Study On Adsorption Characteristics Of Antibiotics By The Manganese-oxide Modified Biochars In Aqueous Solution

To alleviate the shortage of water resources,improving the quality of surface water and reuse the urban sewage are two key ways.But the antibiotics remaining in the effluent of municipal sewage treatment plant will threaten the water quality of the receiving water body or the ecosystem security after reuse.Adsorption as one of mature water treatment technology shows good prospects for antibiotics removal,due to the simple operation and good economic benefits.Biochar is considered a promising,environmentally friendly and economical adsorbent due to its broad sources of raw material and low cost,but the adsorption capacity of primary biochar is limited.Therefore,in order to further enhance the adsorption capacity of biochar with optimizing its pore structure and psysicochemical properties,the modified biochar with manganese oxides was prepared in this study,which was used as adsorbent to study the removal efficiency and adsorption mechanism of tetracycline（TTC）,norfloxacin（NOR）and sulfamethoxazole（SMX）antibiotics in aqueous.This study provides a theoretical basis for the removal of organic pollutants and the resource utilization of waste biomass in the field of water treatment.Using sorghum straw biomass as raw material,manganese oxides-loaded biochar（MBC）was prepared with carbonized at 500℃for 1h after immersion in Mn Cl₂（0.5mol/L）solution for 2 h,which had good adsorption efficiency for antibiotics in water.By characterizing the row biochar and modified biochar,it can be seen that the manganese oxide was successfully loaded on the biochar,and the specific surface area and pore volume of the modified compsite increased by about 1 times,which provide more action sites for the adsorption of antibiotics in water.On the basis of obtaining the modified biochars,the influencing factors of MBC adsorption of antibiotics in water was explored with TTC,NOR and SMX as target antibiotics.The research results show that the p H of solution significantly affects the adsorption,and it has a good adsorption effect under acidic and neutral conditions,while alkaline conditions inhibited adsorption.The divalent cations(Ca²⁺、Mg²⁺)had an inhibitory effect on adsorption,while the monovalent cations（Na⁺、K⁺）and humic acid had a weak effect on adsorption.The adsorption characteristics of antibiotics by MBC were further explored through adsorption kinetics,isothermal adsorption and adsorption thermodynamics.The results showed that the adsorption basically reached equilibrium within 4 h,and the adsorption process could be described by pseudo-second-order kinetic model,which meant adsorption process controlled by physical and chemical effects.Besides,the intra-particle diffusion was not the only rate-limiting step.The adsorption process of TTC,NOR and SMX by MBC were fitted the Langmuir model well,and the maximum adsorption capacities were 736,40 and 26 mg/g,which were 15,6 and 4 times higher than that of BC.Adsorption is a spontaneous endothermic process,and the temperature rise is a favorable factor to promote adsorption.In the practical water application experiment,the residual concentration of antibiotics,COD and UV₂₅₄ in the effluent of secondary sedimentation tank decreased after the treatment of modified biochar adsorption combined with coagulation sedimentation technology,thus the modified biochar can be used for the removal of organics in advanced wastewater treatment.Combined with the material characterization of biochar and the adsorption efficiency and physicochemical charateristics of antibitotics to reveal the mechanism of antibiotics adsorbed by MBC from water.The results show that the specific surface area and pore volume of modified biochars were increased,and manganese oxides were loaded on the biochar,which provide more adsorption sites for MBC to adsorb antibiotics in water.Hydrogen bonding,n/π-πelectron transfer,electrostatic interaction,surface coordination and hydrophobic interaction are the main adsorption mechanisms.Antibiotics molecules with more hydroxyl functional group and lower HOMO-LUMO energy are more likely to migrate and attach to biochar surface.Quantitative structure property relationship（QSPR）model was constructed to explore the adsorption mechanism of tetracycline antibiotics on MBC,and the results show that hydrogen bonding andπ-πelectron transfer are very important for MBC to adsorb tetracycline antibiotics.