Degradation Of Tetracycline Hydrochloride By Sulfur Modified Iron-based Activated Persulfate

Tetracycline antibiotics,as one of the most common antibiotics,are widely used in medical,aquaculture and other industries because of their low price.However,due to the large amount of use and the limitations of wastewater,soil and other treatment technologies,a large number of tetracycline antibiotics remain in the environment,and it has caused great harm to the environment.The traditional water treatment technology can not achieve the ideal removal effect of tetracycline antibiotics,and there is even the risk of introducing secondary pollution.Activated persulfate is a new advanced oxidation technology,which has low cost and easy reaction conditions.In addition,it has mild and rapid reaction and is friendly to the environment.It is a green and efficient treatment technology.Iron based activators have the advantages of low cost,simple activation conditions and convenient recovery and recycling,and have great development prospects.However,the activation efficiency of existing iron-based activators for persulfate needs to be improved.Therefore,the modification of iron-based catalysts may be an effective method to improve their activation efficiency.In this paper,as the target pollutant,tetracycline hydrochloride（TCH）was used in the study,sodium thiosulfate and ammonium ferrous sulfate were co precipitated in the molar ratio of sulfur to iron of 1:2,and then the sulfur modified iron-based catalyst was prepared by high-temperature calcination.The effect of activating persulfate to remove tetracycline hydrochloride was studied.The prepared catalyst was labeled as S-Fe and characterized by scanning electron microscope,X-ray diffraction and X-ray photoelectron spectroscopy.The characterization results show that the catalyst is columnar,and the main components are FeS,Fe₁₂S₁₁O₅₁,FeS₂,Fe O（OH）,and Fe₃O₄.In addition,the catalyst was adsorbed by magnet and found to have certain magnetism,which is convenient for recovery.The effect of activated persulfate on TCH degradation under different experimental conditions was studied by single factor method.Besides,the response surface analysis method was used to the study for optimizing the best reaction conditions.The experimental results show that the degradation rate of TCH is subjected to the initial concentration of tetracycline hydrochloride,the dosage of persulfate,the dosage of catalyst and the initial pH value.The higher the initial concentration of TCH,the lower the final degradation rate.In the wake of the increase of the dosage of catalyst S-Fe and persulfate,the degradation rate of tetracycline hydrochloride TCH also gradually increases.However,when the dosage of catalyst and PS increases by a certain value,the degradation rate of TCH reaches the highest value.After increasing the dosage,the degradation rate will no longer increase significantly.PH value has a certain influence on the degradation rate of TCH.With the raise of pH value,the degradation efficiency of TCH gradually decreases,but the difference of degradation rate of TCH under different pH conditions is small,indicating that the S-Fe catalyst prepared in this study can adapt to a wide pH range.At the same time,it was found that the initial concentration of TCH was 20mg/L,the dosage of Na₂S₂O₈was 2.0g/L,the dosage of activator S-Fe was 1.0g/L,and pH=3 were the best reaction conditions.The maximum degradation rate optimized by response surface analysis method is 96.31%.The degradation conditions are:Na₂S₂O₈dosage of 2.0g/L,S-Fe dosage of 1.33g/L and reaction time of 30min.Furthermore,the S-Fe activator was recovered and the experiment was repeated for many times.The experimental results showed that S-Fe still had good catalyst activity after being recycled for 3 times.The reaction mechanism of S-Fe/PS system for degradation of TCH was explored.Through quenching free radical experiment,after adding tert butyl alcohol（TBA）and methanol（MeOH）separately,it is determined that sulfate radical is the central free radical in the degradation of TCH in S-Fe/PS system.The mineralization degree of TCH in the reaction system was investigated by measuring the TOC（total organic carbon）value of the reaction solution.The reaction products were determined by mass spectrometry,and the possible degradation path of TCH was speculated.Under the optimum reaction conditions,the effects of several anions(SO₄^2-,CO₃^2-,NO₃^-,Cl^-)and humic acid on the degradation of TCH by S-Fe/PS were studied.The results reflected that SO₄^2-,CO₃^2-,NO₃^-,Cl-and humic acid（HA）had significant inhibitory effects on the degradation of TCH.The results of this study provide a theoretical basis for the efficient treatment of tetracycline antibiotic wastewater.