Effects Of Chlortetracycline And Oxytetracycline On Biological Phosphorus Removal And Microbial EPS

Antibiotics are widely distributed in the environment,and tetracycline drugs represented by chlortetracycline and tetracycline are widely used by people,with a high detection rate in urban sewage treatment plants,which inevitably affects the biological treatment function of sewage treatment plants.Extracellular polymeric substance(EPS)affect the flocculation,adsorption capacity,surface structure and other functions of activated sludge.Therefore,the study of the effects of chlortetracycline and oxytetracycline on biological phosphorus removal and microbial EPS is of great significance for revealing the effect of antibiotics on biological phosphorus removal.However,pollutants in the real environment are often mixed,which has a more complex impact on biological phosphorus removal process.Meanwhile,there are few studies on the effects of chlortetracycline and oxytetracycline on biological phosphorus removal and microbial EPS.Therefore,the mixture concentration ratio of the test was designed by direct equalization ray method and dilution factor method,and the influence on the performance of biological phosphorus removal system was reflected by measuring the effluent index of the reactor and the contents of protein and polysaccharide in EPS.Threedimensional fluorescence(3D-EEM)and Fourier infrared spectroscopy(FT-IR)were used to reveal the mechanism of effects of chlortetracycline,oxytetracycline and their mixtures on the components,functional groups and protein secondary structure of microbial EPS fluorescent substances.The main results of this study are as follows:(1)Effects of different concentrations of chlortetracycline on biological phosphorus removal and microbial EPS.The results show that with the increase of chlortetracycline treatment time and concentration,the effluent concentrations of orthophosphate and COD gradually increase.When the concentration reaches 20 mg/L,the effluent concentration of orthophosphate is higher than the effluent concentration,and the COD removal rate is only 13.73% when the concentration reaches 40 mg/L at 96 h.High concentration of chlortetracycline seriously interferes with the biological phosphorus removal process.The contents of protein and polysaccharide in microbial EPS increased first and then decreased with the increase of chlortetracycline treatment time and concentration.The fluorescence intensity of tyrosine and tryptophan increased first and then decreased with the increase of chlortetracycline concentration.Humic acids and two fulvic acids were produced under the influence of 5 mg/L concentration.Chlortetracycline mainly shifted the C=O stretching vibration of protein amide Ⅰ band and carbohydrate C-OH stretching vibration,and the absorption peaks of P=O stretching vibration and P-O stretching vibration gradually disappeared.Chlortetracycline had an effect on the secondary structure of proteins.After chlortetracycline supplementation,the relative content of random curling increased,and the relative content of β-folding,α-helix and reverse parallel β-folding decreased,which was 1.75 times that of blank group.(2)Effects of different concentrations of oxytetracycline on biological phosphorus removal and microbial EPS.The results show that with the increase of oxytetracycline treatment time and concentration,the effluent concentrations of orthophosphate and COD increase continuously.When the concentration reaches 20 mg/L in the later stage of the reaction,the effluent concentration of orthophosphate is higher than the influent concentration,the COD removal rate is less than 40%,and the performance of the biological phosphorus removal system is seriously deteriorated.The contents of protein and polysaccharide in microbial EPS increased first and then decreased with the increase of oxytetracycline treatment time and concentration.As the concentration of oxytetracycline increased,the fluorescence intensity of tyrosine and tryptophan first increased and then decreased.At a high concentration of 20 mg/L,new substances like humic acid and fulvic acid were also produced,but they lacked one fulvic acid substance compared with chlortetracycline.Oxytetracycline was mainly offset with C=O stretching vibration of protein amide Ⅰ band and carbohydrate C-OH stretching vibration absorption peak,and the absorption peak of P=O stretching vibration,P-OH stretching vibration,PO stretching vibration and amino acid COO variable Angle vibration gradually disappeared with the increase of oxytetracycline concentration.Compared with chlortetracycline,oxytetracycline has more P-OH stretching vibration and amino acid COO variable Angle vibration.The secondary structure of proteins was affected by oxytetracycline,and the relative contents of random curling increased,while the relative contents of β-corner and reverse parallel β-folding decreased.(3)Effects of different concentrations of oxytetracycline on biological phosphorus removal and microbial EPS.The results show that the effluent concentrations of orthophosphate and COD increase with the increase of reaction time and concentration,and the performance of biological phosphorus removal system deteriorates continuously,and the orthophosphate concentrations of Ratio1 and Ratio2 exceed the influent concentrations in the later stage.The contents of protein and polysaccharide in microbial EPS with 3 combinations increased first and then decreased with the increase of mixture treatment time and concentration.In the same cycle,the protein and polysaccharide showed Ratio1> Ratio2> Ratio3.With the increase of mixture concentration of 3components ratio,the change trend of tyrosine and tryptophan in microbial EPS as well as humic acids and fulvic acids produced at high concentration(except ratio Ratio3)was similar to that of chlortetracycline and oxytetracycline alone,but the fluorescence intensity showed chlortetracycline> oxytetracycline> Ratio1> Ratio2> Ratio3.The FTIR spectra of mixed concentration were very similar to that of chlortetracycline and oxytetracycline,both of which affected the C=O bond of protein amide Ⅰ band and carbohydrate C-OH stretching vibration.The main difference was that chlortetracycline alone acted on and Ratio 1 did not show P-OH stretching vibration,and amino acid COO variable Angle vibration did not show on chlortetracycline alone.There was an obvious antagonism between chlortetracycline and oxytetracycline in the secondary structure of proteins,and the changes of the secondary structure of the five proteins were significantly different.The β-folding and β-angle contents were the highest to maintain the stability of activated sludge and the activity of microorganisms.The comparison between the test group and the blank control group showed that the relative content of random curling in the test group was 1.75 times of that in the blank control group.The ratio of chlortetracycline to oxytetracycline in Ratio2 was close to the chaotic changes of protein secondary structure,and the relative content of α-helix in Ratio3 test group was 1.9 times of that in blank control group.In this experiment,a sequencing batch activated sludge reactor was used to study the effects of chlortetracycline,oxytetracycline and their mixtures on biological phosphorus removal,and the effects of chlortetracycline and oxytetracycline on EPS were taken as the entry point to reveal the influence characteristics of chlortetracycline,oxytetracycline and their mixtures on biological phosphorus removal.It provides the analytical method and theoretical basis for studying the effect of antibiotic mixture on biological phosphorus removal and microbial EPS.Figure [30] Table [8] Reference [136]...