Study On The Adsorption Performance Of Tetracycline On Biochar Derived From Aerobic Granular Sludge

A lot of antibiotics have been detected in water environment in China due to long-term unreasonable use.Even at low concentrations,antibiotics are seriously harmful to the environment and human health,and potentially have long-term adverse influence on ecosystems.As the most widely used antibiotic,the efficient removal of tetracycline?TC?in water has become the focus of attention.Aiming at the problems of low efficiency and high cost of traditional adsorbents in removing TC,in this study,aerobic granular sludge?AGS?with high carbon content and large surface area was used as a substrate to prepare biochar.Factors influencing TC adsorption performance on original biochar?BC?were measured,and kinetic,isotherm and diffusion models of TC removal on BC were analyzed;aiming at the problem of limited TC adsorption performance on BC,Zn-BC with excellent TC adsorption performance was prepared.Based on the characterization of Zn-BC,TC adsorption performance on Zn-BC,the reusability of Zn-BC,and the adsorption kinetic,thermodynamic,isotherm and diffusion models were studied.In addition,the mechanism of TC adsorption on Zn-BC was analyzed in order to provide a reference for exploring adsorbents with low cost and high efficiency to removal antibiotics and other organic substances.TC adsorption performance on BC derived from AGS was related to the carbonization temperature and time,but the size of AGS had little influence on it.When the carbonization temperature and time were 700 ^oC and 2 h,TC adsorption performance on BC reached the maximum?16.59 mg/g?at 24 h.BC contained micropores,mesopores and macropores,and mainly contained-OH,C=O and C=C.TC adsorption performance on BC was affected by the amount of BC added,the initial p H of solution,the concentration of TC,the reaction time and the concentration of salt added.As the concentration of TC increased and the amount of BC added,TC adsorption performance on BC was gradually increased.When they were 0.015 g and 20 mg/L,TC adsorption performance became stable;the initial p H of solution affected TC adsorption performance on BC.When the p H was 7.0,TC adsorption performance on BC reached the maximum;low concentration of salt?0.05mol/L Na Cl and 0.025 mol/L Ca Cl₂?obviously promoted the process of adsorption and high concentration of salt inhibited the adsorption process.The results of kinetic and isotherm models showed that the pseudo-second-order kinetic model and Langmuir isotherm model fitted the experimental data better.The results of diffusion models showed that intraparticle diffusion and liquid film diffusion were rate-limiting steps in the entire reaction.The types and the amount of modified substances?CH₃COOH,H₃PO₄,Na OH,KOH,Na₂CO₃,Fe Cl₃ and Zn Cl₂?had great effect on TC adsorption performance on BC.The results of modification experiments showed that the adsorbent modified by Zn Cl₂?Zn-BC?had large specific surface area?852.41 m²/g?and a large number of micropores,which is conducive to ion exchange and diffusion.At the same time,the crystallinity of Zn-BC was improved and the properties were more stable.-OH,C=O and C=C participated in the adsorption process.After adsorption,the pores on the surface of Zn-BC disappeared and showed wrinkled structure.Zn-BC had a wide range of p H application,efficient TC adsorption performance and excellent reusability.When the p H was in the range of 4-9,Zn-BC had excellent TC adsorption performance,and the optimal p H value was 5.0.With the increase of initial TC concentration and contact time,TC adsorption performance gradually increased.When they were 80 mg/L and 48 h,TC adsorption performance reached 93.44 mg/g.The pseudo-second-order kinetic model and Langmuir isotherm model better fitted the experimental data.The results of diffusion models showed that intrapaticle diffusion and liquid film diffusion all controlled the reaction rate.The results of thermodynamic models showed that the adsorption process was a spontaneous endothermic reaction.The process of TC adsorption on Zn-BC was mainly controlled by pore filling and?-?conjugation;in addition,the electrostatic interaction and H bonding also took part in the whole adsorption process.The results of regeneration showed that TC adsorption performance on Zn-BC could still reach 90-95%of the initial adsorption performance after three cycles of regeneration desorbed by Na OH solution and C₂H₅OH.