Study On The Catalytic Adsorption Mechanism Of DEHP By Arthrobacter Sp. JQ-1 Extracellular Polymer (EPS)

Di-（2-ethylhexyl）phthalate（DEHP）with long-chain hydrocarbons is widely used in the industrial field.DEHP is one of the most common plasticizers with the strongest plastic resistance.DEHP belongs to the category of endocrine disruptors（EDCs）and has a"triple cause"effect.The harm caused by DEHP to the environment should not be overlooked.Therefore,it has been listed as a priority pollutant.Biosorption is a new adsorption method being developed in recent years.It is cheap,easy to obtain raw materials,low cost,simple operation,large adsorption capacity and high efficiency.Extracellular polymeric complex organic polymers secreted by microorganisms can act as good biosorbents.In this study,extracellular polymers were extracted and used as adsorbents for DEHP by Arthrobacter sp.JQ-1,which used DEHP as the sole carbon source.The adsorption of Extracellular polymers（EPS）on different concentrations of DEHP was investigated.Mn²⁺plays an important role in cell life activities and is a cofactor and activator of many enzymes.This article also examined whether Mn²⁺has a catalytic effect on adsorption of DEHP by EPS and further discussed the catalytic mechanism.The research will provide us a theoretical basis for the restoration of DEHP pollution.The main research contents were summarized as follows:The extracellular polymer of Arthrobacter sp.JQ-1 was extracted by heating.Main components concluded protein,polysaccharide,and humic acid and their contents were 381.1±1.02,199.1±3.26,and 159.42±1.96 mg·g^-1,accounting 40%,20%,and 16%of the total EPS,respectively.These components play a major role in biosorption of DEHP.In all influencing factors of DEHP adsorption by EPS,temperature and pH had a great influence,with optimal values of 25°C and pH=7.Under this condition,the kinetic adsorption test showed the maximum adsorption of DEHP,with initial amount of 100 mg·L^-1,could reach 170.14mg·g^-1,which was balanced at 48 h.The whole adsorption process was better in line with the pseudo-second-order kinetic model（R²>0.98）.The adsorption isotherm conformed to the Freundlich isothermal model（R²>0.99）and was adsorbed by multiple molecules,among which the K value was large,indicating that EPS has strong affinity for DEHP.The effect of 1 mg·L^-1 Mn²⁺on the adsorption of DEHP by EPS was determined.Temperature had no major influence on the adsorption process,but the pH was different.The removal rate reached the highest value of 92%at pH=6.To conduct DEHP adsorption kinetics experiments by EPS,adsorption conditions in experiment group was set at pH=7,25°C,1 mg·L^-1 Mn²⁺,and 100mg·L^-1 DEHP.The maximum adsorption capacity was 194.84 mg·g^-1,which was significantly higher than control group(without Mn²⁺).Besides,adsorption equilibrium in experiment group reached earlier（about 24 hours）than control group.Addition of a small amount of Mn²⁺contributed to the adsorption of DEHP by the EPS,and the advancement of the equilibrium time illustrated Mn²⁺probably catalyzed the adsorption process.Adsorption of DEHP by EPS is still better consistent with the pseudo-second-order kinetic model（R²>0.99）and the Freundlich isothermal model fitting（R²>0.98）after addition of Mn²⁺.The K value increased compared to no Mn²⁺addition,indicating that the addition of Mn²⁺promoted the affinity of EPS to DEHP.To investigate the mechanism of the catalytic adsorption of DEHP on the extracellular polymer of Arthrobacter sp.JQ-1,the hydrophobicity,Scanning Electron Microscope（SEM）,Fourier transform infrared spectroscopy（FITR）,and Three-Dimensional Excitation Emission matrix Fluorescence Spectrophotometer（3D-EEM）determination of DEHP adsorption on EPS were performed.The increase in hydrophobicity of EPS over time was mainly due to the hydrophobic substances（aliphatic compounds,humic acids,and aromatics on the protein）in the EPS.After 1 mg·L^-1 Mn²⁺was added,the hydrophobicity of EPS after adsorption of DEHP changes with the adsorption time.The hydrophobicity also increased with the increase of DEHP concentration,therefore DEHP adsorption amount increased.Compared with no Mn²⁺addition,the overall hydrophobicity of EPS increases.Namely,addition of Mn²⁺promoted the adsorption of DEHP by EPS.This reason may be that Mn²⁺combined with various hydrophilic functional groups in the polysaccharide components on the EPS surface to enhance the binding strength of EPS to DEHP.When Mn²⁺was present,the surface structure of the EPS adsorbing DEHP became rough and a holey filament formed according to SEM results.The FIRL spectrum of EPS adsorbing DEHP showed that the vibration of the peak at different wavelengths indicated that hydroxyl,carboxyl,and carbonyl groups may promote adsorption of DEHP by EPS.The adsorption process was inseparable with proteins and polysaccharides.After Mn²⁺addition,the peaks of-OH,-CH₂-,C=O,-NH,-CN,C-O-C,and C-O drifted,indicating that both Mn²⁺and DEHP reacted with the EPS groups and interacted with different components.3D-EEM spectra showed EPS mainly contained proteins,aromatic proteins and humic acid components.The peak changes indicated that these substances could reacted with DEHP.After adding Mn²⁺,the peaks of EPS substances changed again,indicating that Mn²⁺indeed has a close relationship with the adsorption of DEHP by EPS.Combined with the whole kinetic adsorption process,Mn²⁺had a catalytic effect on DEHP adsorption on EPS.