United States Research and EPA/540/2-91/002
Environmental Protection Development February 1931
Agency. .
&EPA Understanding
Bioremediation
A Guidebook for Citizens
Cover Photo: Traverse City, Michigan. A
6°0°'h8'
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UNDERSTANDING
BIOREMEDIATION:
A GUIDEBOOK FOR
CITIZENS
Bioremediation—a process that uses microorganisms to transform
harmful substances to nontoxic compounds—is one of the most
promising new technologies for treating chemical spills and hazardous
waste problems. In order to improve this technology and better understand
its capabilities, the U.S. Environmental Protection Agency (EPA) is
encouraging field tests and evaluation of waste site cleanups using
bioremediation.
As bioremediation is considered more frequently as a cleanup
alternative, citizens need information about this; process to help them
contribute to informed decision-making regarding the cleanup of waste
sites in their communities. This brochure answers some questions about
what bioremediation is, where it can be used effectively, and its advantages
and disadvantages.
What is bioremediation?
Bioremediation uses naturally occurring microorganisms, such as
bacteria, fungi, or yeast, to degrade harmful chemicals into less toxic or
nontoxic compounds. Microorganisms, like all living organisms, need
nutrients (such as nitrogen, phosphate, and trace metals), carbon, and
energy to survive. Microorganisms break down a wide variety of organic
(carbon-containing) compounds found in nature to obtain energy for their
growth. Many species of soil bacteria, for example, use petroleum
hydrocarbons as a food and energy source, transforming them into
harmless substances consisting mainly of carbon dioxide, water, and fatty
acids. Bioremediation harnesses this natural process by promoting the
growth of microorganisms that can degrade contaminants and convert them
to nontoxic by-products.
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If biodegradation is a naturally
occurring process, why do some
biodegradable organic chemicals
persist in the environment?
A number of environmental conditions can slow down or stop the
biodegradation process. For example:
• The concentration of the chemical may be so high that it is toxic to the
microorganisms.
• The number or type of microorganisms may be inadequate for
biodegradation. ;
H Conditions may be too acidic or alkaline.
• The microorganisms may lack sufficient nutrients (such as nitrogen,
phosphorous, potassium, sulfur, or trace elements), which they need to
use the chemical as a food source. (Petrochemical residues, for example,
are not "nutritionally balanced.")
• Moisture conditions may be unfavorable (too wet or too dry).
m The microorganisms may lack the oxygen, nitrate,'or sulfate they need to
use the chemical as an energy source.
In many instances, these environmental conditions can be altered to
enhance the biodegradation process. To accomplish this, samples are
collected at the site and analyzed to determine what types of
microorganisms are present and what nutrients and climatic conditions
(such as pH, moisture, temperature, and oxygen levels) can enhance
microbial degradation. For example, if inadequate nitrogen or phosphorous
are available, these nutrients can be added to enliance the growth of the
microorganisms. If the concentration of the waste is too high, other
chemicals or uncontaminated soil can be added to reduce toxicity so that
biodegradation can occur.
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Bioremediation projects are being considered, planned, or implemented at
over 100 sites across the country.
Table 1. Classes of Chemicals that May Be Suitable for Bioremediation
Using Using
Aerobic Anaerobic
Biodegiradation Biodegradation
Class
Monochlorinated
aromatic compounds
Benzene, toluene, xylene
Nonhalogenated
phenolics and cresols
Polynuclear aromatic
hydrocarbons
Alkanes and alkenes
Polychlorinated biphenyls
Chlorophenols
Nitrogen heterocyclics
Chlorinated solvents
Alkanes
Alkenes
Example
Chlorobenzene
2-methyl phenol
Creosote
Fuel oil
Trichlorobiphenyl
Pentachlorophenol
Pyridine
Chloroform
Trichloroethylene
Process
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Process
•
*
•
•
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What are the advantages of
bioremediation?
Bioremediation can be an attractive option for several reasons:
• It is an ecologically sound, "natural" process. Existing microorganisms
can increase in numbers when a food source (the contaminants) is
present. When the contaminant is degraded, the microbial population
naturally declines. The residues from the biological treatment are usually
harmless products (such as carbon dioxide, water, and fatty acids). The
bioremediation process is carefully monitored to reduce the possibility
that a product is more toxic than the original pollutant.
• Instead of merely transferring contaminants from one environmental
medium to another (for example, from water to the air or to land),
bioremediation destroys the target chemicals.
• Bioremediation is usually less expensive than other technologies thai: are
often used to clean up hazardous waste. For example, cleaning up a site
with bioremediation may cost $45 to $50 million, while it may cost $140
million if an incinerator must be built to dispose of the wastes.
H Bioremediation can often be accomplished where the problem is located.
This eliminates the need to transport large quantities of contaminated
waste off site and the potential threats to human health and the
environment that can arise during such transportation.
What are the disadvantages of
bioremediation?
Several limitations have prevented more widespread use of
bioremediation as a cleanup technology:
• Research is needed to develop and engineer bioremediation technologies
that are appropriate for sites with complex mixtures of contaminants.
• Cleanup using bioremediation often takes longer than other remedial
actions, such as excavation and removal of soil or incineration.
E In some cases, depending on the parent compound, by-products may be
formed. Some of these by-products may be toxic. The process must be
carefully monitored to ensure the effectiveness of degradation.
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Figure 1.
wells.
Ground-water treatment using extraction and Injection
source (such as air, pure oxygen, hydrogen peroxide, or ozone), and
reinjecting the water using injection wells or trenches (Figure 1).
Subsurface drains (Figure 2) can also deliver nutrients and oxygen to
depths of about 40 feet or less.
Contaminants above the water table can be biodegraded in situ if the soil
is relatively porous and permeable to air and water. A treatment solution
containing nutrients can be delivered directly to the surface using spray
irrigation, flooding, or ditches. Venting wells can be installed at intervals
throughout the contaminated area to deliver oxygen to the contaminated
soil.
Aboveground bioremediation
A variety of aboveground biological treatment processes can effectively
treat soil and water contaminated with organic chemicals. Composting is
one method for treating soil containing hazardous organic compounds.
Highly biodegradable materials, such as wood chips, are combined with a
small percentage of biodegradable waste materials. Air can be provided by
mixing the compost material or by forced air systems. Composting can also
occur in closed bioreactors.
Slurry-phase treatment (Figure 3) combines contaminated soil or sludge
with water to create a slurry, which is then biodegraded in a mobile
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Figure 2. Subsurface drain.
Water for Reuse
or Disposal
Water
Mixing and
Oxygen Transfer
Clean
Soil
Contaminated
Soil
Figure 3. Slurry-phase treatment.
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more effective after dechlorination, can be used to complete the soil
restoration. Researchers are working to develop methods combining
biological, chemical, and physical treatment processes to handle a variety
of contaminants at hazardous waste sites. :
What steps must be taken before
bioremediation can be used at a
hazardous waste site?
Careful information-gathering and evaluation of remediation options are
required before bioremediation is selected as the cleanup technology for a,
hazardous waste site. An in-depth site investigation, including extensive
sampling and laboratory analysis, is conducted to determine the nature and •
extent of the contamination, to obtain a description of the environmental
characteristics of the site, and to make an initial assessment of appropriate :
remediation technologies. Questions that must I)e answered to evaluate
bioremediation as a remediation technology for the site include the
following:
• Are the chemicals at the site potentially biodegradable?
• Are any of the contaminants potentially toxic to microbial degradation
processes? Is another type of treatment necessary before bioremediation
can be used?
• What levels of contamination represent the clean-up goals for the site?
• What are the microbiological characteristics of the environment at the
site? (For example, do aerobic or anaerobic organisms predominate?)
• Is the environment appropriate for bioremediation or can environmental
conditions be adjusted to make it more appropriate for biological
treatment (such as alteration of pH, preremoval of toxic metals, or
changes in moisture content)?
• What are the microbiological needs of the site? (For example, would
nutrients or bacteria that can break down specific substances need to be ;
added?)
If bioremediation is identified as a potentially; applicable remediation
technology, treatability studies are conducted to further evaluate this
option. These are laboratory and pilot studies that test potential approaches
to bioremediation for the site. Bioremediation is then compared to other
remedial action alternatives with respect to performance, reliability, ease of
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Waste
Flow Distributor
Inert Packing
Clarifier
Effluent
Excess Biomass
Figured. Trickling filter.
implementation, safety, regulatory issues, public health and environmental
concerns, and costs, and the most appropriate alternative is selected.
Bioremediation is a technology that holds enormous promise for the '
future. It can be a nondisruptive, cost-effective, and efficient means of
destroying harmful chemicals at many chemical spill and hazardous waste ;
sites. As scientists learn more about its capabilities and develop practical
techniques to biodegrade an increasing number of wastes, bioremediation is
likely to take a prominent place among the technologies used to clean up
and protect the environment.
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What are some additional sources of
information about bioremediation?
RCRA/Superfund Hotline
800-424-9346 outside of Washington D.C.; 202-382-3000 in
Washington, D.C. For the hearing impaired, the number is_TDD
800-553-7672 or 202-475-9652. "
Publications
Office of Research and Development, U.S. Environmental Protection
Agency. Bioremediation of Hazardous Wastes. EPA/600/9-90/041.
September 1990.
This document summarizes the results of bioremediation research
projects under EPA's Biosystems Technology Development
Program.
Office of Research and Development, U.S. Environmental Protection
Agency, Alaskan Oil Spill Bioremediation Project: Update.
EPA/600/8-89/073. July 1990.
This brochure describes field and laboratory studies initiated
following the Exxon Valdez oil spill to evaluate the effectiveness of
bioremediation to remove oil from contaminated beaches.
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Following the Exxon Valdez oil spill, patches of oil spread onto an
estimated 1,000 miles of shoreline in Alaska. Inset shows that a site
where nutrients were applied to enhance biodegradation is much
cleaner than a site where no nutrients were added.
-&U.S. GOVERNMENT PRINTING OFFICE: 1991 - 548-187/40645
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