Facilitated transport of a PAH mixture by a rhamnolipid biosurfactant in porous silica matrices

Abstract

Ž. The facilitated transport of a mixture of three polycyclic aromatic hydrocarbons PAH Ž . naphthalene, fluorene, and phenanthrene by a rhamnolipid biosurfactant was determined with silica, octadecyl-coated silica, and humic acid-coated silica columns. The retardation factors for Ž . the contaminants in the absence of rhamnolipid ranged from 1.8 naphthalene with silica to 708 Ž . phenanthrene with octadecyl-coated silica . The retardation factors for phenanthrene were up to eightfold lower in the presence of 500 mgrl rhamnolipid compared to the situation where no rhamnolipid was present. The facilitated transport of the contaminants in the presence of rhamnolipid could be predicted by accounting for sorption, solubilization and admicellar sorption. In the octadecyl-coated matrix, transport of fluorene and phenanthrene was enhanced even in the Ž . presence of sub-micellar solution of rhamnolipid 20 mgrl , showing that adsorbed surfactant reduced the affinity of these compounds to this stationary phase. Linear free-energy relations Ž . LFERs indicated that the matrix-water, micelle-water, and admicelle-water partitioning constants for PAH were correlated with their 1-octanol-water partitioning constants. These correlations were used to simulate the facilitated transport of contaminants of varying hydrophobicity by a surfactant. It was concluded that surfactants have the greatest transport facilitating effect on the more hydrophobic components. The effectiveness of surfactants for enhancing removal of the less Ž . hydrophobic compounds log K -3.4 may considerably be reduced due to admicellar sorption.

Rhamnolipid Stimulates Uptake of Hydrophobic Compounds by Pseudomonas aeruginosa

“…The biosurfactant did not facilitate just one of the two steps in equation 1 and leave the other unaffected, since a good fit could not be obtained when using the values for k 1 and k Ϫ1 or for k 2 and k Ϫ2 from the experiment without rhamnolipid and accounting for solubilization of NPN by rhamnolipid by using rhamnolipid-water partitioning constants for NPN that were estimated from a linear free-energy relationship (27). Thus, it may be that the uptake process in the presence of rhamnolipid becomes more complex than suggested by equation 1, e.g., due to the direct uptake of NPN solubilized by rhamnolipid.…”

Surfactant-enhanced remediation of organic contaminated soil and water

“…The removal of HOCs from soil matrix in presence of surfactants is a complex process, since the surfactants first remove the HOCs from the soil and at the same time surfactants are also adsorbed on the soil surfaces and change the surface characteristic, as a result, some times HOCs are readsorbed on the soil surface. Due to the complex nature of the process many researchers have studied on removal efficiency of the organic compounds from the soil matrix using different surfactants like single synthetic [28,95,105,[257][258][259][260][261][262][263][264], mixture of synthetic [105,261,264,265], and biosurfactants [28,193,[266][267][268] to improve the basic understanding.…”

Structural and physiochemical characterization of rhamnolipids produced by Acinetobacter calcoaceticus, Enterobacter asburiae and Pseudomonas aeruginosa in single strain and mixed cultures

“…Zhang et al (1997) reported that solubilization of phenanthrene in absence of biosurfactant was 0.69 mg/l whereas in the presence of purified rhamnolipids from P. aeruginosa ATCC 9027 (0.30-0.35 mmol/l) the solubilization of phenanthrene increased up to 35 mg/l. Study by Noordman et al (2000) reported that rhamnolipids concentration below its CMC did not display solubilization activity for PAHs.…”