Agriculture Reference
In-Depth Information
i.
Generation of fugitive emissions may be a problem during operations.
ii.
The distance from the contaminated site to the nearest disposal facility will affect cost.
iii.
Depth and composition of the media requiring excavation must be considered.
iv.
Transportation of the soil through populated areas may affect community acceptability.
In this respect, the on-site removal and treatment can often yield significant savings and, in
addition, the treated soil may have beneficial secondary use (e.g. as construction fill or road
base material) at the same site.
3.2 Bioremediation techniques
Bioremediation is one of the most viable options for remediating soil contaminated by
organic and inorganic compounds considered detrimental to environmental health.
Bioremediation is a process defined as the use of microorganisms/plants to detoxify or
remove organic and inorganic xenobiotics from the environment. It is a remediation option
that offers green technology solution to the problem of hydrocarbon and heavy metals
contamination. The main advantage of bioremediation is its reduced cost compared to
conventional techniques. Besides cost-effectiveness, it is a permanent solution, which may
lead to complete mineralization of the pollutant. Furthermore, it is a non-invasive technique,
leaving the ecosystem intact (Perelo, 2010). Bioremediation can deal with lower
concentration of contaminants where the cleanup by physical or chemical methods would
not be feasible. For bioremediation to be effective, microorganisms must enzymatically
attack the pollutants and convert them to harmless products. Bioremediation can be
effective only where environmental conditions permit microbial growth and activity, its
application often involves the manipulation of environmental parameters to allow microbial
growth and degradation to proceed at a faster rate (Vidali, 2001).
Hydrocarbon considered to be one of the major sources of energy supply across the world
usually constitutes major contaminants to both aquatic and terrestrial ecosystems. Various
techniques has been employed to remediate soil environment contaminated by
hydrocarbons, ranging from physical, to chemical and mechanical forms of treating or
removing the contaminants. Bioremediation offers a better technique for treatment and
removal of these contaminants into an innocuous substance. Effective bioremediation of
hydrocarbons in the soil environment can be achieved by either or both of the following
techniques: Biostimulation and Bioaugmentation.
Microorganisms play a significant and vital role in bioremediation of heavy metal
contaminated soil and wastewater. Though when microorganisms especially bacteria are
exposed to higher concentration of metal, it may have cidal effects on them. Hence,
microorganisms are effective only at low metal concentration in the soil. Microorganisms are
usually used for the removal of heavy metals. Microorganisms can interact with metals and
radionuclides via many mechanisms, some of which may be used as the basis for potential
bioremediation strategies (Lloyd et al., 2005). Mechanisms by which microorganisms act on
heavy metals includes biosorption (metal sorption to cell surface by physiochemical
mechanisms), bioleaching (heavy metal mobilization through the excretion of organic acids
or methylation reactions), biomineralization (heavy metal immobilization through the
formation of insoluble sulfides or polymeric complexes) intracellular accumulation, and
enzyme-catalyzed transformation (redox reactions) (Lloyd, 2002). Biosorption seems to be
the most common mechanisms (Haferburg and Knothe, 2007). It is the only option when
dead cells are applied as bioremediation agent. However, systems with living cells allow
more effective bioremediation processes as they can self-replenish and remove metals via
