Adsorption Mechanism Of LDHs Modified Biochar Bioretention Tank For Compound Antibiotics

The extensive use of antibiotics makes many bacteria resistant,which weakens the effectiveness of antibiotics.Therefore,it is necessary to pay more attention to the pollution of antibiotics in the environment.In this study,three kinds of LDHs modified biochar with different metal ion ratios were prepared from walnut shell for the simultaneous removal of various antibiotics in water.The adsorption characteristics and mechanism of biochar for tetracycline Hydrochloride(TC),Norfloxacin(NOR)and Levofloxacin(LEV)and the action mechanism of external environmental conditions on the adsorption process were explored.The material with the best effect in the adsorption experiment was added to the biological retention tank as filler,The control effect of biological retention tank on antibiotics was investigated to determine the possibility of modified biochar as filler modifier.The main contents and conclusions of this study are as follows:(1)MnFe-LDHs modified biochar was successfully prepared.SEM characterization results showed that a large number of MnFe LDHs particles appeared on MFBC and increased with the increase of ferromanganese modification ratio;XRD results show that MnFe LDHs structure with weak characteristic diffraction peak appears on MFBC;FT-IR results show that the three modified proportions of MFBC have similar spectra with BC,but the modified MFBC has stronger aromaticity and can provide π electrons for the antibiotic removal process.Other functional groups such as O-H group,Mn-O group,Fe-O group and aromatic functional groups also play an important role in the adsorption process;The results of zeta potential analysis showed that the 3:1MFBC modified material was relatively stable in most pH ranges,and the surface of biochar was negatively charged.(2)The removal effects of different materials on TC,NOR and LEV were compared.It was found that 3:1MFBC had the highest adsorption capacity for three antibiotics.And the removal of different antibiotics is also different.In the single antibiotic environment,the maximum adsorption capacities of 3:1MFBC for TC,nor and LEV were 18.72,10.66 and 16.84mg/g respectively.In the mixed solution of the three antibiotics,3:1MFBC showed the maximum adsorption capacity for the three antibiotics.The order of adsorption capacity for different antibiotics was: NOR > LEV >TC;In addition,the adsorption capacity of TC and LEV by 1:1MFBC is higher than that of 2:1MFBC,while the adsorption capacity of NOR is the lowest.With the increase of biochar dosage,the removal rate and adsorption capacity of nor by BC and 3:1MFBC also increase gradually;The pH of the solution will change the functional group morphology of the three antibiotics and the surface charge of 3:1MFBC,so that the antibiotics and MFBC have different charges at different pH;In addition to electrostatic interactions,there are strong hydrogen bonds and π-π electron donor receptor interactions.(3)The results of adsorption model show that in a single antibiotic solution,the quasi second-order kinetic model can more accurately describe the adsorption process of 3:1MFBC on three antibiotics,indicating that the adsorption process of 3:1MFBC on three antibiotics is mainly controlled by chemical mechanism,and the adsorption rate is affected by the number of surfactant sites.In addition,Freundlich model can better fit the adsorption of three antibiotics by 3:1MFBC in isothermal adsorption,indicating that multi-layer adsorption is more likely to occur at room temperature,and it is more likely that physical and chemical adsorption processes exist at the same time.In the compound antibiotic solution,the results of three modified biochar adsorbing the compound antibiotic solution show that the correlation coefficient R2 fitted by the quasi second-order kinetic model is higher than that of the quasi first-order kinetics,while the isothermal adsorption results show that in the adsorption of three antibiotics in the mixed solution,except that the interaction between 2:1MFBC and LEV is more in line with the Langmuir adsorption model,the other adsorption processes are more in line with the Freundlich isothermal adsorption model.(4)After selecting the best ratio,3:1MFBC is used as the filler layer modifier of bioretention cells,and the modified biochar based bioretention cells is successfully constructed and put into trial operation.The addition of 3:1MFBC can significantly improve the removal effect of antibiotics in biological detention tank,and is better than the improvement of green zeolite on the filler layer of biological detention tank.