Degradation Of PAHs In Soil By Zero-valent Iron Activated Sodium Persulfate

Polycyclic aromatic hydrocarbons（PAHs）are carcinogenic,teratogenic and mutagenic organic pollutants with strong toxicity and high environmental persistence.They usually exist in industrial pollution sites such as petrochemical industry and coking gas.PAHs enter the soil and groundwater by natural settlement and migration,which seriously threatens the ecological environment and human health.Based on advanced oxidation technology of persulfate activation is an effective method for remediation of PAHs contaminated soil.In this study,the PAHs contaminated soil was the research objective,and it was deoxidized by sodium persulfate activated by zero-valent iron.The degradation effect and optimal conditions of PAHs with different ring numbers were investigated.Moreover,the reaction mechanism was analyzed,and the changes of soil physical-chemical properties and microbial community structure after oxidation were explored.The results of the study are as follows:（1）Batch experiments were conducted to determine the optimum addition of Na₂S₂O₈ and the ratio of Na₂S₂O₈ to Fe in the degradation of PAHs-contaminated soil by activating Na₂S₂O₈ with Fe²⁺and Fe⁰,respectively.The results showed that when Na₂S₂O₈ was activated by Fe²⁺,the optimum addition amount of Na₂S₂O₈ was 8 mmol and the ratio of Na₂S₂O₈ to Fe²⁺was 300:1,the degradation efficiency of PAHs was the best.However,when Fe⁰ was used as activator,the optimum dosage of Na₂S₂O₈ was10 mmol,n（Na₂S₂O₈）:n（Fe⁰）was 200:1.（2）The effects of water-soil mass ratio,temperature,initial pH and reaction time on the activation of Na₂S₂O₈ by Fe⁰ were analyzed.The results showed that PAHs had the best degradation effect when the water-soil mass ratio was 2:1,reaction temperature was 60 C and initial pH was 6.The degradation rate of PAHs was the highest at the first9 hours,and the reaction tended to be gentle after 72 hours.The degradation of naphthalene,phenanthrene,fluoranthene and benzo[a]pyrene conformed to the first order reaction kinetics.（3）The reaction mechanism was analyzed by EPR,and the type of free radicals and the change of free radical intensity with time were determined.The results showed that both Fe²⁺activated Na₂S₂O₈ and Fe⁰ activated Na₂S₂O₈ were co-existing systems of·OH and SO₄^-·.The free radical intensity of Na₂S₂O₈ activated by Fe⁰ was higher than that activated by Fe²⁺at 40 min.（4）The effects of chemical oxidation on soil environment were evaluated by the changes of soil pH,organic matter and microbial community diversity.After oxidation,the soil pH changed from 7.2 to 6.5;the organic matter content decreased from 5.2mg/kg to 3.8 mg/kg;And the abundance and evenness of soil microbial community decreased,and the dominant microbial population changed from Actinobacteria to Firmicutes.