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Degradation Potential of Chlorinated Ethenes in the Rhizosphere of Wetland PlantsEPA Grant Number: F07A70195
Title: Degradation Potential of Chlorinated Ethenes in the Rhizosphere of Wetland Plants
Investigators: Powell, Christina Lynn
Institution: Wright State University - Main Campus
EPA Project Officer: Zambrana, Jose
Project Period: September 1, 2007 through September 1, 2009
RFA: GRO Fellowships for Graduate Environmental Study (2007) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Hazardous Waste/Remediation , Fellowship - Environmental Science
A wetland research facility was constructed in the year 2000, at the Wright-Patterson Air Force Base (WPAFB) in Dayton, OH, for the removal of perchloroethene (PCE) in the groundwater. A unique design of the constructed wetland allows the spatial details of various anaerobic and aerobic biogeochemical processes that degrade chlorinated ethenes (CEs) to be examined through different seasons. The geochemical data collected from the treatment wetland site so far has provided evidence that PCE is degrading in the treatment wetland, as measured by its disappearance along with formation of its daughter products, e.g., trichloroethene (TCE), dichloroethene isomers (DCEs), vinyl chloride (VC). There is increasing evidence that the degradation of PCE and its daughter products may occur more rapidly and perhaps differently than in a typical shallow aquifer by processes and pathways characteristic only to a wetland. This project allows for groundbreaking research of the role of vegetation, in the shallow wetland zones, plays in the destruction of chlorinated organic groundwater pollutants. The proposed research will provide a fresh perspective on CEs degradation processes in shallow subsurface environments, particularly those processes facilitated within the plant rhizosphere. This study will characterize the biogeochemical factors that may affect the oxidative degradation of daughter CEs (e.g; TCE, DCEs, and VC), and determine their fate in the shallow subsurface of a vegetated wetland. These processes within the wetland plant rhizosphere may provide a natural pathway for CEs to be degraded and mineralized to carbon dioxide.
This research will be completed in three phases. The first phase will consist of groundwater sampling and analysis and will characterize the seasonal changes in water chemistry and redox processes in 3-dimensions at the WPAFB wetland site. The data will provide high-resolution profiles of CE and redox sensitive species. The second phase will utilize bench-scale systems to study CE mineralization potential coupled to Fe (III) reduction and methane oxidation. The main objective of this important phase is to gather proof-of-concept of CE mineralization potential by microbial processes with the plant roots using radio-labeled cis1,2-DCE and VC. The third phase will be designed to validate the results of the bench-scale experiments and field measurements in phases I and II. This will be accomplished by greenhouse mesocosms designed to simulate CE degradation typical of field conditions. During this phase of the research in situ rate constants for oxidative degradation of CEs at simulated field conditions will be obtained.
It is expected that the oxygenated conditions and methanotrophic activity in the plant rhizosphere can support the co-metabolic and metabolic aerobic degradation of CEs in the shallow vegetated wetland. It is also expected that the DCEs and VC oxidation/mineralization can be coupled to Fe(III) reduction processes which occur in wetland rhizosphere and surrounding soil. It is further expected that CE removal rates through oxidative (aerobic metabolic, aerobic cometabolic and iron-reducing) processes may change seasonally; the oxidative degradation rate may increase as methane oxidation and Fe(III)-reduction is greater in spring (period of root growth), and may decrease after the plants mature and the roots become anaerobic in late summer/fall months.