The Remediation Effects Of Electrical Resistance Heating Coupling Chemical Oxidants On Polycyclic Aromatic Hydrocarbons Contaminated Soils Of Sites

PAHs are a class composed of benzene rings with three characteristics(carcinogenic,teratogenic and mutagenic)of persistent organic pollutants(POPs).Coking and steel industries are one of the industrial pollution sources of PAHs.The polluted sites caused by the closure and relocation of coking enterprises in cities and surrounding areas have caused serious harm to the ecological environment and human health,and urgent secondary development and utilization are needed.The removal of PAHs from the soils has become the main way to eliminate or reduce its harm,and is also the hot and difficult point in the remediation of contaminated soils.In-situ thermal remediation,in-situ chemical oxidation and other remediation techniques do not need to excavate and transport of contaminated soils,and secondary pollution is relatively controllable,which attracts more and more attention.Action plan for soil pollution prevention and control promulgated in 2016 and The law of the People's Republic of China on soil pollution prevention and control implemented in 2019 explicitly require contaminated soils to be remediation in situ in principle.Based on Ohm's law,ERH uses electric current to pass through the soils to generate resistance,converts electrical energy into heat energy to raise soil temperature,and the pollutants are eventually transferred and disposed of by gas extraction.In this study,the artificial preparation of contaminated soils and the actual soils in steel mill are used as treatment object,ERH is used to treat contaminated soils of PAHs and selected to optimize the conditions,and the difference between ERH and TCH methods are compared.Then,ERH coupling four chemical oxidants to treat PAHs contaminated soils,compares the difference in removal effects,and the changes of microbial composition in the soil after treatment by using high-throughput sequencing technology are analyzed.The results obtained are as follows:(1)By analyzing the factors affecting ERH such as water,salt and electric strength,it is clarified that the soil water is the basic condition forERH,and the salt and electric strength are the important factors of ERH.During the process of ERH,adding water can maintain the soil water content,which is the primary condition to maintain the good operation of ERH.In the experiment,6 m L water must be added every 30 minutes.The optimal condition for laboratory-scale ERH is adding 6 m L 0.1% Na Cl solution at the electric strength of 8 V/cm.After 90 minutes of treatment,the removal rate of PAHs by ERH is 51.6%,higher than 49.4% of the disposal of TCH,and the energy consumption required by ERH is about 3.06 k J/g,lower than 10 k J/g of the disposal of TCH.(2)At the electric strength of 8 V/cm,the best removal effect of ERH coupling four oxidants treated on contaminated soils by PAHs is: ERH coupling sodium persulfate(Fe2+ activation)has the best removal effect,that the removal efficiency is 98% when the addition amount was 2 mmol/g;The removal effect of ERH coupling sodium persulfate is second,that the removal efficiency is 94% when the addition amount is 1.5 mmol/g;The removal effect of ERH coupling Fenton reagent is third,that the removal efficiency is 84% when the addition amount is 1.5 mmol/g;The removal effect of ERH coupling hydrogen peroxide is poor,that the removal efficiency is 81% when the addition amount is 3 mmol/g.In general,thermally activated sodium persulfate is more likely to generate free radicals than hydrogen peroxide and Fenton reagent,and sodium persulfate is a very effective additive for ERH to repair contaminated soils of PAHs.(3)ERH reduces the soil p H value from 6.72 to 6.36,a decrease of 0.36,and the organic matter content from 9.43% to 8.33%,a decrease of 11.7%.The ERH coupling sodium persulfate(Fe2+ activated)reduces the soil p H value from 6.72 to 5.04,a decrease of 1.68,and the organic matter content from 9.43% to 6.52%,a decrease of 30.9%.ERH reduces the diversity and evenness of soil microbial communities.After ERH,Proteobacteria and Firmicutes become the dominant Phylum in soil.Bacillus is the main bacteria genus in Firmicutes that can degrade PAHs.Pseudomonas and Achromobacter are the tolerant genus in this study.From what has been discussed above,ERH has a good remediation effect on remediation of PAHs contaminated soils,and its ecological impact on soil is relatively acceptable,which suggests that it is suitable for remediation of PAHs contaminated soils,and sodium persulfate is a very effective additive for ERH.