Sorption Isotherm of Rhamnolipids onto Sediment: Effect of Different Rhamnolipidic Type and Sediment Properties

Microbe produced rhamnolipids are often mixtures containing multicomponent homologues. To understanding the rhamnolipid sorption affected by its homologue compositions is of considerable importance to its application for environmental restorations, including rhamnolipids pump-and-treat for polluted groundwater, rhamnolipids flushing to mobilize hydrophobic contaminants, as well as effects of contaminants transfer from solid to aqueous phases by such biosurfactants. In this study, the adsorption of two representative rhamnolipidic homologue fractions, RL-F1 and RL-F2, which were separated and purified from the crude extracts by Pseudomonas aeruginosa mutant strain MIG-N146, onto three sediments was comparatively investigated. Application of the Langmuir and multi-interaction isotherm models indicates that the rhamnolipidic type and the degree of their hydrophobicity created predominant influences on adsorbability. The rhamnolipid adsorption behaviors showed larger tendency to be the S-shaped multi-interaction sorption isotherm, which was mostly driven by hydrophobic interactions between the rhamnolipidic molecules. RL-F1 fraction exhibited generally much higher adsorption plateaus than that for RL-F2. It was also found that the organic carbon and clay contents were important sediment-parameters affecting sorption. These results giving insight into the sorption behavior influenced by different rhamnolipidic type and sediment properties may provide useful information for rhamnolipid application in environmental remediations.