Abstract
This study investigated the solubilization capabilities of rhamnolipids biosurfactant and synthetic surfactant mixtures for the application of a mixed surfactant in surfactant-enhanced remediation. The mass ratios between Triton X-100 and rhamnolipids were set at 1:0, 9:1, 3:1, 1:1, 1:3, and 0:1. The ideal critical micelle concentration values of the Triton X-100/rhamnolipids mixture system were higher than that of the theoretical predicted value suggesting the existence of interactions between the two surfactants. Solubilization capabilities were quantified in term of weight solubilization ratio and micellar-water partition coefficient. The highest value of the weight solubilization ratio was detected in the treatment where only Triton X-100 was used. This ratio decreased with the increase in the mass of rhamnolipids in the mixed surfactant systems. The parameters of the interaction between surfactants and the micellar mole fraction in the mixed system have been determined. The factors that influence phenanthrene solubilization, such as pH, ionic strength, and acetic acid concentration have been discussed in the paper. The aqueous solubility of phenanthrene increased linearly with the total surfactant concentration in all treatments. The mixed rhamnolipids and synthetic surfactants showed synergistic behavior and enhanced the solubilization capabilities of the mixture, which would extend the rhamnolipids application.
Highlights
Hydrophobic organic compounds are commonly found in soil and groundwater in industrialized areas
When the surfactant concentration is above its critical micelle concentration (CMC), the micelles with hydrophilic surfaces and lipophilic core can dramatically improve the solubility of hydrophobic organic compounds in the water phase, thereby further promoting the desorption of contaminants from the soil
The nonionic surfactant Triton X-100 (TX100) was with purity higher than 98%, and phenanthrene was with purity greater than 97%, both substances were obtained from Tokyo Chemical Industry Co., Ltd., Tokyo, Japan
Summary
Hydrophobic organic compounds are commonly found in soil and groundwater in industrialized areas. Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds composed of two or more aromatic rings fused with carbon and hydrogen atoms [1] Due to their poor aqueous solubility, high hydrophobicity and strong sorption to soil particles or sediment matrix, PAHs are difficult to recover from the subsurface system and represent a long-term source of soil and aquifer contamination [2,3]. Based on this different principle, various remediation methods for PAH-contaminated sites have been proposed [4,5,6].
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