| Polycyclic Aromatic Hydrocarbons (PAHs) are common contaminants in soils and groundwater aquifers, resulting from anthropogenic activities. Major concerns with these compounds are their recalcitrance, toxicity and other unique characteristics in the environment. In situ bioremediation has been successfully used for some PAH degradation in soils, but the optimum conditions for the continuous active growth of microbial communities are not well-understood, so biodegradation processes cannot be properly enhanced.; Lab-scale column reactors simulating sandy aquifer environments were used as attachment medium for the biofilm. The biological degradation of a low molecular weight PAH, naphthalene, was investigated, resulting in a 93.5% removal using acetate as a co-substrate. Biofilm mass and extracellular polymeric substances were greatly improved by the presence of acetate, which also promoted the degradation of naphthalene. Biofilm morphology and structure were characterized qualitatively and quantitatively by using confocal microscopy and image analysis, suggesting that porous media biofilms are complex matrixes that develop and change with specific environmental conditions.; Sole-substrates, as well as binary/tertiary mixtures of 2-, 3- and 4-ringed PAHs, were examined for competitive/inhibitive interactions on porous media biofilms. While phenanthrene and pyrene could not be degraded as sole carbon sources, binary systems of the 3- and 4-ring PAHs with acetate and naphthalene supplements stimulated their degradation, with up to 87.4% and 70.1% removal efficiencies, respectively. However, inhibition of pyrene degradation by phenanthrene was observed in the tertiary systems. Heterogeneous surface films and a variety of biological aggregate structures and growth patterns were observed by confocal microscopy.; A nonionic surfactant was tested for water solubility enhancements of naphthalene, phenanthrene and pyrene. Solutions of Triton X-100 above the critical micelle concentration (CMC) showed great solubilization of the three PAHs. Batch experiments were also conducted to investigate the sorption effects of PAHs and/or Triton X-100 to the porous media, as well as the partitioning to live/killed biofims. Low amounts of surfactant were found to be adsorbed onto sand and biofilm; Triton X-100 appeared to increase PAH sorption, but sorbed concentrations were still considered negligible.; The effects of the nonionic surfactant on the biodegradation of PAHs were also investigated. Column experiments showed that the degradation of the 2-ring PAH alone was not affected and only a small enhancement of 3- and 4-ring PAH (as sole-substrates) degradation occurred by Triton X-100 addition. Higher biodegradations were always achieved by having just PAH mixtures without the surfactant, indicating the importance of cross feeding/cometabolic mechanisms over improved solubilization of PAHs. |
