| In order to promote the growth of livestock and prevent microbial infections,antibiotics have been used in livestock feeds.However,abundant antibiotics are excreted in the original form through urine and feces since antibiotics cannot be completely uptaked by the gastrointestinal tract of livestock,resulting in the livestock wastewater contaminated by higher concentration of veterinary antibiotics,even up to 1000 μg/L.Due to the toxic effects of antibiotics on microorganisms,conventional treatment methods(such as the activated sludge methods)often encounter problems when utilized for livestock wastewater treatment,such as the decreases of removal efficiency.In addition,livestock wastewater also contains high concentrations of nitrogen and phosphorus,it will cause widespread water pollution if improperly handled.Meanwhile,recover the nitrogen and phosphorus from livestock wastewater via phytoremediation is an effective technology which also accord with sustainable development principle.However,high concentrations of antibiotics which contains in livestock wastewater have brought severe challenges to the phytoremediation of livestock wastewater.Therefore,this study takes oxytetracycline(OTC)as a pollutant to investigate its effects on the removal of nutrients from anaerobically digested swine wastewater via Lemna aequinoctialis systems.It is expected to provide a reference for the design,application and operation of the phytoremediation of livestock wastewater which contains antibiotics and recovery of high-value resources from plants.The main research contents and results are as follows:Firstly,the effects of OTC on the removal of NH3-N and TP from the ADSW by L.aequinoctialis were investigated.The results showed that OTC has significant inhibitory effects on the removal of NH3-N and TP from ADSW,which conforms to the "dose-response" relationship.With the increase of OTC concentrations,the removal efficiency of NH3-N and TP was decreased,when the concentration of OTC was 1.00 mg/L,the removal rate of NH3-N and TP decreased by 33.44%and 39.25%respectively compared with the control group.Secondly,the effects of OTC on the growth of L.aequinoctialis were evaluated,and the mechanisms of OTC on the growth of duckweed in ADSW were the same as the nutrients removal,which also conforms to the "dose-response" relationship.Thirdly,the effects of OTC on the antioxidant abilities of L.aequinoctialis were analyzed.Results showed that OTC could significantly promote the production of H2O2 and POD in duckweed at the initial stage of exposure and resulted in duckweed to suffer severe oxidative stress.But after prolonged exposure,duckweed could withstand the stress caused by low levels of OTC(<0.50 mg/L).Fourthly,the effects of OTC on the contents of the photosynthetic pigment in L.aequinoctialis were determined.The results showed that the low concentration of OTC could significantly promote the synthesis of photosynthetic pigments in duckweed.When the concentration of OTC was 0.05 mg/L,the production of chlorophyll and xanthophyll increased 28.36%and 28.57%respectively,compared with the control group.Fifthly,the effects of OTC on the synthesis of high-value nutrients such as proteins,starches,vitamin C,and flavonoids in duckweed were studied.The results showed that OTC could significantly enhance proteins synthesis in duckweed at the initial stage,but with the extension of the cultivation,the synthesis of proteins was inhibited.When the concentration of OTC was 0.05 and 0.25 mg/L,the production of flavonoids and starches could enhance in duckweed,while inhibitory effects of synthesis of vitamin C were observed in all treatment groups.Sixthly,the effects of OTC on the community-level physiological profile of rhizosphere microorganisms were explored.According to the results,0.05 mg/L OTC could significantly increase the metabolic activity of duckweed associated microorganisms.The PCA analysis showed that 0.10-1.00 mg/L OTC groups have more similar carbon source utilization profile,and antibiotic stress could significantly alter the carbon source utilization pattern of microorganisms.Seventhly,the removal kinetics of OTC and its accumulation in duckweed was researched.The results showed that the Michaelis-Menten kinetic model fitted the removal process of OTC by the duckweed systems from ADSW.Meanwhile,the bioconcentration study illustrated that the BCF of the 0.05 mg/L treatment group could reach to 0.61.Eighthly,the degradation pathways of OTC in ADSW treatment by the duckweed systems were detected.The results showed that twelve OTC degradation intermediates were detected by LC-MS/MS,and two possible degradation pathways of OTC were proposed. |
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