Technology Solutions
the electricity from heating very effectively, Heath explains. Heath says his company is offering the technology at Heat provided by several methods is In one recent application at a $20-80 yd'3. being used by a number of firms to former AT&T electronics manufacAnother method, in situ thermal cleanse the earth of a variety of conturing facility in Skokie, IL, the destruction (ISTD), uses electrical taminants. According to EPA, there are method significantly lowered the levheating elements in wells to heat the at least 50 sites where heat is being els of trichloroethylene and trichlosurrounding soil. Soil particles conused, has been used, or is under conroethane, according to an October duct the heat, explains Ralph Baker, sideration as a treatment method. The 1999 report by EPA's Office of TechCEO of TerraTherm of Fitchburg, MA Netherlands has used heat to deconnology Innovation. The process ran The company licensed the technology, taminate soils, and the Czech Repubfor nine months. which is now owned by the University lic is evaluating the technologies, says At the Illinois facility, the contamiof Texas but was developed by Shell EPA hydrologist Eva Davis. nants were in clay. Pipes containing Oil Corporation. Temperatures can electrodes were drilled 11-21 ft below The idea of using heat to get at reach 500 °C. "We can deal with polythe surface. The cleanup took far less dense nonaqueous phase liquids cyclic aromatic hydrocarbons (PAHs), time than expected, says Stan Kornp(DNAPLs) such as pentachlorophepolychlorinated biphenols (PCBs), erda of the Illinois EPA. "I was very nol, trichloroethylene, and creosote, owes its heritage to oil pesticide residues, dioxins, drilling. "The same princiand furans," says Baker, ple has been used for noting that all have boiling Six-phase heating targeted zones years in enhanced oil repoints higher than water. covery," says C. Herb Ward, Six-phase heating, which is also known as resistive heating, The method destroys 99% director of the Energy and is one of the methods of using heat to clean up a variety of of the contaminants in Environmental Systems underground contaminants. place. The remainder are Institute at Rice University removed by vacuum and in Houston. treated on the surface. Depending on the site The technologies work size and the nature of the by applying a source of contaminant, the cost can heat—which can take the range from $60 to $400 yd"3 form of either steam or of soil. That compares faelectricity—through a vorably to bids for destroywell. This heat volatilizes ing PCBs by ex situ thermal most of the contaminants. desorption of $400-$500 yd-3, Any not destroyed below and $500-$1000 yd"3 for the surface can be exincineration, says Baker. tracted through a second He also notes that simply well, typically by means of excavating and landfilling a vacuum. Source: Current Environmental Solutions. contaminated soil can be Filtering this contamias low as $35 yd-3, whereas, nated steam through actiin some cases, capping in place can vated carbon or a related method alsurprised," he says. 'Areas that had cost even less, but the liability associlows it to be safely disposed. DNAPL—boom it was gone." He also ated with the waste is not eliminated says the $32 yd"3 cost noted in the A key difference among the techin either case, whereas it is with ISTD. report is a "pretty good price." A stannologies is the way the heat is supBaker says cleanup using ISTD is dard tipping fee to dispose of such plied. Resistive heating, which is also fast—based on half a dozen field waste at a landfill he says is more, known as six-phase heating, uses projects completed by Shell, one of electricity taken directly from power The technology can also be used in which took a year, but more typically lines and converted by means of a any medium except coarse, dry, gravpatented technology developed at elly soils, says William Heath, the prin- 45-60 days. By contrast, soil vapor extraction or bioremediation can the Department of Energy's Batelle cipal inventor, who is now a vice presoften take 3-5 years, and even then Northwest Labs. This technology has ident of Current Environmental may fail to clean up marginal sites been exclusively licensed to Current Services and also remains a Batelle that ISTD can tackle successfully. Environmental Services of Mission employee. Soils with low water conTerraTherm currently has contracts Viejo, CA. tent—below 3-5% by weight—prevent
Cleaning up with heat treatment
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to clean a portion of the Department of Defense's Rocky Mountain Arsenal, which is contaminated with pesticides, as well as an Alhambra, CA, wood treatment site contaminated with creosote, according to Baker. Jim Cummings, of EPA's Office of Technology Innovation, says the costs of both these heating methods are favorable compared to other methods of contaminant cleanup but also notes that in some cases, the "deeper you get, there is no alternative. So it's not a matter of if it's cheaper or not, it's just that you have a tool to do something you couldn't do before." Heath sees heat as a way to deal with areas of high pollution concentration. Other methods such as oxidation and natural attenuation can be used to attack any remaining contaminants, he comments. Heat is workable, Davis agrees. "Conductive heat can only be used above the water table or where the water is controlled, but resistive heating has been used above and below the water table in sandy soils, as well as in tighter clays," she says. The task now is to see how widely it can be used. "It's been used in simpler geologic settings. The issue is how to expand the envelope as to where it can be used in more challenging geologic settings." Fractured bedrock, she notes, is one such medium. —HARVEY BLACK
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Correction In the May 1 issue of ES&T, the Technology Solutions column (Environ Sci. Technol, 2000, 34 (9), p. 217A) describing Oberlin College's new environmental studies building, which was designed and constructed to embody as many green building techniques as possible, incorrectly stated that the building included a photovoltaic array. Although this array has been ordered by Oberlin College, it has yet to be installed on the building's roof. The article also stated that the structure uses geothermal energy for heating and cooling, but did not add that the building also draws electricity from the grid for these purposes. In the long run, however, Oberlin's David Orr expects to invest in additional technologies like fuel cells that will enable the environmental studies building to be a net energy exporter.
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