Superfund Research Program
Use of Microbial Surfactants for Enhanced Removal of Metals from Contaminated Soils
Presently there is great interest in developing novel technologies that expedite the remediation of metal contaminated soils because many of the conventional technologies have proven to be both time consuming and expensive. In response to the need for innovative remediation technologies that effectively clean up metal contaminated soils, researchers at the University of Arizona have been investigating the use of microbial surfactants (biosurfactants) for enhancing the removal of soil-bound metals. Because of their detergent-like properties, microbial surfactants may have the potential to impact the factors that cause the removal of metals from soil to be so difficult.
Initial experiments demonstrated that microbial surfactants known as rhamnolipids, which are secreted extracellularly by Pseudomonas aeruginosa, can complex cadmium, lead and zinc in solution and are able to remove such metals from soil. More recent studies have focussed on understanding the behavior of the rhamnolipids in soil. It was discovered that the ionic strength of the rhamnolipid solution applied to the soil is extremely important in determining the surfactant's effectiveness. With this knowledge it has been possible to scale up from batch experiments to column studies that more closely mimic field conditions. Extensive laboratory column experiments have been carried out with cadmium and they demonstrated that up to 80% of cadmium from several soil types can be successfully removed using microbial surfactant flushing. This success in understanding microbial surfactant flushing at the laboratory scale means that in the coming year efforts will be made to scale this technology up to the intermediate and field scales.
These results are significant in that they suggest that current soil washing strategies can be greatly enhanced by the use of microbial surfactants to increase the desorption of soil-bound metals and facilitate their transport through the soil. This research is also noteworthy for proposing an environmentally sound and cost effective remediation technology that seeks to take advantage of a naturally occurring process, biosurfactant production, to aid in overcoming the factors which make metals resistant to remediation. The potential impact of these recent accomplishments is that clean-up costs of metal contaminated soils may be reduced significantly by using microbial surfactants without causing negative side effects on the environment.
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To learn more about this research, please refer to the following sources:
- Torrens JL, Herman DC, Maier RM. 1998. Biosurfactant (rhamnolipid) sorption and the impact on rhamnolipid-facilitated removal of cadmium from various soils under saturated flow conditions. Environ Sci Technol 32(6):776-781.
- Herman DC, Artiola JF, Maier RM. 1996. Removal of metals from soil by an anionic rhamnolipid biosurfactant. In: Proceedings of the 95th General American Society for Microbiology Meeting, Washington, DC.
- Maier RM. 1995. Biosurfactant-facilitated remediation of metal-contaminated soils. Environ Health Perspect 103(1):59-62. PMID:7621801
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