BIODEGRADATION KINETICS OF PHENANTHRENE PARTITIONED INTO THE MICELLARPHASE OF NONIONIC SURFACTANTS

Surfactants above their critical micelle concentration can solubilize hydrophobic contaminants into their micelles. This process enhances th e apparent solubility of contaminants such as hydrocarbons and, theref ore, also their desorption from soils. Conceivably, in the absence of any inhibitory effects, such surfactants may enhance the biodegradatio n of the hydrocarbon. Through a set of screening experiments, a series of nonionic surfactants were identified that do not inhibit the biode gradation of phenanthrene. A mathematical model was formulated to desc ribe the interaction of the biomass-contaminant-water-surfactant syste m. Assumptions that the model formulation is based on are that the phe nanthrene in solution, partitioned into the micellar phase and sorbed onto the biomass and other solid surfaces,is at equilibrium and that t hese equilibria can be described by simple partition coefficients. It was also assumed that the presence of the surfactant does not affect t he biochemical characteristics of the biomass. An effective bioavailab le micellar-phase concentration of phenanthrene was defined. The model simulates experimental data well, indicating that a fraction of the m icellar-phase phenanthrene is directly bioavailabie. For three of the surfactants tested (Triton N101, Triton X100, and Brij 30), the micell ar-phase bioavailable fraction of phenanthrene decreased with an incre asing surfactant concentration. For Brij 35, it was found that the fra ction of the phenanthrene associated with the micellar phase was not d irectly bioavailable.