Oxidative Degradation Of 16-polycyclic Aromatic Hydrocarbons In Industrial Contaminated Soil Using Chlorine Dioxide Catalyzed By Divalent Manganese

As a typical organic pollutant in soil,polycyclic aromatic hydrocarbons（PAHs）have"three effects"and strong toxicity,which is a research hotspot in recent years.However,with the implementation of the policy of"retreating from two to three"and the relocation of coking plants and other enterprises,large areas of industrial contaminated land are left in the city.These sites are widely distributed and have high concentrations of pollutants such as PAHs,which pose a great threat to the environment and human beings.How to efficiently repair industrial contaminated sites polluted by PAHs is a difficult problem.Advanced oxidation process is often used to repair soil contaminated by PAHs.Chlorine dioxide（Cl O₂）oxidation remediation system is a clean,safe and efficient oxidation remediation system.Adding divalent manganese ion catalyst to this oxidation system can improve the degradation rate of PAHs,reduce the addition amount of Cl O₂ and reduce the remediation cost.In this paper,divalent manganese ion solution was used as catalyst and Cl O₂ was used as oxidant to catalyze and degrade PAHs in industrial contaminated soil.The kinetics of PAHs degradation in industrial soil was investigated with GC-MS The catalytic oxidation process was inferred by analyzing the valence state of manganese ion by XPS and qualitatively determining the degradation products by GC-MS.Using Eisenia foetida as indicator organism,the ecotoxicity of soil before and after remediation was compared and analyzed.The concentration of PAHs in contaminated soil is 2283 mg/kg.Factors such as exploring the optimal ratio of divalent manganese ion solution to Cl O₂,the dosage of Cl O₂ under the optimal ratio conditions,and p H will all have important effects on the oxidation of PAHs in contaminated soil catalyzed by divalent manganese ion solution.Adding 2500 mg/L Cl O₂ and appropriate amount of divalent manganese ion solution（the concentration of divalent manganese ion solution in the reaction system:Cl O₂=1:20）can oxidize and degrade 83.7%of PAHs.The lower the p H of the reaction system,the better the removal effect of PAHs.After the reaction,adding a small amount B to the reaction system can further improve the degradation rate of PAHs.The contaminated soil itself contains less manganese,which is not enough to catalyze the reaction,so it is necessary to add catalysts to improve the degradation effect of PAHs.During the reaction,the valence state of the catalyst changes constantly.First,the catalyst is oxidized,the valence state increases,and then it is reduced to manganese with lower valence state.After the reaction reaches equilibrium,a small amount of reducing agent can be added to reduce the oxidized catalyst again,further participate in the reaction,and improve the degradation effect of Cl O₂.In the product analysis of several single pollutants,it is found that there are oxidation products quinones,chlorine substituted substances and ring bond breakage.Using Eisenia foetida as an indicator organism,the ecotoxicological analysis of the soil before and after remediation showed that the acute mortality rate of earthworms was 90%in the contaminated soil after three days of exposure to poison,and the acute mortality rate of earthworms in the remediation soil after three days of exposure to poison was 50%.With the increase of poisoning time,the weight of poisonous earthworms in contaminated soil decreased faster than that in remediation soil,In the contaminated soil,the avoidance rate of earthworms for 48 h reached 80%,which had obvious avoidance effect.Which indicated that contaminated soil had strong ecological toxicity to earthworms.After remediation,the toxicity in soil decreased,but there was still some toxicity.In this paper,the degradation of PAHs in industrial contaminated soil using Cl O₂catalyzed by divalent manganese ions was studied for the first time,and its oxidation mechanism was preliminarily analyzed to evaluate the biological toxicity of Cl O₂catalyzed by divalent manganese ions in remediation of PAHs contaminated soil.It provides methods and data support for oxidation treatment and evaluation of PAHs in industrial contaminated soil.