United States
Environmental! Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-F-96-007
April 1996
vvEPA A Citizen's Guide to
Technology Innovation Office
Technology Fact Sheet
What is bioremediation?
Bioremediation is a treatment process that uses naturally
occurring microorganisms (yeast, fungi, or bacteria) to
break down, or degrade, hazardous substances into less
toxic or nontoxic substances. Microorganisms, just like hu-
mans, eat and digest organic substances for nutrients and
energy. In chemical terms, "organic" compounds are those
that contain carbon and hydrogen atoms. Certain microor-
ganisms can digest organic substances such as fuels or sol-
vents that are hazardous to humans. The microorganisms
break down the organic contaminants into harmless prod-
ucts—mainly carbon dioxide and water (Figuire 1). Once
the contaminants are degraded, the microorganism popula-
tion is reduced because they have used all of their food
source. Dead microorganisms or small populations in the
absence of food pose no contamination risk.
How does it work?
Microorganisms must be active and healthy in order for
bioremediation to take place. Bioremediation technologies
assist microorganisms' growth and increase rnicrobial
populations by creating optimum environmental conditions
for them, to detoxify the maximum amount of contami-
nants. The specific bioremediation technology used is de-
termined by several factors, for instance, the type of micro-
organisms present, the site conditions, and the quantity and
toxicity of contaminant chemicals. Different microorgan-
isms degrade different types of compounds and survive
under different conditions.
Indigenous microorganisms are those microorganisms that
are found already living at a given site. To stimulate the
growth of these indigenous microorganisms, the proper
soil temperature, oxygen, and nutrient content may need
to be provided.
If the biological activity needed to degrade a particular
contaminant is not present in the soil at the site, microor-
ganisms from other locations, whose effectiveness has
been tested, can be added to the contaminated soil. These
are called exogenous microorganisms. The soil conditions
at the new site may need to be adjusted to ensure that the
exogenous microorganisms will thrive.
Bioremediation can take place under aerobic and anaero-
bic conditions. In aerobic conditions, microorganisms use
available atmospheric oxygen in order to function. With
sufficient oxygen, microorganisms will convert many or-
ganic contaminants to carbon dioxide and water. Anaero-
bic conditions support biological activity in which no
oxygen is present so the microorganisms break down
chemical compounds in the soil to release the energy
they need. Sometimes, during aerobic and anaerobic
processes of breaking down the original contaminants,
intermediate products that are less, equally, or more
toxic than the original contaminants are created.
Bioremediation can be used as a cleanup method for con-
taminated soil and water. Bioremediation applications fall
into two broad categories: in situ or ex situ. In situ biore-
mediation treats the contaminated soil or groundwater in
the location in which it was found. Ex situ bioremediation
processes require excavation of contaminated soil or
pumping of groundwater before they can be treated.
A Quick Look at Bioremediation
Uses naturally occurring microorganisims to break down hazardous substances into less toxic or nontoxic
substances.
A cost effective, natural process applicable to many common organic wastes.
Many techniques can be conducted on-site.
Printed on Recycled Paper
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In Situ Bioremediation of Soil
In situ techniques do not require excavation of the con-
taminated soils so may be less expensive, create less dust,
and cause less release of contaminants than ex situ tech-
niques. Also, it is possible to treat a large volume of soil at
once. In situ techniques, however, may be slower than ex
situ techniques, may be difficult to manage, and are most
effective at sites with permeable (sandy or uncompacted)
soil.
The goal of aerobic in situ bioremediation is to supply
oxygen and nutrients to the microorganisms in the soil.
Aerobic in situ techniques can vary in the way they supply
oxygen to the organisms that degrade the contaminants.
Two such methods are bioventing and injection of hydro-
gen peroxide. Oxygen can be provided by pumping air
into the soil above the water table (bioventing) or by deliv-
ering the oxygen in liquid form as hydrogen peroxide. In
situ bioremediation may not work well in clays or in
highly layered subsurface environments because oxygen
cannot be evenly distributed throughout the treatment area.
In situ remediation often requires years to reach cleanup
goals, depending mainly on how biodegradable specific
contaminants are. Less time may be required with easily
degraded contaminants.
Bioventing. Bioventing systems deliver air from the atmo-
sphere into the soil above the water table through injection
wells placed in the ground where the contamination exists.
The number, location, and depth of the wells depend on
many geological factors and engineering considerations.
An air blower may be used to push or pull air into the soil
through the injection wells. Air flows through the soil and
the oxygen in it is used by the microorganisms. Nutrients
may be pumped into the soil through the injection wells.
Nitrogen and phosphorous may be added to increase the
growth rate of the microorganisms.
Injection of Hydrogen Peroxide. This process delivers
oxygen to stimulate the activity of naturally occurring mi-
croorganisms by circulating hydrogen peroxide through
contaminated soils to speed the bioremediation of organic
contaminants. Since it involves putting a chemical (hydro-
gen peroxide) into the ground (which may eventually seep
into the groundwater), this process is used only at sites
where the groundwater is already contaminated.
What Is An Innovative Treatment
Technology?
Treatment technologies are processes applied to the
treatment of hazardous waste or contaminated
materials to permanently alter their condition through
chemical, biological, or physical means. Innovative
treatment technologies are those that have been
tested, selected or used for treatment of hazardous
waste or contaminated materials but lack well-
documented cost and performance data under a
variety of operating conditions.
A system of pipes or a sprinkler system is typically used
to deliver hydrogen peroxide to shallow contaminated
soils. Injection wells are used for deeper contaminated
soils.
In Situ Bioremediation of Groundwater
In situ bioremediation of groundwater speeds the natural
biodegradation processes that take place in the water-
soaked underground region that lies below the water table.
For sites at which both the soil and groundwater are con-
taminated, this single technology is effective at treating
both.
Generally, an in situ groundwater bioremediation system
consists of an extraction well to remove groundwater from
the ground, an above-ground water treatment system
where nutrients and an oxygen source may be added to the
contaminated groundwater, and injection wells to return
the "conditioned" groundwater to the subsurface where
the microorganisms degrade the contaminants.
One limitation of this technology is that differences in un-
derground soil layering and density may cause reinjected
conditioned groundwater to follow certain preferred flow
paths. Consequently, the conditioned water may not reach
some areas of contamination.
Another frequently used method of in situ groundwater
treatment is air sparging, which means pumping air into
the groundwater to help flush out contaminants. Air
sparging is used in conjunction with a technology called
soil vapor extraction and is described in detail in the docu-
ment entitled A Citizen's Guide to Soil Vapor Extraction
and Air Sparging (see page 4).
Ex Situ Bioremediation of Soil
Ex situ techniques can be faster, easier to control, and
used to treat a wider range of contaminants and soil types
than in situ techniques. However, they require excavation
and treatment of the contaminated soil before and, some-
times, after the actual bioremediation step. Ex situ tech-
niques include slurry-phase bioremediation and solid-
phase bioremediation.
Slurry-phase bioremediation. Contaminated soil is com-
bined with water and other additives in a large tank called
a "bioreactor" and mixed to keep the microorganisms—-
which are already present in the soil—in contact with the
contaminants in the soil. Nutrients and oxygen are added,
and conditions in the bioreactor are controlled to create the
optimum environment for the microorganisms to degrade the
contaminants. Upon completion of the treatment, the water is
removed from the solids, which are disposed of or treated
further if they still contain pollutants.
Slurry-phase biological treatment can be a relatively rapid
process compared to other biological treatment processes,
particularly for contaminated clays. The success of the
process is highly dependent on the specific soil and
chemical properties of the contaminated material. This
technology is particularly useful where rapid remediation
is a high priority.
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Figure 1
Schematic Diagram of Aerobic Biodegradation in Soil
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•>f; »tT-1V<.# VS.?** -,^?-," "^ "* *-*£. 't4**"-r*
Microorganisms digest od and ^ Microoganisms
convert it to carbbmJio^ide*{Ct>2)^ - - give off CO2 and
' ^ i ^aMw|ftfft20} ^ ^ " ^?'< >%2Q^> >?
^^t^^ui.^;, ™™*j., •vjf&a^aHHr 4^- —»~~J—V. „* iu»«^jS5j*,jV4«!<1|\, -> - « ^ t \. ^a, •* -^ K „ K V,
Solid-phase bioremediation. Solid-phase bioremediation
is a process that treats soils in above-ground treatment
areas equipped with collection systems to prevent any con-
taminant from escaping the treatment. Moisture, heat, nu-
trients, or oxygen are controlled to enhance foiodegradation
for the application of this treatment. Solid-phase systems
are relatively simple to operate and maintain, require a
•large amount of space, and cleanups require more time to
complete than with slurry-phase processes. Solid-phase
soil treatment processes include landfarming, soil biopiles,
and composting.
Landfarming. In this relatively simple treatment method,
contaminated soils are excavated and spread, on a pad with
a built-in system to collect any "leachate" or contaminated
liquids that seep out of contaminant-soaked soil. The soils
are periodically turned over to mix air into the waste.
Moisture and nutrients are controlled to enhance bio-
remediation. The length of time for bioremediation to oc-
cur will be longer if nutrients, oxygen or temperature are
not properly controlled. In some cases, reduction of con-
taminant concentrations actually may be attributed more to
volatilization than biodegradation. When the process is
conducted in enclosures controlling escaping volatile con-
taminants, volatilization losses are minimized.
Soil biopiles. Contaminated soil is piled in heaps several
meters high over an air distribution system. Aeration is
provided by pulling air through the heap with a vacuum
pump. Moisture and nutrient levels are maintained at lev-
els that maximize bioremediation. The soil heaps can be
placed in enclosures. Volatile contaminants are easily con-
trolled since they are usually part of the air stream being
pulled through the pile.
Composting. Biodegradable waste is mixed with a bulking
agent such as straw, hay, or corn cobs to maike it easier to
deliver the optimum levels of air and water to the microor-
ganisms. Three common designs are static pile composting
(compost is formed into piles and aerated with blowers or
vacuum pumps), mechanically agitated in-vessel
composting (compost is placed in a treatment vessel where
it is mixed and aerated), and windrow composting (com-
post is placed in long piles known as windrows and peri-
odically mixed by tractors or similar equipment).
Will it work at every site?
Biodegradation is useful for many types of organic wastes
and is a cost-effective, natural process. Many techniques
can be conducted on-site, eliminating the need to transport
hazardous materials.
The extent of biodegradation is highly dependent on the
toxicity and initial concentrations of the contaminants,
their biodegradability, the properties of the contaminated
soil, and the particular treatment system selected.
Contaminants targeted for biodegradation treatment are
non-halogenated volatile and semi-volatile organics and
fuels. The effectiveness of bioremediation is limited at
sites with high concentrations of metals, highly chlorinated
organics, or inorganic salts because these compounds are
toxic to the microorganisms.
Where has it been used?
At the Scott Lumber Company Superfund site in Missouri,
16,000 tons of soils contaminated with poly aromatic hy-
drocarbons (PAHs) were biologically treated using land
treatment application. PAH concentrations were reduced
by 70%.
At the French Ltd. Superfund site in Texas, slurry-phase
bioremediation was used to treat 300,000 tons of lagoon
sediment and tar-like sludge contaminated with volatile or-
ganic compounds, semi-volatile organic compounds, met-
als, and pentachlorophenol. Over a period of 11 months,
the treatment system was able to meet the cleanup goals set
by EPA.
Some additional examples of Superfund sites where differ-
ent types of bioremediation have been selected as a treat-
ment method are listed in Table 1 on page 4.
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Table 1
Examples of Superfund Sites Using Bioremediation Technologies*
Name of Site
Treatment
Applied Environmental Services, NY Bioventing
Onalaska Municipal Landfill, Wl
Eielson Air Force Base, AK
Brown Wood Preserving, FL
Vogel Paint& Wax, IA
Broderick Wood Products, CO
Burlington Northern (Somers), MT
Bioventing
Bioventing
Land treatment
Land treatment
Land treatment/Bioventing
Land treatment/
In Situ Bioremediation
Contaminants
Volatile organic compounds (VOCs),
semi-volatile organic compounds (SVOCs)
VOCs, polyaromatic hydrocarbons (PAHs)
VOCs, SVOCs, PAHs
PAHs
VOCs
SVOCs, PAHs, dioxins
SVOCs, PAHs
Fora listing of Superfund sites at which innovative treatment technologies have been used or selected for use,
contact NCEPl at the address in the box below for a copy of the document entitled Innovative Treatment
Technologies: Annual Status Report (7th Ed.), EPA 542-R-95-008. Additional information about the sites listed
in the Annual Status Report is available in database format. The database can be downloaded free of charge from
EPA's Cleanup Information bulletin board (CLU-IN). Call CLU-IN at 301-589-8366 (modem). CLU-IN's help line is
301-589-8368. The database also is available for purchase on diskettes. Contact NCEPl for details.
' Not aH waste types and site conditions are comparable. Each s/te must be individually investigated and tested.
Engineering and scientific Judgment must be used to determine if a technology is appropriate fora site.
For More Information
The publications listed below can be ordered free of charge by calling NCEPl at 513-489-8190 or faxing your request
to 513-489-8695. If NCEPl is out of stock of a document, you may be directed to other sources. Write to NCEPl at:
National Center for Environmental Publications and Information (NCEPl)
P.O. Box 42419
Cincinnati, OH 45242
• Selected Alternative and Innovative Treatment Technologies for Corrective Action and Site Remediation: A
Bibliography of EPA Information Sources, January 1995, EPA 542-B-95-001. A bibliography of EPA
publications about innovative treatment technologies.
• Bioremediation Resource Guide, September 1993, EPA 542-B-93-004. A bibliography of publications and
other sources of information about bioremediation technologies.
• A Citizen's Guide to Soil Vapor Extraction and Air Sparging, EPA 542-F-96-008
• Engineering Bulletin: In Situ Biodegradation Treatment, April 1994, EPA 540-S-94-502.
• Engineering Bulletin: Slurry Biodegradation, September 1990, EPA 540-2-90-016.
• Abstracts of Remediation Case Studies, March 1995, EPA 542-R-95-001.
• WASTECH9 Monograph on Bioremediation, ISBN #1 -883767-01 -6. Available for $49.95 from the American
Academy of Environmental Engineers, 130 Holiday Court, Annapolis, MD 21401. Telephone 410-266-3311.
NOTICE: This fact sheet /s intended solely as general guidance and information. It is not intended, nor can it be relied upon, to create any rights enforceable by any
party In litigation with the United States. The Agency also reserves the right to change this guidance at any time without public notice.
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