BIOAVAILABILITY OF MIXTURES OF PAHS PARTITIONED INTO THE MICELLAR PHASE OF A NONIONIC SURFACTANT

Recent work has shown that a fraction of a contaminant solubilized in the micellar phase of some nonionic surfactants is directly available for biodegradation, meaning that the contaminant can be transferred di rectly from the core of the micelle to cell without having to transfer to the water phase first. This study extends the understanding of the bioavailability of the micellar phase for a single compound to a mult icomponent system of contaminants. Biodegradation experiments were con ducted with binary and ternary mixtures of naphthalene, phenanthrene, and pyrene in the presence of a nonionic surfactant, Triton X-100, A m ixed bacterial culture, isolated and enriched from a PAH-contaminated soil at the Wurstsmith Air Force Base, MI, was used for the biodegrada tion experiments. In the absence of the surfactant and at surfactant c oncentrations below cmc,the multisubstrate Monod kinetics adequately s imulated the biodegradation kinetics of the binary and ternary mixture s. In the multicomponent systems, as in single solute systems, the sol utes in the micelle were found to be directly bioavailable, and the bi oavailability of each compound in the micellar phase decreased with in creasing surfactant concentration. For a given surfactant concentratio n, the bioavailability was higher for the lower molecular weight PAHs. There was little difference in the bioavailability of the same compou nd as a single solute or in different binary and ternary mixtures. To predict the bioavailability of the micellar phase substrates, a mass t ransfer-based model was formulated that describes the transfer of subs trate from the micellar phase to the microorganisms. The predictions m atched the experimental observations well, indicating the validity of the model and its potential for applications in remediation designs.