Study On Removal Of Sulfamethoxazole And Antibiotic Resistance Genes In Secondary Effluent Via An Integrated Magnetic Activated Carbon Adsorption And Ultrafiltration Process

In recent years,sulfonamide antibiotics and antibiotic resistance genes（ARGs）are frequently detected in the secondary effluent of urban wastewater treatment plants,which pose potential threat to the reuse safety of reclaimed water.At present,there is no special removal process for antibiotics and ARGs in wastewater treatment plant,so exploring effective advanced reduction process is the key to remove them.The combined process of powdered activated carbon and ultrafiltration has been proved to have a complementary effect in the removal of pollutants,but it still has the disadvantages of easy leakage of powdered carbon and serious membrane fouling.To solve these problems,magnetic nanoparticles were loaded on the powdered activated carbon in this study to make it easy to separate from water in an external magnetic field.Through characterization and performance study,the best magnetic activated carbon was selected from four kinds of magnetic activated carbon.Then sulfamethoxazole（SMX）was set as the target antibiotic,and the adsorption mechanism of SMX on magnetic activated carbon was analyzed by adsorption batch experiments,kinetic and thermodynamic analyses.Finally,the combined process was applied to the removal of SMX and ARGs from actual secondary effluent,and the membrane fouling mechanism was further studied.In order to improve the recovery rate of powdered activated carbon in water,four kinds of magnetic activated carbon such as C-Fe₃O₄（co-precipitation method）,C-Ni Fe₂O₄（hydrothermal method）,C-Co Fe₂O₄（co-precipitation method）and C-Co Fe₂O₄（hydrothermal method）were prepared by alkaline co-precipitation and hydrothermal methods,and their characterization and properties were studied.The characterization results showed that the four kinds of magnetic activated carbon were successfully prepared.BET results showed that the specific surface area and pore volume of C-Fe₃O₄（co-precipitation method）were second only to the unloaded carbon.VSM results suggested that C-Fe₃O₄（co-precipitation method）has strong magnetic properties and its saturation magnetization could reach 27.3 emu/g.The results of metal ion leaching experiment and adsorption pre-experiment showed that the C-Fe₃O₄（co-precipitation method）has the best magnetic retention property,whose Fe ion leaching concentration was the lowest.When SMX concentration was10 mg/L and the adsorbent dosage was 100 mg/L,the adsorption capacity of C-Fe₃O₄（co-precipitation method）was second only to the unloaded carbon.Therefore,C-Fe₃O₄（precipitation method）was selected as the optimal magnetic activated carbon.For further research the magnetic activated carbon adsorption mechanism of SMX,a series of batch experiments were carried out with dosage,temperature and p H adsorption influencing factors,and the adsorption kinetics and thermodynamics were analyzed.The SMX adsorption properties of magnetic activated carbon were studied.The results showed that when the initial concentration of SMX was 10 mg/L and the dosage of adsorbent was 100～700 mg/L,the removal rate of SMX could reach60.78%～94.81%.In the temperature range of 15℃～35℃,the lower the temperature was,the greater the adsorption capacity of magnetic activated carbon was.In the p H range of 3～10,the adsorption capacity decreased with the increase of p H,which was attributed to the hydrophobicity of SMX and the surface electrical properties of the adsorbent.The results of adsorption kinetics analysis showed that the pseudo-second-order kinetics equation could better fit the adsorption process.Through isotherm model fitting,it was found that Freundlich model had the best fitting,and the adsorption was multi-layer adsorption.Thermodynamic calculation results showed that the adsorption type of magnetic activated carbon was exothermic physical adsorption.Due to the complexity of the secondary effluent,in order to study the influence of other factors（such as dissolved organic matter）on the process,the combined process was used to remove SMX and ARGs from secondary effluent,and the membrane fouling mechanism was further analyzed.The results showed that the removal rate of SMX mainly depended on the adsorption of magnetic activated carbon,which could reach 90.22%when the dosage of adsorbent was 1400 mg/L,while the removal of ARGs mainly depended on the interception of ultrafiltration membrane.The removal capacity of sulⅠ,sulⅡ,sulⅢ,tet M,tet Q and tet W could reach 1.54～3.09,2.06～3.77,0.89～1.96,2.26～4.33,2.93～3.85,2.57～2.75 logs,respectively.Moreover,the removal of tet M,tet Q,tet W was observed to be significantly correlated with the fulvic acids,dissolved microbial metabolites and humic acids in secondary effluent（p<0.01）.The results of membrane fouling analysis showed that the standard blocking and the cake filtration were the main fouling mechanisms of ultrafiltration membrane.When the dosage of magnetic activated carbon was 1400 mg/L,the reversible resistance and irreversible resistance could be reduced by 61.4%and 88.9%,respectively,which could effectively reduce the membrane fouling.In this study,a new advanced treatment combined process was proposed to remove sulfamethoxazole and ARGs from secondary effluent,which could provide reference significance for controlling the spread of antibiotic resistance in wastewater treatment plant and improving the water safety of reclaimed water.