PHYTOREMEDIATION OF METHYL-TERT-BUTYL-ETHER (MTBE)
1Ellen Rubin and 2Anu Ramaswami
1,2Department of Civil Engineering, University of Colorado-Denver, Campus Box 113, PO Box 173364, Denver, CO 80217; 1Phone: (303) 556-4734, 1E-mail: ; 2E-mail: .
Methyl-tertiary-butyl-ether (MTBE) is used as a gasoline additive in EPA's oxyfuels program. MTBE in fuel can help control air pollution, but it is a potential water and groundwater pollutant. MTBE has been found widespread across the nation in municipal supply wells, irrigation wells, and groundwater monitoring wells.
MTBE is very water-soluble and does not sorb much to soil; it is also essentially non-biodegradable and non-reactive in water. Therefore, once MTBE gets into water, an MTBE plume develops rapidly that is difficult to remediate by conventional methods. Phytoremediation is an innovative technology that utilizes plant systems to remediate hazardous waste sites. Phytoremediation is an efficient mechanism of contaminant removal for compounds whose octonal-water partition coefficient, log K o/w, is between 1 and 3. Since the Log Ko/w for MTBE is 1.24, which is in the range that is readily transpired in plants and trees, phytoremediation may be a feasible remedial technique for subsurface MTBE plumes. Plants and trees may transpire many volatile-organic compounds (VOCs) into the air. While MTBE does not degrade in soil, atmospheric MTBE reacts with hydroxyl radicals in air, yielding a half-life in the order of days. Thus, transpiration of MTBE from the subsurface to air via plants can offer a low-cost method for destruction of the pollutant to benign products. Currently, there is no data available for removal of MTBE from water due to plant transpiration.
The objective of this project is to examine the potential for phytoremediation of MTBE-contaminated waters using poplar trees. Poplar trees (populus deltoids x nigra) were selected for this project because they are hardy, rapid-growing phreatophytes. A closed-chamber system was developed to quantify MTBE movement through the poplar tree's roots, shoots, leaves, and finally to the air. Experimental data showed the following:
- 69-80% reduction in MTBE mass.
- 46-56% reduction in MTBE concentration.
- MTBE was extracted from plant roots and shoots at a concentration of 5-10 ppb, indicating MTBE movement through the plant.
These results indicate that MTBE was readily taken up by hybrid poplar saplings in the laboratory. Ongoing experiments are evaluating MTBE phytoremediation in larger-scale soil-water systems.