Relationship Between Micellar and Hemi-Micellar Processes and the Bioavailability of Surfactant-Solubilized Hydrophobic Organic Compounds
Derick G. Brown, Department of Civil & Environmental Engineering, Lehigh University, 13 East Packer Avenue, Bethlehem, PA 18015
Surfactants are able to enhance the apparent aqueous concentration of hydrophobic organic compounds (HOC's) through partitioning of the HOC's within surfactant micelles. Many studies have been performed that examined if this effect can result in an enhancement in the biodegradation rate of HOC's. The results have been mixed and the conditions under which enhanced biodegradation may occur remain unknown. One key study demonstrated that a fraction (f) of micellar-phase HOC is directly bioavailable to bacterial cells and a theoretical model for f was provided that gave a good match to a subset of the experimental results, but could not accurately represent all of the surfactants tested. Here, the results of a recent study on surfactant sorption onto the bacterial cell surface are used to describe hemi-micelle formation on the cell surface, and this process is incorporated into the pathway describing micellar HOC bioavailability. The revised model is validated against HOC bioavailability data for five different C12Ey surfactants and it is shown that this model is able to replicate the complete dataset, including that of C12E23 which eluded the original model. The results indicate that surfactant sorption and hemi-micelle formation are important processes governing surfactant-enhanced bioavailability, and these processes are placed into context with other important considerations for surfactant-enhanced biodegradation of HOC's.