Study On Degradation Efficiency And Mechanism Of Antibiotics In Different Structures By Sludge Activated Carbon

With the widespread use of antibiotics,various antibiotics have been frequently detected in water environment in recent years,which poses a threat to the ecological environment and human health.At present,the adsorption and degradation mechanisms of antibiotics are not fully studied.In this study,the sludge activated carbon was prepared by two-step activation method from the waste sludge of domestic sewage treatment plant,and the prepared sludge activated carbon was used to adsorb and remove tetracycline,ceftriaxone sodium,ofloxacin and erythromycin from sewage,so as to achieve"waste treatment".Physical and chemical properties of sludge activated carbon were analyzed by various characterization methods.Combined with adsorption isotherm model,adsorption kinetics,intramolecular diffusion and diffusion rate control model,classical Elovich kinetics model and chemical reaction kinetics model,the adsorption mechanism of sludge activated carbon on four antibiotics was analyzed.The mechanism and pathway of sludge activated carbon adsorption and removal of antibiotics with different structures were analyzed by Fourier transform in-situ infrared spectroscopy（FTIR）combined with liquid chromatography mass spectrometry（LC-MS）.The main conclusions are as follows:（1）The adsorption and removal rate of 50 mg/L tetracycline wastewater by activated sludge activated carbon prepared under the optimal activation conditions was99.93%,33.92%higher than dry sludge,89.01%higher than sludge biochar.The characterization results showed that the specific surface area of sludge activated carbon was 303.13 m~2/g,and the average BJH pore size was 3.74 nm,which belonged to microporous adsorption material;The surface of sludge activated carbon forms rough granular structure,mainly amorphous carbon.（2）When the initial substrate concentration gradually increased from 10-50 mg/L,the removal efficiency of tetracycline remained stable,the removal of ceftriaxone sodium and ofloxacin first increased and then decreased,and the removal rate of erythromycin decreased with the increase of the initial substrate concentration.The optimal p H values of tetracycline,ceftriaxone sodium,ofloxacin and erythromycin were 9,5,7 and 7.5,respectively.（3）When the initial concentration of antibiotics was 50 mg/L,the adsorption capacity of sludge activated carbon to four antibiotics was（99.93%）>Ceftriaxone sodium（95.44%）>Ofloxacin（85.80%）>Erythromycin（69.70%）;The adsorption and removal effect of sludge activated carbon on 20 mg/L mixed wastewater is very significant,and the removal rate is 92.9%at 30 min and 97.7%at 60 min.（4）Through the comparative analysis of adsorption mechanism,it was found that the process of sludge activated carbon adsorption to remove tetracycline was in line with Freundlich adsorption isothermal model,which was multi-molecular layer uneven adsorption,and the theoretical adsorption capacity was larger and the adsorption capacity was good;The adsorption and removal processes of ceftriaxone sodium,erythromycin and ofloxacin were more consistent with Langmuir adsorption isothermal model,and were monolayer and uniform adsorption.The fitting results of pseudo-first-order and second-order adsorption kinetics,intramolecular diffusion and liquid film diffusion rate control models show that the main rate-limiting step of sludge activated carbon adsorption removal rate of tetracycline is external diffusion rate limitation.The removal rates of ceftriaxone sodium erythromycin and ofloxacin were mainly limited by intramolecular diffusion rates.The fitting results of classical Elovich model showed that the chemisorption performance of sludge activated carbon adsorption in the removal of tetracycline and ceftriaxone sodium was strong,but the chemisorption performance of erythromycin and ofloxacin was poor.The results of chemical reaction kinetics model fitting showed that the initial concentration of substrate had the greatest effect on the adsorption of ofloxacin by sludge activated carbon,followed by ceftriaxone sodium and tetracycline,except erythromycin which did not conform to the three reaction kinetics models.（5）In the process of tetracycline removal,the intermediate products are mostly alcohols,which are less toxic and easy to crack and do less harm to the environment.In the removal process of ceftriaxone sodium,the left thiazole side chain,the right triazine side chain andβ-lactam ring were decomposed first,and the intermediate products were mostly carboxylic acid structure,amide group,olefin structure,ester group and aldehyde substance.In the process of erythromycin removal,the intermediate products were mainly cyclic ethers,carboxylic acid structure,amide group,ester group and aldehyde.The removal process of ofloxacin can be divided into halogen decomposition,diazocyclic decomposition,azo heterocyclic decomposition and carboxyl decomposition.The main products are amides,aromatic amines and symmetric nitrobenzene.