| Polycyclic Aromatic Hydrocarbons(PAHs)are typical persistent organic pollutants in the soil of petrochemical contaminated sites.In recent years,the contamination of soil and groundwater in the vadose zone caused by oil spills and production process emissions from petrochemical contaminated sites poses a serious risk to the surrounding environment and human health safety.The migration simulation of PAHs in the soil vadose zone can help to identify the source-sink relationship of soil contamination in petrochemical contaminated sites and provide a reference for the construction of a risk control system for petrochemical sites,and the lateral percolation in the capillary water zone has an important influence on the water flow and solute transport in the vadose zone,but related studies on PAHs are rarely reported.In this study,the migration patterns of PAHs naphthalene,phenanthrene,and benzo[a]anthracene in the soil in the inclusion zone were investigated based on the HYDRUS model to determine the relevant soil and solute parameters,combined with indoor sandbox experiments,and the HYDRUS-3D model was used to predict and simulate the migration process of benzo[a]anthracene in the soil medium at the petrochemical contaminated site in Wuhan,with a view to providing The main results obtained are as follows.The main research results obtained are as follows:1.The changes of soil sorption parameters of PAHs under different soil properties with different molecular weight PAHs were studied by batch experiments using soils with different textures and different organic matter contents.The results showed that the adsorption processes of naphthalene and phenanthrene in soil were consistent with the quasi-secondary adsorption kinetic model,while benzo[a]anthracene could be fitted with both the quasi-first-order and quasi-secondary adsorption kinetic models.Compared with sandy soils,the sorption rates of PAHs in powdered loamy soils were fast and large.For example,the adsorption equilibrium of naphthalene and phenanthrene was reached around3 h with the adsorption amounts of 34.03μg/g and 38.14μg/g,respectively,and that of benzo[a]anthracene was reached around 1 h with the adsorption amount of 139.78μg/g,while the adsorption equilibrium of naphthalene,phenanthrene and benzo[a]anthracene was reached around 4 h with the adsorption amounts of 8.08μg/g,10.06μg/g and 12.38μg/g,respectively,in the sandy soil.The isothermal adsorption curves in soil were consistent with the linear isothermal adsorption model for naphthalene,Freundlich adsorption model for phenanthrene,and linear adsorption model for benzo[a]anthracene.2.The simulated tracers and solute transport processes of naphthalene,phenanthrene and benzo[a]anthracene in the soil vadose zone were analyzed based on the HYDRUS-2D model combined with indoor sandbox tests.The mismatch coefficients of tracers were above 0.9.The solute transport model of PAHs in chalky loam was a two-point chemical non-equilibrium model,and the best fit was obtained for benzo[a]anthracene,followed by phenanthrene and naphthalene,with mismatch coefficients of 0.904,0.960 and 0.989,respectively.Naphthalene is easy to migrate in the soil and has a wide migration range,migrating to 24 cm in length and 15 cm in depth within 45 d with a hindrance factor of R=3.25.The lateral migration in the capillary zone is not obvious and the adsorption in the soil is based on kinetic point adsorption.The adsorption in the soil was mainly kinetic point adsorption,which accounted for 95%of the total.The migration of phenanthrene to a length of 12 cm and a depth of 9 cm within 45 d was consistent with that of the tracer,and the lateral percolation near the capillary zone was obvious.Benzo[a]anthracene was difficult to migrate in the soil,and the migration range was small,migrating to 5 cm in length and 3 cm in depth within 45 d.The migration lag time was long,and the hysteresis factor R=26.42.The proportions of transient equilibrium adsorption sites and kinetic adsorption sites in the two-point adsorption model were similar,51%and 49%,respectively.3.Based on the HYDRUS-3D model,the migration process of benzo[a]anthracene leaking into the soil vadose zone of the petrochemical contaminated site was predicted and simulated.The results showed that the simulation results were in good agreement with the measured values at the sampling sites,with the root mean square error RMSE=0.255mg/kg and the relative error RE mean 0.120.The solute transport model of benzo[a]anthracene in soil was a two-point chemical nonequilibrium model.The simulation results showed that,considering the shallow groundwater depth of about 2.5 m and rainfall infiltration at the petrochemical site,the migration range of benzo[a]anthracene was about 700 m~2 at the surface and about 3 m at the soil profile in 45 years,and the maximum benzo[a]anthracene content was 11.22 mg/kg at the soil point 1 m from the surface near the source in the 20th year.In the unsaturated zone near the surface of the soil,the dispersion rate was fast,while in the capillary water zone,the dispersion rate slowed down.The migration process was mainly influenced by the solute reaction parameter sorption coefficient K_d.The model solute reaction parameters f,K_d,αand solute transport parameters D_L and D_T were ranked from largest to smallest sensitivity as K_d>f>αand D_L>D_T,respectively.In addition,it was found that the migration process of PAHs in the soil in the inclusion zone could be fitted based on the two-point chemical nonequilibrium model in the HYDRUS model,and the more strongly adsorbed PAHs were better fitted,and the lower-ring PAHs were less adsorbed and more migrated deeper into the soil than the medium-ring PAHs.The capillary water zone has a lateral percolation feature,which has a certain effect on blocking pollutants from entering groundwater,but there is still a risk that the more strongly adsorbed benzo[a]anthracene will enter shallow groundwater in practical petrochemical site applications. |
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