Biological Treatment of Contaminated Soil

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    BY301 11/2/2010

    Biological treatment of contaminated soil

    Contamination of soils occurs from environmental pollution by toxic chemicals such as

    oil and heavy metals. Technology is continuously being developed in order to treatcontaminated soil and bioremediation is among the most promising due to its low cost

    and effectiveness in destroying pollutants. Bioremediation is a process that uses

    microorganisms, green plants, fungi or their enzymes to restore a contaminated site to its

    original condition. Bioremediation can be applied either in-situ or ex-situ, dependent on

    the technique. Limitations to this technology include heavy metals being not readily

    absorbed by organisms.

    Some examples of this technology are landfarming, biostimulation, bioaugmentation, and

    phytoremediation.

    Landfarming is the process of incorporating contaminated cells, sludge or sediments into

    the soil surface while ploughing in order to allow air into the mixture. This technique is

    useful in the management and disposal of oily sludge and other petroleum based refinery

    wastes (Hejazi et al., 2003). Hydrocarbons and pesticides are treated via the use of in-situ

    systems for near surface soil contamination.

    Limitations to the technique is that it requires large space for its in-situ application,

    inorganic materials are not biodegraded, potentially present metal ions could be toxic to

    microbes and large amounts of particulate matter could potentially be released via use of

    landfarming (Hejazi et al., 2003).

    Biostimulation is the process of modifying the environment with the goal of stimulatingexisting bacteria capable of bioremediation. Various forms of rate limiting nutrients and

    electron receptors i.e. phosphorus, nitrogen, oxygen or carbon is added in order to make

    biostimulation possible (Stucki et al., 2007). Additives are added to the subsurface via

    injection wells. Removal of contaminated material is possible, yet expensive.

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    BY301 11/2/2010

    The main advantage with this process is the use of well distributed spatially, indigenous

    microbes rather than the introduction of exogenous microbes potentially not as well

    suited to the subsurface environment. A limitation posed by local geography i.e. clay can

    hinder even distribution of nutrients to microbes (Stucki et al ., 2007).

    Bioaugmentation is the introduction of natural or genetically engineered microbes in

    order to achieve bioremediation. Generally, indigenous microbes are studied in order to

    determine if biostimulation is possible. Should the indigenous microbes be incapable of

    performing the remediation process, other microbes with sufficient metabolic pathways

    are introduced (Fantroussi et al, 2005).

    Phytoremediation is the treatment of environmental problems through the use of plants.

    This technique involves depolluting contaminated soils with plants capable of absorbing,

    degrading or eliminating solvents, metals, crude oil, pesticides, etc. from the surrounding

    environment (Cunningham et al., 1995). Advantages are that it is clean, inexpensive,

    efficient and is an in-situ technique thus being environmentally undisruptive.

    Phytoremediation is limited to the surface area and depth occupied by roots as well as

    slow growth and low biomass means this technique requires a long term commitment as

    well as the survival of the plant affected by the toxicity of the soil (Cunningham et al.,1995).

    The use of biological means to treat environmental problems is not a new one. However,

    it has been shown to be of great use. Bioremediation is not limited to the examples above.

    Other examples include composting and bioventing. Techniques range from being

    expensive to inexpensive and differ also in how intrusive they are to the surrounding

    environment.

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