Bioremediation of Contaminated Soils What It Is and How - PDF by kna16892

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									                                                                                  Fact Sheet 757



            Bioremediation of Contaminated Soils
                         What It Is and How To Do It

         Why Do We Need                            not be guaranteed under landfill conditions;
                                                   in fact, for some compounds, breakdown or
         Bioremediation?                           stabilization processes are retarded in land-
                                                   fills. Pollutants and their by-products that
   The production, distribution, use, misuse,
                                                   are not converted into harmless products
disposal, or accidental spills of many chemi-
                                                   under landfill conditions will remain a seri-
cals have polluted some environments to            ous potential threat to sensitive ecosystems
levels that threaten the health of humans,         should breaches occur in landfills.
livestock, wildlife and, indeed, whole ecosys-
                                                      Incineration, another traditional waste dis-
tems. Most of these chemicals are produced
                                                   posal method has been known to generate
and used in efforts to improve human
                                                   even more toxic compounds. Materials
health, standards of living and safety
                                                   released into the air from imperfect incinera-
through advancements in manufacturing,             tion of pollutants cause either undesirable
agriculture and agribusiness, medicine, and        imbalances in the atmosphere (e.g., ozone
to strengthen national defense. Ironically,        depletion), or they will ultimately fall back to
their unplanned intrusions into the environ-       the earth and pollute vulnerable ecosystems.
ment can reverse the same standards of liv-
                                                      The past two decades have seen a tremen-
ing that they are intended to foster.              dous upsurge in the search for cost-effective
   Traditional methods for the cleanup of          and environmentally sound alternatives to
pollution have usually involved removal of         traditional methods for dealing with wastes.
the polluted materials, and their subsequent       Research, and technology development and
disposal by landfilling or incineration (so-       implementation to address waste issues now
called ‘dig, haul, bury, or burn’ methods).        rank very high among the fastest growing
These disposal/cleanup methods are often           activities in the world. The technologies that
prohibitively expensive. Furthermore, avail-       have emerged as most promising are those
able space for siting landfills and incinera-      that closely mimic time-tested, natural sys-
tors is declining. Perhaps one of the greatest     tems which have restored environments to
limitations to traditional cleanup methods is      their natural statuses following undesirable
the fact that in spite of their high costs, they   perturbations. Chemicals from natural ori-
do not always ensure that contaminants are         gins (animal, vegetable, or mineral) are
completely destroyed.                              transformed, destroyed, removed, or other-
   For example, landfilling of polluted mater-     wise stabilized through natural processes so
ial simply transfers contamination from a          they do not accumulate to levels that threat-
site of concern to one that is out of sight        en ecosystem balance or sustainability. In
and mind. Unfortunately, the breakdown             fact, the world, as we know it, would have
and/or stabilization of many pollutants can-       long ceased to exist if these self-restoring
processes were not in place. In the past, the                How is Bioremediation
environment’s resiliency had led to the con-
cept of nature’s infinite self-cleansing ability,                 Practiced?
which in turn resulted in use and disposal of
                                                           A good number of bioremediation strate-
chemicals in ways that frequently overbur-
                                                        gies have been explored and successfully
den ecosystems and threaten their life-sup-
                                                        implemented. Furthermore, combinations of
port functions.
                                                        various bioremediation approaches alone, or
   A growing public awareness and concern               their integration with other cleanup strate-
about environmental pollutants fostered a
                                                        gies continue to grow. The following is a
collaboration between government and
                                                        partial list and general description of some
industry for the development of safe and
                                                        of the current, most commonly used soil
cost-effective alternative approaches for deal-
                                                        bioremediation strategies. Deliberately, they
ing with wastes. Of the technologies that
                                                        are not placed in order of predominance or
have been investigated, bioremediation has
                                                        effectiveness; successful bioremediation
emerged as the most desirable approach for
                                                        strategies are those that are tailored to satisfy
cleaning up many environmental pollutants.
                                                        specific pollutant, site, public, regulatory,
                                                        cost- and environmental effectiveness con-
          What Exactly is                               siderations, or can be well integrated into
          Bioremediation?                               other waste cleanup schemes. For example,
                                                        landfarming (which is described immediately
   Bioremediation describes several technolo-           below) will be sufficient for the cleanup of
gies and practices that take advantage of nat-          certain pollutants; however, the practice
ural systems and processes to clean up pollu-           must be combined with very aggressive
tion. The technologies entail the science of            interventions such as nutrient additions and
understanding natural processes that pro-               alterations in environmental conditions
mote and accelerate destruction, transforma-            (biostimulation) for expeditious and more
tion, removal, or stabilization of pollutants.          effective cleanup of persistent wastes.
Practices involve implementation and man-
agement of strategies that enhance those
                                                           • Landfar ming: Landfarming is the prac-
processes.
                                                             tice of spreading high concentrations of
   Bioremediation strategies are based on
                                                             polluted material over a large uncontam-
identification of impediments to the
                                                             inated area to encourage breakdown or
removal, dissipation, or stabilization of intol-
                                                             stabilization of pollutants.
erable levels of pollutants in the environ-
ment, and provision of the necessary condi-
tions to remove those impediments, so nat-                 Landfarming is based on the assumption
ural restoration processes can proceed.                 that chemicals that will ordinarily be degrad-
Bioremediation approaches are popular with              ed or transformed in the environment
the public, industry, and regulatory agencies           become persistent because their high concen-
because, in general, they are considerably              trations are toxic to, or otherwise impair the
less expensive than traditional cleanup                 natural processes that cause their dissipation
methods, and their proper implementation                or stabilization. Dilution of such high concen-
results in complete destruction, removal, or            trations, therefore, will cause natural remedia-
stabilization of pollutants, thereby alleviat-          tion and restoration processes to proceed.
ing future health, environmental and fiscal
liability concerns. Bioremediation costs are               • Biostimulation: As the name implies,
lowered even further when the technologies                   this strategy involves some stimulation
can be implemented in place, i.e., in situ,                  of the numbers and activities of natural
thereby eliminating the need for excavation,                 populations, usually bacteria or fungi,
shutdown of operations, transportation of                    so they can better break down pollu-
hazardous materials and attendant liabilities                tants into harmless products.
associated with each one of these activities.


                                                    2
   Biostimulation is based on the assumption               wastes from the oil industry (petroleum
that a polluted medium (soil, water, etc.)                 sludges) into harmless products.
already contains microbes that are capable of
destroying or detoxifying particular pollutants           Composting is now increasingly used to
in that medium. The reason for the persis-             accelerate the breakdown and transforma-
tence of a pollutant, therefore, may be due to         tion of pollutants including pesticides and
one or more of the following: a) unbalanced            munitions wastes, and for the stabilization
and/or inappropriate levels of nutrients or            of heavy metals in soil. How and why does
aeration; b) strong binding of the pollutant to        composting work? From the start of a com-
the medium (adsorption) that prevents the              posting process to maturation of the prod-
availability of the pollutant for destruction or       uct, several different groups and successions
transformation by microbes; or c) inactivity of        of microbes come into play, dictated and
the native microbes caused by excessively              modulated by complex interactions between
high (toxic) concentrations of pollutants.             changes in levels of moisture, temperature,
Accordingly, provision of appropriate nutrient         and nutrients. These interactions ensure
and environmental conditions, including alle-          that pollutants are exposed to a broad range
viation of toxicity problems, should allow             of microbe-environment conditions thereby
natural pollutant cleanup or stabilization to          increasing chances of their breakdown or
proceed.                                               transformation by some consortia of
                                                       microbes during the succession.
   • Bioaugmentation: Bioaugmentation is               Additionally, some organic compounds
     the practice of adding specialized                formed during composting can bind some
     microbes or their enzyme preparations             metals in ways that prevent their easy
     to polluted matrices to accelerate trans-         removal and thus their translocation into
     formation or stabilization of specific            sensitive ecosystems.
     pollutants.
                                                         • Phytoremediation: This strategy takes
   Under some pollutant-environment condi-                 advantage of naturally occurring, specif-
tions there are simply no competent or effi-               ically selected, or genetically engineered
cient, naturally occurring microbes to break               plants for environmental cleanup opera-
down or transform pollutants into innocu-                  tions. It is a particularly appealing tech-
ous products. In fact, sometimes inefficient               nology because, it employs a more
transformations by native microbial popula-                familiar system, plants, rather than
tions can result in the production of even                 invisible microbes, for waste cleanup.
more toxic by-products. A solution to such a               Phytoremediation is arguably the fastest
problem may be the addition of specialized                 growing area of interest among biore-
microbes or their enzyme preparations                      mediation approaches.
(bioaugmentation agents) that can accelerate
cleanup processes. Specialized microbes that              Phytoremediation can be used on sites
are used in bioaugmentation may come from              that are polluted with heavy metals, as well
the following sources:                                 as organic chemicals. This flexibility is
   1) natural adaptations for transforming             afforded by two evolutionary adaptations:
particular pollutants stemming from pro-               First, certain plants have evolved the capaci-
longed exposures to those compounds, or 2)             ty to take up and accumulate selected metals
laboratory manipulations that produce in               in their shoots at levels that are toxic to
microbes entirely new pathways for the                 ordinary plants. In a remediation scheme,
breakdown of specific pollutants.                      these plants may be used to remove metal
                                                       contaminants from a matrix, then the metals
   • Composting: This is based on an                   can be recovered by extraction procedures.
     ancient technology for turning house-             Secondly, plants have evolved interactions
     hold wastes into useable organic amend-           and associations with organisms that can
     ments. More recently, composting has              cause accelerated breakdown or transforma-
     been used as a strategy for transforming          tions of certain pollutants in the plant root


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zones to products that no longer pose envi-                                                         processes through which pollutants from
ronmental hazards. Phytoremediation has                                                             agriculture, manufacturing, mining, recre-
several appealing attributes: a) it is an in situ                                                   ation as well as defense industry sources are
technology; b) it is applicable to the treat-                                                       transformed, stabilized, or removed from
ment of polluted soils, as well as polluted                                                         contaminated soils. Strategies are being
water systems. Natural or constructed wet-                                                          developed to capitalize on natural processes
land systems are now widely used for clean-                                                         for enhanced pollutant bioremediation.
ing up a broad range of contaminants
                                                                                                    These activities will be detailed in forthcom-
including petroleum hydrocarbons, muni-
                                                                                                    ing Extension publications.
tions wastes, as well as inorganic pollutants;
and c) it is no longer limited to the cleanup
of surface contamination. At the beginning                                                                           Acknowledgments
of its full exploitation as a bioremediation                                                          Acknowledgments are due to Drs. Scott
strategy, phytoremediation was considered to                                                        Angle and Ray Weil for useful comments and
be limited to the cleanup of surface contami-
                                                                                                    suggestions.
nation only. Now, trees with deep-rooting
systems and high evapotranspiration rates
are being used to intercept and remove pol-                                                                                  Reveiwed by:
lutants from subsurface environments.                                                               Dr. R. M. Zablotowicz
   The bioremediation strategies listed above                                                         Research Scientist, USDA, ARS
can be combined in different ways, or inte-                                                           Southern Weed Science Laboratory
grated with other strategies such as chemical                                                         Stoneville, MS
or physical remediation technologies to
develop effective waste cleanup of contami-
nants in soils, as well as in water. Within the                                                     Dr. H. K. Speidel
Soil Biochemistry/Bioremediation Program at                                                           Principal Scientist
the University of Maryland, College Park,                                                             Environmental Engineering Staff, West
research attention is being focused on eluci-                                                         Tennessee Valley Authority
dating the biochemical mechanisms and                                                                 Muscle Shoals, AL




                                Bioremediation of Contaminated Soils: What It Is and How To Do It
                                                                                             by

                                                                        E. Kudjo Dzantor
                                                                       Assistant Professor
                                                              Soil Biochemistr y/Bior emediation
                                                           Depar tment of Natural Resource Sciences
                                                                  and Landscape Ar chitectur e

 Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, University of Maryland, College Park,
 and local governments. Thomas A. Fretz, Director of Maryland Cooperative Extension, University of Maryland.
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 IX of the Educational Amendments; Section 504 of the Rehabilitation Act of 1973; and the Americans With Disabilities Act of 1990; or related legal requirements should be directed
 to the Director of Personnel/Human Relations, Office of the Dean, College of Agriculture and Natural Resources, Symons Hall, College Park, MD 20742.


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