Desorption kinetics of polycyclic aromatic hydrocarbons (PAHs) from contaminated soil and the effect of biosurfactant supplementation on the rapidly desorbing fractions

Abstract

There are often two phases in the desorption of polycyclic aromatic hydrocarbons (PAHs): an initial phase of rapid desorption and a subsequent phase of much slower release. By assessing the rapidly desorbing fraction of PAHs, a direct measure of the microbially degradable component of PAH contamination can be obtained and achievable bioremediation performances can be predicted. In this study, microbial biosurfactant produced by a Pseudomonas aeruginosa strain, identified as a lipopeptide by attenuated total reflectance Fourier transform infrared spectroscopy, was investigated for its efficacy in enhancing PAH desorption and mobilization in a spiked soil system. The desorption of pyrene and phenanthrene from the artificially spiked soil was enhanced 3.5 4.0 times at 700 mg L ¡1 lipopeptide amendment than at 150 mg L ¡1 amendment or in the unamended soil. The amount desorbed was generally in direct proportion to the amount of lipopeptide present. Mathematical modelling using a first-order two-compartment model was applied to simulate the process of desorption from the soil in the presence of different concentrations of lipopeptide and to predict the effect of the biosurfactant on the rapidly desorbing fraction. With the increase of supplementation of lipopeptide from 150 to 700 mg L ¡1, the rapidly desorbing fraction, which is generally considered to be the bioavailable fraction, increased from 18% to 73% and from 6% to 51% for phenanthrene and pyrene, respectively. This shows the potential application of the biosurfactant in increasing the bioavailable fraction and enhancing the bioremediation of PAH contaminated media.