A relatively simple chemical treatment that involves the use of emulsified iron has been found to be effective in remediating groundwater contaminated with trichloroethylene and other dense chlorohydrocarbon liquids. These liquids are members of the class of dense, non-aqueous phase liquids (DNAPLs), which are commonly recognized to be particularly troublesome as environmental contaminants. The treatment converts these liquids into less-harmful products.
As a means of remediation of contaminated groundwater, this treatment takes less time and costs less than do traditional pump-and-treat processes. At some sites, long-term leakage and/or dissolution of chlorohydrocarbon liquids from pools and/or sorbed concentrations in rock and soil gives rise to a need to continue pump-and-treat processes for times as long as decades in order to maintain protection of human health and the environment. In contrast, the effects of the emulsified-iron treatment are more lasting, decreasing the need for long-term treatment and monitoring of contaminated areas.
The material used in this treatment consists of iron particles with sizes of the order of nanometers to micrometers contained within the micelles of a surfactant-stabilized, biodegradable, oil-in-water emulsion. The emulsion is simple to prepare and consists of relatively inexpensive and environmentally acceptable ingredients: One typical formulation consists of 1.3 weight percent of a food-grade surfactant, 17.5 weight percent of iron particles, 23.2 weight percent of vegetable oil, and 58.0 weight percent of water.
The emulsion is injected into the ground via a push well. Free-phase chlorohydrocarbon molecules diffuse through the oil membranes of the emulsion particles to the surfaces of the iron particles, where dehalogenation takes place. The dehalogenation reactions generate hydrocarbon byproducts (primarily ethylene in the case of trichloroethylene), which diffuse out of the emulsion micelles and are benign in nature.
Experiments have demonstrated several aspects of the effectiveness of this treatment by use of emulsified iron:
- This treatment is more effective in degrading free-phase trichloroethylene than is a similar treatment that uses only pure iron particles.
- Emulsions containing iron can be injected into soil matrices, where they become immobilized and remain immobile, even in the presence of flowing water.
- Iron emulsions can exert an effect equivalent to pulling globules of trichloroethylene into their micelles.
- No chlorinated byproducts from the degradation of trichloroethylene pass out of the micelles. The only degradation products that have been observed to leave the iron emulsions are ethylene as mentioned previously, plus trace amounts of other innocuous hydrocarbons.
Laboratory studies have shown that the amount of emulsion needed to degrade a given amount of trichloroethylene is approximately eight times the mass of the trichloroethylene. Because there are no continuing operating costs after the emulsion has been injected through push wells, the iron-emulsion treatment offers a substantial economic advantage over the long-term pump-and-treat method.
This work was done by Jacqueline Quinn of Kennedy Space Center and Christian A. Clausen III, Cherie L. Geiger, Debra Reinhart, and Kathleen Brooks of the University of Central Florida. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Materials category.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Technology Commercialization Office
Kennedy Space Center
Refer to KSC-12246.