Distribution And Migration Characteristics Of Petroleum Hydrocarbon Components In Soil And Groundwater Environment

The components of petroleum hydrocarbon pollutants are complex with different physical and chemical properties,and their equibrium distributions in soil-water system varies.In this study,n-dodecane,phenanthrene and phenol were selected as the representative components of aliphatic,aromatic,and heteroatom-containing compounds.The distribution mechanism and effect factors in the coexistence system of n-Dodecane,Phenanthrene and Phenol in the soils of southern China were studied by batch-balance experiments.Furthermore,an indoor simulation test was conducted to explore the characteristics of the dissolution and release of residual pollutants in saturated zone,aming at providing standards and references for contaminated site investigation,risk assessment and rehabilitation.This study has the following new understandings and conclusions:(1)This paper has developed the simultaneous determination of n-Dodecane,Phenanthrene and Phenol in water sample by gas chromatography-mass spectrometry.The method showed good linearity,fine precision,and reasonable detection limit.The results have application and reference value for the detection of petroleum hydrocarbon contaminants.(2)The results show that the adsorption of the three contaminants in soil can be well described by the second-order kinetic equation,with the adsorption rate of n-Dodecane>Phenanthrene>Phenol.The adsorption strength of three pollutants in soil in the coexisting system are related to the hydrophobicity of the pollutants.The order of adsorption strength is:n-dodecane>phenanthrene>phenol.The desorption kinetics test showed that the soil had different residual levels of the three petroleum hydrocarbon components,and there was a possibility of slow desorption that might cause pollution.(3)When the initial concentrations of dodecane,phenanthrene,and phenol in the coexistent system were in the range of 0.01-0.2 ppm,0.05-1 ppm,and 0.5-10 ppm,respectively,the adsorption isotherms of n-Dodecane and Phenol can be well fitted by Freundlish isotherm equation,while the Langmuir isotherm equation can be employed for the fitting of the adsorption isotherms of Phenanthrene.Moreover,the adsorption of n-dodecane and phenanthrene in the soil is a spontaneous exothermic process,whereas the adsorption of phenol is a spontaneous endothermic process,and the adsorption of soil to the three contaminants is dominated by chemical adsorption.(4)The balance distribution of n-dodecane in soil-water system and soil organic matter content is in positive correlation with the organic matter content in the soil,and the correlation coefficient was 0.94 and 0.85.But there was no significant correlation between the balanced distribution of phenol in the soil-water system and soil organic matter content(R~2=0.31).The order of n-dodecane adsorbed by soils in different particle size is:silt>clay>fine sand>coarse sand,the order of phenanthrene adsorption is:silt>fine sand>clay>coarse sand,and that of phenol adsorption is:clay>silt>fine sand>coarse sand.The influence of soil particle size for the balance distribution of n-dodecane is not significant,but the silt and fine sands had strong adsorption to phenanthrene.Phenol can easily interacts with the minerals in the soil,especially clay minerals or clay components during the adsorption process.(5)The simulation test of the dissolution and release of n-dodecane,phenanthrene and phenol in the aquifer zone was run for one month.Due to the differences of the hydrophobicity between the pollutants,the result shows that the cumulative dissolution rate of each residual component is phenol(2.90%~10.41%)>phenanthrene(0.03%~0.10%)>n-dodecane(0.00030%~0.01%).The release rate of residual phenanthrene in the soil was not found to have a decreasing trend,so a longer period of observation was required.The effect of soil bulk density on the dissolution and release of the three pollutant components varies with the soil texture.When the soil bulk density changes,there may be differences in the pore structure changes in different texture soils,thus affecting the release of pollutants;Under a small flow rate(1.0 cm/d),soil texture has a significant effect on the dissolution and release of weak hydrophobic pollutants.When assessing the effect of different soil textures on the dissolution and release of pollutants,the impact of the hydrophobicity of the pollutants and the groundwater flow rate must be considered;When discussing the influence of groundwater flow rate on the dissolution and release of pollutants,the influence of the hydrophobicity of pollutants must be considered.In this study,under the higher flow rate(1.5cm/d),the weak hydrophobic components release more.This study recommends that in the process of investigation,assessment and remediation of petroleum hydrocarbon contaminated sites,the composition of pollutants and their properties,the soil texture,the pore structure and the groundwater flow rate need to be sufficiently collect.In the study of the environmental behavior of petroleum hydrocarbon pollutants in soil-water systems,the interaction of the above factors should be considered.