Abstract

An evaluation of the efficiency of rhamnolipids (biosurfactants) used in electrokinetic remediation of soil contaminated with phenanthrene was presented. Bench scale tests were conducted using four experimental series in order to determine the feasibility and mechanisms of biosurfactant-enhanced phenanthrene removal from mica soil. The bench-scale study showed that bacteria ( Pseudomonas aeruginosa ) could survive to a certain extent when a low voltage DC electric field was applied. In addition, it was found that these bacteria could produce rhamnolipids in the clayey soil under the electric field. Experimental results showed that during the 14-day experimental period, phenanthrene was partially removed. The highest removal was achieved in the cathode area (85% removal). These promising results are an indication that this process can be applied as an in-situ enhancement technique for improving the efficiency of electrokinetic soil remediation. It was proved that bio-micelles, formed due to the introduction of ex-situ produced biosurfactants, could be transported to the electrode areas due to both electroosmotic and electrophoretic phenomena. It also indicated that the electrokinetic introduction of engineering produced biosurfactants into the contaminated clayey soil was feasible. The mechanisms involved in the formation of bio-micelles, were described in a bench-scale test using Fourier Transform Infrared Spectrometers (FTIR) and Atomic Force Microscopy (AFM). Results permitted to describe that the transformation of bio-micelles kinetically changed under the electric field. It was found that spherical, bilayer, and multi-lamellar micelles were formed at different phases of the electrokinetic experiment. The presence of clayey particles and the electric field attenuated and deferred the formation of bio-micelles. Knowledge of the kinetics of bio-micelle formation process are paramount to the accurate application of biosurfactants in electrokinetic remediation of PAH contaminated clayey soil. The effort to desorb and solubilize phenanthrene, by promoting the formation of bilayer bio-micelles, became successful in bench-scale electrokinetic experiments. In addition, the successful ex-situ production of biosurfactants can be used on an industrial scale for electrokinetic soil remediation. The above-described developments can be applied as a new in-situ remediation technology: bio-electrokinetics.