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2005 10:59 AM
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CPEO Review of Enhanced Bioremediation
The Center for Public Environmental Oversight http://www.cpeo.org has a very useful “Tech Tree” tool on its web site that evaluates different remediation methodologies. The site gives a description of the methodologies and the limitations and concerns. The Tech Tree is maintained by CPEO and also has USEPA sponsorship. I have pasted in the remediation methods (or similar to those) used by Cherokee and Gates.
Enhanced Bioremediation
Description
Bioremediation is a general term used to describe the destruction of contaminants by biological mechanisms, including microorganisms (e.g. yeast, fungi, or bacteria), in contaminated soil and water. Microorganisms eat and digest organic substances for nutrients and energy. Certain microorganisms can digest organic substances such as fuels or solvents into harmless products such as carbon dioxide and water. Once the contaminants are degraded, the microorganism population dies off, having consumed their entire food source. Bioremediation may rely on either indigenous microorganisms (those that are native to the site) or exogenous microorganisms (those that are imported from other locations). In either case, bioremediation technologies optimize the environmental conditions so the appropriate microorganisms will flourish and destroy the maximum amount of contaminants.
Air Sparging and Bioventing). Vapor extraction is often used in conjunction with gaseous nutrient injection. The most common added gas is air. In the presence of sufficient oxygen, microorganisms convert many organic contaminants to carbon dioxide, water, and microbial cell mass. In the absence of oxygen, organic contaminants are metabolized to methane, limited amounts of carbon dioxide, and trace amounts of hydrogen gas. Another gas that is added is methane. It enhances degradation by cometabolism. That is, as bacteria consume the methane, they produce enzymes that react with the organic contaminant and degrade it to harmless minerals. See description of Cometabolism.
Oxygen Enhancement with Hydrogen Peroxide An alternative to pumping oxygen gas into groundwater involves injecting a dilute solution of hydrogen peroxide. Its chemical formula is H2O2, and it easily releases its extra oxygen atom to form water and free oxygen. This circulates through the contaminated groundwater zone to enhance the rate of aerobic biodegradation of organic contaminants by naturally occurring microbes. A solid peroxide product [e.g., oxygen releasing compound (ORC)] can also be used to increase the rate of biodegradation.
Nitrate Enhancement A solution of nitrate is sometimes added to groundwater to enhance anaerobic biodegradation.
Bio-augmentation Sometimes acclimated microorganisms are added to soil to increase biological activity. Spray irrigation is typically used for shallow contaminated soils, and injection wells are used for deeper contaminated soils. For example, see the description of White Rot Fungus.
Limitations and Concerns
Under anaerobic conditions, contaminants may be degraded to a product that is more hazardous than the original contaminant. For example, trichloroethylene (TCE) anaerobically biodegrades to the persistent and more toxic vinyl chloride.
Introducing cold water or gas may slow the remediation process, as lower temperatures do not support degradation.
Concentrations of hydrogen peroxide greater than 100 to 200 parts per million (ppm) in groundwater inhibit the activity of microorganisms.
Amended oxygen can be consumed very rapidly near the injection well, which creates two significant problems: biological growth can be limited to the region near the injection well, limiting adequate contamination/microorganism contact throughout the contaminated zone; and bio-fouling of wells can retard the input of nutrients.
Bioremediation is not well suited for soils with low permeability (e.g., fine clays). High permeability is required to allow the nutrients to reach the indigenous microorganisms.
It is possible that the subsurface injection of gases below the water table can induce groundwater flow. It may be necessary to use a pump-and-treat system in conjunction with gas injection for hydraulic control.
The circulation of water-based solutions through the soil may increase contaminant mobility and necessitate treatment of underlying groundwater. If the process is enhancing groundwater bioremediation, a groundwater circulation system must be created so that contaminants do not escape from zones of active biodegradation. See description of Circulating Groundwater Wells.
Nitrate injection to groundwater is of concern because nitrate is a regulated compound. Bio-augmentation using non-native microorganisms is also controversial.
Very high contaminant concentrations may be toxic to microorganisms.
Safety precautions must be used when handling hydrogen peroxide.
Because gaseous injection increases pressure in the soil, vapors can build up in building basements.
Applicability
Enhanced bioremediation techniques have been successfully used to remediate soils and groundwater contaminated with fuel, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and pesticides. Pilot-scale studies have demonstrated microbial degradation of soils contaminated with munitions waste. While bioremediation cannot degrade inorganic contaminants such as metals, it can be used to immobilize these contaminants.
Technology Development Status
Most forms of bioremediation are commercial. Gaseous Nutrient Injection is currently being applied, and certain applications are considered commercial. The development of nitrate enhancement is still at the pilot scale. Techniques for immobilizing metals are largely experimental.
Web Links
http://www.frtr.gov/matrix2/section4/4_2.html
http://www.frtr.gov/matrix2/section4/4_34.html
http://www.em.doe.gov/plumesfa/intech/isbuhw/index.html (nutrients, air sparging, horizontal wells)
http://clu-in.org/download/citizens/bioremediation.pdf
http://enviro.nfesc.navy.mil/erb/restoration/technologies/remed/bio/bio-05.asp
Other Resources and Demonstrations
See http://hq.environmental.usace.army.mil/tools/it/itsuccess/quonset/quonset.html, http://hq.environmental.usace.army.mil/tools/it/itsuccess/tdock/tdock.html, http://hq.environmental.usace.army.mil/tools/it/itsuccess/ftord1/ftord1.html, http://hq.environmental.usace.army.mil/tools/it/itsuccess/aua/aua.html for descriptions of demonstrations.
See In Situ Anaerobic Bioremediation, Pinellas Northeast Site, Largo, Florida: Cost and Performance Report, 1998. D.S. Ingle, M. Hightower, G.W. Sewell, EPA 600-R-98-115, NTIS: PB98-168008. A pilot scale demonstration of nutrient injection to stimulate in situ bioremediation of chlorinated solvents was performed at the Pinellas Science, Technology and Research (STAR) Center, formerly the U.S. DOE Pinellas Plant in Largo, Florida, from January through June of 1997. The innovative remedy is known as reductive anaerobic biological in situ treatment technologies (RABITT). A vertical flow system with two horizontal wells and a series of infiltration galleries was constructed that allowed development of an effective ground-water recirculation pattern to enable continuous nutrient addition and enhance system performance.
See http://www.epa.gov/tio/products/newsltrs/gwc/gwccurre.htm#enhanced for a recently completed pilot study on the potential for achieving reductive dechlorination of perchloroethylene (PCE) under “geochemically challenged” conditions of the Ogallala Ground Water Contamination (Superfund) Site in Ogallala, Nebraska. Treatment of PCE-contaminated ground water in the pilot study consisted of substrate injection into the plume downgradient of a dry cleaning facility over a period of one year.
See http://www.regenesis.com/ORC/default.htm for a description of Oxygen Release Compound, which has been used on over 5,000 soil and groundwater restoration projects in the U.S. and in several foreign countries, including Canada, Japan, Australia, Korea, Denmark, Italy, England, Germany, Holland, and Poland.
See http://www.regenesis.com/HRC/default.htm for a description of Hydrogen Release Compound (HRC®). HRC helps bioremediation through a complex series of chemical and biologically mediated reactions. Initially, when in contact with subsurface moisture, the HRC slowly releases lactic acid. Indigenous anaerobic microbes metabolize the lactic acid, producing consistent low concentrations of dissolved hydrogen. The resulting hydrogen is then used by other subsurface microbes (reductive dehalogenators) to strip the chlorine atoms and allow for further biological degradation.
See http://www.epa.gov/ahaazvuc/research/stjoseph.html#contam for a description of Reductive Dechlorination. Reductive Dechlorination is the process whereby chlorine atoms are removed from a chlorinated organic compound by adding electrons and hydrogen atoms. The organic compound is reduced by this process because the oxidation number of the carbon atoms decreases in the process of removing the chlorine atoms. TCE can biodegrade under certain circumstances. When there is a substrate that is potentially oxidized, such as a petroleum hydrocarbon, the reductive dechlorination of the TCE may occur. Depending upon conditions, the reaction may continue until all of the chlorine atoms have been removed from the TCE and ethene is produced. An alternative pathway is for vinyl chloride, one of the daughter products of TCE, degrade by oxidation to carbon dioxide.
See http://toxics.usgs.gov/bib/bib-Biodegradation.html for a bibliography of biodegradation and Natural Attenuation.
See http://www.clu-in.org/download/remed/542r01019.pdf, “Use of Bioremediation at Superfund Sites,” EPA 542-R-01-019, September 2001, 48 pages. This document provides site-specific information about 104 Superfund remedial action sites where bioremediation has been applied, including available performance data.
See “In Situ Bioremediation for the Hanford Carbon Tetrachloride Plume: Innovative Technology Summary Report,” 1999. DOE/EM-0418, 22 pp. In situ bioremediation of the Hanford carbon tetrachloride plume treats ground water contaminated with volatile organic compounds and nitrates under anaerobic conditions.
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STATUS: The preceding technology description and links were last updated
06/2002.
If you believe any of the information is out of date, please let us know at
cpeo@cpeo.org.
Description
In-Situ Chemical Oxidation (ISCO) involves injecting chemical oxidants into the vadose zone and/or groundwater to oxidize organic contaminants. The common oxidants are hydrogen peroxide-based Fenton’s reagent, and potassium manganate (KMnO4), better known as permanganate. Ozone can also oxidize organic contaminants in-situ, but it has been used less frequently. Complete mineralization to carbon dioxide and water is the desired endpoint of an ISCO process.
Fenton’s reagent is produced on site by adding an iron catalyst to a hydrogen peroxide solution. A 50 % solution of peroxide is common for this application. A pH adjustment may be needed, as Fenton’s reagent is more effective at acidic pH. For permanganate application, a 1% to 5% solution is prepared on site from potassium permanganate crystals that are delivered in bulk to the site. The most common oxidant delivery methods involves the injection of oxidants. Where a significant hydraulic gradient exists, the targeted delivery of oxidants to the contaminant zones may require both injection and extraction wells. ISCO delivering KMnO4 through recirculation wells has been successful at some demonstrations. A patented process is used to inject the Fenton's reagent.
Limitations and Concerns
Subsurface heterogeneity can cause uneven distribution of oxidants. There is no control of the subsequent movement of the oxidant after its release. Hence, recirculation is sometimes the preferable delivery system.
The number and pattern of injection and extraction wells and monitoring wells must be designed to ensure maximum coverage of the treatment zone. Because cost is related to the depth and quantity of dense non-aqueous phase liquids of (DNAPL), the number and spacing of the wells becomes critical. A system for handling precipitated solids may need to be incorporated when high concentrations of oxidants are recirculated. Injection and extraction wells may eventually become clogged from entrained silt, biological growth, mineral precipitates, or other factors.
Porosity of the subsurface may be reduced due to the formation of metal oxide precipitates. ISCO often requires more than one application of oxidant to address rebound effects.
Native organic matter exerts a demand for oxidants, thus increasing costs for chemicals. An Underground Injection Permit may be required. For example, Florida, New Jersey, South Carolina, and Tennessee regulators have stated that they would require a such a permit.
With ISCO systems using KMnO4, the pH of the system must be between 3 and 10 and the rate of the reaction increases with higher oxidant-to-contaminant loading rates. With ISCO systems using Fenton's Reagent, reduction of pH to levels between 3 and 6 is needed. Naturally occurring buffering agents, such as carbonates, may prevent pH from being reduced to this level.
Hydrogen peroxide in Fenton's reagent decomposes rapidly before it travels far from the well. Anaerobic bioremediation will be impeded if oxygen from the hydrogen peroxide is introduced in the treatment zone. In addition, Fenton's reagent is toxic to microbial populations.
ISCO requires strict health and safety procedures for high-pressure injection. For Fenton's reagent, care should be given for exothermic reactions (i.e., release of heat) and handling hydrogen peroxide. For example, the application of Fenton's Regent at Cherry Point Naval Air Station in NC resulted in an explosion. Fenton’s Reagent is typically not applicable at sites where more than six inches of contaminant free product is present.
Natural oxidant demand within a treatment area, as it relates to oxidant dosing requirements, needs to be better understood. There is no screening procedure for evaluating site-specific geochemical factors for compatibility with ISCO.
At this time, problems exist in differentiating between dissolved contaminant displacement and treatment, as well as dilution and treatment.
Applicability
ISCO using permanganate for soil and groundwater treatment has been demonstrated at a number of sites on the following organics: chlorinated solvents (such as trichloroethylene [TCE]), naphthalene, and pyrene. Fenton’s Reagent can be used to treat a wide range of organic contaminants in soil and groundwater, including chlorinated solvents, petroleum hydrocarbons, semi-volatile organic compounds (SVOCs), and pesticides. ISCO has also been used to remediate polyaromatic hydrocarbons (PAHs), petroleum products, and ordnance compounds.
Technology Development Status
ISCO is still an emerging technology for the treatment of hazardous waste. H.J.H. Fenton developed Fenton's Reagent in the 1890’s. This chemistry is widely used by the wastewater industry for the treatment of organic waste.
Web Links
http://enviro.nfesc.navy.mil/erb/restoration/technologies/remed/phys_chem/phc-43.asp
http://apps.em.doe.gov/ost/pubs/itsrs/itsr167.pdf
http://www.tri-s.com/articles/abstract07.htm
http://www.envnet.org/scfa/prodlines/dnapl/factsheets/tms2161.pdf
Other Resources and Demonstrations
See http://www.itrcweb.org/ISCO-1.pdf Technical and Regulatory Guidance for in Situ Chemical Oxidation of Contaminated Soil and Groundwater (ISCO-1) 2001. ISCO refers to a general group of specific technologies, with each technology representing specific combinations of oxidants and delivery techniques. Specific primary oxidants addressed in this document are hydrogen peroxide, potassium and sodium permanganate, and ozone
See http://enviro.nfesc.navy.mil/erb/erb_a/support/wrk_grp/raoltm/case_studies/rao_kingsbay.pdf, http://bigisland.ttclients.com/frtr/00000231.html and http://toxics.usgs.gov/highlights/dnapl_removal.html for descriptions of demonstrations of ISCO at Old Camden County Landfill, Naval Submarine Base (NSB) Kings Bay.
See http://www.frtr.gov/cost/00000208.html for a demonstration of permanganate to treat TCE present as DNAPL at the Portsmouth Gaseous Diffusion Plant in 1997.
See http://bigisland.ttclients.com/frtr/pdf/ButlerCleaners.htm for a description of permanganate treatment at a dry cleaning facility in Jacksonville, FL.
A full-scale demonstration of in-situ destruction of DNAPL by Fenton’s Reagent was successfully completed at the Savannah River Site in April, 1997. Six hundred pounds of DNAPL was oxidized at this four-day demonstration. Groundwater chemistry showed that there are lingering effects from the demonstration. The effects of the relatively vigorous reaction on the mineralogy, chemistry, and microbiology of the aquifer are detailed in the second publication below.
See Jerome, K.M., B. Riha, and B.B. Looney, Final Report for Demonstration of In Situ Oxidation of DNAPL Using the Geo-Cleanse Technology, Westinghouse Savannah River Company, Aiken, SC and Denham et al, Effects of Fenton’s Reagent on Aquifer Geochemistry and Microbiology at the A/M Area, Savannah River Site, Westinghouse Savannah River Company, Aiken, SC.
See http://enviro.nfesc.navy.mil/erb/erb_a/restoration/technologies/remed/phys_chem/tds-2071-chem-ox.pdf and http://bigisland.ttclients.com/frtr/00000230.html for descriptions of demonstrations at the Pensacola Naval Air Station.
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STATUS: The preceding technology description and links were last updated
10/2002.
If you believe any of the information is out of date, please let us know at
cpeo@cpeo.org.
Don Holmstrom
Denver Area Labor Federation, AFL-CIO
Front Range Economic Strategy Center
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