The apparent solubility of polycyclic aromatic hydrocarbon compounds such as phenanthrene can be increased in the presence of surfactants above their critical micelle concentration. A fraction of the phenanthrene partitioned into the micellar phase of some nonionic surfactants can be directly bioavailable to phenanthrene-degrading microorganisms. A model describing the biodegradation of the directly bioavailable micellar-phase substrate is presented. The hypothesis on which the model is based considers the following steps: (a) the contaminant is transported by filled micelles from the bulk solution to the proximity of the cells; (b) the exchange of the filled micelle with the hemimicellar layer around the cell delivers the contaminant to the cell; (c) the contaminant diffuses into the cell and is biodegraded. The biodegradation kinetics were explained in terms of a series of mass- transfer processes, which lead to a similar equation as the Monod kinetics. The theoretically derived expression, describing the micellar-phase substrate that is directly bioavailable, includes a series of surfactant dynamics and mass transfer rate parameters that are not readily available or easily determined. A simplified formulation, which can be used to estimate the direct bioavailability of the micellar-phase substrate was therefore obtained and was used to explain experimental observations. The bioavailable fraction of the micellar-phase substrate was independent of the biomass concentration and was a function of the surfactant concentration, the polyoxyethylene chain length of the surfactant, and the biomass surface characteristics.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry