Bioremediation- Types, Factors, Advantages, & Limitations | ScienceMonk

Bioremediation deals with the use of living organisms such as microorganisms like bacteria and fungi to remove contaminants, pollutants and toxins from soil and water. It can be used to clean up environmental problems like an oil spill or contaminated groundwater.

The global environment is now facing a highly critical situation due to rapid urbanization and industrialization as well as increasing population in the limited natural resources. The population growth reflects the drastic changes in the lifestyle of the people that created anthropogenic stress on the environment.

Bioremediation- Types, Factors, Advantages, & Limitations | ScienceMonk

The world is investing billions of dollars in cleaning up polluted groundwater and soils, yet this large investment may not be producing the benefits that citizens expect. Recent studies have revealed that there are several limitations of the clean-up technologies which have been employed to decontaminate the natural surroundings.

The main concern is the high cost of the various technologies being employed. Because of the limitations, alternative clean-up technologies, like bioremediation, specifically, in situ bioremediation, have emerged.

With advances in biotechnology, bioremediation has become one of the most rapidly developing fields of environmental restoration, utilizing microorganisms to reduce the concentration and toxicity of various chemical pollutants, such as petroleum hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, phthalate esters, nitroaromatic compounds, industrial solvents, pesticides, and metals.

Principle Of Bioremediation

The most important principle of bioremediation is that microorganisms can be used to destroy hazardous contaminants or transform them into less harmful forms. The microorganisms act against the contaminants only when they have access to a variety of materials—compounds to help them generate energy and nutrients to build more cells.

Bioremediation relies 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 into small amounts of water and harmless gases like carbon dioxide.

Effective bioremediation needs a combination of the right temperature, nutrients, and food; otherwise, it may take much longer for the clean-up of contaminants. If conditions are not favourable for bioremediation, they can be improved by adding “amendments” to the environment, such as molasses, vegetable oil or simply air.

These amendments create optimum conditions for microbes to flourish and complete the bioremediation process. The process of bioremediation can take anywhere from a few months to several years. The amount of time required depends on variables such as the size of the contaminated area, the concentration of contaminants, conditions such as temperature and soil density, and whether bioremediation will take place in situ or ex-situ.

Classification:

There are two ways in which bioremediation is carried out:

  • In-Situ:

It is done at the contamination site itself. It can be described as the process whereby contaminants are biologically degraded under natural conditions to either carbon dioxide and water or an attenuated transformation product. 

It is a low cost, low maintenance, environment-friendly, and sustainable approach for the clean-up of the contaminated natural surroundings. The benefit of in situ treatment is that it prevents the spread of contamination during the displacement and transport of the contaminated material.

  • Ex-Situ:

Ex-situ refers to treatment that occurs after the contaminated waste has been removed and taken to a treatment area. If we take the example of contaminated soil, the soil may be removed and transported to an area where the bioremediation methodologies may be employed.

Ex-situ bioremediation may be necessary if the climate is too cold for microbe activity, or the soil is too dense for nutrients to be spread evenly. The main advantage of ex-situ bioremediation is that it helps to contain and control the bioremediation products, as well as making the area that was contaminated available for use.

On the other hand, this entire process is expensive and requires good maintenance of the treatment plant.

Factors For Effective Microbial Bioremediation

  • Microbial Population: Suitable kinds of microorganisms that can biodegrade all types of contaminants.
  • Oxygen: Oxygen should be enough to support aerobic biodegradation (about 2% oxygen in the gas phase or 0.4 mg/liter in the soil or water).
  • Water: Soil moisture should be from 50–70% of the water holding capacity of the soil (if bioremediation of contaminated soil is taken as an example).
  • Nutrients: Nitrogen, phosphorus, sulphur, and other nutrients to support good microbial growth.
  • Temperature: Appropriate temperatures for microbial growth, something between 0–40˚C.
  • pH: The Best range of pH should be around 6.5 to 7.5 to ensure good microbial growth and timely biodegradation.

Some Biodegradable Pollutants:

Due to industrial development to produce a range of products, highly toxic organic compounds have been synthesized and released into the environment for direct or indirect application over a long period. These products are different fuels, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, pesticides, and dyes.

There are some other synthetic chemicals like radionuclides and metals that are not biodegradable using native flora compared with the naturally occurring organic compounds that are easily degraded in the natural environment.

Hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pesticides, dyes, radionuclides, heavy metals are categorized as biodegradable pollutants and offer effective results with bioremediation technologies.

An example of Bioremediation of Hydrocarbons:

Petroleum and its products are the best examples of hydrocarbons and have much economic importance. Oil is made up of a variety of hydrocarbons, viz., xylenes, naphthalene, octanes, camphor, etc. If these are present in more amounts in the environment, these cause pollution, as in the cases of oil spills, both in the water bodies as well as land.

In a toxic environment, microorganisms perform their regular activities, if the growth conditions, e.g., temperature, pH and inorganic nutrients, are as per requirement. Oil is insoluble in water and is less dense. It floats on the water surface and forms slicks. It has been noticed that in oil storage tanks, microbial growth is not possible although water and air are supplied.

Read more on- Environmental Toxicology- Study of Toxicants present In the Atmosphere

The microorganisms which are capable of degrading petroleum include Pseudomonas, various corynebacteria, mycobacteria, and some yeasts. However, with the use of a mixture of bacteria, and genetically engineered microbial strains, bioremediation of petroleum products have been carried out successfully.
A large number of bacteria live in interfaces of water and oil droplets. Each strain of bacteria consumes a particular type of hydrocarbons, so, methods have been developed to introduce a mixture of bacteria and not a single strain.

The mixture of bacteria has been used successfully to control oil pollution in water or oil spills from ships. Bacteria living in interface degrade oil at a very slow rate. The rate of degradation could be accelerated with human efforts.

The artificially well-developed mixture of bacterial strain along with inorganic nutrients such as phosphorus and nitrogen is pumped into the ground or applied to oil spill areas as required for treatment. This increases the rate of bioremediation at the target site. 

A strain of Pseudomonas putida that has been obtained by the genetic engineering technique of making a hybrid of two plasmids. It can grow rapidly on crude oil because it had the capability of metabolizing hydrocarbons more efficiently than any other single plasmid.

Advantages Of Bioremediation:

1. Bioremediation is a Natural Process:

Bioremediation is a natural process and accepted by the public as a waste treatment process for contaminated material such as soil. Microbes degrade the contaminant, increase in numbers and release harmless products. The residues for the treatment are usually harmless products such as carbon dioxide, water, and cell biomass.

2. Complete Destruction:

Bioremediation is useful for the complete destruction of a wide variety of contaminants. Many hazardous compounds can be transformed into harmless products. This reduces the chance of future liability associated with the treatment and disposal of contaminated material.

3. On-Site Treatment:

Bioremediation can be carried out on the site of contamination itself, without causing a major disruption of normal activities. This removes the need to transport huge quantities of waste off-site and thus reduce potential harm to human health and the environment that can arise during transportation.

4. Cost-Effective Process:

Bioremediation is less expensive compared to other methods that are used for the removal of hazardous waste.

Limitation Of Bioremediation:

Limited up to biodegradable compounds-Bioremediation is limited to those compounds that are biodegradable. This method is susceptible to rapid and complete degradation. Products of bio-degradation may be more persistent or toxic than the parent compound. 

1. Specificity:

Biological processes are highly specific. Important site factors required for success include the presence of metabolically capable microbial populations, suitable environmental growth conditions, and appropriate levels of nutrients and contaminants.

2. Technological Advancement:

Research is needed to develop and engineer bioremediation technologies that are suitable for sites with complex mixtures of contaminants that are not evenly distributed in the environment. It may be present as solids, liquids, and gases.

3. Time Taking Process:

Bioremediation takes a longer time to compare to other treatment options, such as excavation and removal of contaminants from the site.

5. Regulatory Uncertainty:

We are not certain to say that remediation is 100% completed, as there is no accepted definition of clean. Due to this, the performance evaluation of bioremediation is difficult, and there is no acceptable endpoint for bioremediation treatments.

Read more on –Toxicology- Definition, Branches, Terminologies & Measures Of Toxicity

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