Rhamnolipid morphology and phenanthrene solubility at different pH values

Kyung Hee Shin, Kyoung Woong Kim, Ju Yong Kim, Kyung Eun Lee, Sung Sik Han

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)


The effect of pH and rhamnolipids on the solubility of phenanthrene was investigated in a sand-water system. Batch phenanthrene solubilization experiments in this system showed that the highest phenanthrene solubility occurred at pH 5 in the presence of 240 and 150 mg L-1 rhamnolipids. As the pH was increased from 5 to 7, the apparent solubility of phenanthrene decreased and then stabilized from pH 7 to 8. At pH 4, a dramatic decrease in phenanthrene solubility was observed. This result is in contrast to previous findings obtained in an aqueous system without soil particles. To investigate the reason for this decrease, the critical micelle concentrations (CMCs) were measured in the presence or absence of sand particles, and the maximum amount of sorbed biosurfactant at each pH was calculated based on the differences of the two CMC values. More thamnolipid molecules were lost by the sorption into sand particles at pH 4 than at other pH values; this explains the dramatic decrease of solubility at pH 4 in the sand-water system. To confirm the explanation for the different solubilizing capacity that results from the structural change of biosurfactant aggregate, cryo-transmission electron microscopy was used. Micrographs showed that the rhamnolipid morphology changed from large lamellar sheets, to vesicle, and then to micelle as the pH increased. The large and multilamellar vesicles at pH 5 were considered to be the most effective structure for the solubilization of phenanthrene.

Original languageEnglish
Pages (from-to)509-514
Number of pages6
JournalJournal of Environmental Quality
Issue number2
Publication statusPublished - 2008 Mar

ASJC Scopus subject areas

  • Environmental Engineering
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution
  • Management, Monitoring, Policy and Law


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