Thermal Treatment: Ex Situ

For more information on Thermal Desorption, please contact:

Jim Cummings
Technology Assessment Branch
(703) 603-7197
cummings.james@epa.gov

Overview Guidance Application Training Additional Resources

Overview

Ex situ thermal treatment generally involves the destruction or removal of contaminants through exposure to high temperature in treatment cells, combustion chambers, or other means used to contain the contaminated media during the remediation process. The main advantage of ex situ treatments is that they generally require shorter time periods, and there is more certainty about the uniformity of treatment because of the ability to screen, homogenize, and continuously mix the contaminated media; however, ex situ processes require excavation of soils, which increases costs and engineering for equipment, permitting, and materials handling worker safety issues.

Thermal processes use heat to separate, destroy, or immobilize contaminants. Thermal desorption and hot gas decontamination are separation technologies. Pyrolysis and conventional incineration destroy the contaminants. Vitrification destroys or separates organics and immobilizes some inorganics.

Incineration is a heat-based technology that has been used for many years to burn and destroy contaminated materials. Because it is considered to be a conventional rather than an innovative technology, its treatment here is limited to information listed under "Additional Resources."

EX SITU THERMAL DESORPTION involves the application of heat to excavated wastes to volatilize organic contaminants and water. Typically, a carrier gas or vacuum system transports the volatilized water and organics to a treatment system, such as a thermal oxidation or recovery unit. Based on the operating temperature of the desorber, thermal desorption processes can be categorized as either high-temperature thermal desorption (320 to 560ºC or 600 to 1,000ºF) or low-temperature thermal desorption (90 to 320ºC or 200 to 600ºF).

HOT GAS DECONTAMINATION involves raising the temperature of contaminated solid material or equipment to 260ºC (500ºF) for a specified period of time. The gas effluent from the material is treated in an afterburner system to destroy all volatilized contaminants. This method will permit reuse or disposal of scrap as nonhazardous material.

PLASMA HIGH-TEMPERATURE RECOVERY uses a thermal treatment process applied to solids and soils that purges contaminants as metal fumes and organic vapors. The vapors can be burned as fuel, and the metals can be recovered and recycled.

PYROLYSIS is defined as chemical decomposition induced in organic materials by heat in the absence of oxygen. Pyrolysis typically occurs under pressure and at operating temperatures above 430ºC (800ºF). The pyrolysis gases require further treatment. The target contaminant groups for pyrolysis are SVOCs and pesticides. The process is applicable for the separation of organics from refinery wastes, coal tar wastes, wood-treating wastes, creosote-contaminated soils, hydrocarbon-contaminated soils, mixed (radioactive and hazardous) wastes, synthetic rubber processing wastes, and paint waste.

THERMAL OFF-GAS TREATMENT is one of several approaches that can be used to cleanse the off-gases generated from primary treatment technologies, such as air stripping and soil vapor extraction. In addition to the established thermal treatments, organic contaminants in gaseous form can be destroyed using innovative or emerging technologies, such as alkali bed reactors.

VITRIFICATION technology uses an electric current to melt contaminated soil at elevated temperatures (1,600 to 2,000ºC or 2,900 to 3,650ºF). Upon cooling, the vitrification product is a chemically stable, leach-resistant, glass and crystalline material similar to obsidian or basalt rock. The high temperature component of the process destroys or removes organic materials. Radionuclides and most heavy metals are retained within the vitrified product. Vitrification can be conducted in situ or ex situ.

A Citizen's Guide to Thermal Desorption
EPA 542-F-01-003, 2001

The Citizen's Guide Series are 2-page fact sheets that provide a general description on approaches to clean up contaminated was sites. The fact sheets cover five questions about each clean up approach: What is it?, How does it work?, Is it safe?, How long will it take?, and Why use it?

A Citizen's Guide to Vitrification
EPA 542-F-01-017, 2001

Guía del Ciudadano para la Desorción Térmica (Spanish Translation)
EPA 542-F-01-003S, 2001

La Serie de Guías del Ciudadano son boletines de dos páginas con datos que proveen una descripción general en cómo sanear sitios contaminados. Estos boletines con datos que cubren cinco preguntas acerca de cada procedimiento de saneamiento: ¿Qúe es?, ¿Cómo trabaja?, ¿Es seguro?, ¿Cúanto tiempo requerirá?, y ¿Por qué debe de usarse?

Overview of Thermal Desorption Technology
R.J. Feeney, P.J. Nicotri, and D.S. Janke. NFESC-CR-98-008-ENV, NTIS: ADA352083, 32 pp, 1998.

This report summarizes a presentation on thermal desorption designs, identifies contaminants for which thermal desorption is known or believed to be effective, and presents generalized cost data for a range of project sizes.

Remediation Technologies Screening Matrix and Reference Guide, Version 4.0
Federal Remediation Technologies Roundtable.

Treatment Technologies for Site Cleanup: Annual Status Report (ASR), Twelfth Edition
EPA 542-R-07-012, 2007

The Twelfth Edition of this report, published by the EPA Office of Superfund Remediation and Technology Innovation (OSRTI) in September 2007, documents treatment technology applications at more than 1,900 soil and groundwater cleanup projects at National Priorities List (NPL) sites. The status of more than 1,200 projects included in the ASR Eleventh Edition is updated, and information about 192 new projects derived from Records of Decision (ROD) signed from 2002 through 2005 is added. The report also includes a special section about on-site containment remedies. The ASR is based on the analysis of nearly 3,000 RODs signed since 1982 at 1,536 NPL sites. The online version includes new downloadable spreadsheets with the data for several of the key tables and figures in the report. Specific information about each technology application included in the ASR Twelfth Edition is available in the ASR Remediation Database.

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Last updated on Monday, October 1, 2007