Abstract:
Polycyclic aromatic hydrocarbons (PAHs) are a diverse class of toxicants that are ubiquitously and persistently present in the environment. These compounds present a risk for human health and the environment, as they are mutagens, carcinogens and teratogens. Bioremediation has shown promise as a potentially effective and low-cost treatment option, but concerns about the slow process rate and bioavailability limitations have hampered more widespread use of this technology. In the fundamental work of this thesis a series of experiments was designed utilizing the biosurfactant produced by Pseudomonas aeruginosa LBP5, LBP9 and CB1. Specifically, these experiments were designed to determine if the presence of various levels of partially purified biosurfactants produced by the isolates, would affect the degradation of a range of PAHs. The biodegradation and biotransformation of PAHs were studied in three bioremedial systems: soil slurry, liquid culture experiments with enriched consortium on PAHs from petroleum contaminated sites and Bioslurry reactor study with autochthonous consortium. Biosurfactant-producing and polycyclic aromatic hydrocarbon degrading microorganisms were isolated from petroleum-contaminated crane service station soil and creosote contaminated wood treatment plant soils in Pretoria area. Bacterial isolates LBP9 and LBP5 isolated from crane service station soil and isolates CB1, CN2, CN3, CN5 isolated from creosote contaminated soil were found to be the most efficient biosurfactant producing strains. The biosurfactant produced by the strains LBP9, LBP5 and CB1 were extracted and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR) and Thin layer chromatography (TLC).
Evaluation of the ability of the LBP9 biosurfactant for applications in enhancing biodegradation of mixed polycyclic aromatic hydrocarbons (PAHs) with a consortium of bacteria indicated that the biosurfactant was able to enhance the removal of significant amount of PAHs from the liquid culture medium at different concentrations. In this study at 400 mg/L amendment of lipopeptide the solubility of Phenanthrene, Fluoranthene and Pyrene was increased to 19.4, 33 and 45.4 times their aqueous solubility, respectively, and the extent of substrate utilization rate of the PAHs was enhanced up to 3 fold in the sole substrate microcosms.
A second goal of these experiments was to discern the efficacy of exogenous lipopeptide application and stimulation of in situ biosurfactant production through biostimulation / nutrient amendments in the removing of polycyclic aromatic hydrocarbons (PAH) from creosote PAH contaminated soil. This work also suggests that it may be more practical to stimulate indigenous biosurfactant production within a soil than to add pre-purified compound. In general, the results presented in the studies show the potential of biosurfactants in assisting the bioremediation of polycyclic aromatic hydrocarbon contaminated environmental media in a reasonable timeframe.
