7 Bioremediation Techniques Explained
Bioremediation techniques are; biosparging, biopiling, windrowing, bioventing, land farming, bioslurping, and bioreactor utilization.
In some studies, they are referred to as bioremediation technologies, due to the attribute of practical implementation involved.
This article discusses bioremediation techniques, as follows;
1). Biosparging (as one of the Bioremediation Techniques)
Biosparging is a technique whereby pressurized air or oxygen is injected into the subsurface of contaminated environments, in order to stimulate native microorganisms and increase their metabolic activity [7].
The technique is effective for restoration of sites which have been subjected to pollution by organic compounds like polycyclic aromatic hydrocarbons (PAHs).
Because it depends on microorganisms that are already present, biosparging can be described as an in situ technique, and may be classified among natural attenuation bioremediation approaches.
Natural attenuation bioremediation is a compound term that is used to refer to all methods, techniques and types of bioremediation that are driven primarily by natural factors and processes like hydrological and nutrient cycling, recycling of biomass and bioenergy, and biodegradation among others.
Biosparging has some advantages and disadvantages.
The advantages of biosparging include its relative simplicity and cost-effectiveness; while the disadvantages of biosparging include the technical requirements, and practical limitations of the technique.
It is recommendable for biosparging to be implemented where conditions are favorable, such as with cases involving less-persistent pollutants and suitable in-situ microbe species.
2). Biopiling
Biopiling is a technique of bioremediation that involves heaping or accumulating contaminated soil in piles, to facilitate the build-up of microbes and the aerobic biodegradation of contaminants [4].
The ideology behind biopiling is similar to that behind composting in sustainable agriculture, and the piles formed in the process are referred to as biopiles (or bio-piles).
Biopiles are accumulations of degraded media that have been deliberately isolated to enable them undergo treatment.
It must be noted that biopiles are ex situ features, since they are made up of materials that have been excavated or physically removed from the site of degradation.
Biopiles work by providing relatively-stable conditions and sufficient biomass to allow microbes thrive and multiply, so that the metabolic activities of these microbes can help breakdown harmful materials in the substrate, and convert them to less-harmful materials that can safely be released into the ecosystem.
Some conditions that are necessary for biopiling to be both suitable and effective, are; soil as the primary degraded medium/substrate, moderate moisture content, no mechanical disturbance of the biopile, presence of suitable microbe species, optimal pH and temperature, and dominance of biodegradable pollutants.
Biopiling technique has the potential to be effective for treating hydrocarbon and heavy metal pollution.
3). Windrowing (as one of the Bioremediation Techniques)
Windrow bioremediation (or windrowing) is a treatment technique that involves accumulation of polluted media in piles that are turned periodically to facilitate aeration and biodegradation of pollutants by microbes [1].
Like Biopiling, it is mainly dependent on the activities of aerobic microorganisms, and the ability to establish suitable conditions for the rate of these activities to be increased. However, unlike biopiling which utilizes relatively-stable conditions, windrowing ensures that the substrate is mobilized periodically.
Because there is minimal demand for skill and equipment, windrow bioremediation is a cost-effective and simple technique.
However, turning of the bio-pile can lead to greenhouse emission, which is unfavorable for the environment [6].
4). Bioventing
Bioventing is a bioremediation technique whereby oxygen or air is directly introduced into the unsaturated subsurface (or vadose zone) to facilitate the growth and multiplication of aerobic microbes that can help degrade pollutants.
In bioventing, air is usually introduced by injection, into the polluted soil.
It is an in situ technique because it depends mainly on native microorganisms that already occur on the site, and does not involve extraction or removal of polluted material.
Bioventing is particularly suitable for scenarios where degradation occurs below the ground surface and above the groundwater table.
The length of bioventing (in terms of temporal span or duration), may range from few months to several years, depending on the pollutants and microbes involved, and the specific approach to gas injection.
5). Land Farming (as one of the Bioremediation Techniques)
Land farming (or landfarming) is a technique for biological treatment of degraded soil, that involves the isolation, inoculation, and aeration of such soil to facilitate microbial breakdown.
The procedure of land farming is often implemented under ex situ conditions. Here, degraded soil is placed on the ground surface, or on impermeable liner material, and treated by adding soil amendments and turning the soil periodically.
These measures lead to microbe multiplication, increased biodegradation rate, and resultant detoxification of the substrate.
The biggest advantage of land farming is its simplicity and cost-effectiveness. However it is not suitable for cases where time-saving is an objective.
Successful application of land farming can be found in soil restoration projects for oil spill-related degradation, among others [2].
6). Bioslurping
Bioslurping is a bioengineering and bioremediation technique that comprises of a combination of bioventing and vacuum-enhanced pumping as well as free-product recovery, and which is used mainly for the treatment of degraded groundwater resources.
The technique is highly adaptive, and is best suited for cases involving groundwater pollution by hydrocarbons and other low-density pollutants.
Because it does not involve any notable chemical changes, bioslurping can be used in combination with other bioremediation techniques for complex degradation cases.
The effectiveness of bioslurping can also be enhanced through preliminary assessment [5].
7). Bioreactor Utilization (as one of the Bioremediation Techniques)
A bioreactor is simply any container, enclosure or vessel in which biological processes can occur under controlled conditions.
The utilization of bioreactors is essentially an ex situ technique, since the contaminated media must be displaced from their original position on the degraded site, and transferred into the vessel.
Bioreactors are used in bioremediation by maintaining their interior at suitable physicochemical conditions of pH, temperature, microbial concentration, and humidity among others. These conditions are regulated to suit the requirements for effective degradation of the pollutant.
The above can be rephrased to state that bioreactors are used in bioremediation to establish suitable conditions for rapid biological activity, effective pollutant-breakdown, and medium quality-improvement [3].
Using bioreactors is a helpful way to minimize the environmental impacts of bioremediation itself, such as the release of volatiles that can contribute to air pollution and climate change, among others.
An advantage of bioreactor utilization technique is its versatility; as it can be used to treat soil, groundwater, wastewater, and industrial effluents under diverse conditions [8].
Conclusion
Bioremediation techniques are;
1. Biosparging
2. Biopiling
3. Windrowing
4. Bioventing
5. Land Farming
6. Bioslurping
7. Bioreactor Utilization
References
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2). Brown, D.; Okoro, S.; Gils, J. V.; Spanning, R. V.; Bonte, M.; Hutchings, T.; Linden, O.; Egbuche, U.; Bruun, K. B.; Smith, J. (2017). "Comparison of landfarming amendments to improve bioremediation of petroleum hydrocarbons in Niger Delta soils." Science of The Total Environment 596597:284-292. Available at: https://doi.org/10.1016/j.scitotenv.2017.04.072. (Accessed 7 January 2023).
3). Chikere, C.; Chikere, B. O.; Okpokwasili, G. (2012). "Bioreactor-based bioremediation of hydrocarbon-polluted Niger Delta marine sediment, Nigeria." Biotech 2(1):53-66. Available at: https://doi.org/10.1007/s13205-011-0030-8. (Accessed 8 January 2023).
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5). Kim, S.; Krajmalnik-Brown, R.; Kim, J-O.; Chung, J. (2014). "Remediation of petroleum hydrocarbon-contaminated sites by DNA diagnosis-based bioslurping technology." Science of The Total Environment 497-498C:250-259. Available at: https://doi.org/10.1016/j.scitotenv.2014.08.002. (Accessed 7 January 2023).
6). Sharma, I. (2020). "Bioremediation Techniques for Polluted Environment: Concept, Advantages, Limitations, and Prospects." Trace Metals in the Environment - New Approaches and Recent Advances. Available at: https://doi.org/10.5772/intechopen.90453. (Accessed 7 January 2023).
7). Sharma, J. (2019). "Advantages and Limitations of In Situ Methods of Bioremediation." Recent Advances in Biology and Medicine 5:1. Available at: https://doi.org/10.18639/RABM.2019.955923. (Accessed 7 January 2023).
8). Tekere, M. (2019). "Microbial Bioremediation and Different Bioreactors Designs Applied." In E. J. -Lopes, & L. Q. Zepka (Eds.), Biotechnology and Bioengineering. IntechOpen. Available at: https://doi.org/10.5772/intechopen.83661. (Accessed 8 January 2023).
