Description:

Aerobic

In the presence of sufficient oxygen (aerobic conditions), and other nutrient elements, microorganisms will ultimately convert many organic contaminants to carbon dioxide, water, and microbial cell mass.

Enhanced bioremediation of soil typically involves the percolation or injection of ground water or uncontaminated water mixed with nutrients and saturated with dissolved oxygen. Sometimes acclimated microorganisms (bioaugmentation) and/or another oxygen source such as hydrogen peroxide are also added. An infiltration gallery or spray irrigation is typically used for shallow contaminated soils, and injection wells are used for deeper contaminated soils.

Although successful in situ bioremediation has been demonstrated in cold weather climate, low temperature slows the remediation process. For contaminated sites with low soil temperature, heat blankets may be used to cover the soil surface to increase the soil temperature and the degradation rate.

Enhanced bioremediation may be classified as a long-term technology which may take several years for cleanup of a plume.

Anaerobic

In the absence of oxygen (anaerobic conditions), the organic contaminants will be ultimately metabolized to methane, limited amounts of carbon dioxide, and trace amounts of hydrogen gas. Under sulfate-reduction conditions, sulfate is converted to sulfide or elemental sulfur, and under nitrate-reduction conditions, dinitrogen gas is ultimately produced.

Sometimes contaminants may be degraded to intermediate or final products that may be less, equally, or more hazardous than the original contaminant. For example, TCE anaerobically biodegrades to the persistent and more toxic vinyl chloride. To avoid such problems, most bioremediation projects are conducted in situ. Vinyl chloride can easily be broken down further if aerobic conditions are created.

White Rot Fungus

White rot fungus has been reported to degrade a wide variety of organopollutants because of its lignin-degrading or wood-rotting enzymes. Two different treatment configurations have been tested for white rot fungus, in situ and bioreactor. An aerobic system using moisturized air on wood chips is used in a reactor for biodegradation. A reactor was used in the bench-scale trial of the process. In the pilot-scale project, an adjustable shredder was used for making chips for the open system. The open system is similar to composting, with wood chips on a liner or hard contained surface that is covered. Temperature is not controlled in this type of system. The optimum temperature for biodegradation with lignin-degrading fungus ranges from 30 to 38° C (86 to 100° F). The heat of the biodegradation reaction will help to maintain the temperature of the process near the optimum. 

Although white rot fungus degradation of TNT has been reported in laboratory-scale settings using pure cultures, several factors increase the difficulty of using this technology for full-scale remediation, and it has not yet been proven successful at this level. These factors include competition from native bacterial populations, toxicity inhibition, chemical sorption, and the inability to meet risk-based cleanup levels. White rot works best in nitrogen-limited environments.

In bench-scale studies of mixed fungal and bacterial systems, most of the reported degradation of TNT is attributable to native bacterial populations. High TNT or PCP concentrations in soil also can inhibit growth of white rot fungus. A study suggested that one particular species of white rot fungus was incapable of growing in soils contaminated with 20 ppm or more of TNT. In addition, some reports indicate that TNT losses reported in white rot fungus studies can be attributed to adsorption onto the fungus and soil amendments, such as corn cobs and straw, rather than actual destruction of TNT. Another study tested a variety of white rot fungus for PCP sensitivity. Eighteen species tested for PCP sensitivity were inhibited by 10 mg per liter of PCP when grown on agar plates. Within 2 weeks, 17 of the 18 species grew in the inhibition zones. In liquid-phase toxicity experiments, all 18 species were killed by 5 mg per liter of PCP.

Synonyms:

Applicability:

The contaminant groups treated most often are PAHs, non-halogenated SVOCs (not including PAHs), and BTEX. The types of Superfund sites most commonly treated by bioremediation have been contaminated through processes or wastes associated with wood preserving and petroleum refining and reuse. Wood preserving commonly employs creosote, which has a high concentration of PAHs and other non-halogenated SVOCs. Similarly, petroleum refining and reuse processes frequently involve BTEX.

Because the two contaminant groups most commonly treated using bioremediation are SVOCs (PAHs and other non-halogenated SVOCs), it may be difficult to treat them using technologies that rely on volatility, such as SVE. In addition, bioremediation treatment often does not require heating, requires relatively inexpensive inputs, such as nutrients, and usually does not generate residuals requiring additional treatment or disposal. Also, when conducted in situ, it does not require excavation of contaminated media. Compared with other technologies, such as thermal desorption and incineration (which require excavation and heating), thermally enhanced recovery (which requires heating), chemical treatment (which may require relatively expensive chemical reagents), and in situ soil flushing (which may require further management of the flushing water), bioremediation may enjoy a cost advantage in the treatment of nonhalogenated SVOCs

While bioremediation (nor any other remediation technology) cannot degrade inorganic contaminants, bioremediation can be used to change the valence state of inorganics and cause adsorption, immobilization onto soil particulates, precipitation, uptake, accumulation, and concentration of inorganics in micro or macroorganisms. These techniques, while still largely experimental, show considerable promise of stabilizing or removing inorganics from soil.

Limitations:

• Cleanup goals may not be attained if the soil matrix prohibits contaminant-microorganism contact.
• The circulation of water-based solutions through the soil may increase contaminant mobility and necessitate treatment of underlying ground water.
• Preferential colonization by microbes may occur causing clogging of nutrient and water injection wells.
• Preferential flow paths may severely decrease contact between injected fluids and contaminants throughout the contaminated zones. The system should not be used for clay, highly layered, or heterogeneous subsurface environments because of oxygen (or other electron acceptor) transfer limitations.
• High concentrations of heavy metals, highly chlorinated organics, long chain hydrocarbons, or inorganic salts are likely to be toxic to microorganisms.
• Bioremediation slows at low temperatures.
• Concentrations of hydrogen peroxide greater than 100 to 200 ppm in groundwater inhibit the activity of microorganisms.
• A surface treatment system, such as air stripping or carbon adsorption, may be required to treat extracted groundwater prior to re-injection or disposal.
  

Many of the above factors can be controlled with proper attention to good engineering practice. The length of time required for treatment can range from 6 months to 5 years and is dependent on many site-specific factors.

Data Needs:

Soil characteristics that need to be determined include the depth and areal extent of contamination; the concentration of the contaminants; soil type and properties (e.g., organic content, texture, pH, permeability, water-holding capacity, moisture content, and nutrient level); the competition for oxygen (e.g., redox potential); the presence or absence of substances that are toxic to microorganisms; concentration of other electron acceptors, nutrients; and the ability of microorganisms in the soil to degrade contaminants.

Treatability or feasibility tests are performed to determine whether enhanced bioremediation is feasible in a given situation, and to define the remediation time frame and parameters. Field testing can be performed to determine the radius of influence and well spacing and to obtain preliminary cost estimates.

Performance Data:

Remediation times are often years, depending mainly on the degradation rates of specific contaminants, site characteristics, and climate. Less than one year may be required to clean up some contaminants, but higher molecular weight compounds take longer to degrade.

There is a risk of increasing contaminant mobility and leaching of contaminants into ground water. Regulators often do not accept the addition of nitrates or non-native microorganisms to contaminated soils. Enhanced bioremediation has been selected for remedial and emergency response actions at an increasing number of Superfund sites. Generally, petroleum hydrocarbons can be readily bioremediated, at relatively low cost, by stimulating indigenous microorganisms with nutrients.

Cost:

References:

Engineered Approaches to In Situ Bioremediation of Chlorinated Solvents: Fundamentals and Field Applications, July 2000, EPA-542-R-00-008

Abstracts of Remediation Case Studies, Volume 4,  June, 2000, EPA 542-R-00-006

MTBE Treatment Case Studies presented by the USEPA Office of Underground Storage Tanks.

Treatment Technologies for Site Cleanup: Annual Status Report (ASR), Tenth Edition, EPA 542-R-01-004

Innovative Remediation Technologies:  Field Scale Demonstration Project in North America, 2nd Edition

Remediation Technology Cost Compendium - Year 2000

Groundwater Cleanup: Overview of Operating Experience at 28 Sites, September 1999, EPA 542-R-99-006,

Treatment Experiences at RCRA Corrective Actions, December 2000, EPA 542-F-00-020

Guide to Documenting and Managing Cost and Performance Information for Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007

A brief description of the  Applicability and Limitations of  In situ Enhanced Bioremediation can be found at the NFESC website.

Aggarwal, P.K., J.L. Means, R.E. Hinchee, G.L. Headington, and A.R. Gavaskar, July 1990. Methods To Select Chemicals for In-Situ Biodegradation of Fuel Hydrocarbons, Air Force Engineering & Services Center, Tyndall AFB, FL.

Arthur, M.F., T.C. Zwick, G.K. O'Brien, and R.E. Hoeppel, 1988. "Laboratory Studies To Support Microbially Mediated In-Situ Soil Remediation", in 1988 DOE Model Conference Proceedings, Vol. 3, NTIS Document No. PC A14/MF A01, as cited in Energy Research Abstracts, EDB-89:134046, TIC Accession No. DE89014702.

EPA, 1993. Augmented In-Situ Subsurface Bioremediation Process, Bio-Rem, Inc., EPA RREL, Demonstration Bulletin, EPA/540/MR-93/527.

EPA, 1994. Ex-Situ Anaerobic Bioremediation System, Dinoseb, J.R. Simplot Company, EPA RREL, Demonstration Bulletin; EPA/540/MR-94/508.

EPA, 1997. Best Management Practices (BMPs) for Soil Treatment Technologies: Suggested Operational Guidelines to Prevent Cross-media Transfer of Contaminants During Clean-UP Activities, EPA OSWER, EPA/530/R-97/007.

Federal Remediation Technologies Roundtable, 1995. Remediation Case Studies: Bioremediation, EPA/542/R-95/002.

• In Situ Bioremediation Using Horizontal Wells at the U.S. Department of Energy's Savannah River Site, M Area, Aiken, South Carolina

Federal Remediation Technologies Roundtable, 1998. Remediation Case Studies: In Situ Soil Treatment Technologies (Soil Vapor Extraction, Thermal Processes), EPA/542/R-98/012

• Air Sparging, In Situ Bioremediation, and Soil Vapor Extraction at the Texas Tower Site, Fort Greely, Alaska
• Soil Vapor Extraction at the Seymour Recycling Corporation Superfund Site, Seymour, Indiana

Wetzel, R.S., C.M. Durst, D.H. Davidson, and D.J. Sarno, July 1987. "In-Situ Biological Treatment Test at Kelly Air Force Base", Volume II: Field Test Results and Cost Model, AD-A187 486, Air Force Engineering & Services Center, Tyndall AFB, FL.

• Naval Air Station Yorktown, VA 
• EPA Remedial Action: Seymour Recycling, IN
• EPA Removal Action: Roseville Drums, CA
• EPA Removal Action: Gila River Indian Reservation, AZ
• EPA Removal Action: Gila River, Indian Reservation, AZ
• Navy Demo: Naval Communication Station, Scotland
• Army Demo: U.S. Army Construction Engineering Research Laboratory, IL
• Air Force Demo: Kelly AFB, TX & Eglin AFB, FL
• FAA Technical Center-Area D Atlantic County, NJ
• Eglin AFB, FL
• Department of Energy's Savannah River Site, M Area, Aiken, South Carolina
• Texas Tower Site, Fort Greely, AK
• Seymour Recycling Corporation Superfund Site, Seymour, IN
• 

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A list of vendors offering In Situ Biological Soil Treatment is available from EPA REACH IT which combines information from three established EPA databases, the Vendor Information System for Innovative Treatment Technologies (VISITT), the Vendor Field Analytical and Characterization Technologies System (Vendor FACTS), and the Innovative Treatment Technologies (ITT), to give users access to comprehensive information about treatment and characterization technologies and their applications.

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