Study On The Oxidative Degradation Of Tetracycline Antibiotics By Manganese Dioxide

The tetracycline types of antibiotics,including oxytetracycline(OTC),chlortetracycline(CTC),tetracycline(TC)and semi-synthetic derivative doxycycline(DC),is a broad-spectrum antibiotics produced by actinomycetes.In recent years,the production and use of antibiotics is increasing,and a lot of antibiotics have entered into the environment which would bring in some potential risk to environment.MnO2 is one of the strongest natural oxidants in the soil system,which can degrade a variety of organic pollutants.Hence,oxidative degradation of antibiotics by MnO2 have been used as a new direction to control antibiotics pollution.The oxidative transformation of OTC and DC,which are widely used,by the hydrous manganese oxide(?-MnO2)were investigated in batch experiments.The influence of pH,manganese oxides dosage and coexistence solutes on the reaction kinetics were discussed.The results suggested that OTC and DC were rapidly degraded by MnO2 along with the generation of Mn2+,meanwhile the reaction rate decreased.Under the conditions that the concentration of substrate was 50 ?mol/L and the initial concentration of MnO2 were 750 ?mol/L and 500 ?mol/L,respectively,the rest of substrate were 5.95 ?mol/L and 7.78 ?mol/L after 2 min,in which the degradation rate reached 88.1%and 84.7%respectively.Furthermore,the oxidation reaction of the OTC and the DC deviated from the pseudo-first-order kinetics but follow the complex reaction kinetics at pH 5 and with enough excess of ?-MnO2.While,a good linear fit(R2=0.96)can be obtained at the first 2 min of OTC and 1.5 min of DC,which is fit to the pseudo-first reaction kinetics.Using oxalic acid damage or membrane filtration to quench the reaction,the results showed that the remaining concentration of OTC using membrane filtration method was 10.1 ?mol/L,which was lower than that with oxalic acid damage method(13.9 ?mol/L).Thus,about 7.6%of OTC was removed by MnO2 adsorption within 1 min of reaction.Furthermore,the reaction rate of OTC and DC increased with the increase of initial MnO2 concentration,while decreased as pH increased from 4.0 to 8.0.Both of coexisting metal ions and organic acid had inhibition on OTC and DC removal.The inhibitive capacity on OTC removal followed the order of Mn2+>Fe3+>Ca2+>Mg2+,and tannic acid>humic acid at first 2 min.And,higher concentrations of coexistence solutes resulted in a higher inhibitory effect.In the reaction system of DC degradation by MnO2,the inhibitive capacity on DC removal followed the order of Fe3+>Mn2+>Ca2+>Mg2+ and tannic acid>humic acid at first 1.5 min.Higher concentrations of cation ion displayed strong suppressive effects.Annic acid had significant inhibition on DC degradation while humic acid have little effect.This study may provide useful information to better understanding the fundamental knowledge relevant to the interaction of tetracycline types of antibiotics and manganese oxides in natural environment.