Electrokinetic Combined Peroxymonosulfate（PMS） Remediation Of PAH Contaminated Soil

Persistent organic pollutants（POPs）in site soil have attracted widespread attention.Polycyclic aromatic hydrocarbons（PAHs）,as typical organic pollutants in contaminated sites,because of their widespread presence and persistence.Owing to their low aqueous solubility and lipophilicity,PAHs tend to be bioaccumulated in aquatic organisms and can be a source of various toxicities,such as hepatotoxicity,immunosuppression,reproductive and developmental toxicity,endocrine disruption,neurotoxicity and carcinogenicity.Many conventional treatment technologies have been successfully applied for efficient removal of PAHs from soils,including incineration,leaching,chemical oxidation,etc.However,these methods have some drawbacks,such as incineration will produce dioxins,halogenated polycyclic aromatic hydrocarbons and other more toxic byproducts;Physical leaching can only transfer PAHs from soil to liquid medium,and therefore does not completely eliminate PAHs from soils.Chemical oxidation treatment of organic pollution in soil is also difficult to transport oxidants.Therefore,it is urgent to develop a fast and effective technology to treat PAHs pollution in low permeability soil.Electric remediation is a kind of in-situ soil remediation technology for low permeability soil,which has good remediation effect for organic and inorganic pollution.For low permeability soil,electrokinetic remediation technology and its enhancement technology combined with other technologies show a broad application prospect in the field of soil organic pollution remediation.In recent years,peroxomonosulfate（PMS）has been used to degrade toxic and persistent pollutants,but rarely used in contaminated soil.Because of its superior oxidation performance,persulfate has become a potential oxidant for remediation of organic contaminated soil.Starting from the combination of chemical oxidation and electrokinetic remediation technology,series of laboratory experiments were conducted to investigate the effect of the different enhancement measures and the mechanisms of this combined technology.In this study,a real PAHs polluted site soil was selected as a typical soil,and peroxomonosulfate used as oxidant.The effects of EK combined with chemical oxidation on the contaminated soil were investigated under different enhancement measures.In the first part,the transmission of PMS and its efficiency of EK enhanced PMS remediation system for PAHs contaminated soil.At the same time,the mechanism of combined technology was revealed.To improve the remediation effect of PAHs in soil,solute HPCD and Tween 80 were added in the second part experiments to analyze the migration of solute and its influence on the electrokinetic remediation process driven by electric field.The free radicals generated by activation of PMS during electrokinetic-oxidation remediation were determined,and the primary mechanism were investigated.The third part mainly investigated the influence of Periodic voltage on the electrokinetic remediation,the influence mechanism of four kinds of periodic power outage frequency was tested.The main results are shown as follows:（1）The addition of PMS in electrokinetic remediation significantly improved the degradation efficiency of PAHs in soil.Although oxidant PMS can decontaminate PAHs in polluted soils,its removal of PAHs was only 11.0% without the enhanced methods.The enhancements increased the removal efficiency for PAHs from 0.33 to 2.10 times.The activation effect of Co ions on PMS was stronger than that of Fe ions.At fixed catholyte p H of 4,the highest removal efficiency（34.1%）was achieved because it enhanced PMS migration from cathode to anode.（2）The addition of solubilizer to the electrokinetic remediation system with oxidizer could also enhance the degradation of PAHs in soil,especially high-molecular ones.The addition of 5%（weight ratio）HPCD and Tween 80 in anolyte significantly decreased the electroosmosis flow and the migration of anolyte to cathode.Hydroxyl radicals produced by decomposition of PMS in soil solution were detected by in-situ method for the first time,in the electric remediation coupled with PMS oxidant.In this study,PMS can be activated to produce hydroxyl sulfate radicals,which were detected both in anolyte and catholyte.（3）The periodic electrokinetic remediation significantly enhanced the removal rate of PAHs（32.9%）,compared with that in the constant electric experiment（22.9%）.The frequency of 2:1 periodic outage was the most beneficial to the degradation of PAHs.The application of periodic electric field could weaken the electrode polarization effect,which was conducive to the desorption and removal of PAHs（especially HMW ones）in soil.