One of the major environmental
problems today is hydrocarbon contamination resulting from the activities
related to the petrochemical industry. Oil hydrocarbons are one of the most
prevalent soil contaminants in the world. It has been estimated that the
natural crude-oil seepage amounts to 0.6 Mt per year, with a range of
uncertainty of 0.2–2 Mt per year. Accidental releases of petroleum products are
of particular concern in the environment. Hydrocarbon components have been
known to belong to the family of carcinogens and neurotoxic organic
pollutants. Soil contamination by
petroleum hydrocarbons was found to result from petroleum extraction, refining,
transportation, bad practices, theft, aircraft accidents, train accidents,
transportation accidents, illegal dumping, bad storage, terrorism, at wars,
leakage of tanks, and pipeline ruptures. Remediation of the petroleum
contaminated soil is essential to maintain the sustainable development of soil
ecosystem.
Currently accepted disposal methods of incineration or burial insecure landfills can become prohibitively expensive when amounts of contaminants are large. Technologies commonly used for the soil remediation include natural attenuation, land farming, biopiling or composting, slurry bioreactor, bioventing, soil vapor extraction, thermal desorption, incineration, soil washing, and land filling. However, these technologies are usually expensive and can lead to incomplete decomposition of contaminants. As mechanical and chemical methods generally used to remove hydrocarbons from contaminated sites have limited effectiveness and expensive.
Currently accepted disposal methods of incineration or burial insecure landfills can become prohibitively expensive when amounts of contaminants are large. Technologies commonly used for the soil remediation include natural attenuation, land farming, biopiling or composting, slurry bioreactor, bioventing, soil vapor extraction, thermal desorption, incineration, soil washing, and land filling. However, these technologies are usually expensive and can lead to incomplete decomposition of contaminants. As mechanical and chemical methods generally used to remove hydrocarbons from contaminated sites have limited effectiveness and expensive.
Crude oil contamination
is a threatening to the public health and safety. Crude oil contamination leads
to explosions, causing fire hazards, deteriorate air and water quality,
agriculture and recreational areas. It has a severe environmental impact on
ecosystems by harming or killing wildlife and plants, and destroying habitats
and food. Petroleum hydrocarbon (PHC) contamination affects soil properties and
in turn, soil properties also have significant impacts on PHC degradation.
Crude oil contamination is responsible for alterations of soil physico-chemical
properties and hurdles in nutrient cycling. It increases the heavy metal
contents in soil affecting the soil pH, electrical conductivity and many other
soil properties (Baruah et al.,
2011). The amount of the oil spills also has an impact on the leaching of the
PHCs to the ground water.
Bioremediation is the
promising technology for the treatment of these contaminated sites since it is
cost-effective and will lead to complete mineralization. Bioremediation
functions basically on biodegradation, which may refer to complete
mineralization of organic contaminants into carbon dioxide, water, inorganic
compounds, and cell protein or transformation of complex organic contaminants
to other simpler organic compounds by biological agents like microorganisms.
Bioremediation using microorganisms and plants to detoxify or remove pollutants
owing to their diverse metabolic capabilities is an evolving method for the
removal and degradation of many environmental pollutants including the products
of petroleum industry. There are two main approaches
to oil spill bioremediation: Bioaugmentation (addition of oil-degrading
bacteria) and biostimulation where the growth of indigenous oil degraders is
stimulated by the addition of nutrientsor other growth-promoting co-substrates
(Das and Chandran, 2011). In
bioremediation many indigenous microorganisms in water and soil are capable of
degrading hydrocarbon contaminants. Remediation of the polluted soil can be
accomplished by either use of microbes like Pseudomonas, Mycobacterium,
Rodococcus, Arthobacter, Acinetobacter, Nocardia,
Bacillus, Asperzillus, etc.
Meanwhile, studies have shown that
plants and mostly weeds like Axonopus
compressus, Cynadon dactylon, Eleusine indica etc. helps in reclamation of
crude oil contaminated soil. Plants have the ability to detoxify some
xenobiotics in soil by direct uptake of the contaminants, followed by
subsequent transformation, transport and product accumulation by the method
known as Phytoremediation. Phytoremediation can be achieved by
Phytoimmobilization, Phytoextraction, Phytodegradation, Phytovolatilization and
Phytostimulation (Chibuike and Obiora, 2013). In phytoimmobilization plants
reduce the mobility and bioavailability of pollutants in soils by adsorbing the
pollutants into their structure whereas phytoextraction is the method where
plants extract the pollutants from the soil by accumulating them into their
roots and shoots which are later harvested and incinerated. In Phytodegradation
the pollutants are degraded by compounds produced or exuded by plants and the
technique whereby plants adsorb and release the pollutants or their metabolites
into the atmosphere is known as Phytovolatilization. In Phytostimulation, the
associated role of rhizosphere microorganisms plays an important tool in
biodegradation processes. The microbes present in the rhizosphere stimulate the
plants growth and help in hydrocarbon degradation. Reclamation can be achieved
by combining plants and microbes which
increases the efficiency of this method of remediation. Gao et al. (2014) reported that coupling of
different remediation techniques was more effective in degrading crude oil
contaminants like the combined effect of fertilizers, microbial inoculants and
plants enhances the efficiency of the degradation process.
Reference
- D. Barua, J. Buragohain and S.K. Sarma (2011). “Certain physico-chemical changes in the soil brought about by contamination of crude oil in two oil fields of Assam, NE India,” European J. Expt. Biol., 1(3): pp. 154-161.
- G. U. Chibuike and S. C. Obiora (2013). “Bioremediation of hydrocarbon-polluted soils for improved crop performance,” International Journal of Environmental Sciences,4(3)
- N. Das and P. Chandran (2011). “Microbial degradation of petroleum hydrocarbon contaminants – an overview,” Biotechnol. Res. Int. 11: pp. 1-13.
- Yong-chao Gao, Shu-hai Guo, Jia-ning Wang, Li. Dan, Hui. Wang, and De-Hui Zeng(2014). “Effects of different remediation treatments on crude oil contaminated saline soil,” Chemosphere 117: pp. 486-493.
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Amrita Phukan |
About the Author: Miss Amrita Phukan, did her B. Sc. and M.
Sc. in Agriculture majoring in Soil Science from Assam Agricultural University
(AAU), Jorhat, Assam (India) with first class. At present, besides working as a
Junior Research Fellow in a DBT funded project, Miss Phukan has been pursuing
her Ph.D. in Agriculture (Soil Science) in the Department of Soil Science, AAU,
Jorhat, Assam (India). Her area of specialization is Soil Microbiology and
Biofertilizer Production. [Read More]
Dr Rosy Yenn has been recently awarded PhD by Assam University, Silchar (A Central University) on the same topic under joint supervision of Dr Ajit K Tamuli, Assoc. Prof. Diphu Campus, AU and Dr H P Deka Boruah of NEIST and has a n impact factor publication in an international journal. Topic is extremely important and relevant.
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