Geosafe Corporation's (Geosafe) in situ vitrification (ISV) process uses electricity to melt soil or other earthen materials at temperatures of 1600 to 2000 °C, destroying organic pollutants by pyrolysis. Inorganic pollutants are immobilized within the vitrified glass and crystalline mass. Water vapor and organic pyrolysis products are captured in a hood, which draws the off-gases into a treatment system that removes particulates and other pollutants.
To begin the vitrification process, an array of four large electrodes is inserted into contaminated zones containing enough soil for melting to occur (see photograph below). A graphite starter is used to melt the adjacent soil, which then becomes the primary current-carrying medium for further processing. As power is applied, the melting continues downward and outward at an average rate of 4 to 6 tons per hour, or 1 to 2 inches per hour. The electrode array is lowered progressively, as the melt grows to the desired treatment depth. After cooling, a vitrified monolith with a glass and microcrystalline structure remains. This monolith possesses high strength and excellent weathering and leaching properties.
In Situ Vitrification Process Equipment
Air flow through the hood is controlled to maintain a negative pressure. Excess oxygen is supplied for combustion of any organic pyrolysis by-products. Off-gases are treated by quenching, pH-controlled scrubbing, dewatering (mist elimination), heating (for dew point control), particulate filtration, and either activated carbon adsorption or thermal oxidation may be employed as a final off-gas polishing step.
Individual melt settings may encompass a total melt mass of up to 1,400 tons, a maximum width of 40 feet, and depths as great as 22 feet. Special settings to reach deeper contamination are also possible. Void volume and volatile material removal results in a 30 to 50 percent volume reduction for typical soils.
The mobile ISV system is mounted on three semi-trailers. Electric power may be provided by local utility or on-site diesel generator. Typical power consumption ranges from 800 to 1,000 kilowatt-hours per ton of processed soil. The electrical supply system has an isolated ground circuit to provide safety.
The ISV process can destroy or remove organics and immobilize most inorganics in contaminated soils, sediments, sludges, or other earthen materials. The process has been tested on a broad range of volatile and semivolatile organic compounds, other organics including dioxins and polychlorinated biphenyls (PCB), and on most priority pollutant metals and heavy metal radio-nuclides. The process also treats large amounts of debris and waste materials present in soil.
This technology was accepted into the SITE Demonstration Program in 1988. The demonstration of the process occurred during March and April 1994 at the former Parsons Chemical (Parsons) site in Grand Ledge, Michigan. The soil at Parsons was contaminated with pesticides, metals, and low levels of dioxins. The Innovative Technology Evaluation Report (EPA/540/R-94/520) and the Demonstration Bulletin (EPA/540/MR-94/520) are available from EPA.
In November 1995, Geosafe was issued a National Toxic Substances Control Act permit for the treatment of soils contaminated with up to 17,860 parts per million PCBs. All air emissions and vitrified product samples had nondetectable levels of PCBs and dioxins and furans. In December 1995, Geosafe completed the remediation of the Wasatch Chemical Superfund Site in Salt Lake City, Utah. This site contained about 6,000 tons of dioxin, pentachlorophenol, herbicide, pesticide, and other organic-contaminated soil and debris.
ISV has also been selected for the remediation of radioactively contaminated soil at Oak Ridge National Laboratory, Tennessee and an isolated nuclear test site in southern Australia. ISV is also being researched for the treatment of coal ash in Japan.
During the SITE demonstration, about 330 cubic yards (250 cubic meters) of a saturated clayey soil was vitrified in 10 days. This is the equivalent to a production rate of 53 tons per day.
The technology met cleanup levels specified by EPA Region 5 for chlordane, 4,4-dichlorodiphe- nyltrichloroethane, dieldrin, and mercury. Pesticide concentrations were nondetectible in the vitrified soil. Results also indicated that leachable mercury was below the regulatory guidelines (40 CFR part 261.64), and no target pesticides were detected in the leachate.
No target pesticides were detected in the stack gas samples, and metal emissions were below regulatory requirements. Continuous emission monitoring showed that total hydrocarbon and carbon monoxide emissions were within EPA Region 5 limits.
EPA PROJECT MANAGER:
Teri Richardson
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7949
Fax: 513-569-7105
TECHNOLOGY DEVELOPER CONTACTS:
James Hansen or Matthew Haass
Geosafe Corporation
2950 George Washington Way
Richland, WA 99352
509-375-0710
Fax: 509-375-7721
E-Mail:
GEOSAFE@oneworld.out.com