Study On Remediation Technology Of Polycyclic Aromatic Hydrocarbons(PAHs) Contaminated Soil From Coking Sites

Polycyclic aromatic hydrocarbons（PAHs）are one of the typical contaminants in polluted soils of coking sites,with the characteristics of environmental persistence,bioaccumulation,long-range migration and"tri-causing",etc.High-ring PAHs are a difficult and painful point in the remediation of contaminated soils of coking plant sites,and remediation treatment is urgent.Common remediation techniques for PAHs-contaminated soil include thermal desorption,chemical oxidation,and surfactant drenching,etc.Although there have been numerous studies on this topic,the nature of soil and contamination conditions vary from region to region,so the remediation efficacy of PAHs needs to be further investigated.In view of this,we investigated the removal efficiency of five oxidants,including H₂O₂,Fenton,KMnO₄,Na₂S₂O₈and O₃,on PAHs-contaminated soil at a coking site in Shanxi.In addition,the removal efficiency of PAHs by surfactant drenching-chemical oxidation was investigated on PAHs-contaminated soil at a coking site in Anhui Province,and the process parameters（surfactant concentration,liquid-solid ratio,drenching time and number of drenching times）were optimized to further investigate the removal efficiency of PAHs by chemical oxidation on drenched soil.The main conclusions of this paper are as follows:（1）The remediation effect of PAHs treated by chemical oxidation technology was studied along with the analysis of microbial response relationships.The results showed that:1)H₂O₂,Fenton,KMnO₄and Na₂S₂O₈had the highest removal rates ofΣPAHs at a liquid-solid ratio of 4:1,98.9%,98.7%,98.3%and 96.4%,respectively,while O₃had the highest removal rates ofΣPAHs at a liquid-solid ratio of 8:1（91.48%）.2)The removal rates of the five oxidants were higher for the low-ring（2-4 ring）phenanthrene and acenaphthene,while for the high-ring（5-6 ring）benzo[a]pyrene,the removal effect of KMnO₄was obviously due to the other oxidants,with a removal rate of 97.37%;3)Microbial population analysis showed that the number of soil microorganisms in the coking site decreased abruptly after KMnO₄treatment,from 10⁸copies/g to 10⁵copies/g,while the other oxidants did not change significantly;4)The microbial diversity at the genus level changed significantly at the liquid-solid ratio of 4:1 and 6:1for the five oxidants,and the relative abundance of various microorganisms capable of degrading PAHs（e.g.,Ralstonia and Acinetobacter etc.）increased significantly in relative abundance.（2）By investigating the effect of surfactant drenching-chemical oxidation technique for the treatment of PAHs,the results showed that 1)Tween 80（TW80）was more effective than triton 100（TX-100）and rhamnolipids in drenching PAHs in soil,with a drenching efficiency of 42.3%for PAHs,which was used in the follow-up experiments;2)When TW80 was used as the drenching agent,it was found that the best single drenching effect was found at a concentration of 6 g/L,a liquid to solid ratio of10:1 and a drenching time of 4 h,reaching 43.5%.After three successive douches,the efficiency ofΣPAHs was 63.3%,and the douche rate increased to 71.2%after five douches;3)TW80 combined with chemical oxidation treatment increased the removal rate of PAHs.After three drenches of TW80,theΣPAHs removal rate increased from63.4%to 78.31%after combined treatment with KMnO₄at 10%mass ratio,which was14.9%higher.After five drenches of TW80 and oxidation with KMnO₄at 10%mass ratio,theΣPAHs removal rate increased from 72.1%to the highest 81.2%after the combined treatment,which increased by 9.1%,and the benzo[a]pyrene removal rate increased from 71.7%to 98.3%,which increased by 26.6%.