Goal: The goal of this research is to gain an understanding that will allow us to select surfactants and their concentration to enhance the solubilization and biodegradation of residual PAHs (i.e. phenanthrene) in contaminated soils. Specifically we want to determine the following:
Rationale: Bioavailability of low-solubility hydrocarbons in soils is limited by their sorption onto the soil matrix. Surfactants above their critical micelle concentration enhance desorption of these hydrocarbons, and we know that the fraction of PAHs dissolved in the micelles can be bioavailable depending on the surfactant structure and its concentration in the aqueous phase. The surfactant/pollutant behavior in soils is complex, since surfactants may solubilize the pollutants, but may also sorb onto the soil, providing an additional phase that increases sorption, and may also have an oxygen demand. Therefore, even though surfactant-enhanced bioremediation of contaminated soils is a promising technique, it will only work if surfactant and their dose are selected carefully with considerations of site-specific conditions.
Approach: This research consists of a series of experiments and their mathematical/thermodynamical interpretation. Biodegradation experiments are conducted in 25 ml reaction vessels, that contain in their headspace a cup in which the carbon dioxide that evolves during the biodegradation can be absorbed into a KOH solution. Stoppers are lined with aluminum foil to minimize losses due to sorption from the headspace. A solution (15 ml) containing phenanthrene, seed and surfactant is placed in each reaction vessel, and 0.25 ml of 1N KOH is placed in each head-space cup. Reaction vessels are sealed and placed on a magnetic stirrer to mix the reactant continuously. At the end of the desired reaction time, concentrated sulfuric acid is introduced into the vessels to stop the reaction and to release any dissolved carbon dioxide from the aqueous solution. After an additional 6 to 8 hour period, samples from the KOH cup and reaction chamber are analyzed for radioactivity, to determine the mass of carbon dioxide produced and the loss of phenanthrene respectively. These experiments are being conducted in the presence and absence of soils, and for a series of different non-ionic surfactants and surfactantconcentrations.
Status: A model describing the micellar bioavailability as a function of the surfactant dose has been developed. A series of surfactants are being screened which will allow us to generalize the model describing the bioavailability.
Clients/Users: oil remediation for sites containing coal tars.
Publications:
Guha, S., and P.R. Jaffi, "The Bioavailability of Hydrophobic
Compounds Partitioned into the Micellar Phase of Nonionic
Surfactants," Environmental Science and Technology, Vol. 30,
No. 4, 1996, pp. 1382-1391.