Fenton-driven Regeneration Of Activated Carbon Saturated With Typical Antibiotic

Antibiotics are widely used in human and animal disease prevention,livestock farming,aquaculture and agricultural production.As the main source of antibiotics in the environment,veterinary antibiotics are discharged into the environment with feces and urine in the form of protoplasts or metabolites.The accumulation of resistant bacteria and the spread of resistance genes have posed a huge threat to environmental and ecological safety.The removal or reduction of antibiotics in the environment has become one of the research hot topics and difficulties in the environment field.In this paper,tetracycline in tetracyclines and ciprofloxacin in fluoroquinolones were target compounds,the adsorption characteristics of the target antibiotics were tested in the granular activated carbon adsorption/Fenton regeneration?GAC/Fenton system?and activated carbon amended with Fe²⁺adsorption/Fenton regeneration?Fe-GAC/Fenton system?.Based on batch experiments,the suitable operating conditions of GAC/Fenton system and Fe-GAC/Fenton system were investigated,and the regeneration efficiency of GAC and Fe-GAC was analyzed through six consecutive cycles of adsorption/regeneration process.Under the conditions,the removal effect of the target antibiotics was investigated,and the possible degradation pathways of the target antibiotics were preliminarily discussed.The experimental results can provide basic data and theoretical support for the adsorption and removal of antibiotics by activated carbon and activated carbon regeneration.The main research contents and conclusions of the thesis are as follows:?1?Adsorption experiments of typical antibiotics by GAC and Fe-GACThe optimum pH for adsorption of tetracycline and ciprofloxacin by GAC and Fe-GAC were 3 and 5,respectively.The adsorption process accorded with the pseudo-second-order kinetic equation,and the adsorption isotherm followed the Langmuir model.Among them,when the initial concentration was 5²5mg/L,the equilibrium adsorption capacities of GAC and Fe-GAC for adsorption of tetracycline were 19.5mg/g and15.3mg/g,respectively,and the equilibrium adsorption capacity of adsorbed ciprofloxacin were 8.5mg/g and 5.8 mg/g,respectively.?2?Batch experiment study of adsorption/regeneration systemA series of single-factor static experiments were carried out to investigate the effects of initial pH,Fe²⁺/H₂O₂ molar ratio,H₂O₂ dosage and reaction time on GAC regeneration,and the most suitable operating conditions for GAC/Fenton system were obtained.The experimental results show that the suitable regeneration conditions for tetracycline as target antibiotic are:initial pH 3,Fe²⁺/H₂O₂ molar ratio 1:25,H₂O₂ dosage 8 mM/g,reaction time 45min,regeneration effect 99.48%;The suitable regeneration conditions for ciprofloxacin as target antibiotic were:initial pH 3,Fe²⁺/H₂O₂ molar ratio 1:25,H₂O₂dosage 10 mM/g,reaction time 45min,regeneration effect 70.7%.A series of single-factor static experiments were carried out to investigate the effects of initial pH,Fe²⁺loading concentration,H₂O₂ dosage and reaction time on the regeneration of Fe-GAC.The suitable operating conditions for Fe-GAC/Fenton system were obtained:initial pH 3,the concentration of Fe²⁺was 40 mg/L,the reaction time was60 min,and the dosage of H₂O₂ was 9 mM/g?tetracycline?and 12.5 mM/g?ciprofloxacin?respectively.The regeneration effects were 104.3%and 104%,respectively.?3?Evaluation of regeneration efficiency during cyclic continuous adsorption/regeneration operationsThe regeneration effects were excellent during the adsorption/regeneration operation for 6 consecutive cycles.When the target antibiotic is tetracycline,the regeneration efficiency of GAC/Fenton system was 92.3%¹01.3%;the regeneration rate of Fe-GAC/Fenton system is 101.5%¹07.1%.When the target antibiotic is ciprofloxacin,the regeneration efficiency of GAC/Fenton system was 62.5%⁹3.0%;the regeneration rate of Fe-GAC/Fenton system was 98.5%¹20.1%.Compared with the GAC/Fenton system,the Fe-GAC/Fenton system increased the dosage of H₂O₂ by only 12.5%?tetracycline?and 25%?ciprofloxacin?,but thetotal Feamendedin Fe-GAC/Fenton system was 1/21 of the 6-cycle Fe²⁺dosage in GAC/Fenton system.The Fe-GAC/Fenton system is more advantageous than the GAC/Fenton system.?4?Degradation mechanism of target antibiotic regeneration processSolution of the target antibiotic,the second adsorption/regeneration operation in GAC/Fenton and Fe-GAC/Fenton system were detected by three-dimensional fluorescence spectrometry.The fluorescence peak position and peak point fluorescence intensity of each system have significant differences,indicating that tetracycline and ciprofloxacin adsorbed on activated carbon are significantly degraded,and the degradation effect of GAC/Fenton is better.This is because the external Fe²⁺addition in the GAC/Fenton regeneration system is more likely to catalyze the production of more hydroxyl radicals by H₂O₂.On the other hand,the external Fe²⁺addition reduces the adsorption capacity of antibiotics in GAC to some extent,resulting in better apparent regeneration.In addition,the ferric hydroxide polymer produced by the external Fe²⁺addition also has a flocculation sedimentation effect on tetracycline and ciprofloxacin.For the regeneration operation of the GAC/Fenton system,the product was tested by quadrupole time-of-flight liquid chromatography-mass system?Q-TOF LC/MS?.In the tetracycline adsorption/regeneration system,14 intermediate products were detected,and three possible degradation mineralization pathways of tetracycline were deduced.The final mineralized products were inorganic ions such as H₂O,CO₂,NH₄⁺and NO_3.;ciprofloxacin in the adsorption/regeneration system,13 intermediate products were detected,and five possible degradation mineralization pathways of ciprofloxacin were deduced.The final mineralized products were inorganic ions such as H₂O,CO₂,NH₄⁺and NO_3.and F^-.This paper was funded by the Chongqing Construction Science and Technology Project?Chengkezi 2017 No.?162??.The adsorption characteristics of typical antibiotics by GAC and Fe-GAC were compared in the study.The The regeneration efficiency of the GAC/Fenton system and Fe-GAC/Fenton were compared and analyzed.The decomposition and transformation characteristics and the possible degradation pathways of tetracycline and ciprofloxacin in GAC/Fenton system and Fe-GAC/Fenton system were preliminarily explored.Results of the paper can provide theoretical support and technical reference for in-depth studies of the adsorption/regeneration of antibacterial granular activated carbon.