| Tetracycline is widely used in the world as drug treatment for human diseases and animal feed additive.However,only about 10%to 20%of tetracycline will be absorbed by human or animal body,and most of tetracycline will be discharged into the external environment in the form of metabolites.The existence of low-dose tetracycline and its by-products in the environment will cause the spread of drug-resistant bacteria and resistance genes,and ultimately threaten human health.Therefore,it is very important to find a suitable method to remove tetracycline.Adsorption is an effective method to treat tetracycline wastewater.The core of adsorption method is the selection and preparation of adsorbent materials.How to develop an efficient adsorbent to remove tetracycline is also one of the research hotspots in recent years.At the same time,the problem of large sludge production and difficult treatment in wastewater treatment plant has been concerned.In this paper,activated sludge and magnetic biochar were used as the adsorbent materials to carry out the adsorption experiment.This paper was divided into the following two parts.The first part took activated sludge as the research object to study the tolerance and removal effect of tetracycline content in water by activated sludge from municipal wastewater treatment plant.Batch experiments showed that the high removal efficiency of tetracycline by activated sludge was obtained.When the initial concentration of tetracycline increased from 5to 50 mg/L,MLSS concentration was 1500 mg/L and p H was 5,the removal rate and maximum adsorption capacity of tetracycline by activated sludge was 94.46%and 31.49 mg/g,respectively.The kinetic experiment found that the pseudo second order kinetics was more suit for this adsorption process with R2=0.997,indicating that the chemical mechanism was dominant in the process.The model of Langmuir and Sips reflect the adsorption process well（R2=0.987-0.999）,indicating that this process was a chemical adsorption process,and the higher temperature was beneficial for the reaction.The effects of different metal ions on the adsorption of tetracycline by activated sludge were different.Except Cu2+which promoted the adsorption process,K+,Na+,NH4+,Ca2+,Mg2+,Cd2+all inhibited the adsorption process,and the inhibition effect of divalent metal ions was more obvious than that of monovalent metal ions.Through various characterization methods,it was found that the adsorption of tetracycline by activated sludge involves electrostatic interaction,hydrophobic interaction,complexation,hydrogen bonding,cation-πinteraction andππinteraction.The second part took the residual sludge as the research object,it was to prepare the biochar first,and then to obtained the magnetic biochar by magnetic modification.In this paper,biochar,magnetic Fe3O4 and magnetic biochar were used as adsorbents to compare the adsorption efficiency and removal mechanism of tetracycline.The results of adsorption experiments found that the optimal p H of the three adsorbents were between 4 to 7.When the dosage of three kinds of adsorbents was 3 g/L and the initial tetracycline content was 100mg/L,the best adsorption effect was magnetic Fe3O4,with the adsorption rate of 94.3%,followed by the modified magnetic biochar,with the adsorption rate of 88.2%,and the worst was biochar,with the adsorption rate of 65.7%.The kinetic experiment found that the pseudo second order kinetics was more suit for adsorption process of three kinds of adsorbents,indicating that the chemical mechanism was dominant in these process.The model of Langmuir and Sips reflect the adsorption process well（R2=0.961）,indicating that this process was a chemical adsorption process,and the higher temperature was certainly beneficial for the reaction.In addition,the results of adsorption isotherm showed that the saturated adsorption capacity of biochar for tetracycline in water was 65.08 mg/g at 25℃,while the saturated adsorption capacity of magnetic biochar for tetracycline in water was 140.74 mg/g.Results showed that the the magnetic biochar’s surface area and pore volume were much larger than that of the biochar.The porous structure on the surface of the magnetic biochar was tightly filled with tetracycline.The important action sites were hydroxyl and carboxyl groups,respectively.It is accepted that the increase of adsorption sites of the modified magnetic biochar should responsible for the higher removal efficiency.Finally,the adsorption mechanism of three adsorbents was compared,and it was found that the adsorption effects of the three adsorbents on tetracycline removal in water were pore filling,electrostatic,hydrogen bonding and cationπ.The complexation bridging was a special adsorption mechanism of magnetic Fe3O4 and magnetic biochar.In addition,ππaccumulation was also present in the magnetic biochar. |
