Selection of a biosurfactant for a treatment for soils impacted by Polycyclic Aromatic Hydrocarbons (PAHs)
Résumé
Background/Objectives: Former industrial sites contaminated with Polycyclic Aromatic Hydrocarbons (PAHs) are an environmental and human health concern in Europe. These sites, often former gasworks and coke factories, are close to or are nowadays part of urban areas and are persistent sources of pollution that have to be cleaned. Bioremediation of PAHs in pore water and soils is possible and had already been achieved but is inhibited by the low solubility of such molecules, which reduces their bioavailability. Surfactants can enhance the apparent solubility of hydrophobic compounds, like PAHs, entrapping them by the formation of micelles. Chemically-produced surfactants, widely used in soil remediation (i.e. soil washing techniques, etc.) are impaired by their low biocompatibility. Using biosurfactants, produced by bacteria, can improve this biocompatibility and then enhance PAHs bioavailability.
The objective of this project is to treat an industrial soil impacted by PAH with biosurfactant washing and biodegradation at the same time.
Approach/Activities The first step focuses on the biosurfactant production and optimization at lab scale. The optimal balance parameters have been selected to improve bacterial growth: carbon sources, mineral nutrients, oxygen supply and temperature. PAHs biodegradation trials were performed with contaminated water and contaminated soil samples. Biosurfactant injection, carbon source injection, and several nutrient injection techniques and balance were achieved. Scale-up from lab scale to bioreactor production of biosurfactant had been successful. The extraction and purification of the produced biosurfactant allowed to characterize it.
The second step concentrates on the use of the produced biosurfactant for the desorption of PAHs in soil. Tests of injection in columns (constituted of sand and sand + clay) had been made, using the biosurfactant and commercial surfactants to confront them.
Results/Lessons learned: From our soil samples, a biosurfactant-producing isolate was selected. This isolate can produce biosurfactant using soluble and insoluble carbon sources, even in rich culture medium. The nutrient balance determines the success of the production of biosurfactant. Biodegradation trials have already proved the high potential of bacterial strains for their ability to produce biosurfactant, which pushes the PAHs up to micellar state. After a first scaling up in biosurfactant production in 6L-biorectors, the column injection tests of the
biosurfactant show a high potentiality of the product to be used on a soil washing method by a low sorption in the soil and high desorption capacity of the pollutants.
During the final step of this work, those lab trials will be extended to an in situ pilot treatment on an industrial site.