Oxidation Enhanced With Electrokinetic Remediation Of Phenanthrene In Soil

In this paper,the removal process of organic pollutants in the soil by electro-enhanced chemical oxidation remediation technology was studied.The effects of oxidant dosing point,oxidant system,voltage gradient and energization mode on the removal of phenanthrene were investigated.The degradation of phenanthrene in dual-oxidantion system at different temperatures was investigated.The difference of active intermediates in the process of phenanthrene degradation was investigated by molecular probes.The degradation intermediates of phenanthrene were explored and the possible degradation pathways were analyzed.The main conclusions are as follows:?1?In the process of electro-enhanced chemical oxidation remediation,the effect of electroosmotic flow on oxidant is higher than that of electromigration,so the anode is the best point for oxidant.The average removal rate of phenanthrene was 20.9%in mono-oxidant system;the average removal rate of phenanthrene to phenanthrene was30.6%in dual-oxidant system,which indicating that the average removal effect of dual-oxidant system on phenanthrene was significantly higher than that of mono-oxidant system.?2?The removal rate of phenanthrene is different under different voltage gradient conditions.The average removal rate of phenanthrene in the soil increases with the increase of voltage gradient.When the voltage gradient was 2V/cm,the average removal rate of phenanthrene was 41.62%.However,the excessive voltage gradient will cause great changes to pH and conductivity of the soil.Therefore,it is necessary to consider the appropriate voltage gradient.The voltage gradient is 1.5V/cm,and the intermittent energization mode of 36h power-12h off has relatively uniform removal of phenanthrene in the soil,and the average removal rate is 35.1%.?3?The removal rate of phenanthrene by the dual-oxidant becomes larger as the reaction time increases and the reaction temperature increases in the water bath experiment.At 30°C,the dual-oxidant system is relatively stable.After 12h of reaction,the removal rates of phenanthrene at 40°C and 50°C were 70%and 96%,respectively;at 60°C,the removal rate of phenanthrene was as high as 98.5%.The degradation reactions of phenanthrene at different temperatures were similar and they meet the quasi-first-order kinetic equation at 4h before the experimental reaction.The reaction rate becomes larger as the temperature increases,and Ea=72.44kJ·mol^-1 is calculated.?4?The molecular probe was used to determine the presence of·OH and SO₄^-·in the dual oxidant system,and·OH was dominant.In the dual oxidant system,the dissolution of calcium peroxide makes the solution alkaline and releases a certain amount of H₂O₂.The sodium persulfate mainly produces·OH in the alkaline solution.The hydrogen peroxide released by the calcium peroxide also produces a small amount of·OH and this increases the amount of·OH in the solution.?5?During the oxidation reaction,free radicals may undergo two pathways of degradation by attacking the 9,10 or 1,3 positions on the phenanthrene ring.The main retention times were 5.29min,10.28min,11.42min and 12.88min,respectively.The corresponding products were phthalate,Mixed oxalate,2-methoxybiphenyl and3-Methyl-hexanol,which ultimately produces carbon dioxide and water.