Effects of Rhamnolipid Biosurfactants on Removal of Phenanthrene from Soil

Solubilizing agents may enhance remediation of soils contaminated with hydrophobic organic contaminants by diminishing sorption of the contaminants or increasing desorption rates. The effectiveness of rhamnolipid biosurfactants to enhance the removal of sorbed contaminants from soil was determined using column studies. Soil columns were contaminated with phenanthrene and subsequently eluted with electrolyte solution or with electrolyte solution containing 500 mg/L rhamnolipid. For the four soils studied, removal of 50% of the phenanthrene from the soil columns was accomplished in a 2−5-fold shorter time period, and the time required for 90% removal was reduced up to 3.5-fold when elution was performed with the rhamnolipid-containing solution as compared to the treatment without rhamnolipid. The effect of rhamnolipid on the removal of phenanthrene was satisfactorily simulated using independently obtained parameters with a two-component advective−dispersive model accounting for micellar solubilization and admicellar sorption. A more detailed analysis of the system showed that desorption rates of phenanthrene in the presence of 500 mg/L rhamnolipid were higher than predicted on the basis of desorption rate constants of phenanthrene determined in the absence of rhamnolipid. It is concluded that rhamnolipid enhanced the removal of phenanthrene mainly by micellar solubilization and also by influencing sorption kinetics.