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Effects of in situ Bioremediation Strategies on the Biodegradation of Polycyclic Aromatic Hydrocarbons and Microbial Community Dynamics in Soil

  • Author(s): Wolf, Douglas Carl
  • Advisor(s): Gan, Jay
  • et al.
Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Public License
Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a class of compounds of environmental and public health concern because of their toxicity and environmental ubiquity that will be further exacerbated by increasing anthropogenic pollution. In situ bioremediation is a common cleanup technique for PAH-contaminated soils because it is considered to be cost-effective and environmentally-friendly. However, PAHs are often bound to nonpolar soil domains and become resistant to microbial degradation, the primary PAH removal pathway. This dissertation addresses these limitations by evaluating bioremediation-enhancement technologies such as biosurfactant amendment, bioaugmentation, and phytoremediation to increase PAH bioavailability and/or soil microbial activity. The use of biosurfactants to increase PAH bioavailability has the potential to be an environmental alternative to synthetic surfactants. Therefore, rhamnolipid biosurfactant was compared to Brij-35 surfactant in two soils contaminated with 14C-pyrene that were also bioaugmented with a PAH-degrading microbe, Mycobacterium vanbaalenii PYR-1. The effect of the surfactants and bioaugmentation on PAH biodegradation and soil microbial community dynamics was evaluated. The addition of Brij-35 increased 14C-pyrene mineralization in both soils, but the rhamnolipid biosurfactant inhibited PAH degradation in a dose-dependent manner, which was likely due to preferential utilization of the biosurfactant as an easier carbon source by the degrading microorganisms. The bioaugmentation of M. vanbaalenii PYR-1 resulted in efficient 14C-pyrene dissipation. Using 16S rRNA analysis, it was determined that the pyrene biodegradation was associated with changes in the soil microbial communities. The addition of pyrene resulted in a large increase in Bacillus, a genus associated with PAH degradation. However, the addition of rhamnolipid biosurfactant decreased the abundance of Bacillus microorganisms, which was reflected in 14C-pyrene mineralization. These bioremediation-enhancement technologies were further assessed in a phytoremediation setting in PAH-contaminated soil from a shooting range site due to the accumulation of clay target fragments. Bermudagrass and switchgrass enhanced soil enzyme activity and PAH biodegradation. The bioaugmentation of M. vanbaalenii PYR-1 enhanced high-molecular-weight PAH biodegradation. The decrease in PAH concentrations was also reflected in lettuce seed germination toxicity assays. Overall, this research highlights the importance of physical and biological mechanisms in the evaluation and implementation of in situ bioremediation-enhancement technologies for successful PAH remediation of contaminated soils.

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