United States Environmental Protection Agency Solid Waste And Emergency Response (OS-220) Directive 9200 5-251FS November 1989 ,EPA Innovative Technology In-Situ Vitrification TECHNOLOGY DESCRIPTiON In-situ vitrification (ISV) can be used to treat soils and sludges contaminated with mixtures of various waste types (e.g., radio- active, inorganic, and/or organic). The pro- cess electrically melts the waste media, cre- aLing an extremely stable glass-like solid. A schematic diagram of a typical ISV treatment facility is shown in Figure 1. Four electrodes connected to a utility distribution system or to an on-site diesel generaLor are treated. The need for off-gas collection and treatment, however, is a disadvantage SITE CHARACTERISTICS AFFECTING TREATMENT FEASIBILITY Generally, the acceptable levels for treatment of contaminants in soil are 5 to 10 weight percent organics and 5 to 15 weight percent inorganics. Due to the need to con- sider several other factors (e g , soil type) in determining feasibility, treatability tests are required The ISV process can be used to treat saturated soils; however, the water must be evaporated first, requiring additional energy and further expense. If the soil permeability is high and the soils are recharged by an aquifer, a ground water diversion system may need to be installed, adding additional expense. Table 1 Effectiveness of In-Situ Vitrification Treatment on General Contaminant Groups for Soil and Sludge Treatability Groups Effectiveness 0 Haiogonated volatfies Hatogenated seml-volatiies Non-halogenaied volaties Non-haJogenaied serni-voiatiles PCBs Pesticides Dioxlnslfurans Organic cyanides Organic corrosees • ‘ Volatde nietals Q Non-volatile rneiais Asbestos Radioactive materials • inorgartic corrosives inorganic cyanidos T Oxidizers Reducers O.monaos.d Eflect .nse No E*poct.d ES scxvenezn 0 Po ereat EffecOven.se Q Potenbaily Deti,rnental X over the process area collects both organic and inorganic gases, which are treated be- fore being released into the atmosphere. An off-gas treatment system is designed to handleconditionsatmostsites. Ifnecessary, the treatment system may be modified to meet specific site reqwrements. The off-gas treatment may include any of the following units: a wet scrubber system, a heat ex- changer with a glycol cooling system, a heater, a filter, and/or an activated charcoal assembly The hood draws in large amounts Figure 1: Schematic Diagram of a Typical In-Situ Vitrification Treatment FacIlIty Nan ata ed irom aarlona Paic Northeast L oratorlas ioi Boos. Azen & HarriSon inc inserted into the soil Because soil typically has low electrical conductivity, flaked graph- ite and glass frit are deposited between elec- trodes to provide a starter path for the elec- trical current. As the current flows between electrodes, the adjacent soil is heated to 1600 - 2000°C, well above a typical soil’s melting temperature. The graphite starter path eventually bums off and the current is transferred to the now highly conductive melted soil. Within the melt, organic contaminants are vaporized and pyrolyzed (i e , thermally decomposed); the pyrolysis products rise to the surface and combust in the presence of oxygen. Non-volatile inorganic elements are dissolved or incorporated into the melt. Volatile metals may vaporize and rise to the surface along with the pyrolysis products. Table 1 lists the effectiveness of ISV on general contaminant groups. A negatively pressurized hood placed of outside air which helps to oxidize com- bustible vapors and pyrolysis products All equipment involved with the ISV process, including the off-gas treatment system, are contained in three mobile trailers When the treatment is completed, the power is shut off and the equipment (i e, electrodes and hood) is moved to another treatment area where the treatment process is repeated Following treatment, the sur- face of the vitrified area is covered with clean soil, and the melt is allowed to cool slowly, producing an amorphous solid re- sembling obsidian Several months are required for the treated area to cool to ambi- ent temperature; however, after four to five days, the melt has cooled sufficiently for equipment tobe moved onto the treated area The advantages of ISV include the potential ability to destroy, remove, or immobilize all contaminant groups and to reduce the volume of the waste/media being ------- The presence of significant amowus of buried metals (e.g., drums) may cause shorting between electrodes, therefore, the metal concentration limit is 5 to 16 percent of the melt weight. Addition- ally, metals cannot occupy more than 90 percent of the continuous linear distance between electrodes. Table 2 lists those factors that affect ISV feasibility. TECHNOLOGY CONSIDERATiONS Currently, ISV technology can be used to treat a maximum area of 30 ft. x 30 ft.; the maximum depth of treatment is 30 ft. Note that the maximum mass ofcontaminated material that can be treated per sening is 800 to 1,000 tons. When processing a 30 ft. x 30 ft. area, the mass limit will be reached before the depth reaches 30 ft.; con- sequently, ills impossible to reach all three maximums simultane- ously. Conversely, the minimum area that can be treated is lOft. x 10 ft.; the recommended minimum depth of treatment is 5 to 7 ft. Most soil types contain sufficient glass-forming materials (e.g., silicon and aluminum oxides) for treatment to be effective; however, it may be necessary to add a fluxing material (e.g., sodium carbonate) to supply adequate amounts of monovalent cations to provide sufficient electric conductivity. Dunng ISV, the soil vol- ume decreases 20 to 40 percent necessitating the backfilling of the subsided area with clean soil. During full-scale operation, ISV processes 4 to 6 tons of soil per hour, requiring 0.3 to 0.5 kwh per pound of soil. The power level required is 1.9 Mw/phase. The base price of a typical treatabiity study, conducted in Geosafe Corporations laboratory, is estimated to be $25,000. Ana- lytical costs, however, can raise the total cost to between $35,000 and $100,000. TECHNOLOGY STATUS Bauelle Memorial Institute is exclusively licensed by the U.S Department of Energy (DOE) to perform ISV. Geosafe Corpora- tion, primarily owned by Battelle, holds the exclusive sublicense to perform ISV commercially. More information concerning Geosafe is found in Table 3. Battelle and Geosafe have cumulatively per- formed more than 70 tests of various scales for DOE and other clients. At the DOE Hanford Site in Washington State, ISV success- fully treated soils contaminated with radioactive wastes. The ISV process has been selected for evaluation under the SITE Program. Formal demonstration and testing of the process has been postponed until the developer has obtained funding for a dem- onstration at an appropriate site. Currently, EPA’s Emergency Response Division in Region 5 Table 3 Vendor information Company Contact Address Geosafe Corporalon James Hansen DaJe Timmons 303 Parkplace Suite 126 Kirkland, WA 98033 (206) 822-4000 Notw Geosafe Corporaflon is the exdusive cemmercial sublicensee of the ISV process Table 2 She-specific Characteristics and Impacts on In-Situ Vitrification Treatment characteristics Impacting Process Fsa&bfllty Reasons for Potential Impact Actions to MInimize impacts Presence of ground water Waler affects the efficiency of the vrl4rcatpon process, limits ecorcm practicality Oewaler before treatment or p niip to lower water table Sod permeabthty greater than 1 a 10 aTi/soc Soil a re-eaturaled faster than waier can be evaporated mateS ground waler diversion system Buned metals (eg . drums), grealerihan 5to 15 percent of the rne weight between etedrodes Bimed metals can result in a condictivepathihalwould leaf to shorting between electrodes Use feeding electrodes Loosely packed rubbish and/or buned coal May start underground Ire Install barriar wals or sheei piling Combustible Iquds, greater than 9,600 Ib/yd of depth or 5 to 10 percent by weight lime-ordered tuna to the capacity of the off-gas system to contan combustion gas, (riot cumulative capacity) Increase hood capacity, process at a slower rate, or employ smaller process setting volumes Combustible sol (e g, wood), greater than 6,400 Iblyd of depth or 47 perceil by weight lime-ordered Imits to the capacity of the off-gas system to cordan combustion gas, (not cumulative capacity) mo-ease hood capacity, process at a slower rate, or employ smaller process setting volumes Combustible packages (e g, boxes of dothing packaged for disposai), greater thai 3211 lime-ordered tuna to the capacity of the on-gas system to conan combustion gas, (net cumulative capacity) Increase hood capacity, process at a slower rate, or employ smaller process setting volumes Volatile metal content and depth Relent’on 01 votalle metals in meftislessnearsurfacathan further below Before treatment, place cleansodontopto increase met depth Void volumes greater than 152ft 3 lime-ordered Imits to the capacityoftheofl-gassystem to contan combustion gas, (net cumulative capacity) Increase hood capaaty, processat astowermie, or employ smaller process setting volumes has selected ISV to treat pesticides, heavy metals, and low-level dioxins. ISV has also been selected to treat contaminated soils at the lonia Landfill in Region 5 and the Northwest Transformers site in Region 10. The status of ISV application at CERCLA sites is sum- marized in Table 4. OFFICE OF RESEARCH AND DEVELOPMENT CONTACTS Further information regarding the ISV process may be obtained from Steve James, U.S. EPA, Risk Reduction Engineering Labora- tory, Cincinnati, Ohio 45268, (513) 569-7877 orFTS (684-7877), Table 4 in-Situ Vitrification Status at CERCLA Sites SELECTED: Reglon 5-lone Landfill, MI 9/89 Regton 5- Parsons/ElM, MI (Removal on) FY90 Regmonlo-Northwesttransformers, WA 9(89 Heavy me ls, organtcs In So! Pestctdes, heavy metals iow-Iev oxtns in Soil PCBs in Soil 5000 cubic yards Not Provided Not Provided ------- |