Definition Bioremediation, Principle, Categories, Types and Applications
- Bioremediation refers to the use of natural microorganisms or deliberately introduced to consume and decompose environmental pollutants, to clean up a polluted site.
- It is a process that primarily uses microorganisms but also plants or microbial or plant enzymes to detoxify contaminants in soil and other environments.
- The concept includes biodegradation, which refers to the partial and sometimes total transformation, or detoxification of contaminants by microorganisms and plants.
- The bioremediation process improves the rate of natural microbial degradation of contaminants by supplementing native microorganisms (bacteria or fungi) with nutrients, carbon sources or electron donors (biostimulation, bio-restoration) or by adding a culture enriched with microorganisms which have characteristics which allow them to degrade the desired contaminant more quickly (bioaugmentation).
Objective of Bioremediation
The goal of bioremediation is to reduce at least the levels of pollutants to undetectable, non-toxic, or acceptable levels, that is, within the limits set by regulatory agencies or, ideally, to completely mineralize the pollutants organic carbon dioxide.
Principle of Bioremediation
- Bioremediation is based on stimulating the growth of certain microbes that use contaminants like oil, solvents, and pesticides as a source of food and energy.
- These microbes consume the contaminants, converting them to small amounts of water and harmless gases like carbon dioxide.
- Effective bioremediation requires a combination of the right temperature, the right nutrients, and food; otherwise, it may take much longer to clean up the contaminants.
- If conditions are not favorable for bioremediation, they can be improved by adding “amendments” to the environment, such as molasses, vegetable oil, or just air.
- These changes create optimal conditions for microbes to thrive and complete the bioremediation process.
- The bioremediation process can take anywhere from a few months to several years.
- The time required depends on variables such as the size of the contaminated area, the concentration of contaminants, conditions such as temperature and density of the soil, and whether bioremediation will take place in situ or ex-situ.
Categories of Bioremediation
Biological sanitation can be classified into two types: microbial sanitation and phytoremediation.
- Microorganisms are well known for their ability to break down a wide range of organic compounds and to absorb inorganic substances. Currently, microbes are used to clean up pollution treatment in processes known as bioremediation.
- Different microbial systems such as bacteria, fungi, yeast, and actinomycetes can be used to remove toxic and other contaminants from the environment.
- Microorganisms are readily available, quickly characterized, very diverse, ubiquitous, and can use many harmful elements as a source of nutrients.
- They can be applied under in situ and ex-situ conditions; besides, many extreme environmental conditions can be cleaned by these entities.
- Although many microorganisms are capable of degrading the crude oil present in the soil, it has proven to be advantageous to use a mixed culture approach than pure cultures in bioremediation because it shows synergistic interactions.
- Different bacteria can be used to remove contaminants from petroleum hydrocarbons from the soil.
- Bacteria that can degrade the main pollutants include Pseudomonas, Aeromonas, Moraxella, Beijerinckia, Flavobacteria, cyanobacteria, Nocardia, Corynebacteria, Acinetobacter, Mycobacteria, Modococci, Streptomyces, Bacilli, Arthrobacter, Aeromonas, and Cyanobacteria.
- Phytoremediation is a bioremediation process that uses various types of plants to remove, transfer, stabilize and/or destroy contaminants in the soil and groundwater.
- There are several types of phytoremediation mechanisms.
- Biodegradation of the rhizosphere: In this process, the plant releases natural substances through its roots, providing nutrients to microorganisms in the soil. Microorganisms increase biological degradation.
- Phytostabilization: in this process, the chemical compounds produced by the plant immobilize the contaminants rather than degrading them.
- Phyto-accumulation (also called phytoextraction): In this process, the roots of the plants absorb the contaminants along with other nutrients and water. The mass of contaminants is not destroyed but is found in the shoots and leaves of plants. This method is mainly used for waste containing metals.
- Hydroponic systems for the treatment of watercourses (hemofiltration): Rhizofiltration is similar to phytoaccumulation, but the plants used for cleaning are raised in greenhouses with their roots in water. This system can be used for the ex situ treatment of groundwater. In other words, groundwater is pumped to the surface to irrigate these plants. Hydroponic systems generally use an artificial soil medium, such as sand mixed with perlite or vermiculite. When the roots are saturated with contaminants, they are harvested and eliminated.
- Phytovolatilization: in this process, plants absorb water containing organic contaminants and release the contaminants into the air through their leaves.
- Phyto-degradation: In this process, plants metabolize and destroy contaminants in plant tissue.
- Hydraulic control: In this process, the trees indirectly sanitize by controlling the movement of groundwater. Trees act as natural pumps when their roots descend to the water table and establish a dense root mass that absorbs large amounts of water. A popular, for example, pulls 30 gallons of water from the ground per day, and poplar can absorb up to 350 gallons per day.
Types of Bioremediation Methods
- Natural attenuation or intrinsic bioremediation: bioremediation occurs by itself without adding anything.
- Biostimulation: Bioremediation is stimulated by the addition of fertilizers to increase bioavailability in the environment.
Technologies can generally be classified as in situ or ex-situ.
In-situ bioremediation: it involves treating contaminated materials on site.
Ex-situ bioremediation: involves the elimination of contaminated materials to be treated elsewhere.
Methods of Bioremediation
Here are some examples of technologies related to bioremediation:
Applications of Bioremediation
- Bioremediation is used for the remediation of metals, radionuclides, pesticides, explosives, fuels, volatile organic compounds (VOCs), and semi-volatile organic compounds (SVOCs).
- Research is underway to understand the role of phytoremediation in cleaning up perchlorate, a contaminant that is persistent in surface and groundwater systems.
- It can be used to clean up contaminants from soil and groundwater.
- For radioactive substances, chelating agents are sometimes used to make the contaminants likely to be absorbed by plants.
Advantages of Bioremediation
Bioremediation has some advantages over other cleaning methods.
- Since it only uses natural processes, it is a relatively green method that causes less damage to ecosystems.
- It often takes place underground, since soil improvers and microbes can be pumped underground to clean up contaminants in groundwater and soil; therefore, this does not greatly disturb neighboring communities.
- The bioremediation process creates few harmful byproducts since contaminants and pollutants are converted to harmless water and gases like carbon dioxide.
- Bioremediation is less expensive than most cleaning methods, as it does not require a lot of equipment or labor.
- Bioremediation can be adapted to the needs of the polluted site in question and the specific microbes necessary for the decomposition of the pollutant are encouraged by selecting the limiting factor necessary to promote their growth.
Limitations and Concerns of Bioremediation
- The toxicity and bioavailability of biodegradation products are not always known.
- Degradation by-products can be mobilized in groundwater or bio-accumulated in animals.
- Additional research is needed to determine the fate of various compounds in the plant’s metabolic cycle to ensure that excrement and plant products do not contribute to toxic or harmful chemicals in the food chain.
- Scientists need to determine whether the contaminants that accumulate in the leaves and wood of trees are released when the leaves fall in the fall or when firewood or tree mulch is used.
- Disposing of harvested plants can be a problem if they contain high levels of heavy metals.
- The depth of the contaminants limits the treatment. In most cases, it is limited to shallow soils, streams, and groundwater.
- Typically, the use of phytoremediation is limited to sites with lower contaminant concentrations and contamination of shallow soils, streams, and groundwater.
- The success of phytoremediation can be seasonal, depending on the location. Other climatic factors will also influence its effectiveness.
- The success of sanitation depends on the establishment of a selected plant community. The introduction of new plant species can have widespread ecological ramifications. It must be studied beforehand and monitored
- If the contaminant levels are too high, plants can die.
- Some phytoremediation transfers contamination through the media (for example, from soil to air).
- Phytoremediation is not effective for highly sorbed contaminants such as polychlorinated biphenyls (PCBs).
- Phytoremediation requires a large area of land for sanitation.