Degradation Of Polycyclic Aromatic Hydrocarbons By Magnetic Chitosan Immobilized Laccase In Water And Soil

Polycyclic Aromatic Hydrocarbons（PAHs）,which cause serious water and soil environmental pollution,seriously endanger human health and ecological safety.How to safely and efficiently remediate PAHs contaminated water and soil is of great significance for the resource development and utilization of contaminated water and soil.Laccase,secreted by organisms,can catalyze the degradation of PAHs to achieve the purpose of safely and effectively remediating PAHs contaminated water and soil.However,free laccase is easily inactivated,difficult to recycling,which limits its activity and application in the remediation of contaminated water and soil.In this study,laccase was immobilized to improve the chemical stability and reusability.The conditions for the preparation of immobilized laccase were optimized,and acid and alkaline resistance and reusability of immobilized laccase were studied at the optimum condition.The influencing factors for PAHs degradation by immobilized laccase in soil and waterwas explored.The degradation intermediate products and pathway of PAHs were illustrated.（1）Preparation and properties of laccase immobilized by Fe₃O₄@SiO₂-ChitosanThe core-shell Fe₃O₄@SiO₂ was synthesized by sol-gel method.The chitosan was coated on the surface of the magnetic particles by co-precipitation method.The morphology and physicochemical properties of the Fe₃O₄@SiO₂-Chitosan were investigated by scanning electron microscopy,fourier transform infrared spectroscopy.Results show that the chitosan were successfully wrapped in magnetic Fe₃O₄@SiO₂ particle surface,the average Fe₃O₄@SiO₂-Chitosan particle size is about 220 nm,and the Fe₃O₄ crystal structure did not significantly change before and after saturation.Magnetization intensity was 53.18 emu/g,remanence and coercivity are approximately 0,have superparamagnetism,carrier stability in a wide range of p H and good thermal stability.Fe₃O₄@SiO₂-Chitosan was used as the carrier of laccase and glutaraldehyde was used as the crosslinking agent.The immobilized laccase onto the carrier was produced at the optimum reaction conditions.The optimum immobilized condition was:4%glutaraldehyde concentration,1.0 mg/m L laccase concentration,2 h crosslinking time and 6 h fixing time.Under this condition,the load concentration of the enzyme reached 158 mg/g,and the activity recovery of immobilized laccase was 61.3%with the assistant of magnetic particles carrier.Immobilized laccase had high storage stability,p H and temperature stability.The Km of the immobilized laccase was 111.5μmol/L,compared with 63.5μmol/L for the free enzyme.The affinity of the immobilized enzyme was slightly weakened,and the catalytic efficiency was a littlereduced.（2）Degradation of PAHs by Fe₃O₄@SiO₂-Chitosan immobilized laccase in water and soil.Fe₃O₄@SiO₂-chitosan immobilized laccase to degrade degradation of PAHs by Fe₃O₄@SiO₂-chitosan immobilized laccase in water and soil was studied and the optimal degradation condition were obtained as p H=4,35℃of temperature,and 300 mg of the immobilized enzyme addition Under this condition,81.87%and 69.15%of anthracene and benzopyrene in water were degradated within 48 h,respectively.The degradation rate of anthracene and benzopyrene in soil was 60.12%and 51.23%,respectively The intermediatedegradation products of anthracene and benzo pyrene by the immobilized laccase were anthraquinones and benzopyrene quinones,respectively.Addition of mediators significantly promoted the degradation of anthracene and benzopyrene by the immobilized laccase in water and soil and the promotion.Effects was HBT>PCA>ABTS.