| Tetracycline antibiotics are a kind of broad-spectrum antibiotics,which are widely used to prevent and control human and animal diseases because of their good bactericidal effect and low price.Tetracycline antibiotics are difficult to be digested and absorbed after they enter human body or animal body.The unabsorbed part is mainly discharged into the environment through urine and feces,causing pollution,which leads to certain environmental risks.Therefore,how to effectively remove Tetracycline antibiotics from water environment has become one of the hot issues in the field of pollution control.In this paper,the degradation of Chlortetracycline Hydrochloride was studied by using the advanced persulfate oxidation technology,which was combined with activated carbon,modified activated carbon and iron-carbon microelectrolysis system,and the effects of various environmental factors on the degradation of pollutants were investigated,and the corresponding reaction mechanism was revealed.The main results were as follows:In the first part,the degradation effect and mechanism of Chlortetracycline Hydrochloride(CTC)by activated carbon(AC)activated peroxydisulfate(PDS)were investigated.The results showed that the removal efficiency of CTC in the combined system of AC and PDS was better than that in the single system of AC and PDS.The optimum conditions for AC/PDS system were as follows:the mass of AC was 0.2 g,the molar ratio of CTC to PDS was 1:50,and pH was 3.Under these conditions,the degradation rate of CTC with initial mass concentration of 50 mg L-1 could reach more than 80%.The reusability of AC was high,and the degradation rate remained above 60%after three times of reuse.Inorganic ions could inhibit the oxidative degradation of CTC.The results of free radical identification test showed that SO4-· played an important role in the degradation of the whole treatment system.UV-vis Spectrum analysis showed that the benzene ring structure of CTC was destroyed in the process of decomposition.Activated carbon activated persulfate oxidation process can effectively remove tetracycline antibiotics in water.In the second part,the degradation characteristics and mechanism of PDS activated by H2O2 were discussed on the basis of comparing the effect of different modified AC on the degradation of CTC.The results showed that the activation effect of different modified AC on PDS was as follows:H2O2 modification>NaOH modification>NH3·H2O modification>HNO3 modification;the activation effect of different concentrations of H2O2 modified AC was as follows:30%H2O2 modification>20%H2O2 modification>10%H2O2 modification.Increasing the dosage of H2O2 modified AC could accelerate the degradation of CTC by PDS.When the dosage was 1 g,CTC with a concentration of 50 mg L-1 was almost completely removed after 2 h.The removal rate of CTC decreased with its initial concentration increasing from 20 mg L-1 to 100 mg L-1.The pH of the solution had no obvious effect on the removal of CTC by the activated peroxydisulfate system,but the presence of chloride ion in the solution would inhibit the degradation efficiency of the system.Free radical capture experiments showed that OH·and SO4-·were involved in the degradation of CTC at different reaction stages.UV-vis analysis showed that the benzene ring structure of CTC was destroyed and decomposed.In the third part,the degradation of chlortetracycline(CTC)by sodium persulfate(PDS)activated by zero valent iron/activated carbon microelectrolysis(Fe0-AC/PDS)was studied.The results of different treatment systems showed that:Fe0-AC/PDS>Fe0/PDS>AC/PDS>Fe0-AC>AC>Fe0>PDS.In the Fe0-AC/PDS System,when the dose of Fe0 was 0.4 g L-1,the dose of PDS was 2 g L-1,the pH was 3,and the initial concentration of CTC was 50 mg L-1,the degradation rate of CTC could reach 88%.The presence of Cl-,HCO3-and H2PO4-inhibited the degradation of CTC,while humic acid accelerated the degradation rate of CTC.The degradation rate of CTC was still about 70%after four cycles.The model established by RSM could accurately predict the degradation rate of CTC.In the fourth part,in the Fe0-AC/PDS treatment system,free radical quenching experiments and electron paramagnetic resonance(EPR)techniques showed that SO4-· and O2· participated in the degradation of CTC.Total organic carbon(TOC)analysis showed that the mineralization rate of CTC could reach 31.44%after 7 h.The concentration of S2O82-decreased with the increase of mass ratio of iron to carbon;The concentrations of total iron and Fe2+also increased with the increase of mass ratio of iron to carbon;with the extension of time,the concentration of total iron and Fe2+decreased gradually.UV-vis Spectrum analysis showed that the benzene ring in CTC structure was destroyed and small molecular intermediate products were formed.FTIR spectra showed that the intensity of characteristic absorption peaks corresponding to AC and Fe0 decreased with the extension of reaction time.LC-MS analysis showed that there were six products in the system,and dehydroxylation,amino and methyl reactions took place.Based on the above conclusions,Fe0-AC microelectrolysis is a new heterogeneous catalytic method with green and efficient activation of PDS,which has a potential application prospect in water treatment. |
