Study On The Adsorption And Catalytic Degradation Of Tetracycline Wastewater By Nano-MnFe₂O₄ Biochar

In recent years,tetracycline antibiotics are widely used in the fields of medicine,agriculture,animal husbandry and fishery.Antibiotic residues entered the environment,threatened human health and ecological environment seriously.During the production and application of tetracycline antibiotics,there is a large amount of wastewater produced and discharged into water environment which is not completely removed by sewage treatment facility or without treatment,which seriously threatens the aquatic environment.How to effectively remove antibiotics in the water environment is an urgent problem to be solved.Combining adsorption and advanced oxidation process（AOP）based on modified biochar has great potential for the treatment of refractory organic pollutants in water environment.It has the characteristics of wide application range,high efficiency,and low cost.In this study,rice straw biochar loaded nano-iron manganese acid（MnFe₂O₄biochar）was prepared by chemical co-precipitation.Its adsorption performance and mechanism for tetracycline hydrochloride were studied,it was also used as a catalyst for heterogeneous Fenton-like and activation persulfate degradation to remove tetracycline hydrochloride,and the degradation performance and activation mechanism were explored.The research contents and conclusions are as follows:（1）Using rice straw biochar as substrate,MnFe₂O₄ biochar was prepared by chemical co-precipitation,and the best material was optimized through adsorption and degradation experiments,and was analyzed by SEM,BET,XPS,XRD and FTIR.The results show that the material with 2:1 composite of mass ratio of 700℃pyrolysis carbon to MnFe₂O₄has the best adsorption and degradation performance.MnFe₂O₄ biochar is mesoporous material which has the structure and morphology similar to ordinary biochar.It has higher surface area and average pore size,and shows better adsorption potential.MnFe₂O₄ Nano-particles are mainly combined with biochar in two forms,one of which are more evenly distributed on the rough surface of biochar,and the other part are combined with the surface of biochar in the form of agglomerated particles.（2）MnFe₂O₄ biochar was used in the adsorption testing of tetracycline hydrochloride to investigate the influence of different factors on the removal of tetracycline,and explore the adsorption performance and adsorption mechanism of MnFe₂O₄ biochar on tetracycline.The results show that the maximum removal rate of 95.88%was obtained with the adsorbent dosage was 4.00g/L when the initial p H was 3.0,and the adsorption reaction reached equilibrium within 6h.The p H has little effect on the adsorption of tetracycline.The buffering effect of MnFe₂O₄ biochar on the solution enables the removal rate of tetracycline to be maintained above 94.1%within the initial p H range of 3.0 to11.0.The adsorption process of tetracycline by MnFe₂O₄ biochar conforms to the Freundlich model and pseudo-second-order kinetic model.The adsorption process is a heterogeneous multi-molecular layer adsorption restricted by chemical adsorption.At the same time,high temperature is more conducive to the adsorption of tetracycline by MnFe₂O₄ biochar.Various mechanisms are involved in the adsorption process of tetracycline,including electrostatic interaction,complexation,hydrogen bonding,andπ-πelectron donor-acceptor interactions.（3）MnFe₂O₄ biochar and hydrogen peroxide were used to establish the MnFe₂O₄biochar/H₂O₂ Fenton-like reaction system for the degradation and removal of tetracycline hydrochloride.The factors affecting the degradation of tetracycline hydrochloride were investigated,the active substance involved in the degradation of tetracycline was determined by quenching test and the degradation mechanism was explored.The results show that the combination of MnFe₂O₄ nano-particles and biochar improves the catalytic performance,and the bimetallic Fe and Mn provides the driving force for the generation of free radicals.The MnFe₂O₄ biochar/H₂O₂ reaction system can effectively degrade tetracycline.The optimal reaction conditions are:the dosage is 0.50g/L,the initial p H of the solution is 3.0,and the H₂O₂ concentration is 0.15M.By cooperating with the H₂O₂reaction,the removal rate of tetracycline increased by 23.23%compared with adsorption after 120 minutes of reaction.The free radicals involved in degradation are mainly hydroxyl free radicals,and there are also non-radical pathways involved in the removal of tetracycline.（4）The removal of tetracycline hydrochloride by persulfate activated by MnFe₂O₄biochar conforms to the second-order kinetics,including adsorption and catalytic degradation,and their contributions are 55.19%and 22.69%,respectively.The removal of tetracycline by MnFe₂O₄ biochar activated persulfate reaction system is affected by the catalyst dosage,initial p H and persulfate concentration.The increase in the removal rate by the catalyst dosage mainly comes from adsorption.The reaction system has relatively high removal efficiency,but excessive persulfate will cause the quenching of free radicals.The optimal reaction conditions are:the dosage is 1.00 g/L,the p H value is 3.0,and the persulfate concentration is 10.0m M.The main free radicals involved in degradation are SO₄^-·and HO·,of which SO₄^-·contributes more.MnFe₂O₄ biochar has good adsorption performance,and can increase the removal rate of tetracycline by synergizing hydrogen peroxide and persulfate,which can be used as a stable and effective wastewater treatment way to remove antibiotics and other refractory drugs.