| Polycyclic aromatic hydrocarbons(PAHs)are typical persistent organic pollutants in the soil of petrochemical contaminated sites,which exhibit serious hazards to human health and the ecological environment around the site.The study of the migration and transformation process of polycyclic aromatic hydrocarbons in soil media is of great significance to the identification of soil pollution source-sink relationships in petrochemical contaminated sites and the construction of risk management and control systems.This study carried out the longitudinal leaching and runoff simulation experiments of PAHs to explore the influence of factors such as soil total organic carbon(TOC),leaching water and temperature on the migration behavior of PAHs in the soils.And also,the PAHs biodegradation experiment was carried out to indentify the PAHs degrading bacteria from a petrochemical site.The main results are as follows:(1)The TOC content of the four soil groups selected in this paper were 0.83 %(S1),0.56 %(S2),1.15 %(H1),and 2.43 %(H2),respectively.After leaching,the residual amount of pollutants in the 0～5cm surface soil was H2>H1>S1>S2>S1 in order.The lower the TOC content,the higher the migration amount of PAHs in the topsoil.Soil TOC was an important factor that affected the migration of PAHs in soil.Soils with low TOC content had a greater risk of PAHs migration.Leaching time(leaching volume)could also affect the migration behavior of PAHs in the soil,and the initial stage of leaching had a greater impact on the vertical migration of PAHs.The migration characteristics of PAHs with different rings were obviously different.PAHs with less rings were more likely to migrate downward with the leaching solution,and the migration with more rings was smaller.The leaching amount had a more significant impact on the migration of PAHs with less rings.Leaching had a significant impact on the PAHs source resolution parameters selected in this experiment.After leaching,the value of low molecular weight(LMW)PAHs/high molecular weight(HMW)PAHs decreased significantly.With the progress of leaching,LMW/HMW continued to decrease.(2)In the topsoil runoff experiment,the content of PAHs did not show a correlation with the TOC value.Studies showed that the size of soil particles had an important influence on the migration of PAHs,and more PAHs were likely to be contained in fine silt.The soil powder content of column S1 was the highest which resulted the highest residual amount of PAHs.Column H1 had the highest sand content,and PAHs were more likely to be lost.The temperature influence test showed that the residual amount of PAHs in the soil column decreased with the increase of temperature.Study results showed that the residual amount of PAHs was the highest when the leaching rate was 1.2 ml/min,and the loss of PAHs was greater when the leaching rate was lower or higher.The concentration of PAHs was predicted using Soil Fug model,and the results were lower than the measured values.(3)The sequencing results showed that the degrading bacteria of naphthalene,phenanthrene and benzo[a]pyrene selected in this study were Achromobacter sp,Arthrobacter sp and Pseudomonas sp.Under the conditions set in this experiment,increasing the temperature could accelerate the biodegradation of PAHs.At 32 days,the removal rates of naphthalene,phenanthrene,and benzo[a]pyrene were 99.7 %、97.3 % and49.1 % at 25 ℃;97.7 %、89.4 % and 47.4 % at 15 ℃;92.2 %、89.4 % and 53.2 % at 5 ℃ respectively.The biodegradation of PAHs mainly occured in the early stage of degradation,and the results showed that PAHs with less rings were more easily degraded,while the bioavailability of benzo[a]pyrene was lower.The first-order kinetic equation could describe the biodegradation process of PAHs nicely. |
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