Project ID: 2004MN48B

Title: Phyto-enhanced remediation: A wetland treatment system for surface water protection

Project Type: Research

Focus Categories: Wetlands, Non Point Pollution, Treatment

Keywords: phytoremediation, methanotrophic bacteria, trichloroethylene

Start Date: 03/01/2004

End Date: 02/28/2006

Federal Funds: $24,262

Non-Federal Matching Funds: $40,913

Congressional District: 5

Principal Investigators:
William Alan Arnold
University of Minnesota

Timothy Michael LaPara

Abstract

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 or 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 tend 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 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 to provide proof of concept data as a step towards establishing engineered wetlands as a practicable technology for the treatment of chlorinated ethylenes at the groundwater/surface water interface. It is hypothesized that the wetland plants and soil bacteria will work synergistically to rapidly mineralize contaminants. Specific objectives include: 1) determining the ability of wetland plants to stimulate the growth of methanotrophic bacteria populations and 2) elucidation of the specific roles of the soil and plants 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 this highly interdisciplinary research.

By evaluating 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 of the effect of the plants on contaminant removal and methanotrophic biomass in the wetland and will serve as a feasibility study for the wetland technology. A comparison will be made between the planted and unplanted cells to determine the effect 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.

Progress/Completion Report PDF