Phyto-enhanced Remediation: A Wetland Treatment System for Surface Water Protection
Principal Investigators: William Arnold, Assistant Professor and Timothy LaPara, Assistant Professor, Department of Civil Engineering
USGS-WRRI 104B/ CAIWQ Competitive Grants Program
March 2004 - February 2006
Contamination of groundwater by chlorinated solvents represents one of the most pervasive and difficult remediation challenges. Phyto-enhanced remediation is a potentially low cost and aesthetically pleasing remediation alternative. Phyto-enhanced remediation is a burgeoning technology that utilizes living plants to help remove contaminants from the environment. Natural of engineered wetlands are one phyto-enhanced remediation option for chlorinated solvents. Deep portions of wetlands are anaerobic and facilitate the partial reductive dechlorination of contaminants. In the near surface sediments, where the waters tent to contain dissolved oxygen introduced by the wetland plants, the partially dehalogenated species can be mineralized to non-toxic products by methanotrophic organisms. The wetland, however, is a complicated ecosystem, and the specific roles of the plants and microorganisms in contaminant degradation in such a scheme have yet to be determined. In addition, the extent to which the wetland plants may stimulate or alter microbial activity by introducing oxygen and root exudates into the near surface sediments has yet to be investigated. The overall goal of the proposed research is to establish engineered wetlands as a practicable technology for removal of chlorinated ethylenes at the groundwater/surface water interface. It is hypothesized that the wetland plant and soil bacteria will work synergistically to rapidly mineralize contaminants. Specific objectives include:
- determining the ability of wetland plants to stimulate the growth of methanotrophic bacteria populations, and
- elucidation of the specific roles of the soil and plant and the impact of plant-microbial interactions in the removal of chlorinated ethylenes.
A team with a diverse skill set has been assembled to conduct the highly interdisciplinary research.
By determining the mechanisms of interaction between the wetland plant community and the soil microbial community through the proposed research, the important removal/degradation mechanisms for the treatment of chlorinated ethylenes in the wetland will be discerned. THe proposed multidisciplinary study will evaluate both field data from mesocosm cells installed in an engineered wetland in Mound, Minnesota, and laboratory data from experiments focusing on specific removal/degradation mechanisms and interactions between system components. The field studies will allow direct observations od the effect of the plants on contaminant removal and methanotrophic biomass in the wetland and will serve as a feasibility study for wetland technology. A comparison will be made between the planted and unplanted cells to determine the effects of the plants. In the laboratory, plant evapotranspiration and degradation rates of cis-dichloroethylene will be determined using microcosms. In addition, the capability of the plants to stimulate methanotrophic activity in wetland soils will be evaluated. The microcosm laboratory experiments will result in rate expressions for the microbial and plant assisted removal/degradation of cis-dichloroethylene in the wetland.
Refereed Scientific Journal Articles
DeJournett, T.D., J.M. Fritsch, K. McNeill, and W.A. Arnold. 2005. Preparation of 14C−cis−1,2−dichloroethylene from 14C−trichloroethylene using a cobalt porphyrin catalyst. Journal of Labelled Compounds and Radiopharmeceuticals, 48(5): 353−357.
Theses and Dissertations
DeJournett, T.D. 2006. Removal of cis−1,2−dichloroethylene from groundwater using a restored wetland. Ph.D. Dissertation, Department of Civil Engineering, University of Minnesota, Minneapolis, MN, 140 pp.