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Petroleum spill bioremediation

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Role of petroleum in environmental pollution

Ever increasing oil production, processing and distribution results in contamination of water and soil threatening human and animal health. Most of chronic pollution stems from small but numerous spills of oil and its products from ships, leakages of underground fuel tanks, improper disposal of waste and other oil handling operations.

Massive quantities of petroleum are released into environment during wars, explosions of drilling platforms and damaged tankers. Millions of gallons of oil are spilled annually in medium- and large-scale accidents into U.S. coastal waters. These events usually lead to death of many life forms and have prolonged detrimental effects on ecosystems, which may not restore to pre-spill conditions for decades.

In the Oil Pollution Act of 1990 (P.L. 101-380) Congress enacted oil spill legislation. This law expanded and clarified the authority of the federal government and created new oil spill prevention and preparedness requirements. Further, legislation strengthened liability provisions, providing a greater deterrent against spills. After 1990, spill volume from oil carriers decreased significantly.

Oil tankers in Chesapeake bay

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Bioremediation

In the environment, fate of spilled oil is very complex. Various physical and chemical processes contribute to distribution as well as degradation of the oil components.

Oil-degrading organisms came into focus in the late 1960s, mostly through projects supported by the U.S. Office of Naval Research when U.S. Navy had been in charge of cleaning up the seas. Later, in 1970, the U.S. Environmental Protection Agency (EPA) was founded.

Bioremediation is the use of living organisms, especially microorganisms, to degrade pollutants and restore environmental quality. These organisms are wide-spread. Oil spill kick-starts preferential growth of indigenous oil-biodegrading microorganisms over all other microorganisms causing the enrichment of environment in petroleum-degrading microflora. Bioaugmentation of polluted medium with non-native microorganisms has been considered a valid approach to bioremediation for a long time.

The original studies on the biochemistry and diversity of hydrocarbon biodegradation pathways became fundamental in the science of bioremediation.

The interest in bioremediation arose in 1989, after the Exxon Valdez tanker ran into a rock in Prince William Sound (Alaska, U.S.) and spilled 201,000 m3 (53.1 million gallons of oil). For comparison, the Deepwater Horizon exploded April 20, 2010 setting off a three-month leak that totaled to 206 million gallons of oil.

After Exxon Valdez spill, stretches of contaminated shoreline were physically washed at the cost of $1 million per day. Bioremediation treatment restored the rock to whiteness in contrast with black oily untreated shorelines proving effectiveness of bioremediation.

A recent review lists 79 bacterial genera including 9 cyanobacterial genera, 103 fungal genera and 14 algal genera that are known to degrade or transform hydrocarbons (Prince RC. Petroleum Microbiology, 2005). Here, we listed biodegrading bacterial genera and fungal genera that were confirmed by a publication found in PubMed database.

Traditional molecular genetics has already offered many valuable insights into the genetic basis of hydrocarbon degradation. Also, the genomes of several hydrocarbon-degrading bacteria have now been sequenced. Among the completely sequenced organisms are Pseudomonas putida KT2440 (Nelson KE et al., 2003), Alcanivorax borkumensis (Golyshin PN et al., 2003), Acinetobacter sp. DR1 (Jung J et al., 2010) and several others.

Beach microbial community Beach algal community
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Rates of biodegradation

Crude oil biodegradation is studied in tree types of systems that differ by: (1) scale; (2) controllability of conditions; (3) homogeneity (temporal as well as spatial); (4) composition of microbial community.

The systems are:

  1. Laboratory studies are usually performed under controlled and optimized conditions, in flasks or pilot bioreactors, often with limited array of microorganisms and oil ingredients.
  2. Mesocosm studies are carried out in experimental enclosures that are designed to provide water and soil to imitate natural conditions such as tides, winds, changes in temperatures, etc.
  3. Field studies are performed either after oil was applied experimentally or under conditions of actual spill.

Rates of oil biodegradation in these systems may differ substantially. Stewart PS et al., 1993 compared rates of oil biodegradation of crude oil from 16 published reports. Measured rates of crude oil biodegradation in seawater varied over several orders of magnitude, from approximately 0.01 to 1,000 gC/m3-d (grams of carbon per cubic meter per day). Laboratory measured rates range from approximately 1 to 1,000 gC/m3-d, while field or mesocosm measurements range from about 0.01 to somewhat less than 1 gC/m3-d.

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References/Resources

 

 

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More about oil spill bioremediation at MetaMicrobe

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