.In addition,the antibiotic removal effect and mechanism in plant carbon source SPD process and the ecological risks(such as antibiotic resistance genes(ARGs))caused by antibiotics are still unclear.Aiming at the above problems,the adsorption effect and mechanism of sulfamethoxazole(SMX)/ trimethoprim(TMP)by corncob were studied by batch adsorption experiments in this paper.The effect and mechanism of SMX/TMP for nitrogen removal enhancement from tail water by corncob packed SPD(CC-SPD),the removal effect of SMX/TMP,degradation intermediate,and the change of ARGs were studied by batch experiments and continuous flow CC-SPD filter.The main conclusions were as follows:(1)The adsorption of SMX and TMP on corncob was a non-interactive adsorption process.In single and coexistence systems,the adsorption of SMX and TMP by corncob fitted the pseudo-second-order kinetic well,and the adsorption of SMX and TMP on corncob was mainly through chemical adsorption.(2)In batch shake flask experiments,single antibiotic(50 μg/L SMX or 50 μg/L TMP)significantly increased the denitrification rate,which were 15.63±1.95 mg/(L·d)and 17.14±2.81 mg/(L·d),respectively.Mixed antibiotics(50 μg/L SMX and 50 μg/L TMP)did not show significant inhibition on denitrification.The removal rates of SMX and TMP in the single antibiotic group were 25.44±2.62% and 56.70±3.18%,respectively.There was no significant difference between the single antibiotic group and the mixed antibiotic group.Biodegradation was the main removal mechanism of SMX and TMP.SMX could increase the relative abundance of sulfanilamide resistance genes and increase the risk of ARGs in horizontal transmission.(3)There was no significant difference between the effluent concentrations of Nitrate nitrogen and total nitrogen in the continuous flow CC-SPD filter with antibiotics and those without antibiotics.The same antibiotic might have different effects on denitrification in different biological systems.The average removal efficiencies of SMX and TMP in CC-SPD filters are 60.53±4.84% and 45.35±3.83%in single antibiotics influent filters,which were not significantly different from those in the mixed antibiotic influent filter.Based on the 16 S r RNA gene high-throughput sequencing analysis,SMX supplementation reduced the species richness and diversity of the community,while TMP supplementation increased the species richness and diversity.Based on the metagenomic analysis,the existence of SMX/TMP did not affect the generation of electron donors and energy.SMX supplementation would increase the relative abundance of sulfanilamide resistance genes,especially sul1 and sul2.TMP did not affect the relative abundance of diamidine resistance genes.In the case of containing antibiotics,microorganisms detoxified antibiotics mainly through efflux pumps.SMX was mainly degraded by oxidation,S-N bond breaking,denitrification,sulfonyl removal,and ring opening.TMP was mainly degraded by demethylation,oxidation,ring opening,etherification,and C-C bond cleavage.The degradation pathways of antibiotics were different in the presence of single and mixed antibiotics.CC-SPD filter was an ideal treatment system to control the dissemination of ARGs in tail water treatment with SMX/TMP. |
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