Abstract
Experiments were conducted with a two-dimensional flow cell to examine the effect of monorhamnolipid surfactant at sub-CMC concentrations on solubilization of dodecane in porous media under dynamic flow conditions. Quartz sand was used as the porous medium and artificial groundwater was used as the background solution. The effectiveness of the monorhamnolipid was compared to that of SDBS, Triton X-100, and ethanol. The results demonstrated the enhancement of dodecane solubility by monorhamnolipid surfactant at concentrations lower than CMC. The concentrations (50–210 μM) are sufficiently low that they do not cause mobilization of the dodecane. Retention of rhamnolipid in the porous medium and detection of nano-size aggregates in the effluent show that the solubilization is based on a sub-CMC aggregate-formation mechanism, which is significantly stronger than the solubilization caused by the co-solvent effect. The rhamnolipid biosurfactant is more efficient for the solubilization compared to the synthetic surfactants. These results indicate a strategy of employing low concentrations of rhamnolipid for surfactant-enhanced aquifer remediation (SEAR), which may overcome the drawbacks of using surfactants at hyper-CMC concentrations.
Highlights
Experiments were conducted with a two-dimensional flow cell to examine the effect of monorhamnolipid surfactant at sub-critical micelle concentration (CMC) concentrations on solubilization of dodecane in porous media under dynamic flow conditions
The contamination is difficult to remediate due to the hydrophobic nature of these organic compounds, as indicated by low water solubility and strong tendency to partition into organic phases[1,2]
The dodecane concentration in artificial ground water (AGW) is below the detection limit of the gas chromatograph (GC)-flame ionization detector (FID) (0.1 mg/L) during the entire period of the test, which is consistent with the low water solubility of dodecane at this temperature (0.02 μM or 0.003 mg/L)
Summary
Experiments were conducted with a two-dimensional flow cell to examine the effect of monorhamnolipid surfactant at sub-CMC concentrations on solubilization of dodecane in porous media under dynamic flow conditions. The rhamnolipid biosurfactant is more efficient for the solubilization compared to the synthetic surfactants These results indicate a strategy of employing low concentrations of rhamnolipid for surfactant-enhanced aquifer remediation (SEAR), which may overcome the drawbacks of using surfactants at hyper-CMC concentrations. Of surfactant are (1) introduction of large amounts of surfactant into the aquifer, which may cause secondary contamination or other impacts to the system, and (2) potential impact on migration and distribution of NAPLs via mobilization. These drawbacks have significantly limited the application of SEAR technology
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