Biodegradation of polycyclic aromatic hydrocarbons and other petroleum compounds

The biodegradation of polycyclic aromatic hydrocarbons (PAHs) and other petroleum compounds was investigated through laboratory-scale experiments. A screening experiment involving soil-water slurries and chemically dispersed crude oil was conducted to identify whether biodegradation would occur under anoxic conditions with other electron acceptors. In addition to the aerobic microorganism culture that received oxygen additions, both the Fe(III) and NO₃− addition treatment cultures under anoxic conditions proved capable of biodegrading both alkanes and PAHs associated with a dispersed crude oil. Nitrogen (NH₄Cl) and phosphorus (NaH ₂PO₄) addition effects on the biodegradation of chemically dispersed crude oil were investigated using Corpus Christi Bay seawater. Both alkanes and PAHs biodegraded under all nutrient level treatments including background levels of both nitrogen and phosphorus. The addition of nitrogen increased the rate of biodegradation of both alkanes and PAHs, while the addition of phosphorus increased the biodegradation rate of alkanes but not PAHs. Pseudomonas putida ATCC 17484, a known naphthalene degrader, was cultured for extant kinetic experiments to evaluate biodegradation rates for naphthalene and substituted naphthalene compounds. Biodegradation rates decreased with increasing numbers of methyl substitutions. The biodegradation rates of compounds within groups with a given number of methyl substitutions were generally greater when an alpha position was not substituted. The structural mechanisms responsible for the observed biodegradation rate differences were investigated using a quantitative structural activity relationship (QSAR) software package. Spatial descriptors dominated the frequency distribution in terms of descriptor classes for both inter-methyl and intea-methyl group QSAR models. Chemical structure analyses suggest steric and alpha position substitution are the factors that affect the biodegradation rate differences observed. These results suggest that chemical structure descriptors can be used to estimate biodegradation rates for compounds within the naphthalene family in the absence of experimental data. Through a combination of mixed culture and pure culture experiments, PAH biodegradability was enhanced by nutrient additions for indigenous populations and the rates correlated to specific structural characteristics. This research effort spanned the scope from pure culture pure compound fundamental investigations to complex mixtures with a native mixed population that better approximates real world conditions.