PAHs Contaminated Soil Persulfate Microcapsules Remediation And Environmental Risk Study

With the continuous improvement of industrialization and urbanization,the amount of polycyclic aromatic hydrocarbons（PAHs）discharged from energy consumption,transportation and industrial production is also increasing,leading to the widespread phenomenon that soil PAHs exceed the standard.Chemical remediation using persulfate(S₂O₈^2-)as the main oxidant has a good effect on the treatment of industrial soil contaminated by PAHs.However,the reaction rate of persulfate is fast and non-selective,which is easy to cause waste of reagent and secondary pollution.Therefore,the oil phase separation method was used to prepare potassium persulfate microcapsule sustained-release materials,so as to improve the remediation efficiency of persulfate for soil contaminated with organic pollutants.This paper studies the remediation of PAHs contaminated soil by activated potassium persulfate microcapsule,which is mainly divided into the following four parts:Preparation,characterization and effect verification of potassium persulfate microcapsule;Study on the remediation effect and mechanism of potassium persulfate microcapsule to PAHs contaminated soil;Effect of soil composition on degradation of PAHs by potassium persulfate microcapsules;Potassium persulfate microcapsule remediation of PAHs contaminated soil environmental risk.The main research conclusions are as follows:（1）The encapsulation and sustained-release properties of potassium persulfate microcapsules prepared by oil phase separation method are good,without affecting the active components of potassium persulfate.When the ratio of core material/wall material of the microcapsule was 1:2（w/w）,and the ratio of ferrous sulfate/microcapsule was 1:10（w/w）,the optimal ratio of potassium persulfate microcapsule was verified,and the active bright red X-3B was used as the representative pollutant.When the reaction time was 72 h,the degradation rate of the reactive brilliant red X-3B was 96%.（2）The potassium persulfate microcapsule was used to repair the aged PAHs contaminated soil and the PAHs reaction in deionized water was compared and analyzed.The results showed that the total degradation rate of PAHs in soil reached 53.6%when the reaction time reached72h,among which the degradation rate of PAHs in low ring（2～3 rings）reached 88.1%and that in high ring（4～6 rings）reached 48.7%.In the deionized water medium,the total degradation rate of PAHs was 95.4%at the reaction time of 72h,and the degradation rates of low ring and high ring were 96.6%and 95.1%respectively,both of which were higher than the degradation rates of PAHs in soil medium.This may be because the reductive substances,mineral components and organic matter in the soil reduce the overall degradation rate of PAHs in the soil.Free radical probe experiments showed that potassium persulfate produced SO₄^-·and·OH radicals after activation by Fe²⁺,and these strong oxidizing groups reacted with PAHs to degrade it.The slow release of potassium persulfate also leads to the continuous improvement of PAHs degradation rate.（3）The effects of natural minerals,organic matter and inorganic anions in soil on the restoration of PAHs contaminated soil by potassium persulfate microcapsules and other factors showed that:natural minerals in soil could release Fe²⁺and combine with potassium persulfate to produce SO₄^-·,improving the degradation rate of PAHs.The higher the content of organic matter in the system,the more the amount of·OH and SO₄^-·consumed,and the more obvious the inhibition of PAHs.In the presence of Cl^-in the system,Cl^-can react with SO₄^-·and·OH to generate Cl·,and the chlorine radical reacts with each other to generate chlorine Cl₂and Cl^-,and the generated Cl₂and H₂O combine to form hypochlorous acid,which promotes the degradation of PAHs.When HCO₃^-,CO₃^2-and NO₃^-are present,electron transfer occurs to the main active species SO₄^-·in the reaction system,low active free radicals are generated,and PAHs degradation is inhibited.（4）The study on the environmental risk after the remediation of PAHs contaminated soil by potassium persulfate microcapsules showed that the concentration of Cr in the soil treated by microcapsules decreased to a certain extent,which was 8.5mg/kg lower than that without the addition of microcapsules.The concentrations of As and Pb changed only slightly,and the difference before and after the reaction was not significant.The number of bacteria without microcapsule treatment was 6×10⁴cfu/g.After potassium persulfate microcapsule treatment,the number of bacteria significantly recovered and increased after 12h reaction,and the number of bacteria reached 16×10⁴cfu/g after 72h reaction.The soil plant toxicity after microcapsule treatment decreased gradually with the continuous extension of the reaction time.At the reaction time of 72h,the germination rate of ryegrass seeds was 97.5%,which was 55%higher than that of contaminated soil without potassium persulfate microcapsule treatment.Therefore,potassium persulfate microcapsule remediation technology has a small risk to the soil environment,and has a broad application prospect.