Bioremediation technology utilizes the natural capabilities of living organisms such as plants, microbes, algae, and fungi to remove or degrade contaminants from the environment. This technology is gaining wide acceptance due to its potential to reduce anthropogenic pollutants and toxins from various environmental components. The technology can be applied in both in-situ and ex-situ conditions. Different biotechnological and genetic engineering strategies have been employed to improve the efficacy of this technique for the complete degradation of pollutants. Microbes and plants are used to achieve maximum removal of inorganic and organic contaminants. The process also enhances the potential of both plants and microbes for the successful remediation of one or more pollutants. The technology can be used to clean up contaminated sites, reduce the risk of health problems associated with pollution and ultimately improve the quality of the environment.

Bioremediation:

Bioremediation technology is primarily based on metabolic activities of microorganisms such as microbial degradation of organic pollutants, biosorption, binding of ions, molecules of pollutants, and transformation of pollutants to less toxic forms. In this technique, microbes, microalgae, fungi, plants, and enzymes are used to reduce the concentration of pollutants. Among the microbial species, bacteria, algae, yeasts, fungi, and actinomycetes are most commonly used in bioremediation processes. These microorganisms possess diverse metabolic capabilities and can degrade a wide variety of pollutants. In addition, certain plant species are also used to absorb pollutants from the environment and subsequently degrade them. The metabolic activities of microorganisms and plants are enhanced by the addition of various nutrients, enzymes, and other components. The bioremediation technology is also used to clean up spilled oil, reduce heavy metal contamination and treat wastewater. The bioremediation process is usually monitored by measuring the concentration of pollutants at regular intervals.

Categories of Bioremediation:

In Situ Bioremediation:

In situ bioremediation is a process that uses natural or engineered microorganisms to degrade, transform, or immobilize environmental pollutants in contaminated soil or groundwater. It is one of the most widely used methods of environmental remediation and treating a variety of contaminants. It includes petroleum hydrocarbons, chlorinated solvents, polychlorinated biphenyls (PCBs), and heavy metals.
In situ bioremediation involves the introduction of microorganisms into the subsurface environment, where they are able to degrade or transform contaminants. This process can be or by stimulating the indigenous microorganisms in the contaminated area. In either case, the microorganisms are typically stimulated by the addition of nutrients and/or oxygen to the subsurface environment.

In Situ Bioremediation techniques

Bioventing:

Bioventing is an effective and efficient way to remediate contaminated soil. It has been used successfully to treat hydrocarbons, perchlorate, explosives, and propellants. Bioventing is most suitable for sites with low to moderate levels of contamination and is typically used in conjunction with other methods of remediation such as pump and treat systems or soil vapor extraction. The process can also be used to treat complex contaminants, including petroleum hydrocarbons, polyaromatic hydrocarbons, and phenols. Once the oxygen is introduced into the subsurface, bioventing can be used to stimulate the growth of naturally occurring microorganisms that degrade the target contaminants. Generally, bioventing is used to treat non-aqueous-phase liquids (NAPLs) such as gasoline, diesel, jet fuel, and petroleum products. But it can also be used to treat aqueous-phase contaminants such as chlorinated solvents and explosives.

Biostimulation:

Biostimulation has been used to reduce the toxicity of pollutants in contaminated soil, groundwater, and sediment. A variety of organisms such as bacteria, fungi, and algae have been used to promote the biodegradation of pollutants. Biostimulation is more effective when the pollutant is not very toxic and the environment is conducive to the growth of microorganisms. Biostimulation can be used to degrade persistent organic pollutants (POPs) such as polycyclic aromatic hydrocarbons (PAHs), chlorinated solvents, and polychlorinated biphenyls (PCBs). The addition of nitrogen and phosphorus can enhance the biodegradation of these pollutants by stimulating the growth of indigenous microorganisms. Biostimulation may also reduce the toxicity of pollutants by increasing the biodegradation rate of the pollutant. Thus, reducing the concentration of pollutants in the environment.

Bioattenuation:

Bioattenuation is a process by which contaminants are reduced in mass, toxicity, volume, or concentration. This can be done through a variety of means, including aerobic and anaerobic biodegradation, sorption, volatilization, and chemical or biological stabilization. Bioattenuation is often used on sites where other remedial techniques are not applicable, or where concentrations of contaminants are low.

Biosparging:

Volatile organic compounds (VOCs) can be a major problem for groundwater quality. Biosparging is an effective way to remove them. Biosparging works by injecting air into the aquifer below the zone of contamination. This oxygenates the aquifer and stimulates indigenous bacteria to degrade the VOCs. This process is relatively simple and can be quite effective in cleaning up groundwater contamination.

Ex Situ Bioremediation:

Ex-situ bioremediation is a biological process in which soil is excavated and placed in a lined above-ground treatment area. Where it is aerated to enhance the degradation of organic contaminants by the indigenous microbial population. This process is used to clean up contaminated sites, impacted by oil spills, hazardous waste, and agricultural chemicals.

Ex situ Bioremediation techniques:

Biopiles:

Biopile-mediated bioremediation is an effective way to clean up polluted soil. By excavating the soil and piling it above ground, and treatment bed is also created that is well-aerated and irrigated. This will encourage microbial activity and help to break down pollutants. The addition of nutrients to the soil may also be conducted to help speed up the process. Finally, a leachate collection system can be used to collect and treat any water that leaches from the soil.

Windrows:

Windrows can be used for bioremediation of soils contaminated with hydrocarbons, such as oil spills and refinery waste. Other contaminants include pesticides, heavy metals, and other persistent organic pollutants. The microbes in the windrows degrade the pollutants through oxidation, reduction, and hydrolysis. The pollutants are converted into harmless end products, such as carbon dioxide, water, and biomass. Moreover, windrows can also reduce odors associated with contaminated soils.

Landfarming:

Landfarming is a process through which pollutants are degraded in soil by manipulating its physical conditions. This is usually done by tilling or plowing the soil to create favorable conditions for microbial growth, which in turn would degrade the pollutants. The process of landfarming also includes the addition of certain amendments like organic matter, nitrogen, and phosphorous to stimulate microbial growth and enhance the pollutant degradation process. Land farming can also be used to treat a wide range of pollutants, including hydrocarbons, pesticides, dioxins, and metals.
• The main advantage of land farming is that it is a cost-effective and relatively low-tech technique. Also, making it is suitable for small-scale operations. Furthermore, landfarming offers the possibility to treat a wide range of pollutants at the same time. It is not possible with other bioremediation techniques. Finally, landfarming can be used in a variety of soil types, including clay, loam, and sandy soils.
• However, landfarming also has some drawbacks. For instance, it is a slow process, and it can be difficult to monitor the process and determine the degree of pollutant removal from the soil. Furthermore, landfarming is not suitable for treating pollutants with high concentrations. It may result in the redistribution of pollutants in the soil. Finally, landfarming can cause the release of pollutants into the air and water, which may result in environmental pollution.

Bioreactor:

A bioreactor is used to break down organic matter, reduce chemical oxygen demand (COD), and reduce suspended solids to levels deemed safe for discharge. Bioreactors also have applications in the biodegradation of pollutants, where the bioreactor is used to treat contaminated soils by bioremediation.
Bioreactors are also used in industrial processes to produce chemicals, enzymes, and other products. They are designed to provide optimal conditions for the growth of microorganisms. And to control the process parameters (such as temperature, pH, nutrient supply, and oxygen supply) to yield the desired product.

Types of Bioremediation:

This is the classified basis on the type of microorganisms of living species used for bioremediation purposes.

Microbial Remediation

Microbial remediation is a form of bioremediation that utilizes microorganisms to transform, degrade, or remove contaminants from an environment. This process can occur naturally in the environment or be enhanced through the introduction of additional organisms or even nutrients.

Organic pollutants, such as petroleum hydrocarbons, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs), are among the most common pollutants found in soil and groundwater. Microorganisms, including bacteria, fungi, and yeasts, in the presence of suitable environmental conditions and nutrients, break down the pollutants into less toxic compounds. For example, Pseudomonas bacterial strains have been shown to efficiently degrade petroleum hydrocarbons. While Trichoderma harzianum fungal species have been used to degrade PCBs and PAHs. In addition, various other species of bacteria and fungi have been successfully used for the bioremediation of organic pollutants.

Inorganic pollutants, such as heavy metals, are also of major environmental concern. Microorganisms can be used to reduce the bioavailability of heavy metals and reduce their toxicity. This can be achieved either directly, by binding the metal ions, or indirectly, by creating a complexing agent which reduces the metal’s solubility. In addition, some microorganisms are capable of transforming the metal ions into less toxic forms. For example, a consortium of bacteria, including Pseudomonas fluorescens, has been shown to efficiently reduce the bioavailability of lead ions. Microalgal species like Chlorella sorokiniana and Diatoms and some cyanobacterial species are scientifically proven to have bioremediation activity on many water-soluble pollutants. Moreover, blue-green algae like Rivularia and Phormidium species are rather the best biological indicators of pollution levels in the environment. (Mateo, P. et al. 2015)

Phytoremediation

Phytoremediation has several advantages over more traditional methods of environmental remediation such as incineration and landfills. It is relatively inexpensive, safe, and efficient. Additionally, it can be used in a wide range of environmental conditions and can be implemented rapidly. Furthermore, the process is relatively self-sustaining and can be used in areas where it may be difficult or impossible to use other methods.

The most common techniques used in phytoremediation include phytoextraction, phytodegradation, phytostabilization, and rhizofiltration. Phytoextraction involves the use of plants to extract metals from soils, sediments, and other matrices. These plants accumulate the metals in their tissues and can be harvested for removal and disposal. Phytodegradation involves the use of plants and their associated microorganisms to degrade organic contaminants. This is accomplished through a process known as biotransformation, in which the organisms transform the contaminants into less toxic or non-toxic forms. Phytostabilization involves the use of plants to immobilize or reduce the bioavailability of metals and other contaminants in soils and sediments. Finally, rhizofiltration involves the use of plants and their associated microorganisms to remove contaminants from water, such as heavy metals, pesticides, and other organic contaminants.

Phytoremediation may be applied to polluted soil or static water environment. This technology has been increasingly investigated and employed at sites with soils contaminated heavy metals like with cadmium, lead, aluminum, arsenic, and antimony. Many plants such as mustard plants, alpine pennycress, hemp, and pigweed have proven to be successful at hyper-accumulating contaminants at toxic waste sites. Not all plants are able to accumulate heavy metals or organic pollutants due to differences in the physiology of the plant.

Phycoremediation

Phycoremediation is a type of bioremediation process that uses algae and seaweed to clean up pollutants from a contaminated environment. In this process algae and seaweed help to naturally clean up pollutants, such as heavy metals and organic pollutants, from a contaminated environment. Algae and seaweed are naturally efficient at absorbing a wide range of pollutants and heavy metals.

The phycoremediation process begins with the selection of a suitable site for the algae or seaweed to be placed. The chosen site should have the right amount of light and nutrients, where either algae or seaweed or both are placed and allowed to grow. As the algae or seaweed grows, it absorbs the pollutants and heavy metals from the environment. The pollutants are then metabolized and converted into harmless compounds, which are then released back into the environment.

This process has been used to successfully remove heavy metals, such as lead, chromium, mercury, and arsenic, as well as organic pollutants, such as polycyclic aromatic hydrocarbons, from contaminated sites. Phycoremediation has been used to clean up polluted rivers, lakes, and oceans, as well as contaminated soils and sediments. In addition, it has also been used to treat wastewater from industrial and municipal sources.

The process of phycoremediation is both cost-effective and environmentally friendly. It is a much cheaper and faster method than other conventional remediation processes. Additionally, it does not produce any hazardous chemicals, so it does not contribute to air or water pollution. Phycoremediation is a viable option for cleaning up contaminated environments, and it has been successfully used in many locations around the world.

Mycoremediation

Mycoremediation is a form and a process of using organisms such as fungi, particularly white rot fungus like Phanerochaete chrysosporium, to degrade a multitude of persistent or toxic environmental contaminants. It has several advantages over other remediation methods including low cost, low energy requirement, minimal impact on the environment, and the potential for on-site treatment (Sylvestre et al. 2009). It is attractive for contaminated sites where the cost of excavating and disposing of the contaminated soil is prohibitively high. Mycoremediation is also attractive for sites with groundwater contamination, as the fungi can penetrate deep into the soils and contaminate the groundwater.

Conclusion:

In the current world scenario, bioremediation is being increasingly used to clean up contaminated sites. It is a cost-effective and environment-friendly way of dealing with pollution, as it uses natural organisms to break down hazardous materials. In recent years due to the scarcity of water resources and global warming government agencies are stressing policies for the reuse and reclamation of wastewater has promoted phycoremediation technology for wastewater treatment.

Algae and seaweed are being used extensively in bioremediation and phycoremediation processes, as they are capable of removing toxins and pollutants from the environment. Algae can absorb large amounts of nitrogen and phosphorus and can uptake heavy metals, such as arsenic and lead, from the environment. Seaweed is an important component of ocean ecosystems and is capable of sequestering carbon dioxide from the atmosphere. Algae are also known to utilize double the concentration of carbon dioxide for their biomass production as compared to terrestrial plants.

With advancements in bioremediation technologies and with emerging needs for these solutions in the world. Bioremediation is new hope for land, water resources, pollution control, and climate change.

References:

Sylvestre M., Macek T, Mackova M (2009) transgenic plants to improve rhizoremediation of polychlorinated biphenyls (PCBs). Curr Opin Biotechnol 20: 242–247

Mateo, P., Leganés, F., Perona, E., Loza, V., & Fernández-Piñas, F. (2015). Cyanobacteria as bioindicators and bioreporters of environmental analysis in aquatic ecosystems. Biodiversity and Conservation, 24(4), 909-948.