Electrokinetically enhanced bioremediation (EEB) is a method of engineered bioremediation of soil contaminated by such organic compounds as solvents and petroleum products. As depicted schematically in the figure, EEB involves the utilization of controlled flows of liquids and gases into and out of the ground via wells, in conjunction with electrokinetic transport of matter through pores in the soil, to provide reagents and nutrients that enhance the natural degradation of contaminants by indigenous and/or introduced micro-organisms.
The operational parameters of an EEB setup can be tailored to obtain the desired flows of reagents and nutrients in variably textured and layered soils of variable hydraulic permeability and of moisture content that can range from saturation down to as little as about 7 percent. A major attractive feature of EEB is the ability to control the movements of charged anionic and cationic as well as noncharged chemical species.
The basic components of electrokinetic enhancement of bioremediation are the following:
- Ions are transported by electromigration; that is, with minimum transport of liquid through the soil. The ions of interest include nutrient agents, electron donors (e.g., lactate) or electron acceptors (e.g., nitrate or sulfate) added to the soil. Electromigration is utilized as an efficient mode of electrokinetic transport in vadose-zone soils.
- Water in soil is pumped (horizontally or vertically, depending on the positions of electrode wells) by induced electro-osmotic flow. Whereas the hydraulic flow used in older methods decreases with decreasing pore size and is thus not effective for treating tightly packed soil, electro-osmotic flow is less restricted by tight packing. Electro-osmosis is utilized to enhance the transport of both ions and such noncharged particles as micro-organisms, by moving water from anodes (positive electrodes) toward cathodes (negative electrodes).
- Electrophoresis induced in soil under an applied electric field is used to control the transport and/or distribution of micro-organisms throughout the treated soil volume. The beneficial effect of electrophoresis can be augmented or otherwise modified by use of electro-osmotic flushing of the soil.
- The applied electric current can be utilized to heat the soil to the optimum temperature for bioremediation.
- The gaseous and liquid products of electrolysis of water in the soil are removed from electrode wells and mixed and reinjected into the ground as needed to maintain the pH of the soil within a range favorable for bioremediation.
This work was done by Dalibor Hodko, G. Duncan Hitchens, Tom D. Rogers, James W. Magnuson, and Jeffrey K. Dillon of Lynntech, Inc., for Kennedy Space Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Bio-Medical category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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Refer to KSC-12045, volume and number of this NASA Tech Briefs issue, and the page number.