Abinash Agrawal (Advisor), Songlin Cheng (Committee Member), Don Cipollini (Committee Member), Mark Goltz (Committee Member), Patrick Megonigal (Committee Member)
Doctor of Philosophy (PhD)
Chlorinated aliphatic hydrocarbons (CAHs) are often found as groundwater contaminants because of past industrial activities and disposal practices. CAHs pose a threat to human health and thus, create a need to find both natural and engineered processes that can remove these chlorinated compounds from the environment. Natural attenuation by oxidative biodegradation is especially important because it can allow for mineralization to carbon dioxide, a nontoxic end-product. The goal of this research was to evaluate the potential oxidative biodegradation of CAHs by microorganisms that are naturally associated with wetland plant roots. The research was divided into field work and laboratory batch studies.
The field work consisted of using newly designed pore water samplers to provide a biogeochemical characterization of a constructed wetland environment with an emphasis on the shallow vegetated zone. Reducing conditions were found at the bottom of the wetland with overlapping zones of nitrate, iron, and sulfate reduction and methanogenesis. More oxidizing conditions were found closer to the surface and in the root zone. There was evidence of tetrachloroethene (PCE) degradation by its removal and formation of daughter products, trichloroethene (TCE) and vinyl chloride (VC), both of which disappeared by possible oxidative processes in the near surface environment and root zone.
The laboratory work was done using a unique approach with microcosms containing soil-free washed wetland plant roots. The activity and TCE degradation potential by aerobic methane- and ammonia-oxidizing microorganisms naturally associated with Carex comosa roots was investigated. Methane oxidation developed faster than ammonia oxidation during the respective enrichment periods. After enrichment, methane oxidizers were able to degrade TCE in contrast to ammonia oxidizers, which were rapidly and completely inhibited, perhaps due to the presence of TCE or TCE degradation products. The root morphology, methane-oxidizing activity, and TCE degradation potential was compared between Carex comosa and Scirpus atrovirens. Carex comosa roots were found to have shorter and thicker roots compared to Scirpus atrovirens, which grew longer and were more fibrous. Initial methane oxidation was greater with the Carex comosa roots compared to the Scirpus atrovirens roots, however, TCE degradation was quite similar with roots from both species. The potential for methane oxidizers naturally associated with Carex comosa roots to degrade cis-1,2-dichloroethene (cisDCE), TCE, and 1,1,1-trichloroethane (1,1,1TCA) was investigated and the degradation rates were determined. TCE and cisDCE were both significantly degraded with first order kinetics while 1,1,1TCA degradation was not observed in the presence of active methane oxidizers. Overall, the results presented suggest that microorganisms associated with wetland plant roots have the intrinsic ability to naturally attenuate TCE and cisDCE in contaminated aquatic environments.
Department or Program
Department of Earth and Environmental Sciences
Year Degree Awarded
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