Research Project Description May 18, 1995 - September 30, 1996 Effects of Surfactants on Bioavailability and Biodegradation of Contaminants in Soils W.P. Inskeep and J.M. Wraith, Montana State University; C.G. Johnston, Mycotech Corporation Goals: This project is designed to improve understanding of fundamental relationships between surfactant chemistry, contaminant solubilization, and subsequent biodegradation rates in soils, while developing novel methods which may be useful in the bioremediation of nonpolar organic compounds in soils. Rationale: During the past decade, much discussion has centered on the unavailability of sorbed compounds to soil microorganisms; it is generally now assumed that desorption and diffusion of bound contaminants to the aqueous phase is required for microbial degradation. Furthermore, with aging, many nonpolar contaminants form irreversibly bound residues which are difficult to extract with nonpolar solvents and are essentially unavailable to indigenous microbial communities or to those added as an inoculum to stimulate biodegradation. In a recent workshop convened to discuss major research needs in bioremediation, the bioavailability of soil bound contaminants was consistently identified as a fundamental limitation in enhancing rates of contaminant biodegradation in soils. One of the strategies for enhancing desorption rates and subsequent biodegradation rates of nonpolar contaminants in soils is the use of surfactants. Approach: A series of contaminant partitioning studies using a wide range of surfactants with varying structures will be performed. Functional relationships between surfactant concentration, surfactant structure, and extent of contaminant solubilized will be established using batch and column studies. Effects of surfactants on subsequent biodegradation rates of phenanthrene, PCP, DDT, and PCB will be studied under batch and column conditions using two representative bioremediation strategies: indigenous microbial populations and addition of white-rot fungi. Degradation rates will be determined under batch and flow conditions in previously uncontaminated soils with and without contaminant aging. In addition, contaminant degradation in soil samples from several field sites contaminated with PCP and polyaromatic hydrocarbons will be compared to controlled laboratory experiments. Status: Investigators have completed additional experiments on the relationship among (i) surfactant solubilization of phenanthrene, aqueous phase surface tension and phenanthrene degradation. They are now conducting experiments on the degradation of phenanthrene during transport conditions in the presence and absence of surfactants and hexadecane. Future research plans include continued column experiments and the study of aging effects as they relate to the effectiveness of surfactants in enhancing degradation and transport of phenanthrene. Data from column experiments will be used for testing transport models in which biodegradation kinetics are coupled to the advective dispersion equation. Investigators also plan to publish two manuscripts. This project is in its second year. Clients/Users: This research will be of interest to members of industry and to the U.S. Department of Defense. Key words: surfactants, bioavailability, biodegradation, nonpolar organic compounds. Return to List