Contaminated sites, whether on land or in aquatic environments are increasingly becoming a frequent sight. This is due to rapid increase in population and a fast pace of technological advancement. So direct consequence of such large scale contamination is loss of sources for fresh air and water. On the other hand, exposure to dangerous chemicals lead to loss of natural habitat and its accompanying natural resources (2). Several strategies have been applied time and again to control or restore such polluted habitats. However these methods are either cost-intensive or inefficient in eliminating the pollutant. In such scenarios, bioremediation can be one of the best solutions to mitigate incidences such as:
- accidental oil spills,
- release of mining run-offs,
- discharge of sewage,
- discharge from industries and
- soil contamination with pesticides,
Therefore, significant research is needed to establish the efficiency of bioremediation techniques in mitigating large scale environmental pollution.
Traditional methods of remediation
Traditional methods of cleaning up polluted habitats includes both physical and chemical methods. In traditional method, cleaning is done by removing of the contaminated material from the site and remediating it under controlled conditions (off-site or ex-situ). Another way is to directly treat at the site (in-situ remediation) (3). However, such physicochemical remediation techniques are either expensive or highly destructive, thereby creating more harm than good (3).
As shown in the table below, a wide range of pollutants are present in nature which includes land, groundwater, oceans and other waterbodies. These pollutants have been remediated traditionally using either physical or chemical methods. This is done either by diluting the pollutant or achieving chemical transformation.
For example, remediation using physicochemical strategies include using dispersants and surfactants in treatment of oil spill disasters or chemical leaching of heavy metals to wash off the metal pollutants (4, 5).
|Group of pollutant||Type of pollutant||Source of contamination|
|Polycyclic Aromatic Hydrocarbons (PAH)||Petrochemicals|
|Anthropogenic waste||Solid Waste|
|Inorganic Contaminants (Non-Metals)||Nitrogen|
|Industrial Chemicals||Fertilizers & Pesticides|
|Pharmaceutical waste (Antibiotics, Hormones, antiseptics, analgesics etc.)|
Types of pollutants and their sources
Introduction to Bioremediation
Use of biological systems for degradation or transformation of a pollutant to a lesser toxic form has become important. This is because this process creates less harmful by-products and also it is a more natural form of treatment (6). Bioremediation is the combination of biological organisms and Remediation (Act of stopping environmental damage). It is defined as, ‘the use of living organisms to reduce or eliminate environmental hazards resulting from accumulations of toxic chemicals and other hazardous wastes’ (7). The concept of bioremediation has existed since composting of agricultural waste and sewage wastewater treatment in bioreactors by using different microbial communities for degradation.
The figure above depicts the different types of bioremediation methods commonly applied. Bioremediation essentially takes advantage of the metabolic potential of living organisms. As a result, it enables fast and naturally occurring processes for degradation or conversation of contaminants. Much as, bioremediation involves using microorganisms for processing of the contaminants. However it can also encompass plants, algae or even fungi. This depend on type of pollutant and the resistance by the organism against the contaminant.
For example, even though heavy metals are toxic to humans and animals, certain type of plants and fungi can use them as a source of energy or even accumulate them. This helps in degrading or removing heavy metals from the environment.
In case of microorganisms, these highly diverse group of organisms possess a complex system of enzymes. These enzymes assist them in metabolizing different compounds, including recalcitrant ones such as organochlorines, polychlorinated biphenyls, synthetic polymers and synthetic dyes. The below table shows different types of bioremediation, based on the site of remediation process and the type of treatment given.
|Type of Bioremediation||Type of techniques|
Types of Bioremediation techniques
Since microorganisms possess the most diverse metabolic potential among living organisms capable of metabolism a large range of pollutants and chemicals. Also, they are the ideal agents for remediation of contaminated sites (6). Different microbial strains have been discovered possessing metabolizing properties for remediating a wide range of chemicals such as, hydrocarbons, heavy metals, radioactive metals and recalcitrant compounds.
For example, Pseudomonas spp., a group of gram-negative bacteria, are known for their versatile ability of degrading a large number of pollutants. They can degrade PAHs, heavy metals, phenols, pesticides and radioactive elements (8,9).
In addition, white-rot fungi have been known for their metabolizing power in treating xenobiotic and recalcitrant compounds. As a result of their ability to withstand a large range of pH and because of the complex enzyme system they help in the availability of the pollutants (10). However, main advantage of using microbes for bioremediation includes (11):
- ease of application on the contaminated site.
- minimum disruption of the site.
- permanent removal of pollutant.
- less harmful by-products as compared to other methods.
- applicability in wide range of abiotic factors.
- more accepted by public than the other methods.
Limitations of Bioremediation
Prior to selection of a particular bioremediation technique, extensive research is required for isolation and optimization of optimal microbes. Furthermore, their performance assessment in terms of cost effectiveness and performance on-field should also be analyzed (12). Consequently, these microbial bioremediation techniques often require particular combinations of biotic and abiotic factors. In addition, sometimes they face the threat of competition with indigenous microbial consortium (6). Consequently, implications of introduction of microorganisms in the contaminated site during remediation are difficult to predict. This makes it difficult to assess the safety of such methods. Furthermore, all these factors have to be considered during practical application of bioremediation techniques in cleaning up of contaminated sites.
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- Abdulsalam S, Bugaje IM, Adefila SS, Ibrahim S. Comparison of biostimulation and bioaugmentation for remediation of soil contaminated with spent motor oil. Int J Environ Sci Tech. 2011;8(1):187–94.
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