Removal Of Hygromycin From Water By A Combined Advanced Oxidation System With Iron-loaded Attapulgite

Oxytetracycline（OTC）,as a common tetracycline antibiotic,is still widely used in animal husbandry.The OTC calcium salt approved by the Ministry of Agriculture can be used as the additive of growth promoting feed.It has been reported that OTC can enter the water environment through urine and fecal excretion,causing ecological toxicity in the water environment,and posing a long-term and unpredictable threat to humans and aquatic and terrestrial organisms.In recent years,advanced oxidation methods based on SO₄^-·and·OH have attracted much attention for their ability to remove refractory organic matter.Activated persulfates（PDS）and advanced oxidation of Hydrogen peroxide（H₂O₂）are considered to be effective methods.However,being similar to H₂O₂,PDS directly reacts slowly with most organic pollutants.So how to activate it to improve the activity of the reaction system is of great significance.The activation mode of composite catalyst has become a research hotspot due to its advantages of good stability,reduction of secondary pollution and reusability.Due to its unique crystal structure,attapulgite has a large specific surface area and a large number of activation centers.Therefore,iron-carrying attapulgite prepared by loading Fe on attapulgite has good catalytic performance.Three kinds of iron-bearing attapulgite at different roasting temperatures were prepared by impregnation method.The effects of catalyst type,catalyst dosage,oxidant dosage,initial p H of the solution and different anions and humic acids on OTC removal were investigated.The stability of the catalyst is discussed by reusing the experiment and determining the concentration of total iron ions in the solution.Free radical quenching experiments to investigate the presence of reactive substances in two systems and to briefly speculate on the mechanism of OTC removal.It can provide some scientific basis for the application of advanced oxidation technology for the removal of OTC from water.The main conclusions are as follows:（1）Three kinds of catalysts F300,F500 and F700 were prepared by impregnation method.SEM and FTIR results showed that the rod-like fiber structure was interspersed between the lamellar associated minerals after treatment,and the original crystal structure and characteristic groups of attapulgite were maintained.XRD and XPS analysis showed that iron was mainly loaded on ATP surface in the form of Fe₂O₃.BET results showed that the specific surface area of F300 was 91.89 m²·g^-1,which was slightly higher than the activated ATP,possibly because Fe₂O₃ occupied the pores of attapulgite.The specific surface area of F500 and F700 decreased compared with the activated ATP,which might be due to the pore collapse caused by the increase of roasting temperature.（2）In H₂O₂ oxidation system,at the optimum p H of 3.5,catalyst dosage of 0.3 g·L^-1 and0.5 mmol·L^-1 of H₂O₂ for 65 min,F300 and F500 were used as catalysts,and the OTC removal rate was close to 100%.Using F700 as catalyst,the OTC removal rate was 89.55%.The removal rate of OTC increased with the increase of catalyst dosage.When the concentration of oxidant was 0.25 to 0.5 mmol·L^-1,the removal rate increased with the increase of H₂O₂ concentration.When the concentration was greater than 0.5 mmol·L^-1,the removal rate and rate of OTC decreased.When the initial p H value of the solution was below 5.5,the removal effect of OTC was better,with the removal rate of about 80%.When the p H was neutral or alkaline,the removal rate decreased significantly.The addition of Cl^-and HCO₃^-to the system had no significant effect on the final removal rate of OTC,but had a certain effect on the removal speed.The addition of humic acid had a great effect on the removal of OTC products.The addition of humic acid had a greater effect on the removal of OTC,significantly affecting the removal speed of OTC and reducing the OTC removal rate.In order to explore the stability of the catalyst,the removal rate of OTC reached 57.29%after three times of reuse of F300.The concentration of ferri ion in solution was 2.64 mg·L^-1,which indicated that the catalyst had a certain stability.·OH had the greatest contribution to the removal of OTC in the catalyst activated H₂O₂ system,and ¹O₂ had a certain contribution to the reaction process.Low·O₂^-activity had no effect on the removal of OTC.（3）In PDS oxidation systems,at the optimum p H of 3.5,catalyst dosage of 0.2 g·L^-1 and1 mmol·L^-1 of PDS for 65 min,F300 and F500 were used as catalysts,and the OTC removal rate was close to 100%.Using F700 as catalyst,the OTC removal rate was 84.78%.The removal rate of OTC increased with the increase of catalyst dosage and oxidant concentration.When the concentration of PDS exceeded 1 mmol·L^-1,the removal rate of OTC decreased.When the initial p H value of the solution was 3.5～9.5,83.77%～98.47%OTC could be removed when the catalysts were F300 and F500.The addition of Cl^-and HCO₃^-to the system had no significant effect on the final removal rate of OTC.The addition of humic acid had a great effect on the removal of OTC,and the highest inhibitory rate of OTC removal reached 14.31%.In order to explore the stability of the catalyst,the removal rate of OTC reached 56.67%after three times of reuse of F300.The concentration of total iron ion in solution was 2.85 mg·L^-1,which indicated that the catalyst had a certain stability.According to the experiment of free radical quenching,when the initial p H value of the solution was 3.5,SO₄^-·was dominant in the system,¹O₂ made a certain contribution to the reaction process,and·O₂^-had little effect on the removal of OTC.（4）When p H of 3.5,catalyst dosage of 0.2 g·L^-1,0.5 mmol·L^-1H₂O₂,or 1 mmol·L^-1PDS,the removal rates of OTC were 92.94%and 97.34%,respectively.The reaction rate constant of0.0562 s^-1 in PDS system was higher than that of 0.0373 s^-1 in H₂O₂ system.PDS system has a wider range of adaptation to solution p H;The addition of Cl^-and HCO₃^-had roughly the same effects on the two systems.When humic acid was added in the two systems,the removal rate of OTC was basically not affected,but the reaction process was significantly inhibited.After three reuse experiments under the same optimal conditions,the removal effect was not different.·OH contributed the most to the removal of OTC in H₂O₂ system,while SO₄^-·and·OH were the leading free radicals in PDS system.