Further description:-  In situ treatment technologies 

Glossary Entry
In situ treatment technologies are chemical, physical, biological, thermal or electrical processes 
that remove, degrade, chemically modify, stabilise or encapsulate contaminants within soil or
groundwater (matrices) without removing those matrices from the ground.
2

In situ (as well as ex 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 several remediation techniques (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.

Certain in situ physical/chemical treatment technologies are sensitive to certain soil parameters. For example, the presence of clay or humic materials in soil causes variations in horizontal and vertical hydraulic parameters, which, in turn, cause variations in physical/chemical process performance.

 

 

Thermal Treatments

 

Thermal treatments offer quick cleanup times but are typically the most costly treatment group. This difference, however, is higher in in-situ than in ex-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.

 

 

IN SITU BIOLOGICAL TREATMENTS

 

BIOVENTING

 

Technology Description:

 

Bioventing is a promising new technology which stimulates the naturally occurring soil microorganisms to degrade compounds in soil, by providing oxygen. This is done when the rate of natural degradation is generally limited by the lack of oxygen and other electron acceptors (i.e., a compound that gains electrons) rather than by the lack of nutrients during biodegradation. Oxygen is most commonly supplied through direct air injection into residual contamination in soil. Passive bioventing systems use natural air circulation to deliver oxygen to the subsurface via bioventing wells. In active bioventing systems the circulation of air is induced by injection and extraction devices (e.g. blowers, vacuum pumps, etc.).

 

 

Technology applicability:

 

All aerobically biodegradable constituents can be treated by bioventing. This technique remediates soils contaminated with fuel, in particular gasoline, non-chlorinated solvents, some pesticides, wood preservatives and other organic chemicals. In addition to degradation of adsorbed fuel residuals, volatile compounds are biodegraded.

 

 

Technology advantages:

 

v      Uses readily available and easily installed equipments

v      Creates minimal disturbance to site operations

v      Requires short treatment times

v      Cost competitive

v      Easily combines with other technologies

v      May not require costly off- gas treatment

 

Technology limitations:

 

v      High contaminant concentrations may initially be toxic to microorganisms

v      High soil moisture or low permeability soils reduce bioventing performance

v      Extremely low soil moisture content may limit biodegradation and the effectiveness of bioventing

v      Cannot always achieve very low cleanup standards

v      Permits generally required for nutrient supply

v      Only treats unsaturated zone soils

v      Monitoring of vapour at the soil surface may be required

 

Technology development status:

 

Bioventing is becoming more common and most of the hardware components are readily available. It is receiving increased interest in the remediation consulting community.

 

References:

 

(a)       Technical:

  • Bioventing

http://www.em.doe.gov/define/techs/remdes2.html#372

  • Chapter III: Bioventing.1995. 46 pp. In EPA 510-B-95-007, How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers.

http://www.epa.gov/swerust1/pubs/tum_ch3.pdf

  • Bioventing

www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-1-4007/c-7.pdf

 

 

(b)       Application:

  • Reports of bioventing & biosparging applications by DOD U.S. DoD, Defense Technical Information Center (DTIC) web site

http://stinet.dtic.mil/str/tr_fields.html

  • Demonstration of bioventing for remediation of chlorinated solvent contamination at hill air force base, Ogden, Utah Alleman, Bruce C.; James T. Gibbs Battelle, Columbus, OH Report Nos: AFRL-ML-TY-TR-1999-4507 (Vol.1); AFRL-ML-TY-TR-1999-4508 (Vol.2). NTIS Order Nos: ADA361494; ADA361495. 71 pp (Vol.1), 427 pp (Vol.2), Jan 1999
  • Bioventing nonpetroleum hydrocarbons Gibbs, James T.; B.C. Alleman; R.D. Gillespie; E.A. Foote; S.E. McCall; F.A. Snyder; J.E. Hicks (Battelle, Columbus, OH); R.K. Crowe (TRW Inc., Tyndall AFB, FL); J. Ginn (USAF, Hill AFB, UT) Engineered Approaches for In Situ
  • Bioremediation of Chlorinated Solvent Contamination (Fifth International In Situ and On-Site Bioremediation Symposium, 19-22 April 1999, San Diego, CA. Vol 2) Battelle Press, Columbus, OH. ISBN: 1-57477-075-6. p 7-14, 1999
  • Soil Vapour Extraction and Bioventing for Remediation of a JP-4 Fuel Spill at Site 914, Hill Air Force Base, Ogden, Utah http://bigisland.ttclients.com/frtr/00000005.html

·         Bioventing at Multiple Air Force Test Sites

http://bigisland.ttclients.com/frtr/00000221.html

 

 

ENHANCED BIOREMEDIATION

 

Technology description:

 

Enhanced Bioremediation, also known as Biostimulation or Bioaugmentation, involves the addition of microorganisms (e.g., fungi, bacteria, and other microbes) or nutrients (e.g. oxygen, nitrates) to the subsurface environment, in order to accelerate the natural biodegradation process.

 

There are four major types of enhancements involved: gaseous nutrient injection, hydrogen peroxide circulation, nitrate enhancement and bio-augmentation.

(1)   Gaseous nutrient injection- nutrients are injected into contaminated soil via wells to encourage and feed naturally occurring microorganisms. The most commonly added gas is air.

(2)   Hydrogen peroxide circulation- involves injecting a dilute solution of hydrogen peroxide which circulates through the contaminated soil to enhance the rate of aerobic biodegradation.

(3)   Nitrate enhancement- a solution of nitrate is sometimes added to the contaminated soil to enhance anaerobic biodegradation.

(4)   Bioaugmentation- sometimes acclimated microorganisms are added to soil to increase biological activity.

 

Enhanced bioremediation may be classified as a long-term technology.

 

 

Technology applicability:

 

Enhanced bioremediation techniques have been successfully applied to remediate soils contaminated with petroleum hydrocarbons, VOCs, SVOCs and pesticides. It is especially effective for remediation of low level residual contamination in conjunction with source removal. Anaerobic microbial degradation of nitrotoluenes in contaminated soils has been effectively demonstrated.

 

 

Technology advantages:

 

v      Frequently allows the site to be used during the clean-up

v      Cost competitive

 

Technology limitations:

 

v      Very high contaminant concentrations may be toxic to microorganisms

v      Under anaerobic conditions, contaminants may be degraded to products that are more hazardous than the original contaminants

v      Safety precautions must be used when handling hydrogen peroxide

v      Low-permeability soils are difficult to treat

v      Both biotic and abiotic sinks for oxygen can increase costs, as well as, operation and maintenance duration

v      Use of amended oxygen can produce an increase of biological growth near the injection well reducing the diffusion of oxygen in the remaining contaminated site and the input of nutrients.

v      Concentrations of hydrogen peroxide greater than 100 to 200 ppm in groundwater inhibit the activity of microorganisms

 

Technology development status:

 

Enhanced Bioremediation is a very well known technology. Gaseous nutrient injection is currently being applied and certain applications are considered commercial. Development of nitrate enhancement is still at the pilot scale.

 

References:

 

(a)       Technical:

  • Enhanced Bioremediation

www.frtr.gov/matrix2/section4/4-2.html

  • Enhanced Bioremediation

http://enviro.nfesc.navy.mil/erb/restoration/technologies/remed/bio/bio-05.asp

  • Enhanced Bioremediation

http://www.cpeo.org/techtree/ttdescript/ensolmx.htm

  • Enhanced Bioremediation Technologies

http://enviro.nfesc.navy.mil/erb/erb_a/support/rits/presentations/2000- bioremed.pdf

 

(b)       Application:

  • Engineered Approaches to In Situ Bioremediation of Chlorinated Solvents: Fundamentals and Field Applications

http://clu-in.org/download/remed/engappinsitbio.pdf

 

 

LANDFARMING

 

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 in-situ process, contaminated soils are 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 and to avoid the disadvantages of having heterogeneous degradation. Soil conditions are controlled to optimize the rate of contaminant degradation.

 

The petroleum industry has used landfarming for many years. The enhanced microbial activity results in degradation of adsorbed petroleum product constituents through microbial respiration. If contaminated soils are shallow (i.e. less than 1 metre below ground surface), it may be possible to effectively stimulate microbial activity without excavating the soils. If petroleum-contaminated soils are deeper than 1.5 metres, the soils should be excavated and reapplied on the ground surface.

 

This technique is also applicable in ex-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, non-halogenated-semi-volatile organic compounds, pesticides and wood-preserving wastes such as creosote and PAHs).

 

 

Technology advantages:

 

v      Is extremely simple and inexpensive

v      Requires no extensive process controls

v      Relatively unskilled personnel can perform the technique

v      Certain pollutants can be completely removed from the soil

 

Technology limitations:

 

v      Requires an extensive amount of space and time

v      Certain pollutants cannot be reduced to sufficiently low levels

v      Runoff must be collected and may require treatment

v      Can incorporate contaminated soil into soil that is uncontaminated, creating a larger volume of contaminated material

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

v      The depth of treatment is limited to the depth of achievable tilling

 

Technology development status:

 

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

 

References:

 

(a)       Technical:

  • Landfarming

www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-1-4007/c-11.pdf

  • Alexander, M. 1994. Biodegradation and Bioremediation. San Diego, CA: Academic Press.
  • Freeman, H.M. 1989. Standard Handbook of Hazardous Waste Treatment and Disposal. New York, NY: McGraw-Hill Book Company.
  • Norris, R.D., Hinchee, R.E., Brown, R.A., McCarty, P.L., Semprini, L., Wilson, J.T., Kampbell, D.H., Reinhard, M., Bower, E.J., Borden, R.C., Vogel, T.M., Thomas, J.M., and C.H. Ward. 1994. Handbook of Bioremediation. Boca Raton, FL:CRC Press.

 

(b)       Application:

  • Flathman, P.E. and D.E. Jerger. 1993. Bioremediation Field Experience. Boca Raton, FL: CRC Press.
  • Grasso, D. 1993. Hazardous Waste Site Remediation, Source Control. Boca Raton, FL: CRC Press.
  • Remediation of 25,000 pounds of hydrocarbons in one month

http://www.enzymetech.com/projects/landfarm/hal_pad/HalPad.pdf

 

 

NATURAL ATTENUATION

 

Technology description:

 

Natural attenuation, also known as Intrinsic Bioremediation or Bioattenuation, is a passive remedial approach. It allows contaminants in place to undergo degradation and mineralization using natural subsurface processes such as dilution, volatilization, biodegradation, dispersion, sorption as well as chemical reactions with subsurface materials. These processes, unaided by human intervention, reduce the concentration, toxicity, or mobility of contaminants in soil. 

 

The mechanisms of natural attenuation can be classified as destructive and non-destructive. Biodegradation is by far the most prevalent destructive mechanism. Dilution, dispersion and sorption are generally the most important non-destructive mechanisms.

 

Long-term monitoring is necessary to demonstrate that contaminant concentrations continue to decrease at a rate sufficient to ensure that they will not become a health threat or violate regulatory criteria. The main onus on the remediator is to understand the dynamics of the site and the remediation process and to monitor the containment spread and decontamination until completion of the process.

 

 

Technology applicability:

 

Applicable to nonhalogenated VOCs and SVOCs, including PCBs, fuel hydrocarbons and explosives.

 

 

Technology advantages:

 

v      For simple cases, this option is very inexpensive

v      Minimal disturbance to the site operations

v      Less generation or transfer of remediation wastes

v      Less intrusive as few surface structures are required

 

Technology limitations:

 

v      Extensive site characterization and monitoring are typical to ensure there is no risk to the outside environment prior to completion of the remediation

v      The naturally-occurring decontamination process may not achieve the required clean-up levels

v      This method may take a long time

v      Contaminants may migrate (erosion, leaching and volatilization) before they are degraded or transformed

v      Cannot be effective where constituent concentrations are high

 

Technology development status:

 

Natural attenuation has been selected at numerous sites and is now considered a "commercially available" technology.

 

 

References:

 

(a)       Technical:

  • A Citizen’s Guide to Monitored Natural Attenuation (English Version)

http://www.clu-in.org/download/citizens/mna.pdf

  • Monitored Natural Attenuation of Chlorinated Solvents: U.S.EPA Remedial

Technology Fact Sheet        

http://www.clu-in.org/download/remed/chl-solv.pdf

 

(b)       Application:

  • Remediation of hydrocarbon-contaminated sites by monitored natural attenuation. Project Update Canadian Association of Petroleum Producers, Calgary, AB (Canada. Environmental Research Advisory Council. CAPP Report No. 2001-9710.2 pp, Jan 2001.
  • Monitored Natural Attenuation of Chlorinated Solvents

http://www.clu-in.org/download/techdrct/tdchl-solv.pdf

  • Natural Attenuation of metals and radionuclides: report from a workshop held by Sandia National Laboratories Brady, P.V.; D.J. Borns, Sandia National Labs, Albuquerque, NM. Report No: SAND97-2727, NTIS: DE98001672, 291 pp, 1997

 

 

PHYTOREMEDIATION

 

Technology description:

 

Phytoremediation, also referred to as vegetation-enhanced bioremediation, is a technique which uses plants to remove, transfer, stabilize and destroy contaminants in soil.  Phytoremediation can be classified according to the main mechanism involved in the process:

 

  • Rhizofiltration - technique involving plant roots in the uptake of contaminants
  • Phytoextraction- technique involving the total body of the plant in the uptake of contaminants from soil
  • Phytotransformation-applicable to both soil and water and involving the degradation of contaminants through plant metabolism;
  • Phyto-stimulation or plant-assisted bioremediation- also used for both soil and water and involves the stimulation of microbial biodegradation through the activities of plants in the root zone (rhizosphere)
  • Phytostabilisation- technique which reduces the mobility and migration potential of contaminants in soil

 

General site condition best suited for potential use of phytoremediation includes large areas of low to moderate surface soil contamination. However, some practices now make use of deep-rooted plants such as poplars and alfalfa to attack, mitigate and contain pollutants situated many metres into the subsurface.

 

Phytoremediation is a technologically “soft” and aesthetically pleasing mechanism that can reduce remedial costs, restore habitat and clean up contamination in place.

 

 

Technology applicability:

 

Applicable to a broad range of contaminants including numerous metals and radionuclides, various organic compounds such as chlorinated solvents, BTEX, PCBs, PAHs, pesticides/insecticides, explosives, nutrients and surfactants.

 

 

Technology advantages:

 

v      Has low projected costs for remediating candidate soils

v      Is a very low-tech method since implementing it requires little more than basic agriculture techniques

 

Technology limitations:

 

v      Its operating characteristics and costs for large scale implementation have not been fully assessed

v      The roots of plants can effectively clean soil to a limited depth

v      Plant residues may need to be disposed of as hazardous waste or be further treated

v      Degradation by-products may be mobilized in groundwater or bio-accumulated in animals

v      If contaminant concentrations are too high, plants may die

v      It may be seasonal depending on location

 

Technology development status:

 

Phytoremediation is an emerging technology which is considered a pilot project for most applications. This broad technology type has been demonstrated for some plant species and contaminants and is experimental for others.

 

References:

 

(a)       Technical:

  • A Citizen's Guide to Phytoremediation (English Version)

http://www.clu-in.org/download/citizens/citphyto.pdf

  • Introduction to Phytoremediation. U.S. EPA, Office of Research and Development, National Risk Management Research Laboratory Report No: EPA 600-R-99-107. 104 pp, 2000

 

(b)       Application:

  • Assessment of phytoremediation as an in-situ technique for cleaning oil-contaminated sites Frick, C.M.; R.E. Farrell; J.J. Germida Dept. of Soil Science, Univ. of Saskatchewan, Saskatoon, SK Canada 88 pp, Dec 1999

·         Researchers clean up petroleum spills with plants Purdue News, Aug 2000

 http://www.purdue.edu/UNS/html4ever/0006.Schwab.phyto.html

·         Phytoremediation at the Open Burn and Open Detonating Area, Ensign-Bickford Company, Simsbury, Connecticut

http://bigisland.ttclients.com/frtr/00000164.html

 

 

 

IN SITU PHYSICAL/CHEMICAL TREATMENTS

 

ELECTRORECLAMATION

 

Technology description:

 

Electroreclamation, also known as Electrokinetic remediation, is a process in which pollutants are removed from the soil by means of electric/electrochemical processes. The principle of electroreclamation relies upon application of a low-intensity direct current through the soil between ceramic electrodes that are divided into a cathode array and an anode array. This mobilizes charged species, causing ions and water to move toward the electrodes.

 

Each electrode assembly contains water, a pump and an electrode. The outer casing of the electrode is made of porous ceramic that allows electrical current and water to pass. The porous casing contains water, which is held under pressure so it does not flow out and saturate adjacent soils. The ions flow through the casing, where they are then removed through a number of possible mechanisms including precipitation, adhesion to the electrode surface or processing in an ex situ treatment facility. Depending on the contaminants, a fluid may be circulated through the site to aid in the contaminant migration and collection.

 

 

Technology applicability:

 

Targeted contaminants for electroreclamation are heavy metals, anions and polar organics in soil, mud, sludge and marine dredging and in low permeability soils such as clays.

 

 

Technology advantages:

 

v      Can potentially remove high levels of metal contaminants in situ and can be one of the only applicable methods

v      Many metal species can be simultaneously removed

 

Technology limitations:

 

v      This method can be heavily influenced by heterogeneities in the treated zone- this suggests that an extensive pre-remediation site characterization must be performed

v      Application typically results in widespread acidification of the treated site (pH values of 2-4 are common)

v      Most effective in clays because clay particles have a negative surface charge. The effectiveness is sharply reduced for wastes with a moisture content of less than 10 percent

v      The solubility and desorption potential of the contaminants may limit the success of the technology

 

Technology development status:

 

Electroreclamation is still a developing technology. It is not yet known if it is effective over a wide range of soil contaminant types and site conditions.

 

 

References:

 

(a)       Technical:

  • Electrokinetics

www.gwrtac.org/pdf/elctro_o.pdf

 

(b)       Application:

  • Recent Developments for In Situ Treatment of Metal Contaminated

www.clu-in.org/download/remed/metals2.pdf

  • Electrokinetic remediation of soils contaminated with heavy metals

www.werc.net/researchers/pdf/bowman94.pdf

·         Electrokinetic Extraction at the Unlined Chromic Acid Pit, Sandia National Laboratories, New Mexico

http://bigisland.ttclients.com/frtr/00000173.html

 

 

SOIL VAPOUR EXTRACTION

 

Technology description:

 

In the in-situ Soil Vapour Extraction (SVE) process, also known as enhanced volatilization, a vacuum is applied through extraction wells. This creates a concentration gradient and a zone of low vapour pressure that induces gas phase volatiles to be removed from the contaminated soil through the extraction wells. The contaminated vapour is collected and processed by separate equipment.

 

The process is only effective with volatile compounds, with higher volatilities naturally being more advantageous. The subsurface permeability will also greatly influence the amount of time required for this technique. The gas leaving the soil may be treated to recover or destroy the contaminants, depending on local and state air discharge regulations. Application of air injection can be requested for facilitating extraction of contamination.

 

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

 

 

Technology applicability:

 

The technology is typically applicable to VOCs, volatile metals and fuel contamination. SVE works only on compounds that readily vaporize.

 

 

Technology advantages:

 

v      The equipment requires relatively little attention during operation

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

v      The technology is well-known and has been used extensively

 

Technology limitations:

 

v      High concentrations of organic matter limit contaminant volatilization

v      Exhaust air from in-situ SVE system may require treatment

v      Off-gas treatment usually involves vapour-phase Granular Activated Carbon

v      Soil with a high percentage of fines and a high degree of saturation will require higher vacuums (increasing costs) and/or hindering the operation of the in situ SVE system

 

Technology development status:

 

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

 

 

References:

 

(a)       Technical:

·         Soil Vapour Extraction (SVE)

http://www.epa.gov/swerust1/cat/sve1.htm

·         A Citizen's Guide to Soil Vapour Extraction and Air Sparging (English Version)

http://www.clu-in.org/download/citizens/citsve.pdf 

 

(b)       Application:

·         Experimental setup for the study of soil vapour extraction: a practical approach to determine sorption effect. Rodriguez Maroto, J. M.; C. Gomez Lahoz; C. Vereda Alonso; F. Garcia Herruzo; R. A. Garcia Delgado Dpto. Ingenieria Quimica, Facultad de Ciencias, Universidad de Malaga, 29071 Malaga, Spain Water Science And Technology, v 37 n 8, 1998

·         Performance evaluation report for soil vapour extraction operations at the carbon tetrachloride site, February 1992 - September 1998 Rohay, V.J., Bechtel Hanford, Inc., Richland, WA. Sponsor: U.S. DOE, Office of Environmental Restoration. Report No: BHI-00720, Rev. 3. NTIS Order No: DE00008586. 222 pp, Jun 1999

·         Soil vapour extraction Waste Treatment Technology News, v 13 n 12, Sept 1 1998

·         Soil Vapour Extraction at Camp LeJeune Military Reservation, Site 82, Area A, Onslow County, North Carolina

http://bigisland.ttclients.com/frtr/00000112.html

·         Soil Vapour Extraction at the Verona Well Field Superfund Site, Thomas Solvent Raymond Road (OU-1), Battle Creek, Michigan

http://bigisland.ttclients.com/frtr/00000029.html

 

 

LASAGNATM PROCESS

 

Technology description:

 

The LasagnaTM process is an in situ remediation technology developed by an industrial U.S.A consortium for remediating soils contaminated with soluble organic compounds. It is especially useful for low-permeability soils where electro-osmosis can move water faster and more uniformly than hydraulic methods, with very low power consumption. The technology combines electro-osmosis, biodegradation and physicochemical treatment process to treat soil. It uses electrokinetics to move contaminants in soil pore water into treatment zones where the contaminants can be captured or decomposed. The electrodes are energized by direct current, which causes the water and soluble contaminants to move into or through the treatment layers and also warm the soil. Treatment zones contain reagents that decompose the soluble organic contaminants or absorb contaminants for immobilization or subsequent removal and disposal. A system recycles the water, which accumulates at the cathode, back to the anode for acid-base neutralization. Alternatively, the electrode polarity can be reversed periodically to reverse electro-osmotic flow and neutralize pH.

 

For highly non-polar contaminants, surfactants can be incorporated to solubilise the organics, while for a mixture of organic and metallic contaminants the treatment zones can contain sorbents for binding the metals and contain microbes or catalysts for degrading the organics.

 

 

Technology applicability:

 

The technology is typically applicable to organic compounds and fuels. It has been used to effectively remove trichloroethylene (TCE) from contaminated soils.

 

 

Technology advantages:

 

v      Combines the advantages of different types of techniques (biological and physico-chemical)

v      Compared to other in-situ technologies, it has shown greater accessibility in low permeability soils such as clays, silts and fine sands

 

Technology limitations:

 

v      Limited knowledge on the treatment chemistry and application procedures

v      Possible diffusion from untreated zone during treatment may impede effectiveness of treatment

 

Technology development status:

 

This is an emerging process.

 

References:

 

(a)       Technical:

  • Electrokinetics

www.gwrtac.org/pdf/elctro_o.pdf

  • LasagnaTM

www.netl.doe.gov/products/em/IndUnivProg/pdf/4.pdf

 

     

(b)       Application:

  • "Laboratory and Pilot Scale Experiments of the LasagnaTM Process"

http://207.86.51.66/download/rtdf/lasagna/topic10f.pdf

  • Rapid Commercialization Initiative (RCI) Final Report for an Integrated In Situ Remediation Technology (Lasagna™) (DOE/OR/22459-1)

www.clu-in.org/download/rtdf/lasagna/las-vrfy.pdf

·         Lasagna™ Soil Remediation at the U.S. Department of Energy's Paducah Gaseous Diffusion Plant, Cylinder Drop Test Area, Paducah, Kentucky

http://bigisland.ttclients.com/frtr/00000065.html

 

 

FRACTURING

 

Technology description:

 

Fracturing is a technology that is used to increase the efficiency of removal and in-situ treatment techniques. It is primarily used to enlarge existing fissures and introduce new fractures, primarily in the horizontal direction. They facilitate SVE or methods that inject gases or fluids for enhanced bioremediation. Common soil fracturing technologies include:

 

1)      Pneumatic fracturing- in which wells are drilled in the contaminated zone. Small (0.6-meter or 2-foot) portions of the zone receive short bursts (~20 seconds) of compressed air. This fractures a small radius surrounding each well.

2)      Blast-enhanced fracturing- is used at sites with fractured bedrock formations. Boreholes are drilled, filled with explosives and detonated to create new fractures.

3)      LasagnaTM process- uses electro-osmosis and electrokinetics to move contaminants in treatment layers in the contaminated soil.

4)      Hydrofracturing- injects pressurized water to increase the permeability in the soil matrix. The fissures are filled with porous slurry composed of sand and guar gum gel. The sand grains hold the fracture open while an enzyme additive breaks the guar gum down into a thinned fluid. The fluid is pumped from the fracture, leaving permeable subsurface channels.

 

 

Technology applicability:

 

Generally applicable to the complete range of contaminants with no particular target group. The technology is used primarily to fracture silts, clays, shale and bedrock.

 

 

Technology advantages:

 

v      As a support technology, it enhances the efficiency of other remediation technologies

v      It offers a way of reaching pollution deep in the ground where it would be difficult or costly to dig down so far

v      Can reduce the number of wells needed for certain cleanup methods, which can save time and reduce cleanup costs.

 

Technology limitations:

 

v      May open new pathways for the unwanted spread of contaminants

v      The final location of new fractures is not controllable

v      The technology should not be used in areas of high seismic activity

v      Investigation of possible underground utilities, structures or trapped free product is required

 

Technology development status:

 

Fracturing is widely used in the petroleum and water-well construction industries.

 

 

References:

 

(a)       Technical:

  • A Citizen's Guide to Fracturing

http://www.clu-in.org/download/citizens/fracturing.pdf

  • Fracturing

http://www.frtr.gov/matrix2/section4/4-5.html

 

 

(b)       Application:

  • Laboratory studies on fracturing of low-permeability soils. Alfaro, M.C. (Manitoba Univ., Winnipeg, MB, Canada. Dept. of Civil and Geological Engineering); Wong, R.C.K. (Calgary Univ., AB, Canada. Dept. of Civil Engineering). Canadian Geotechnical Journal, Vol 38 No 2, p 303-315, Apr 2001
  • In Situ Remediation Technology Status Report: Hydrofracturing/Pneumatic Fracturing

http://www.clu-in.org/download/remed/fractur.pdf

·         In Situ Remediation Technology Status Report: Hydraulic & Pneumatic Fracturing, EPA 542-K-94-005

http://www.gwrtac.org/pdf/Epa_frac.pdf

 

 

SOLIDIFICATION/STABILISATION

 

 

Technology description:

 

Solidification and stabilisation (S/S) is a term that refers to a generic set of technologies and/or processes that use binders and additives for remediating contaminated sites.  It is used to reduce the mobility of hazardous substances and contaminants in the environment through both physical and chemical means. It seeks to immobilize contaminants within their “host” medium, instead of removing them through chemical or physical treatment.

 

Solidification is frequently accomplished by simply mixing the contaminated soil with cement or bitumen/asphalt to form a durable mass with low leaching rates. It may be a monolithic waste form, a granular material, a claylike material, or some form considered a solid.

 

Stabilisation typically employs a chemical reaction either to bind the contaminant to the substrate or to yield less mobile compounds, which contain the contaminant. It dos not necessarily yield a solid, but a more chemically stable form.

 

This technique can be used alone or in conjunction with other treatment technologies, as part of a treatment train to yield a product or material suitable for land disposal or, in other cases which can be applied to beneficial use.

 

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

 

 

Technology applicability:

 

It is generally applicable to inorganics, including some radionuclides. It has generally been accepted as applicable for treating many heavy metals, selected organic compounds and soils containing semivolatile and/or non-volatile organics.

 

 

Technology advantages:

 

v      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 may generally be higher 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      Depth of contaminants may limit these processes

v      Organic pollutants 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 contaminant types. Binder formulations designed to be more effective in treating organics are being developed and tested. Another system called the Polyethylene Encapsulation of Radionuclides and Heavy Metals (PERM) process is being developed.

 

 

References:

 

(a)       Technical:

  • A Citizen's Guide to Solidification/Stabilisation

www.clu-in.org/download/citizens/s-s.pdf

http://www.frtr.gov/matrix2/section4/4_10.html

  • Solidification/Stabilisation

www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-1-4007/c-4.pdf

 

(b)       Application:

  • Solidification/Stabilisation of Metals and Explosives in Soils Using an Organic Binder

www.nws.usace.army.mil/geotech/papers/adasoils.htm

 

 

 

SOIL FLUSHING

 

Technology description:

 

Soil flushing, also known as injection/recirculation, is a technology used for extracting contaminants from the soil by the use of water or water solutions. Water is used to treat contaminants that dissolve easily in it. Additives such as acids are used to remove metals and organic contaminants; bases are used to treat phenols and some metals, and surfactants are effective at removing oily contaminants.

 

This technique is accomplished by passing the extraction fluid through in-place soils using an injection or infiltration process. The effectiveness of this process is dependant on hydrogeologic variables (e.g. type of soil, soil moisture, etc.) and type of contaminant. Contaminants that are dissolved in the flushing solution are leached into the groundwater, which is then extracted and treated. In some cases, the flushing solution is injected directly into the groundwater. One variation of this technology is Co-Solvent Enhancement, which involves injecting a solvent mixture to extract organic contaminants. Recovered ground water and flushing fluids with the desorbed contaminants may need treatment to meet appropriate discharge standards prior to recycle or release to wastewater treatment facilities or receiving streams.

 

 

Technology applicability:

 

Soil flushing technology removes metals, including radioactive contaminants and VOCs, SVOCs, fuels and pesticides from soil. It is usually less cost-effective for organic materials. Environmentally compatible surfactants may be used to increase the effective solubility of some organic compounds.

 

 

Technology advantages:

 

v      Is applicable to a wide range of contaminants

v      Can effect a rapid and adequate clean-up of newly deposited contaminants, such as those from an accidental spill

 

Technology limitations:

 

v      The additives for flushing could remain in low amounts in the soil and need to be monitored

v      Only useful when the solution can be contained and recaptured

v      Low permeability or heterogeneous soils are difficult to treat

v      Above ground separation and treatment costs for recovered fluids can drive the economics of the process

 

Technology development status:

 

Soil flushing is a developing technology that has had limited use. Typically, laboratory and field treatability studies must be performed under site-specific conditions before soil flushing is selected as the most suitable remedy.

 

 

References:

 

(a)       Technical:

·         In Situ Flushing - Technology Overview

http://www.gwrtac.org/graphics/pdficon.gif

  • In situ flushing with surfactants and cosolvents U.S. EPA, Technology Innovation Office (TIO). 36 pp, 2000

http://www.clu-in.org/download/remed/strbak_flushing.pdf

 

 

  • Soil Flushing

www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-1-4007/c-2.pdf

 

(b)       Applications:

·         Recent Developments for In Situ Treatment of Metal Contaminated Soils

http://www.clu-in.org/download/remed/surf_co.pdf

·         Technology Status Report: In Situ Flushing

http://www.clu-in.org/download/toolkit/isf_1117.pdf

 

 

POLYMER ADSORPTION

 

Technology description:

 

In Polymer Adsorption technology, water-soluble polymers, functionalized with groups having a strong affinity for specific contaminants, are used to clean up contaminated soils. When solutions of the polymer are passed through the soil, the contaminants are stripped from the soil and become bound to the polymer. The polymer is designed to pass through the soil without being absorbed. The solution collected with the contaminant-loaded polymer is then treated ex situ to release the contaminant from the polymer. The contaminant is then recovered and the polymer recycled. The water solubility, metal binding ability and high molecular weight but compact structures of the polymer, give the material unique capabilities for the removal of contaminants from polluted soils.

 

The diagram below illustrates passive adsorption using a patented polymeric material ReclaimTM , which is composed of 80% divinylbenzene and 20% ethylvinylbenzene, specifically formulated for the absorption of volatile organics . The polymer is enclosed in a box /cylindrical can and placed inside a well in the vadose zone of the contaminated soil. The polymeric material, after its use, can be regenerated by heating in inert atmosphere.  ReclaimTM can be regenerated up to 100 consecutive times without any limitations on its adsorption capacity.

 

 

Technology applicability:

 

The technology is typically applicable to heavy metals (including radionuclides), some inorganics and nonhalogenated VOCs.

 

 

Technology advantages:

 

v      Effective technology for removing toxic metals such as Pb, Cr and Cd

 

Technology limitations:

 

v      Oxidants in water may damage the sorbent polymer

v      Economic trade off of higher capacity at higher cost has not been fully explored

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

 

Technology development status:

 

This technique is in pilot development stage.

 

 

Reference:

 

  • McCoy and Associates, Inc. (1992) Innovative in situ cleanup processes, The Hazardous Waste Consultant, September/October.

 

 

IN SITU THERMAL TREATMENTS

 

 

SOIL VAPOUR EXTRACTION THERMALLY ENHANCED

 

Technology description:

 

Soil Vapour Extraction Thermally Enhanced is a technology that uses electrical resistance/electromagnetic/fiber optic/radio frequency heating or hot air/steam injection to increase the volatilization rate of semi-volatile contaminants and facilitate their extraction. In effect, the process uses a combination of soil heating processes to enhance soil vapour extraction (SVE).

 

The typical system set-up is made by three rows of electrodes placed to a specific depth. Electrical energy is applied to the electrodes which begin to heat the soil and drive off the soil moisture; electrical conductivity can be maintained by adding water between the electrodes. Radio-frequency heating (RFH) is used to heat the soil to over 3000 C. It enhances vapour extraction, the extracted vapour can be collected and treated by a variety of technologies.

 

 

Technology applicability:

 

The technology is designed to treat SVOCs but will consequently treat VOCs in contaminated soil. Can be useful for fuel and pesticide soil decontamination.

 

 

Technology advantages:

 

v      The cost of the use of this technology is typically less than for incineration

v      Applicable to a wide range of pollutants

v      Readily available equipment for onsite or offsite treatment

v      All contaminants are under a vacuum during operation and the possibility of contaminant release is greatly reduced

 

Technology limitations:

 

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

v      Soil with highly variable permeability may result in uneven delivery of airflow to the contaminated regions

v      Performance in extracting certain contaminants varies depending upon the maximum temperature achieved in the process selected

v      A suitable off-gas treatment system for contaminated vapours removed from the subsurface needs to be installed

v      Hot air injection has limitations due to low heat capacity of air

v      Soil that is tight or has high moisture content has a reduced permeability to air and requires more energy to increase vacuum and temperature. A potential explosion hazard exists from concentrated fumes released from the vacuum unit

 

Technology development status:

 

This technology is in the field demonstration stage.

 

Reference:

 

  • Soil vapour extraction thermally enhanced

www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-1-4007/c-7.pdf

 

 

VITRIFICATION

 

Technology description:

 

Vitrification is a technology in which the underlying principle is to subject contaminated soil to a sufficiently high temperature to cause it to melt and form a glass when cooled. It involves the insertion of graphite electrodes into the contaminated encased area at sufficiently close spacing and energizing with a high electrical resistance heating (more than 1700oC) which causes the soil to melt to a molten pool. The organic contaminants are normally destroyed while the inorganics are trapped in the vitrification matrix.  

 

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

 

 

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      Is a destructive process and the soil can no longer support agricultural use

v      Fugitive emissions such as dust and particulates are often a problem during operations; they should be controlled

 

Technology development status:

 

The vitrification process is undergoing field demonstration tests.

 

 

References:

 

(a)       Technical:

·         A Citizen's Guide to Vitrification

www.clu-in.org/download/citizens/vitrification.pdf

 

(b)       Application:

·         Waste Vitrification Systems Lessons Learned

http://tis.eh.doe.gov/ll/WasteVit.pdf

·         Vitrification of Residue (ASH) From Municipal Waste Combustion

www.asme.org/research/imw/ash.pdf

 

 

Authors
Andrea Lodolo
ICS-UNIDO, Italy

Who does what?