Biodegradability of Select Polycyclic Aromatic Hydrocarbon Mixtures

Jennifer N. Stark

Anuradha M. Desai

Dr. Robin Autenrieth

Department of Civil Engineering

Texas A&M University

            Polycyclic aromatic hydrocarbons (PAHs) are chemicals formed from the incomplete burning of such substances as coal, garbage oil and gas.  They are ubiquitous, with both natural and anthropogenic sources, the latter being the growing concern.  Biodegradation is the most viable option to remediate PAHs in the environment.  Biodegradation kinetics research is limited for PAH mixtures.  This research evaluated biodegradation kinetics of select PAHs.

            Biodegradation experiments were conducted using Sphingomonas paucimobilis EPA505.  Sole biodegradation kinetics of naphthalene and phenanthrene, and a binary mixture of naphthalene and phenanthrene were performed.  The second set tested sole substrate mixtures of fluorene and 1-methylfluorene, and a binary mixture of fluorene and 1-methylfluorene.  The Monod model was fitted to the sole substrate data to estimate the biokinetic parameters, the substrate utilization rate () and affinity coefficient (). 

            The biodegradation of the individual PAHs were compared using the first order rate constant (/).  The first order rate constants for all the PAHs were comparable in spite of differences across physical and structural properties of PAHs.  The affinity constants were comparable for naphthalene and 1-methylfluorene, and for phenanthrene and fluorene.  The Monod model for multi-substrate kinetics were used to estimate the parameters in the binary mixtures. 

            The biodegradation of the binary mixtures were compared using time-dependent degradation.      The data set for the naphthalene and phenanthrene mixture suggested sequential metabolism.  The phenanthrene degradation did not begin until after a critical point in the naphthalene degradation, suggesting that when the naphthalene substrate goes to a minimum level, then the phenanthrene gets degraded.  For both the phenanthrene/naphthalene mixture and 1-methylfluorene/fluorene mixture, more experiments need to be performed in order to obtain more data points for fitting the multisubstrate model.

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