Deapika Paul
Microorganisms are known for their ability to adapt any environment. We can find them in the most hazardous places on Earth. Their invisible work has led to visible results ― terraforming the planet billions of years ago and converting it into the viable green world that is today. Their ability to utilize and adapt to any available substrate in order to gain energy kept the balance in the ecosystem until humans become dominant species. Since the industrial revolution, human activity has produced a broad range of novel substances to which microorganisms can naturally adapt. The problem is that biodegradation can’t keep pace with the amount of substances being produced. Thankfully modern science offers a technology which employs microorganisms’ adaptability. It is called bioremediation.
Bioremediation is a biotechnology procedure, in which microorganisms adapted to degrade pollutants from a contaminated site are stimulated to achieve a better biodegradation rate by enrichment with fertilizers and/or oxygen. Another variation of the technology is introducing microorganisms adapted in a laboratory into the
contaminated site. Microorganisms are utilized in bioremediation because of their ability to degrade environmental pollutants due to their metabolism via biochemical pathways related to the organism’s activity and growth. Bioremediation uses micro-organisms to reduce pollution through the biological degradation of pollutants into non-toxic substances. This can involve either aerobic or anaerobic micro-organisms that often use this breakdown as an energy source. There are many categories of bioremediation techniques.
These are –
Soil Treatment:
Introduction of new microbes, ‘biostimulation’ techniques increase natural degradation processes by stimulating the growth of microbes already present. Natural biodegradation processes can be limited by many factors, including nutrient availability, temperature, or moisture content in the soil. Biostimulation techniques overcome these limitations, providing microbes with the resources they need, which increases their proliferation and leads to an increased rate of degradation. Cleaning up oil-polluted soil is an example of where stimulating microbial growth can be used to good effect. Research has shown that poultry droppings can be used as a biostimulating agent, providing nitrogen and phosphorous to the system, which stimulates the natural growth rate of oil-degrading bacteria .Systems like these may prove cheaper and more environmentally friendly than current chemical treatment options.
Air Treatment:
Air is polluted by a variety of volatile organic compounds created by a range of industrial processes. While chemical scrubbing has been used to clean gases emitted from chimneys, the newer technique of ‘biofiltration’ is helping to clean industrial gases. This method involves passing polluted air over a replaceable culture medium containing micro-organisms that degrade contaminates into products such as carbon dioxide, water or salts. Biofiltration is the only biological technique currently available to remediate airborne pollutants.
Water Treatment:
Anaerobic digestion such as bioreactor process is the biological fermentation of organic matter. Organic materials are converted into biogas, which helps to reduce pollutants and contaminants from the water. Anaerobic treatments are used to alter the chemical composition of the organic material found in wastewater to make it more environmentally friendly.
Petroleum Pollution Control:
Biopiles, similar to bioventing, are used to reduce petroleum pollutants by introducing aerobic hydrocarbons to contaminated soils. However, the soil is excavated and piled with an aeration system. This aeration system enhances microbial activity by introducing oxygen under positive pressure or removes oxygen under negative pressure.
Removing Heavy Metal:
Industrialization has led to introduction of heavy metals in the environment. Heavy metals are known to persist in the environment and become a risk for organisms. Micro-organisms are present in industrial effluents. They have adopted different strategies to cope up with the harmful effects of these metals. These strategies can be metabolism dependent or independent. One such strategy is biosorption which is binding of metal ions with metal binding proteins present on the cell wall. Biosorption is exhibited by bacteria, algae, fungi and yeasts. Not only living organisms, but also residuals of dead bodies of microorganisms shows bio sorbent properties like agricultural wastes including husk, seeds, peels and stalks of different crops. Different factors affect the rate of biosorption which includes temperature, pH, nature of bio sorbents, and surface area to volume ratio, concentration of biomass, initial metal ion concentration and metal affinity to bio sorbent. The main microbes which are usually used in bioremediation are- Pseudomonas putida, Dechloromonas aromatica, Deinococcus radiodurans, Methylibium petroleiphilum, Alcanivorax borkumensis, h chrysosporium.
The use of genetic engineering to create organisms specifically designed for bioremediation is under preliminary research. Two category of genes can be inserted in the organism: derivative genes which encode proteins required for the degradation of pollutants, and reporter genes that are able to monitor pollution levels.Numerous members of Pseudomonas have also been modified with the lux gene, but for the detection of the polyaromatic hydrocarbon naphthalene. A field test for the release of the modified organism has been successful on a moderately large scale.
There are concerns surrounding release and containment of genetically modified organisms into the environment due to the potential of horizontal gene transfer. Genetically modified organisms are classified and controlled under the Toxic Substances Control Act of 1976 under United States Environmental protection Agency. Measures have been created to address these concerns. Organisms can be modified such that they can only survive and grow under specific sets of environmental conditions. In addition, the tracking of modified organisms can be made easier with the insertion of bioluminescence genes for visual identification.
Genetically modified organisms have been created to treat oil spills and break down certain plastic.
Bioremediation is not a new technique, but as our knowledge of the underlying microbial reactions grow, our ability to use them to our advantage increases. Frequently, bioremediation requires fewer resources and less energy than conventional technology, and doesn’t accumulate hazardous by-products as waste. Bioremediation has technical and cost advantages, although it can often take more time to carry out than traditional methods.
Many microorganisms can break down metals naturally, but this is not a sufficient solution on a global scale. Therefore, as a means to resolve this problem, engineered microorganisms can be developed with the help of genetic engineering. A better understanding of the way in which both eukaryotes and prokaryotes metabolize heavy metals and the detoxification pathways will help future researchers to deal with this type of environmental problem with maximum efficiency. The choice of the most promising type of biomass must be made, taking into account its cost and availability, and this is necessary on an industrial scale.
The microorganisms should be easy to obtain and to cultivate. For example, industrial-scale application would not be of interest if the microorganism is difficult to cultivate, a rare species or a species in danger of extinction.
Although some progress has been made in the recognition of the importance of microorganisms for the decontamination of polluted waters, some important points still need to be addressed. However, a new challenge has emerged for science. Thus, further studies need to focus on the development of new clean environmentally acceptable technologies with commercial feasibility.
Author is a Student of Environmental Science and Engineering Department at Jatiya Kabi Kazi Nazrul Islam University, Trishal, Mymensingh—2224, Bangladesh
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