Bioremediation of soil : Challanges and Advantages

   Bioremediation of soil : Challanges and Advantages 

Bioremediation: A subfield of biotechnology known as "bioremediation" uses live organisms—such as bacteria and microbes—to remove poisons, pollutants, and contaminants from soil, water, and other environments.

Cleanup of contaminated groundwater and environmental issues like oil spills can be accomplished by bioremediation.

Contaminants with heavy metals are among the most important issues facing modern agriculture. Food security is seriously threatened by high toxicity and the substance's capacity to accumulate in crops and soils. 

It is used in the removal of contaminants, pollutants, and toxins from soil, water, and other environments.

Bioremediation is used to clean up oil spills or contaminated groundwater.
Bioremediation may be done "in situ"–at the site of the contamination–or "ex situ"–away from the site. 

How Bioremediation Works:

The process of bioremediation involves promoting the growth of specific microorganisms that use pollutants such as oil, solvents, and pesticides as food and energy sources. These microorganisms break down pollutants into innocuous gasses like carbon dioxide and little amounts of water.

The ideal balance of foods, nutrients, and temperature is needed for bioremediation. If certain components are missing, the removal of pollutants could take longer. The atmosphere can be made more conducive to bioremediation by introducing "amendments" such molasses, vegetable oil, or plain air. By improving the environment for microorganisms to thrive, these changes hasten the bioremediation process' conclusion.

Bioremediation can be carried out "in situ," or at the actual site of the contamination, or "ex situ," or at a different place. If the soil is too dense for nutrients to disperse evenly or if the environment is too cold for microbial activity to be sustained, ex situ bioremediation may be required. Excavation and soil cleaning above ground may be necessary for ex situ bioremediation, which could result in considerable process expenses.

Depending on factors including the size of the contaminated region, the concentration of toxins, temperature, soil density, and whether bioremediation will take place in situ or ex situ, the bioremediation process could take several months to several years to finish.

Promising strains of Pantoea sp., Achromobacter denitrificans, Klebsiella oxytoca, Rhizobium radiobacter, and Pseudomonas fluorescens were chosen in order to remove heavy metals from soil. As a foundation, consortiums were empiled, which were investigated for the ability to remove heavy metals from nutrient media, as well as to produce phytohormones. 

In order to increase microbial activity for the breakdown of hydrocarbons, nitrogen compounds, metals, halogenated organic compounds, etc., bioremediation of soil uses both aerobic and anaerobic conditions.

Hydrocarbons, for instance, are broken down in the presence of oxygen during the aeration phase of soil bioremediation.

Carbon dioxide and water are the byproducts. There is little or no oxygen consumed in anaerobic situations.

It is noteworthy that, in contrast to artificial chemicals, naturally existing substances in the environment decompose more quickly. As a result, bio-augmentation is now required.

Currently, bio-augmentation can be defined as the process of adding non-native or externally derived bacteria to the soil in order to help it become more detoxified.

Challenges in soil bioremediation:

• Bioavailability or accessibility of pollutants 
• Reversion of pollutant stability
• Microbial adaptability
• Metabolic pathways
• Enzymatic studies
• Pollutant interactions
• End product quality

• Bioavailability or accessibility of pollutants : Pollutants' susceptibility to bacteria in soil is influenced by their adsorption, toxicity, and consumption. The soil has an abundance of organic molecules in a highly sorbet condition, including a variety of pesticides and polycyclic aromatic hydrocarbons (PAHs). Therefore, rather than a low density of microorganisms that break down PAHs, reduced bioavailability is more detrimental to the bioremediation of soil contaminated with pesticides and PAHs. Contaminants' bioavailability varies over time. We call this process aging. One of the biggest obstacles to soil pollution cleanup is the aging of contaminants. Finding a suitable way to increase the bioavailability of contaminants in soil is therefore necessary.

• Reversion of pollutant stability:  One viable and long-term solution to the problem of an accumulation of organic products is to compost the organic matter that remains after waste treatment. Nevertheless, the environment's pH is altered by the mineralization of organic materials, which flips the stability of pollutants.

• Microbial adaptability:  The adaptation of foreign microbes to work on a specific site is slowed down by poor compliance with the polluted soils. As a result, bioaugmentation loses its ability to accelerate the breakdown of contaminants. Appropriate techniques could be required to investigate and resolve this issue.

• Metabolic pathways: There is still much to learn about the microbial metabolic pathways involved in the bioremediation of organic contaminants and heavy metals. Therefore, it is imperative to conduct a thorough investigation of metabolic pathways and microbial community dynamics in order to modify the genetic makeup of external microorganisms. Moreover, high-throughput sequencing and other molecular biology techniques should be applied to comprehend the genetic structure of native bacteria. Technology and synthetic biology techniques are required to get beyond the aforementioned obstacles and remove environmental contaminants.

• Enzymatic studies: Many enzymes have basic catalytic actions that break down contaminants, which are actually hidden. As a result, a great deal of research is needed to understand the kinetics, molecular structure, activity, and inhibition mechanism of different enzymes.

• Pollutant interactions: It is still unknown how contaminants from the same soil/compost mixture would interact with one another in a synergistic or antagonistic way to cause degradation. To overcome this obstacle, more research is necessary.

• End product quality: Ensuring that the final product released after bioremediation is devoid of any harmful organic compounds and metals above a certain threshold is mandatory.

Benefits of Biological Remediation:

Compared to other cleaning techniques, bioremediation has many benefits. It reduces ecosystem damage by depending only on natural processes. The process of bioremediation frequently occurs underground, where pollutants in soil and groundwater can be removed by pumping additives and bacteria. As a result, compared to other cleanup techniques, bioremediation causes less disruption to the populations surrounding it.

Because toxins and pollutants are transformed into water and innocuous gases like carbon dioxide, the bioremediation process produces very little toxic consequences. Finally, because bioremediation doesn't require a lot of work or heavy equipment, it is less expensive than most cleanup techniques.

Three types of bioremediation:

• Biostimulation - Microbes are stimulated to begin the remediation process via chemicals or nutrients that activate them. The bacteria are triggered to start the process, as the name implies. First, the polluted soil is combined with unique nutrients and other essential elements in liquid or gaseous form. It promotes the proliferation of microorganisms, which enables them and other bacteria to quickly and effectively remove pollutants from the environment.

• Bioaugmentation - Used mainly in cleaning up soil contamination, this process adds bacteria to the surface of the affected area, where they are then allowed to grow. Sometimes, in order to remove the pollutants, specific locations call for the use of microorganisms. Take municipal wastewater as an example. The bioaugmentation method is employed in these unique circumstances. There is just one significant flaw in this procedure. Controlling the proliferation of microorganisms throughout the process of eliminating a specific contamination becomes nearly difficult.

• Intrinsic Bioremediation - Vonverts toxic materials into inert ones using the native microbiome to the affected area. Since soil and water are the two biomes most likely to contain pollutants and poisons, these are the environments where intrinsic bioremediation works best. Intrinsic bioremediation is mostly utilized in subterranean environments, such as underground fuel storage facilities. It can be challenging to locate leaks in such areas, and pollutants and other impurities may seep in and taint the gasoline. Solely microorganisms are able to cleanse the tanks and eliminate the poisons.
• Incineration: Wastes and other undesired materials are burned during this procedure. The organic waste burns to produce heat, flue gas, and ash. The waste's inorganic components are still present as ash. Another name for it is thermal therapy.
• Phytoremediation: In this case, pollutants in the soil are directly cleaned up or contained by plants. By using this bioremediation technique, the environmental issue can be lessened without having to remove the contaminated material from the site and dispose of it somewhere else.

Factors Affecting Bioremediations:

• Microbial activity is directly impacted by contaminant concentrations. The pollutants may be harmful to the existing microorganisms at high quantities. Low contaminant concentrations, on the other hand, might inhibit the induction of bacterial breakdown enzymes.

• The degree to which pollutants sorb to solids or are sequestered by molecules in contaminated medium, are dispersed in soil or sediment macropores, and other parameters including whether they are present in non-aqueous phase liquid (NAPL) form all affect how bioavailable they are. Site factors have a considerable impact on the bioavailability of microbial reactions for contaminants that are more broadly distributed in macropores of soil and sediments, more strongly sorbed to solids, encased in matrix of molecules in contaminated medium, or present in NAPL form.

• Site characteristics have a significant impact on the effectiveness of any bioremediation strategy. Site environmental conditions important to consider for bioremediation applications include pH, temperature, water content, nutrient availability, and redox potential.

• pH affects the solubility and biological availability of nutrients, metals, and other constituents; for optimal bacterial growth, pH should remain within the tolerance range for the target microorganisms Bioremediation processes preferentially proceed at a pH of 6-8 

• Redox Potential and oxygen content typify oxidizing or reducing conditions. Redox potential is influenced by the presence of electron acceptors such as nitrate, manganese oxides, iron oxides and sulfate 

• Nutrients are needed for microbial cell growth and division. Suitable amounts of trace nutrients for microbial growth are usually present, but nutrients can be added in a useable form or via an organic substrate amendment , which also serves as an electron donor, to stimulate bioremediation.

• Temperature directly affects the rate of microbial metabolism and consequently microbial activity in the environment. The biodegradation rate, to an extent rises with increasing temperature and slows with decreasing temperature.