Rhamnolipid morphology and phenanthrene solubility at different pH values

Area of Science:

• Environmental Science
• Biotechnology
• Soil Science

Background:

• Phenanthrene, a polycyclic aromatic hydrocarbon, poses environmental risks.
• Biosurfactants like rhamnolipids are explored for contaminant remediation.
• Understanding factors affecting biosurfactant efficacy is crucial for soil cleanup.

Purpose of the Study:

• To investigate the impact of pH and rhamnolipids on phenanthrene solubility in a sand-water system.
• To elucidate the mechanisms behind pH-dependent changes in phenanthrene solubilization.
• To correlate rhamnolipid aggregate structure with its solubilization capacity.

Main Methods:

• Batch solubilization experiments in a sand-water system.
• Measurement of critical micelle concentrations (CMCs) with and without sand.
• Calculation of sorbed biosurfactant amounts.
• Cryo-transmission electron microscopy (cryo-TEM) for aggregate morphology analysis.

Main Results:

• Highest phenanthrene solubility observed at pH 5 with rhamnolipids.
• Significant decrease in solubility at pH 4 due to increased rhamnolipid sorption to sand.
• Rhamnolipid aggregate morphology transitioned from lamellar sheets to vesicles and then micelles with increasing pH.
• Large, multilamellar vesicles at pH 5 were most effective for phenanthrene solubilization.

Conclusions:

• pH significantly influences rhamnolipid-mediated phenanthrene solubility in soil systems.
• Rhamnolipid sorption to soil particles is a key factor affecting its solubilization efficiency.
• The structural morphology of rhamnolipid aggregates dictates their capacity to solubilize phenanthrene.