Removal Of Antibiotic Enrofloxacin By Persulfate Oxidation Activated With Iron Species

Enrofloxacin is a new type of fluoroquinolone broad-spectrum antibacterial drug,which is widely used because of its high-efficiency.It is difficult to biodegrade and has a long halflife period.Remained enrofloxacin in the environment will cause a potential hazard and threat to the ecological environment and human society.Therefore,studying the removal technologies for enrofloxacin degradation will provide an important theoretical basis for practical applications.In recent years,advanced oxidation technologies based on activation of persulfate(PS)to produce sulfate radicals(SO4·-)have received more and more attention.Compared with OH·,SO4·-has a higher redox potential,stronger selectivity and longer halflife,which can effectively destroy the structure of organic compounds.This article focus on the degradation of enrofloxacin in Fe2+/PS homogeneous system and nZVI/PS heterogeneous system.nZVI materials were synthesized and characterized.The influencing factors,degradation products and degradation pathways were studied.Firstly,the effects of Fe2+ concentration,pH,temperature,inorganic salt ion,humic acid,and chelating agent on Fe2+-activated PS degradation of enrofloxacin in water were studied.The degradation efficiency of Fe2+/PS system with Fe3+/PS system were compared.The results showed that at room temperature,the degradation rate of enrofloxacin reaches 77%within 120 min(enrofloxacin concentration 60 μM,Fe2+ concentration 0.048 mM,PS concentration 0.12mM).Increasing Fe2+ concentration can inhabit the reaction;Acidic conditions and elevated temperature are conducive to degradation of enrofloxacin,and the alkaline environment inhibits the reaction significantly;The chloride ion is oxidized by SO4·-to generate active chlorine,which keeps the strong oxidizing ability in system and promotes the degradation reaction;Bicarbonate ion and humic acid can consume SO4·-,which restrains degradation significantly;Neither organic chelating agents(citric acid and oxalic acid)nor inorganic chelating agent sodium pyrophosphate promoted the degradation of enrofloxacin in Fe2+/PS system;Under the same experimental conditions,the degradation reaction rate of Fe3+/PS system is slower than that of Fe2+/PS system.Secondly,nZVI was prepared by a liquid phase reduction method.The constituent elements,chemical structure and magnetic property of nZVI were characterized by X-ray diffraction analysis(XRD),Nitrogen adsorption/desorption isotherm(BET),and Fourier transform infrared spectroscopy(FTIR).XRD test results showed that the prepared nZVI has elemental iron;The BET method determined that the specific surface area of nZVI was 71.03 m2/g and the pore volume was 0.13 cm3/g,with the average pore diameter being 10.88 nm;FTIR identified the major functional groups in the nZVI material;VSM shows that nZVI has good magnetic property;At the same time,during enrofloxacin degradation with nZVIactivated persulfate in water,the effects of nZVI dosage,PS concentration,pH,humic acid,and inorganic salt ions on degradation were studied.The experimental results showed that the degradation rate can reach 84%within 30 min at 25℃(enrofloxacin 60 μM,nZVI dosage 0.025 g/L,PS concentration 0.2 mM).The removal rate of enrofloxacin increases first and then decreases with the increase of the amount of nZVI;The reaction rate constant and removal rate of enrofloxacin increased significantly along the PS concentration increase;Acidic conditions are beneficial for enrofloxacin removal,and alkaline environment inhibits enrofloxacin degradation significantly;Humic acid contains active groups such as hydroxyl and amine groups,which compete with enrofloxacin for oxidative free radicals resulting in reduction of reaction efficiency;Chloride ion promotes the degradation of enrofloxacin,because it is oxidized to produce a large amount of active chlorine to participate in the oxidation of enrofloxacin;Low concentration of bicarbonate ion will be oxidized by SO4·to HCO3·,which will slightly promote the degradation of enrofloxacin.Finally,the results of free radical capture experiments and EPR experiments showed that SO4·-and OH·coexist in Fe2+/PS system and nZVI/PS system,with SO4·-being dominant.Eight degradation products in the degradation of enrofloxacin were detected by HPLC-MS.Two degradation pathways were deduced by mass-to-charge ratio.In the first way,the ethyl group on the piperazinyl group was carbonylated,then the acetyl group was removed.Finally,the piperazinyl group was removed to form the final product.In the second way,two hydroxyl groups replaced the hydrogen atom on the piperazinyl group,and then it was oxidized to the aldehyde group.Finally,it undergone hydrolysis and removes the side chain to form the final product.During the degradation of enrofloxacin,the reactive centers are mainly focused on the piperazinyl moiety.