Remediation Technologies Screening Matrix, Version 4.0 4.29 Enhanced Bioremediation
(In Situ GW Remediation Technology)
  Description Synonyms Applicability Limitations Site Information Points of Contact
Data Needs Performance Cost References Vendor Info. Health & Safety
Table of Contents
Technology>>Ground Water, Surface Water, and Leachate

>>3.9 In Situ Biological Treatment

      >>4.29 Enhanced Bioremediation
Introduction>> The rate of bioremediation of organic contaminants by microbes is enhanced by increasing the concentration of electron acceptors and nutrients in ground water, surface water, and leachate. Oxygen is the main electron acceptor for aerobic bioremediation. Nitrate serves as an alternative electron acceptor under anoxic conditions.


Figure 4-29a:
Typical Oxygen-Enhanced Bioremediation System for Contaminated Ground water with Air Sparging

Figure 4-29b:
Oxygen-Enhanced H2O2 Bioremediation System

Figure 4-29c:
Typical Nitrate-Enhanced Bioremediation System  

Bioremediation is a process in which indigenous or inoculated micro-organisms (i.e., fungi, bacteria, and other microbes) degrade (metabolize) organic contaminants found in soil and/or ground water.

Bioremediation is a process that attempts to accelerate the natural biodegradation process by providing nutrients, electron acceptors, and competent degrading microorganisms that may otherwise be limiting the rapid conversion of contamination organics to innocuous end products.

Oxygen enhancement can be achieved by either sparging air below the water table or circulating hydrogen peroxide (H2O2) throughout the contaminated ground water zone. Under anaerobic conditions, nitrate is circulated throughout the ground water contamination zone to enhance bioremediation. Additionally, solid-phase peroxide products (e.g., oxygen releasing compound (ORC)) can also be used for oxygen enhancement and to increase the rate of biodegradation.

Oxygen Enhancement with Air Sparging

Air sparging below the water table increases ground water oxygen concentration and enhances the rate of biological degradation of organic contaminants by naturally occurring microbes. (VOC stripping enhanced by air sparging is addressed in Technology Profile 4.34). Air sparging also increases mixing in the saturated zone, which increases the contact between ground water and soil. The ease and low cost of installing small-diameter air injection points allows considerable flexibility in the design and construction of a remediation system. Oxygen enhancement with air sparging is typically used in conjunction with SVE or bioventing to enhance removal of the volatile component under consideration.

Oxygen Enhancement with Hydrogen Peroxide

During hydrogen peroxide enhancement, a dilute solution of hydrogen peroxide is circulated through the contaminated ground water zone to increase the oxygen content of ground water and enhance the rate of aerobic biodegradation of organic contaminants by naturally occurring microbes.

Nitrate Enhancement

Solubilized nitrate is circulated throughout ground water contamination zones to provide an alternative electron acceptor for biological activity and enhance the rate of degradation of organic contaminants. Development of nitrate enhancement is still at the pilot scale. This technology enhances the anaerobic biodegradation through the addition of nitrate.

Fuel has been shown to degrade rapidly under aerobic conditions, but success often is limited by the inability to provide sufficient oxygen to the contaminated zones as a result of the low water solubility of oxygen and because oxygen is rapidly consumed by aerobic microbes. Nitrate also can serve as an electron acceptor and is more soluble in water than oxygen. The addition of nitrate to an aquifer results in the anaerobic biodegradation of toluene, ethylbenzene, and xylenes. The benzene component of fuel has been found to biodegrade slower under strictly anaerobic conditions. A mixed oxygen/nitrate system would prove advantageous in that the addition of nitrate would supplement the demand for oxygen rather than replace it, allowing for benzene to be biodegraded under microaerophilic conditions.

These technologies may be classified as long-term technologies, which may take several years for plume clean-up.

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Biostimulation, bioaugmentation.

F11 (Bioremediation - In Situ Groundwater)
H1 (Bioremediation)
H12 (Bioremediation - In Situ)
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Target contaminants for enhanced biodegradation processes are nonhalogenated VOCs, nonhalogenated SVOCs, and fuels. Pesticides also should have limited treatability. Nitrate enhancement has primarily been used to remediate ground water contaminated by BTEX.

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Factors that may limit the applicability and effectiveness of these processes include:
  • Where the subsurface is heterogeneous, it is very difficult to deliver the nitrate or hydrogen peroxide solution throughout every portion of the contaminated zone. Higher permeability zones will be cleaned up much faster because ground water flow rates are greater.
  • Safety precautions must be used when handling hydrogen peroxide.
  • Concentrations of hydrogen peroxide greater than 100 to 200 ppm in ground water are inhibiting to microorganisms.
  • Microbial enzymes and high iron content of subsurface materials can rapidly reduce concentrations of hydrogen peroxide and reduce zones of influence.
  • A ground water circulation system must be created so that contaminants do not escape from zones of active biodegradation.
  • Because air sparging increases pressure in the vadose zone, vapors can build up in building basements, which are generally low pressure areas.
  • Many states prohibit nitrate injection into ground water because nitrate is regulated through drinking water standards.
  • A surface treatment system, such as air stripping or carbon adsorption, may be required to treat extracted ground water prior to re-injection or disposal.

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Data Needs:

A detailed discussion of these data elements is provided in Subsection 2.2.2 (Data Requirements for Ground Water, Surface Water, and Leachate).

Characteristics that should be investigated prior to system design include aquifer permeability, site hydrology, dissolved oxygen content, pH, and depth, type, concentration, redox conditions, temperature, biodegradability of contaminants, and the presence of a competent biodegrading population of microorganisms.

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Performance Data:

As with other in situ biodegradation processes, the success of this technology is highly dependent upon soil properties and biodegradability of the contaminants.

Although oxygen enhancement with air sparging is relatively new, the related technology, bioventing (Treatment Technology Profile 4.1), is rapidly receiving increased attention from remediation consultants. This technology employs the same concepts as bioventing, except that air is injected below the water table to promote the remediation of ground water.

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For oxygen enhancement with air sparging, typical costs are $10 to $20 per 1,000 liters ($40 to $80 per 1,000 gallons) of ground water treated. Variables affecting the cost are the nature and depth of the contaminants, use of bioaugmentation and/or hydrogen peroxide or nitrate addition, and ground water pumping rates.

For nitrate enhanced treatment, one cost estimate is in the range of $40 to $60 per liter ($160 to $230 per gallon) of residual fuel removed from the aquifer.

For hydrogein peroxide enhanced treatment, costs are an order of magnitude more expensive than other methods of oxygen enhancement. O&M cost of hydrogen peroxide enhancement can be significant because a continuous source of hydrogen peroxide must be delivered to the contaminated ground water.

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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

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

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

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

Emerging Technologies for Enhanced In Situ Biodenitrification (EISBD) of Nitrate Contaminated Ground Water
, The Interstate Technology and Regulatory Cooperation Work Group (ITRC) In Situ Biodenitrification Work Team, April 2000

The EPA's Treatment Technologies for Site Cleanup Annual Status Report, Tenth Edition, documents the status, as of the summer of 2000, of treatment technology applications for soil, other solid wastes, and groundwater at Superfund sites.

Technology Evaluation Report: Technologies for Dense Nonaqueous Phase Liquid Source Zone Remediation, Ground-Water Remediation Technologies Analysis Center (GWRTAC), December 1998.

Acree, S.D. et al. 1997. "Site Characterization Methods of the Design of In Situ Donor Delivery Systems," In Situ and On Site Bioremediation: Volume 4. B.C. Alleman and A. Leeson. Battelle Press, Columbus, OH.

Dey, C.D., R.A. Brown, and W.E. McFarland, 1991. "Integrated Site Remediation Combining Groundwater Treatment, Soil Vapor Recovery, and Bioremediation," Hazardous Materials Control, Vol. 4, No. 2, pp. 32-39, March/April 1991.

EPA, 1992. In Situ Bioremediation of Contaminated Ground Water, EPA/540/S-92/003; NTIS: PB92-224336.

EPA, 1997. Anaerobic Biodegredation of BTEX in Aquifer Material, EPA/600/S-97/003.

EPA, 1997. Bioremediation of BTEX, Naphthalene, and Phenanthrene in Aguifer Material Using Mixed Oxygen/Nitrate Electron Acceptor Conditions, EPA/600/SR-97/103.

Federal Remediation Technologies Roundtable, 1997. Remediation Case Studies: Soil Vapor Extraction and Other In Situ Technologies, EPA/542/R-97/009.

Federal Remediation Technologies Roundtable, 1998. Remediation Case Studies: Innovative Groundwater Treatment Technologies, EPA/542/R-98/015.

Hutchins, S.R., G.W. Sewell, D.A. Kovacs, and G.A. Smith, 1991. "Biodegradation of Aromatic Hydrocarbons by Aquifer Microorganisms Under Denitrifying Conditions," Environmental Science and Technology, No. 25, pp. 68-76.

Technology Catalogue, Second Edition, April 1995

Treatment Technologies Applications Matrix for Base Closure Activities, November 1994

U.S. Department of Commerce, National Technical Information Service(NTIS), May 1991. "Nitrate for Biorestoration of an Aquifer Contaminated with Jet Fuel".

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Site Information:

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Points of Contact:

General FRTR Agency Contacts

Technology Specific Web Sites:

Government Web Sites

Non Government Web Sites

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Vendor Information:

A list of vendors offering In Situ Biological Water 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.

Government Disclaimer

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Health and Safety:

Hazard Analysis

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