Sorption And Transport Of Gasoline Components In Typical Porous Media

Organic pollutants, especially the petroleum and its products, have caused serious pollution problems in groundwater and soils. At a gasoline contaminated site, it is important to study the sorption and transport of organic pollutants in vadose zone. In this paper, typical organic pollutants in gasoline such as benzene, toluene, methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) were chosen as the target pollutants. The simulation of sorption and transport of organic pollutants in typical porous media were studied by static batch experiments and dynamic column experiments. The research results were summarized as follows:(1) The sorption of gasoline additive ETBE to six typical Chinese reference soils can be well described by linear sorption isotherms. The average lgKoc value of ETBE was 1.993 L·kg-1. The sorption process of ETBE to soils was exothermic, equilibrium sorption capacity decreased with increasing temperature. The sorption enthalpy change was in a range of -8 to -32 kJ·mol^-1, which showed that ETBE sorption was affected by variety forces.The sorption capacity of ETBE to soil was reduced with the increase of ionic strength in solution, and the soil samples were affected differently by the change of ionic strength.(2) The breakthrough curves of organic contaminants transported in the sand or humic acid column were steep in the left side and relatively flat, with a long tail in the right side. This is because the organic contaminants were affected by sorption/desorption non-equilibrium in the transport process. The competitive sorption was observed when more organic components were added in the mixture. The tailing effect was more significant for the transport of organic components in the humic acid column.(3) Organic components leaching from humic acid column were in the order of MTBE, benzene and toluene. This is because the sorption of toluene to humic acid was the strongest, and MTBE was the weakest, and benzene was in the center. This indicated that the separation of organic components from a mixture can be expected if the vadose zone is thick enough and there is certain amount of organic carbon content (e.g., >0.1% in weight) in the porous media. The leaching rate of benzene and toluene became faster, and the leaching concentration increased if the CaCl2 concentration increased in the solution. The time of peak of breakthrough curve was slightly affected by the change of initial concentration of organic contaminant, which also changed the area of breakthrough curve.(4) The transport of organic pollutants in soil columns can be well simulated by two-site model with CXTFIT. With the increase of organic components, the non-equilibrium sorption process in the column filled with humic acids became more significant. As a result of the model fitted, the Kd value of MTBE, benzene and toluene in humic acid column was 3.71 L·kg^-1, 4.09 L·kg^-1 and 13.53 L·kg^-1, and the lgKoc value was 2.05 L·kg^-1, 2.09 L·kg^-1and 2.61 L·kg^-1.