Further description:-  Ex situ treatment technologies 

Glossary Entry
Ex situ technologies are remediation options where the affected medium (soil, water) is removed 
from it's original location and cleaned on-site or off-site. Examples: bioremediation or soil washing.

Ex situ (as well as in situ) remediation options can be grouped into categories based on their treatment mechanism:  physical, chemical, electrical, thermal and biological. In this digest, physical, chemical and electrical mechanisms have been abridged into one group, called physico-chemical. Due to the complex nature of many polluted soils and the fact that pollution, in many situations, is due to the presence of a “cocktail” of different types of contaminants, it is frequently necessary to apply more than one remediation technique (treatment train) to reduce the concentrations of pollutants to acceptable levels.



Biological Treatments


Biological treatment is a process whereby contaminants in soil, sediments, sludge or groundwater are transformed or degraded into innocuous substances such as carbon dioxide, water, fatty acids and biomass, through the action of microbial metabolism.

Biological processes are typically implemented at low cost. Contaminants can be destroyed and often little to no residual treatment is required. However, the process requires more time and it is difficult, in general, to determine whether contaminants have been completely destroyed. Additionally, microbes may often be sensitive to toxins or highly concentrated contaminants in the soil.



Physical/Chemical Treatments


Physical/chemical treatment uses the physical and/or chemical properties of the contaminants or of the contaminated medium to destroy (i.e., chemically convert), separate, or contain the contamination. In the physical processes the phase transfer of pollutants is induced. In the chemical processes the chemical structure (and then the behaviour) of the pollutants is changed by means of chemical reactions to produce less toxic or better separable compounds from the solid matrix.

These treatments are typically cost effective and can be completed in short time periods (in comparison with biological treatment). Equipment is readily available and is generally not engineering or energy-intensive.



Thermal Treatments


Thermal treatments offer quick cleanup times but are typically the most costly treatment group. This difference, however, is less in ex-situ applications than in in-situ applications. Cost is driven by energy and equipment costs and is both capital and Operation & Maintenance (O & M) intensive.

Thermal processes use heat to increase the volatility, to burn, decompose, destroy or melt the contaminants.

Cleaning soil with thermal methods may take only a few months or several years. The time it takes depends on three major factors that vary from site to site: type and amounts of chemicals present; size and depth of the polluted area; type of soil and conditions present.








Technology description:


Biopiles, also known as biocells or biomounds are engineered systems in which excavated soils are combined with soil amendments, formed into compost piles and enclosed for treatment. They are commonly provided with an air distribution system by blowers or vacuum pumps. Several properties of the process such as nutrients and oxygen can be controlled in order to enhance the remediation procedure. This technology is generally used to reduce concentrations of petroleum constituents in excavated soils. The treatment area is generally covered or contained with an impermeable liner to minimize the risk of contaminants leaching into uncontaminated soil. The leachate must be collected and treated.


Technology applicability:


Has been applied to treatment of nonhalogenated VOCs and fuel hydrocarbons; halogenated VOCs, SVOCs and pesticides can also be treated.



Technology advantages:


v      Very simple technology to design and implement

v      Cost competitive technology

v      Can be designed to be a closed system

v      Can be engineered to be potentially effective for any combination of site conditions and petroleum products


Technology limitations:


v      Concentration reductions > 95% and constituent concentrations < 0.1 ppm are very difficult to achieve

v      Presence of significant heavy metal concentrations may inhibit microbial growth

v      Vapour generation during aeration may require treatment prior to discharge

v      Contaminated soils must be excavated and dust and noise must be controlled

v      Static treatment processes may result in less uniform treatment than processes that involve periodic mixing


Technology development status:


This technology is commercially available for treating fuel contamination.





  • Biopiles


  • Biopiles






Technology description:


A bio-reactor is a generic term for an engineered system in which contaminants are degraded, in a specific media, with microorganisms. This technique also referred to as slurry phase bioremediation, varies considerably in its operating conditions. The principal emphasis is on stimulating the biological degradation rate by choosing the optimum temperature, pollutant concentration, degree of aeration and other factors.


Experience has shown that bioreactors are effective and capable of adapting to differing process/environmental conditions. Typically, the soil is mixed with water and any prescribed additives and placed in a batch reactor vessel. This slurry is kept at controlled operating conditions, with oxygen and nutrients supplied as required, until the remediation is complete. Typically, a slurry contains from 10 to 30% solids by weight. The soil is then dewatered and the resulting liquid reused, discarded or treated, as required. Aerobic systems are effective on the target contaminants while anaerobic bioreactors have been applied more effectively to halogenated hydrocarbons, to effect dehalogenation, prior to breakdown of the hydrocarbon itself. This technology has been successfully implemented to remediate organic compounds at leaking underground storage tank and industrial sites.



Technology applicability:


The bioreactor technique has been successfully used to remediate soils contaminated with petroleum hydrocarbons, petrochemicals, solvents, pesticides, wood preservatives, SVOCs, VOCs and other organic chemicals. Bioreactors are more suitable for heterogenous soils, soils with low permeability, soils belonging to areas where groundwater would be hard to capture, or scenarios requiring relatively short treatment times.



Technology advantages:


v      Is rapid when compared to other bioremediation methods

v      Is widely available

v      Can be particularly effective on contaminated clays


Technology limitations:


v      Is highly dependent upon the specific soil and chemical properties of the contaminated media

v      The process control is complex, more so than for solid-phase bioremediation techniques

v      Contaminated groundwater is often too dilute in nutrients to support an adequate microbial population. At the other extreme, very high concentrations may be toxic to microorganisms

v      Residuals may require further treatment or disposal


Technology development status:


Basic bioreactor technology is well-developed and commercially available for treating fuels and chemical contaminants. Several successful pilot projects have been completed for chlorinated compounds. Laboratory experiments have been done for explosive compounds.





(a)       Technical:

  • Bioreactors


  • Bioreactors, Bioreactors with Cometabolites, Bioreactors with Specially Adapted Microorganisms, and Sequential Anaerobic/Aerobic Bioreactors

http://enviro.nfesc.navy.mil/esc414/techinfo/shortlist/shortlist.htm#B4:%20 Bioreactors

  • Soil and Water Bioremediation Using Bioreactors

http://www.cee.vt.edu/program_areas/environmental/teach/gwprimer/bioreact/ bior.html

  • Cookson, John T.Jr., 1995, Bioremediation Engineering Design and Application, McGraw-Hill, Inc., New York, NY.


(b)       Application:

  • Bioremediation of dinitrotoluene (DNT)


  • Degradation of p-nitrophenol and pentachlorophenol mixtures by Sphingomonas SP UG30 in soil perfusion bioreactors






Technology description:


Composting is a controlled biological process by which organic contaminants in the soil are converted by microorganisms, under both aerobic and anaerobic conditions, to innocuous, stabilized byproducts. Soils are excavated and mixed with bulking agents and organic amendments such as wood chips and plant wastes. Typically, thermophilic conditions (54 to 65 °C) must be maintained to properly compost contaminated soil. Proper conditions of oxygen and moisture help to achieve maximum degradation efficiency.


There are three major designs used in composting:

(1)   Aerobic static pile – compost is formed into piles and aerated with blowers or vacuum pumps.

(2)   Mechanically agitated in-vessel composting- compost is placed in a reactor vessel where it is mixed and aerated.

(3)   Windrow composting- compost is placed in long piles known as windrows and periodically mixed with mobile equipment.



Technology applicability:


The composting process can be used for soils contaminated with biodegradable organic compounds, heavy oils, PAHs and munition wastes such as 2,4,6-trinitrotoluene (TNT). Pilot and full-scale projects have demonstrated that aerobic composting is also applicable to SVOC-contaminated soil.



Technology advantages:


v      Is a demonstrated, efficient technology to treat explosives

v      It is a commercially available, technically attractive technology


Technology limitations:


v      Substantial space and labor costs are required for composting

v      Excavation of contaminated soils is required and may cause the uncontrolled release of VOCs and dust

v      If VOC contaminants are present in soils, off-gas control may be required

v      Results in an increase in material because of the addition of amendment material

v      Although levels of metals may be reduced via dilution, heavy metals are not treated by this method


Technology development status:


The technology is widely used for domestic wastes and explosives. It is in the demonstration phase for hazardous waste degradation and holds promise particularly for treatment of explosives-contaminated soil.





(a)       Technical:

  • Composting



(b)       Application:

  • The Composting Alternative to Incineration of Explosives Contaminated Soils


·         Composting at the Dubose Oil Products Co. Superfund Site, Cantonment, Florida


·         Windrow Composting to Treat Explosives-contaminated Soil at Umatilla Army Depot Activity, Hermiston, Oregon






Technology description:


Landfarming, also known as land treatment or land application, is an above-ground remediation technology for soils. It reduces concentrations of contaminants through biodegradation. In the ex-situ process, the contaminated soil is first excavated, mixed with soil amendments such as soil bulking agents and nutrients and then tilled into the earth. The soil is spread over an area and periodically turned to improve aeration. Turning the soil also avoids the disadvantages of having heterogeneous degradation. Soil conditions are controlled to optimize the rate of contaminant degradation. The enhanced microbial activity results in degradation of adsorbed petroleum product constituents through microbial respiration. The petroleum industry has used landfarming for many years.


This technique is also applicable in in-situ interventions with a different technological setup.



Technology applicability:


Landfarming has been proven most successful in treating petroleum hydrocarbons and other less volatile biodegradable contaminants. It can also be applied to certain halogenated volatile, semi-volatile and non-halogenated semi-volatile organic compounds and to pesticides. Diesel fuel, oily sludge, wood-preserving wastes have also been successfully treated.



Technology advantages:


v      It is extremely simple and rather inexpensive and requires no process controls

v      Relatively unskilled personnel can perform the technique

v      Certain pollutants can be completely removed from the soil


Technology limitations:


v      It requires extensive space and time

v      Certain pollutants cannot be reduced to sufficiently low levels

v      Runoff must be collected and may require treatment

v      It can incorporate contaminated soil into uncontaminated soil, creating a larger volume of contaminated material.

v      Conditions affecting biological degradation of contaminants (e.g. temperature and rainfall) are largely uncontrolled. This may increase the time to complete remediation


Technology development status:


Numerous full-scale operations have been used, particularly for sludges produced by the petroleum industry. Land farming is considered a commercial technology.





  • Landfarming


  • Landfarming









Technology description:


Chemical extraction is a process that separates contaminants from soils, thereby reducing the volume of the contaminant that must be treated. The two major chemical extraction processes, which are based on the type of contaminants present in the soil, are:

(1)       Acid extraction- uses acids to extract contaminants from soils. Heavy metals are potentially suitable for recovery. Clean soils are dewatered and mixed with lime and fertilizer to neutralize any residual acid.

(2)       Solvent extraction- uses solvents to remove metals and mixtures of metal and organic compounds. Soil is removed and treated.


Physical separation is generally used before chemical extraction, on the assumption that the major part of the contamination is on the smaller particles. Physical separation can also enhance the kinetics of extraction by separating out particulate heavy metals, if these are present in the soil.



Technology applicability:


Chemical extraction is used to treat soils containing organic contaminants such as SVOCs, VOCs, explosives, inorganics, some fuels and heavy metals.


Technology advantages:


v      Can be used to extract a wide range of target contaminants

v      High concentrations of pollutants can be treated


Technology limitations:


v      Is generally less effective on high molecular weight organics or on hydrophilic substances

v      Certain solvents will be ineffective in some soil types or if excessive moisture is present

v      Solvent treatment and disposal can be significant factors

v      After acid extraction, any residual acid in treated soil needs to be neutralized

v      The toxicity of the solvent is an important consideration as traces may remain in the treated soil


Technology development status:


Commercial-scale units are in operation.





(a)       Technical:

  • Chemical Extraction



(b)       Application:

  • Solvent Extraction at the Sparrevohn Long Range Radar Station, Alaska


  • Solvent Extraction/Dechlorination at the New Bedford Harbor Superfund Site, New Bedford, Massachusetts






Technology description:


Dehalogenation, also known as dechlorination, is a technology in which the chlorine in organic compounds is displaced by hydrogen or a reducing radical containing a hydrogen donor. This process is achieved by either the replacement of the halogen molecules or the decomposition and partial volatilization of the contaminants. Contaminated soil is screened, processed with a crusher, mixed with chemical reagents and the mixture is heated in a reactor.


There are two dehalogenation processes:

1)      Base-Catalyzed Decomposition (BCD) - where contaminated soil is screened, processed with a crusher and pug mill and mixed with sodium bicarbonate. The mixture is heated to above 330°C (630 °F) in a reactor to partially decompose and volatilize the contaminants. The volatilized contaminants are captured, condensed and treated separately.

2)      Glycolate/Alkaline Polyethylene Glycol- process in which an alkaline polyethylene glycol (APEG) reagent is used. In the APEG process, the reaction causes the polyethylene glycol to dehalogenate to form a glycol ether and/or a hydroxylated compound and an alkali metal salt, which are water-soluble byproducts.



Technology applicability:


Contaminants that can be treated are halogenated SVOCs and pesticides in soils. APEG dehalogenation can be used but may be less effective against selected halogenated VOCs. The technology is amenable to small-scale applications. The BCD can be also used to treat halogenated VOCs but will generally be more expensive than other technologies






v      APEG dehalogenation is one of the few techniques which has been demonstrated to successfully eliminate PCBs

v      BCD dehalogenation uses low-cost reagents that do not need to be recovered and reused


Technology limitations:


v      The APEG process is generally not cost effective for large volumes of contaminated soil

v      Soil with elevated concentrations of chlorinated contaminants requires large volumes of reagent

v      Some glycol ethers are very toxic and persistent. It is still not completely clear what byproducts the APEG technology produces and how they are captured and treated


Technology development status:


The BCD process is still being pilot tested. The APEG system has been field tested. Neither is considered commercially available at this time.





(a)       Technical

·         A Citizen's Guide to Chemical Dehalogenation


·         Dehalogenation



(b)       Application:

·         Thermal Desorption/Dehalogenation at the Wide Beach Development Superfund Site, Brant, New York






Technology description:


Separation techniques reduce the volume of contaminated soil through physical and chemical processes by selectively removing the portion containing the contaminants. There are several types of separation techniques:

1)      Gravity Separation- is used to separate solids from soil, based on the density difference between contaminants and soil e.g., when the metal-contaminated soil is suspended in water, denser materials such as metals sink and are removed

2)      Sieving/Physical Separation- is based on separation according to size of the particles.

3)      Magnetic Separation- is used to separate slightly magnetic particles from soil. All uranium and plutonium compounds are slightly magnetic while most soil is nonmagnetic.

4)      Chemical Leaching processes- use weak acids such as acetic acid to dissolve and wash the metals from the soil. The metals recovered by the process can possibly be recycled.



Technology applicability:


Contaminants that can be treated are fuels, inorganics, heavy metals, some SVOCs and VOCs.



Technology advantages:


v      Can reduce the volume of contaminated soil considerably

v      It has been successfully demonstrated in municipal waste treatment


Technology limitations:


v      It does not work well when the undesirable material is homogeneously distributed in the soil

v      The segregated soil is not at all cleaned by this technique; a subsequent process is required to actually remove the pollutants from the soil particles

v      Special measures may be required to mitigate odor problems resulting from organic sludge that undergoes septic conditions

v      Magnetic separation may leave small suspension of contaminated materials in the slurry, which may be more difficult to remediate than the original soil contamination



Technology development status:


Physical separation techniques like gravity and sieving/physical separation are generally proven. Magnetic separation is in the experimental stage. Chemical leaching is in the field-test stage.




 (a)      Technical:

·         Using Separation Processes from the Mineral Processing Industry for Soil Treatment


·         Separation


·         Separation



(b)       Application:

·         Joint Small Arms Range Remediation (Physical Separation and Acid Leaching)






Technology description:


Solar detoxification, otherwise known as Photolysis, is an emerging remedial technology which is used for the destruction of a wide range of hazardous organic chemicals in soil and/or water by photocatalytic oxidation or direct thermal decomposition. In this process, vacuum extraction is used to remove contaminants from soils. After condensation, contaminants are mixed with a semiconductor catalyst and fed through a reactor illuminated by sunlight or exposed to ultraviolet radiation from electric lamps. The light activates the catalyst and this results in the generation of radicals which oxidize the contaminants into non-toxic byproducts such as waster, carbon dioxide and inorganic salts.



Technology applicability:


Is used for destruction of VOCs, SVOCs, solvents, pesticides, fuels and explosives. Some applications of removing heavy metals from water have been done.



Technology advantages:


v      This system completely destroys the toxic compounds instead of just removing them

v      The solar process has no atmospheric emissions


v      Effective technology for reducing different pollutants to minimum concentrations


Technology limitations:


v      Few full scale applications and no adequate information about costing

v      Biological or physical fouling with suspended solid or precipitates could limit its effectiveness

v      It can only be effectively used during the daytime with normal intensity of sunlight

v      Large spaces are required for the reactor: the larger the reactor, the more efficient the process


Technology development status:


The technology has been proven in pilot-field with success.





(a)       Technical:

·         Solar Detoxification



(b)       Application:

  • Solar detoxification applications






Technology description:


Chemical reduction/oxidation, also known as redox reactions, converts hazardous contaminants to non-hazardous or less toxic compounds that are more stable, less mobile and/or inert. Redox reactions involve the transfer of electrons from one compound to another. One compound is oxidized (loses electrons) and the other is reduced (gains electrons). The oxidizing agents most commonly used are ozone, hydrogen peroxide, hypochlorite, chlorine and chlorine dioxide. A mixture of these reagents or combining them with ultraviolet oxidation makes the process more effective. In the reduction processes, sodium borohydride or metals with low oxidation potential are generally used for unsaturated organic contaminants or high oxidation state metals (e.g. Cr VI).


It is a short to medium term technology.



Technology applicability:


Treats metals and inorganics in soils. Oxidation is most suitable for clay soils contaminated by organics at low redox potentials. Redox processes have also been applied for the treatment of pesticides, cyanides, triazines and formaldehyde contaminated soils. The technology is less effective against non-chlorinated VOCs and SVOCs, fuels.



Technology advantages:


v      Is well established and has been used for decades in related chemical processes

v      The chemistry involved in the process is generally well known


Technology limitations:


v      Excessive oil and grease compete with the contaminants during chemical reactions and may need to be removed prior to treatment

v      The decontamination may be incomplete or result in the formation of intermediate contaminants for certain pollutants or process conditions

v      The process is not cost effective for high contaminant concentrations due to the excessive amounts of reagents required


Technology development status:


Is a full-scale, well-established technology. Enhanced systems are now being used more frequently to treat hazardous substances in soils.





(a)       Technical:

·         Chemical oxidation/reduction


  • In Situ Chemical Oxidation for Remediation of Contaminated Soil and Ground Water



(b)       Application:

·         Chemical Oxidation

·         In Situ Chemical Oxidation: Technology Features and Applications






Technology description:


Soil washing is a technique in which contaminants sorbed onto fine soil particles are separated from bulk soil in an aqueous-based system on the basis of particle size. Contaminants are removed from the soil in one of two ways:

(1)   By dissolving or suspending them in the wash solution

(2)   By concentrating them into a smaller volume of soil through particle size separation, gravity separation and attrition scrubbing


The concept of reducing soil contamination through the use of particle size separation is based on the finding that most organic and inorganic contaminants tend to bind, either chemically or physically, to clay, silt and organic soil particles. Most silt and clay are stuck to larger particles like sand and gravel. Washing separates the small particles from the large ones by breaking adhesive bonds. The separated material is smaller in volume and is more easily disposed of.



Technology applicability:


Contaminants treated are SVOCs, fuels, explosives and heavy metals. The technology can be used on selected VOCs and pesticides. It offers the ability for recovery of metals and can clean a wide range of organic and inorganic contaminants from coarse-grained soils.



Technology advantages:


v      Is a well-established and versatile technique

v      It provides a cost effective and environmentally proactive alternative to stabilisation and landfilling


Technology limitations:


v      Is not always effective on all soil types and works better on coarse-particle and sandy soils

v      High levels of organic matter inhibit desorption

v      The aqueous stream will require treatment at demobilisation

v      Complex mixtures of pollutants may be difficult to remediate with a single wash regime


Technology development status:


The technology of soil washing is used extensively in Europe but has had limited use in the United States.





(a)       Technical:

·         A Citizen's Guide to Soil Washing (English Version)


·         Soil washing



(b)       Application:

·         Remediation of Basford Gasworks [UK] Using Soil Washing. 2002. CL:AIRE (Contaminated Land: Applications In Real Environments) Technology Demonstration Project Fact Sheet TDP2.


·         Full-scale and pilot-scale soil washing Mann, Michael J.; Journal of Hazardous Materials, Vol 66 No 1, p 119-136, 1999.

·         Journal of hazardous materials Special Issue on Soil Washing, R.M. Dennis (ed.). Vol 66 No 1-2, 220 pp, 1999

·         Audit report: soil washing at the Ashtabula environmental management project U.S. DOE, Office of the Inspector General. Report No: DOE/IG-0542. 14 pp, Jan 2002 http://www.ig.doe.gov/pdf/ig-0542.pdf





Technology description:


In ex-situ Solidification/Stabilisation (S/S) contaminants are physically bound or enclosed within a low-permeability mass (solidification), or chemical reactions are induced between a stabilizing agent and contaminants to reduce their mobility (stabilisation). Ex situ S/S, however, typically requires disposal of the resultant materials.


This technique is also applicable in in-situ interventions with a different technological setup..



Technology applicability:


Contaminants treated are inorganics, including radionuclides. Most S/S technologies have limited effectiveness against organics and pesticides.



Technology advantages:


v      Are relatively inexpensive methods for treating soils contaminated with inorganics

v      Can be extremely simple to apply


Technology limitations:


v      The pollutants are neither removed nor made less toxic, only rendered less mobile

v      The volume of the final mass is generally higher than that of the original contaminated soil (when using solidification)

v      The resulting mass may still need to be controlled as a hazardous waste

v      For stabilisation, treatability studies may be required to determine applicability

v      Organic contaminants are generally not immobilized


Technology development status:


Some techniques are commercial while some are being field-tested and can be applied to the most common site and waste types.





  • A Citizen's Guide to Solidification/Stabilisation


·         Solidification/Stabilisation

  • Solidification/Stabilisation






Technology description:


Soil Vapour Extraction (SVE), also known as Soil Venting, is a technology which in principle, is similar to in-situ SVE. However, in the ex-situ process, the contaminated soil is excavated. A vacuum is applied to a network of aboveground piping to encourage volatilization of organics from the excavated media. The soil piles may be covered with a geomembrane to prevent volatile emissions and to prevent the soil from becoming saturated by precipitation. The process includes a system for handling off-gases.



Technology applicability:


Contaminants treated are VOCs, volatile metals and fuels contamination. SVE works only on compounds that readily vaporize under process conditions.



Technology advantages:


v      Is simplistic in design and easily implemented and can prove to be productive in areas where access to the contaminated site is very limited

v      The excavation process forms an increased number of passageways, leachate collection is possible and treatment is more uniform and easily monitored

v      The equipment requires relatively little control during operation

v      As the pollutants are under vacuum conditions, there is little chance of an environmental release during the application of this technique


Technology limitations:


v      Increased excavation costs

v      Excavation and materials handling may pose hazardous emissions to the surroundings

v      Limited to contaminants that will partition into the vapour phase

v      High moisture content, high humic content or compact soil inhibits volatilisation

v      A field-pilot study is necessary to establish the feasibility of the method, the best process conditions, as well as, to obtain information necessary to design and configure the system


Technology development status:


SVE is commercially available and widely used. Some pilot-studies are necessary to establish the feasibility of the process.





(a)   Technical

·         Soil vapour extraction


  • Analysis  of selected enhancements for Soil vapour extraction


  • Soil vapour extraction


  • Soil vapour extraction cost and performance reports



(b)   Application

  • SVE at the Basket Creek Surface Impoundment Site









Technology description:


Hot gas decontamination is essentially a low temperature thermal desorption process. The process raises the temperature of the contaminated soil to approximately 260 °C for a specified period of time by exposing it to hot gases (i.e. heated air), volatilizing the contaminants, and destroying them in an afterburner. This technology can be used to decontaminate equipment and structures that have been contaminated with explosive residues.



Technology applicability:

It is applicable for equipment requiring decontamination for reuse, for explosive items, such as mines and shells, being demilitarized (after removal of explosives) or scrap material contaminated with explosives such as TNT. Can also be used for buildings or structures associated with ammunition plants, arsenals, and depots involved in the manufacture and processing of explosives and propellants.



Technology advantages:


v      Contaminants are completely destroyed


Technology limitations:


v      The largest concern is atmospheric emissions from the thermal oxidizer

v      The furnace design must take into consideration possible explosions

v      The cost of this method is higher than open burning


Technology development status:


The Hot Gas Decontamination process is at the field demonstration stage.





·         Hot gas decontamination


·         http://aec.army.mil/prod/usaec/et/restor/hotgas.htm





Technology description:


Open burning, also known as open detonation, is a technique used to destroy excess, obsolete, or unserviceable munitions and explosive materials. These materials are destroyed by self-sustained combustion, which is ignited by an external source. An auxiliary fuel may be added to initiate and sustain the combustion of materials.


In the past, open burning generally occurred in the surface of the land or in pits. Recently, burn trays and blast boxes have been used to control and contain resulting emissions.



Technology applicability:


This technology is used to destroy explosives.



Technology advantages:


v      With sufficient security systems it is a suitable procedure for delicate explosives and munition


Technology limitations:


v      Emissions of hydrocarbons, metals and other substances from open operations are extremely difficult to capture and may not be permitted in many areas

v      Subsurface processes may minimize release of emissions

v      Substantial space is required for open processes in order to maintain minimum distance requirements for safety purposes

v      Is a process that can lead toxic releases and exposures

v      Safety problems can occur


Technology development status:


Open burning is well established but increasingly restricted due to environmental and safety concerns.





·         Open burning






Technology description:


Thermal desorption is a physical separation process in which water and organic contaminants in contaminated soil are volatized by heating the soil to moderately high temperatures (100o - 550oC). A carrier gas or vacuum system transports the volatilized water and organics to the gas treatment system. The bed temperatures and residence times designed into these systems volatilize selected contaminants but not degrade them.


Based on the operating temperature of the desorber, thermal desorption processes can be categorized into two groups:

(1)   High temperature thermal desorption (HTTD)- contaminants are heated to 320 to 560 oC

(2)   Low temperature thermal desorption (LTTD)- contaminants are heated to between 90 and

320 oC


Two common thermal desorption designs are the rotary dryer and thermal screw. Rotary dryers are horizontal cylinders that can be indirect- or direct-fired. The dryer is normally inclined and rotated. For the thermal screw units, screw conveyors or hollow augers are used to transport the medium through an enclosed trough. Hot oil or steam circulates through the auger to indirectly heat the medium. All thermal desorption systems require treatment of the off-gas to remove particulates and contaminants. Particulates are removed by conventional particulate removal equipment, such as wet scrubbers or fabric filters.



Technology applicability:


Contaminants treated in LTTD systems are VOCs, SVOCs and fuels. For HTTD, the groups are SVOCs, PAHs, PCBs and pesticides. VOCs and fuels may be treated but treatment may be less cost-effective. Volatile metals may be removed by HTTD.



Technology advantages:


v      The cost is typically less than for incineration

v      Applicable to a wide range of pollutants


Technology limitations:


v      Has some limitations with heavy metals; these remain in the solid residue and may form toxic by-products during treatment

v      There are specific particle size and materials handling requirements that can impact applicability or cost at specific sites

v      Dewatering may be necessary to achieve acceptable soil moisture content levels


Technology development status:


Thermal desorption is a well established technology.





(a)       Technical:

·         Innovative Site Remediation Technology, Vol. 6: Thermal Desorption. 1993. William C. Anderson, Consortium for American Academy of Environmental Engineers, Annapolis, MD. (WASTECH) ISBN: 1-883767-06-7, NTIS: PB94-181716, 146 pp.

  • Thermal desorption: a technology review Sullivan, Timothy P. San Antonio Air Logistics Center, Kelly AFB, TX NTIS Order No: ADA331953. 93 pp, Jul 97

·         Destruction technologies for polychlorinated biphenyls (PCBS) Rahuman, M.S.M. Mujeebur (ICS-UNIDO); Luigi Pistone (SiiRTEC NIGI S.p.A., Milan, Italy); Ferruccio Trifio’ (Univ. of Bologna, Italy); Stanislav Miertus (ICS-UNIDO) International Centre for Science and High Technology, United Nations Industrial Development Organization (ICS-UNIDO), Trieste, Italy. 55 pp, Nov 2000


(b)       Application:

  • Remediation case studies: ex situ soil treatment technologies (bioremediation, solvent extraction, thermal desorption). Volume 7 Federal Remediation Technologies Roundtable Sponsor: Environmental Protection Agency, Washington, DC Report No: EPA/542/R-98/011. NTIS Order No: PB99-118481. 166 pp, Sept 1998
  • Thermal desorption treatability studies: removing chlorinated organic compounds from soils Downey, Jerome P. (Hazen Research, Inc., Golden, CO); Lawrence D. May; Kari D. Moore Physical, Chemical, and Thermal Technologies: Remediation of Chlorinated and Recalcitrant Compounds Battelle Press, Columbus, OH. ISBN 1-57477-060-8. p 7-12, 1998
  • Thermal Desorption at the Re-Solve, Inc. Superfund Site, North Dartmouth, Massachusetts


  • Thermal Desorption at the Reich Farm Superfund Site, Pleasant Plains, New Jersey






Technology description:


Plasma arc technology is a pyrolysis process. It uses a plasma arc device to create extremely high temperatures (10000oC or even higher) for destruction of toxic substances in contaminated soil.


In plasma arc treatment an electric current is directed through a low-pressure gas stream to create a thermal plasma field.  Plasma arc fields can reach 5000 to 15000 oC.


Energy is transferred to contaminants exposed to the plasma and contaminants are then atomized, ionized, pyrolysed and finally destroyed as they interact with the decaying plasma species.



Technology applicability:


It is applicable for the treatment of organic substances. Initial test results have shown it is a promising alternative for destruction of difficult to treat wastes such as dioxin contaminated sludges.



Technology advantages:


v      Effective technology to safety destroy PCBs, dioxins, furans and pesticides

v      A plasma system has very intense radiative power and therefore is capable of transferring its heat much faster than a conventional flame

v      Since it is a pyrolysis process, it does not need the energy to heat excess air required by conventional incinerators

v      Needs a smaller capacity of downstream cleanup systems, because no excess air is involved

v      Because of its compactness, the system has potential for use as a mobile treatment system

v      The process has a very short on-off cycle


Technology limitations:


v      Use electricity as an energy source and so is more expensive when compared to using oil to fire incinerators

v      Require a separate extraction process such as solvent extraction or thermal desorption to remove the contaminants from bulk solid media

v      Solids must be first be converted to liquid or gas prior to treatment

v      Metals may impede treatment and must be separated for the technique in order to be effective

v      Because the temperatures are so high, the durability of the arc and the refractory materials could be a potential problem


Technology development status:


Plasma arc technology is undergoing field demonstration tests.





  • Staley  L. (1992) Site demonstration of the retech plasma centrifugal furnace: the use of plasma to vitrify contaminated soil, J.Air Waste Manage. Assoc., vol. 42, n.10
  • Environment Australia, Appropriate Technologies for the Treatment of Schedules Wastes, Review Report Number 4-November 1997


  • Huffman, G.L. and Lee, C.C. Plasma Systems, Standard Handbook of Hazardous Waste Treatment and Disposal, 2nd Ed.





Technology description:


Incineration is a technology which uses high temperatures, 850o - 1200oC and oxygen, to volatize and combust different kinds of hazardous contaminants. Auxiliary fuels are used to initiate and sustain combustion. Proper incinerator design and operation are essential to ensuring adequate destruction of undesirable combustion gases. A properly operated incinerator can meet the stringent requirements for all gaseous emissions. Air pollution-control systems are employed to remove particulates and to neutralize and remove acids.


Incineration is different from other thermal technologies in that it oxidizes bulk quantities of contaminants that may be in liquid and solid phase.


Four common incinerator types are rotary kiln, liquid injection, fluidized bed and infrared kiln.



Technology applicability:


Is used to remediate soils contaminated with hazardous substances (VOCs, SVOCs), particularly halogenated and organic compounds, fuels and explosives.



Technology advantages:


v      Is one of the most mature and well-known treatment technologies

v      At high temperatures it is fast and very effective (99%)

v      Highly effective for a wide range of contaminants in high concentrations


Technology limitations:


v      Is a costly technique

v      Pre-treatment to remove heavy metals may be required because they remain in the solid residue or may possibly leave with the flue gases

v      May release toxic chemicals from their stacks

v      When chlorinated hydrocarbons are incinerated, products of incomplete combustion can be formed; these may include dioxins and furans

v      Wastes with heavy metals can produce a bottom ash of high concentrations


Technology development status:


Incineration is a full scale commercial technology.





(a)       Technical:

·         Incineration



(b)       Application:

·         Incineration of explosive contaminated soil and reactive RCRA waste


·         Incineration at the Baird and McGuire Superfund Site, Holbrook, Massachusetts


·         Incineration at the Bayou Bonfouca Superfund Site, Slidell, Louisiana






Technology description:


Pyrolysis, also known as plasma pyrolysis, is the thermal degradation of organic species in the absence of oxygen or other reactant gases. In practice, as it is not possible to achieve a completely oxygen-free atmosphere, actual pyrolytic systems are operated with less than stoichiometric quantities of oxygen.


This thermal technology is a form of incineration at operating temperatures above 430 °C. Organic materials are transformed into gases, small quantities of liquid and a solid residue (coke) containing carbon and ash. The off-gases may also be treated in a secondary thermal oxidation unit. Particulate removal equipment is also required. Conventional thermal treatment methods such as rotary kiln, rotary hearth furnace or fluidized bed furnace are used for waste pyrolysis.



Technology applicability:


Treats and destroys SVOCs, fuels 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.



Technology advantages:


v      The reactions are endothermic, making it possible to control pyrolysis temperature by regulating heat addition

v      Heavy metal volatilization and emissions are greatly reduced because the waste stream is only exposed to mild temperatures

v      Caustic can be added during pyrolysis of halogenated contaminants to trap halogens as sodium halides, thus reducing exhaust gas scrubber loads

v      Solids produced in this process can be high-value products such as adsorbents, electrodes and catalyst supports


Technology limitations:


v      The technology requires drying of the soil prior to treatment

v      There is concern that systems that destroy chlorinated organic molecules by heat have the potential to create products of incomplete combustion, including dioxins and furans

v      Pyrolysis is not effective in either destroying or physically separating inorganics from the contaminated medium

v      By-products containing heavy metals may require stabilisation before final disposal


Technology development status:


The technology is emerging and is in the pilot test stage.





(a)       Technical:

·         Pyrolysis


·         Pyrolysis


·         Pyrolysis



(b)       Application:

·         Roy, C., B. de Caumia, D. Blanchette, H. Pakdel, G. Couture and A. E. Schwerdtfeger. "Vacuum Pyrolysis Process for the Remediation of Hydrocarbon-Contaminated Soils". Remediation. Winter 1994/95 : 111-130.

·         Advanced Chemical Treatment of Waste






Technology description:


This ex-situ technique is much like in situ vitrification, except that it is done inside a chamber. Heating devices include plasma torches and electric arc furnaces. With plasma torch technology, contaminated soil is fed into a rotating hearth; the contaminants and molten material are held against the side by centrifugal force. During the rotation, the contaminants move through plasma generated by a stationary torch. To remove the molten material from the furnace, the hearth’s rotation slows and the slag flows through a bottom opening. Effluent gases are generally kept in a separate container where high temperatures combust/oxidize the contents. The arc furnace contains carbon electrodes, cooled sidewalls, a continuous feed system, and an off-gas treatment system. In this process, contaminated soil is fed into a chamber where it is heated to temperatures greater than 1500°C. The melt exits the vitrification unit and cools to form a glassy solid that immobilizes inorganics.



Technology applicability:


It is applicable for the treatment of organics, inorganics and radionuclides.



Technology advantages:


v      Effective technology to immobilize heavy metals


Technology limitations:

v      High moisture content increases cost

v      Excavation of radioactively contaminated soils could cause radiation exposure to workers from fugitive gas and dust emissions, and it may increase the risk to nearby populations. There is potential for the accumulation of volatile radionuclides in the melter off-gas system

v      Use, storage, or disposal of the vitrified slag is required


Technology development status:


Demonstrations and studies at several sites indicate that ex-situ vitrification technologies can be implemented without significant difficulties.





(a)       Technical:

·         A Citizen's Guide to Vitrification



(b)       Application:

·         Waste Vitrification Systems Lessons Learned


·         Vitrification of Residue (ASH) From Municipal Waste Combustion





Andrea Lodolo

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