Treatment Of Aged Landfill Leachate By Electrocatalysis Combined With CoFe₂O₄@HAP Activation Permonosulfate

In recent years,the growth rate of municipal garbage continues to rise,and landfill treatment of these garbage will produce a lot of landfill leachate.With the passage of time,the biodegradability of leachate decreases,and it contains high concentration of chemical oxygen demand(COD)and heavy metal ions,etc.,which makes it difficult for conventional treatment methods to meet the discharge requirements.At present,the advanced oxidation technology based on sulfate radical(SO4-·)has been gradually applied in the research field of refractory wastewater.However,the permonosulfate(PMS)in this technology is stable and difficult to decompose,so in this experiment,PMS was activated by the synergistic action of electrocatalysis(EC)and magnetic cobalt ferrite(CoFe2O4).Considering the high magnetic nano material surface can easily reunion,experiment extracted from discarded pig bone hydroxyapatite(HAP)as catalyst carrier,load CoFe2O4,improve its dispersion,with EC and PMS form EC/CoFe2O4@HAP/PMS system processing of the organic pollutants of aging waste leachate,in order to reduce COD,enhance the biological sex,for the subsequent processing process reduce stress.The waste pig bones were dissolved with green solvent ionic liquid to extract HAP.Nano-CoFe2O4 was synthesized by hydrothermal method,and the best preparation conditions and loading ratio were determined by single factor test.Finally,the composite catalyst was prepared by mechanical mixing method.According to X-ray diffraction(XRD)and scanning electron microscopy(SEM),CoFe2O4 has been successfully supported on HAP surface to prepare CoFe2O4@HAP catalyst.Fourier transform infrared spectroscopy(FT-IR)results show that there are a lot of hydroxyl groups in CoFe2O4@HAP structure.BET analysis showed that the specific surface area and total pore volume of the catalyst decreased slightly after HAP loading CoFe2O4.With COD,UV254 and reaction rate as indexes,the degradation efficiency of EC/CoFe2O4@HAP/PMS system under different treatment conditions was investigated.The results show that under the conditions of initial leachate pH=7,PMS concentration 2.Ommol·L-1,CoFe2O4@HAP dosage 1.0g·L-1,current density 15mA/cm2,and electrode spacing 1.5 cm,the system has the best comprehensive degradation effect.The removal rates of COD and UV254 are 76.05%and 84.02%,respectively,and the reaction rate constants are 0.01191min-1,0.01528min-1,respectively,following the first-order reaction kinetics.Then,the recovered ionic liquid and catalyst were recycled for five times.The results showed that the extraction rate of HAP by ionic liquid only decreased by 1.18%,and the COD removal rate by CoFe2O4@HAP in leachate only decreased by about 5.44%.XPS results before and after the reaction showed that the proportion of Co2+ and Fe3+in CoFe2O4@HAP decreased while the content of Co3+and Fe2+ increased.The results show that the REDOX cycle of Co2+/Co3+ and Fe2+/Fe3+ is involved in the catalytic reaction of PMS.Through the free radical quenching test,it was determined that SO4-·,hydroxyl radical(·OH)and monoline oxygen(1O2)were the main active species for oxidative degradation in the treatment system,among which SO4-· played a dominant role.Gel chromatography,gas chromatography-mass spectrometry,three-dimensional fluorescence spectrum and UV-visible absorption spectrum were used to analyze the changes of organic compounds in the effluent under the optimal treatment conditions.The results show that under the action of SO4-· and other substances,the structure of organic compounds in the leachate is destroyed,the unsaturated chemical bond is added,the ring structure of macromolecular organic compounds is opened and decompose into small molecular substances,the degree of aromatic structure is reduced,and its chroma is reduced by 94.97%.Humic acid and other refractory biodegradable organic matter in the leachate were decomposed into intermediate products without fluorescence characteristics,or mineralized into CO2 and H2O,resulting in the overall decrease of molecular weight of organic matter in the leachate,BODs/COD increased from 0.027 to 0.388,and the biodegradability was greatly improved.