Study On Migration Behavior Of Low Concentration Surfactant In Natural Porous Media

Due to wide production and use of petroleum products,e.g.,hydrocarbons and their derivatives,soil and groundwater have been seriously contaminated by these chemicals with a characteristic of low aqueous solubilities and high interfacial tensions(IFT)between water and organic phase.Inasmuch as the surfactants are amphiphilic compounds with both hydrophobic and hydrophilic moieties simultaneously in the molecules and possess surfaceor interface-related properties,they are increasingly used to enhance the remediation of hydrocarbons contaminated soil and groundwater.When the surfactants and hydrocarbons are in contacted during the remediation process,mobilization and solubilization are two main mechanisms of surfactant-enhanced remediation.The first mechanism is the use of surfactants to decrease the IFT between hydrocarbons and water,which in turn helps mobilization and ultimate recovery of hydrocarbons.The other mechanism is the use of solubilization properties of surfactants to enhance the bioavailability of hydrocarbons,and as a result improve their biodegradation.The physiochemical properties of surfactants,i.e.solubilization and mobilization,enable it a potential to enhance the removal of hydrocarbons contaminants,however,an outstanding performance in remediation process also depends on the adsorption and transport behavior of surfactants in soil porous media.In addition,some recent evidences have found that low concentration of surfactants can achieve solubilization to some hydrocarbons(e.g.,hexadecane and dodecane),which avoids the drawbacks associated with the use of high concentration of surfactants.In this paper,the transport of low concentration of sodium dodecyl benzene sulfonate(SDBS)in three different porous media,e.g.,glass beads,quartz sands and soil,was investigated by using one-dimensional column experiments.The uniformity coefficients and mean diameters of glass beads,quartz sands and natural soil were 1.0,1.1,2.4 and 1.16 mm,0.35 mm,0.23 mm,respectively,which were distinctly different.The results showed that the properties of porous media had an obvious effect on the transport of SDBS.And the retardation phenomenon in the natural soil was the most distinct with a retardation coefficient3.45,which was much greater than it in glass beads(1.11)and quartz sands(1.33).With the existing of non-aqueous phase liquids(NAPLs)in the porous media forming a free liquid,the retardation coefficient would be obviously increased since the formed free liquid could provide more additional liquid-liquid adsorption interface with large adsorption capacity.The above-mentioned results indicated that the complexity of composition,particle size and heterogeneity of porous media and the presence of NAPLs had a distinct effect on surfactant transport in porous media.These obtained results are of significance for the application ofsurfactants in the remediation of hydrocarbons contaminated soil and groundwater.