Oil is a general term used to denote petroleum products, which mainly consist of hydrocarbons. Crude oils are made up of a wide spectrum of hydrocarbons ranging from very volatile, light materials such as propane and benzene to more complex heavy compounds such as bitumens, asphaltenes, resins and waxes. Refined products such as petrol or fuel oil are composed of smaller and more specific ranges of these hydrocarbons.With petroleum finding a wide range of applications in the form of vehicle fuel, heating source for homes and industry, for electricity generation and in basic industrial operations, there has been an enormous demand for production and movement of oil. Oil is thus being continuously pumped from the ground, refined, transported and stored, resulting in spilling by “operations” or “accidents”.
Oil Spills have been a major cause of concern as they pose a danger to public health, devastate natural resources and disrupt the economy. When we think of oil spills, we usually think of oil tankers spilling their cargo in the seas and oceans. But the spills can be due to any operations and accidents occurring in the oil industry. As shown in the Table below, the spills can result due to various operations taking place during the generation or movement of oil:
Table 1. Incidence of Spill by Cause
From this table, it can be deduced clearly that main spills are caused during the loading and discharging operations although accidents play a considerable part in oil pollution caused by oil spills.
Picture 1: IXTOC I exploratory well blew out on June 3,1997 in the Bay of Campeche of Cuidad del Carmen, Mexico. The accident resulted in spilling of 140 million gallons of oil.
Picture 2: Part of an oil slick of some 20 miles, follows the stricken Bahamas-flagged, ‘Prestige’ oil tanker, as it is towed away from the northwestern coast of Spain near Maxi by two tugboats to avoid an environmental catastrophe, Tuesday Nov 14,2002.The history of incidents related to oil spills due to Tankers gives us an idea of the great danger posed to the oceanic environment due to oil spills. Some of the major accidents related to the oil industry have been due to tankers and are listed below:
Table 2: Six Major Tanker Spills
The Table above can give us a clear perspective of the amount of crude oil entering our oceans over the time, resulting in a tremendous loss of aquatic wildlife and endangering the human population around the accident site, for years after the incident
Picture 3: The oil spill in the Manawa River.
Picture 4: About 38.3 million litters of crude oil gushed out of a storage tank at Brachia, Las Minas, Panama
Picture 5: In December 1992, Aegean Sea tanker ran aground off the port of La Coruna in north-west Spain, broke up and finally exploded, emptying its entire cargo of about 79,000 tons of crude oil into the sea.
- Natural reasons: - Spills can also be caused by natural disasters like hurricanes. Oil has been in the environment for a long time. Some oil lies below the ocean floor and can seep into the ocean through cracks.
- Man-made reasons: - Sometimes when people change the oil in their cars, they dump the used, dirty oil on the ground and as an action of rain; this oil is carried down to the streams. The amount of oil dumped on the ground for a year can easily surpass a serious oil tanker spill. Deliberate acts by countries at war can also be a major cause for oil spills.
Predominantly, an oil spill is related to the spills caused due to accidents involving tankers, causing a serious impact on coastal activities and on those who exploit the resources of the sea. The severity of impact of an oil spill depends on a lot of factors, including the characteristics of oil and natural conditions prevalent at the time of the spill.
The effects of oil spills can be divided broadly into following specifications-
- Marine contamination
- Marine life can be affected by both the physical and chemical properties of
the oil spilled, the main threat posed by the residues on the contaminated sea surface. A short-term exposure can render unpleasant tastes and smells to aquatic life but a prolonged exposure, to even small concentrations of toxic components can impair the ability of marine organisms to reproduce, grow, feed or perform other functions. Another impact of oil spills can be seen on the shorelines, where large areas of rocks, sand and mud are affected, resulting in a loss of aesthetic value of the beaches.
Picture7: 1989 Exxon Valdez oil spill. Nearly one quarter of the rehabilitated and released sea otters died soon after the release.
Picture 8: Between 300-400 spills per year occur in Alaska. Tens of thousands of animals died in Exxon Valdez spill, 1989.
Picture 9: A bird floats in oil contaminated water in Camelle, northwestern Spain, Sunday, Nov.17, 2002 after oil spilled from the Bahamas-flagged tanker ‘Prestige’ washed ashore, Saturday.
Picture 10: A tanker laden 70,000 tons of fuel oil split in two off northwest Spain November 19,2002.
Rescue workers shovel sand on the oil-covered beach in the fishery village of Malpica, northern Spain.
- Fresh water contamination
- In fresh waters, oil contamination can result in severe impacts on the
habitat because the movement associated with water is minimal, as compared to marine environment. Stagnant water bodies cause the oil to remain in the environment for long, resulting in prolonged exposure of the plants and animals. Incase of flowing streams and rivers, the oil not only tends to collect on plants and grasses growing on the banks but also interacts with sediments, thereby affecting the organisms.
Oil spills, whether or not they are petroleum-based, pose an immediate threat to the environment and require quick and thorough responses. It is important to prevent the oil from spreading and causing further disruption to the subtle ecosystem. The spills can lead to severe surface and groundwater pollution, requiring efficient methods for the cleanup.Oil spills cleanup techniques depend largely on the type of oil, the conditions present at the location and during the time of the spill. The various remediation processes can thus be broadly divided into two categories:
a. Short Term Processes
b. Long Term Processes
Both these categories are the result of the kind of techniques used for treatment of oils spills and the various advantages and disadvantages of these techniques.
This is usually the first measure used to attempt to clean up after an oil spill. Long, floating plastic or rubber barriers called booms are placed around the floating oil slick. These acts like fences, containing the oil and preventing it from further spreading. . In addition, booms may be used to divert and channel oil slicks along desired paths, making them easier to remove from the surface of the water. Booms can be divided into several basic types. Fence booms have a high freeboard and a flat flotation device, making them least effective in rough water, where wave and wind action can cause the boom to twist. Round or curtain booms have a more circular flotation device and a continuous skirt. They perform well in rough water, but are more difficult to clean and store than fence booms. Non-rigid or inflatable booms come in many shapes. They are easy to clean and store, and they perform well in rough seas. However, they tend to be expensive, more complicated to use, and puncture and deflate easily. All boom types are greatly affected by the conditions on the water; the higher the waves swell, the less effective booms become.
Picture 11: Booms used to contain oil in the calm ocean waters.
Picture 12:
Containment booms used in the oceans to prevent further spreading of the spill
After the oil is contained using booms, ‘skimmers’ or boats that skim spilled oil from the water surface are used. In calm waters, vacuum skimmers work well to suck the oil and put it into storage tanks. In choppy waters, floating disk and rope skimmers can be passed through the oil.
Usually, booms and skimmers are the first technique employed to remove oil from marine environments but this technique can recover a very small proportion of the spilled oil. The only disadvantage associated with this technique is that it hampers the natural tendency of oil to spread and disperse. So, even though we deploy this technique, after some time, the oil starts floating at a very low rate rendering the technique ineffective.
- Absorption
Absorption is the technique employed in choppy or fast moving waters, when methods like containment and removal fail. In this method, sorbent materials such as talc, straw, sawdust and synthetic absorbents are added to the oil slick and them removed when they have soaked up some of the oil. These sorbent materials act like a big sponge, removing oil but contaminated absorbent materials must be treated as toxic waste and present disposal problems. Also, straw and sawdust can become waterlogged and difficult to remove.
Picture 13: MYCELX oil spill absorbents are a breakthrough in shoreline protection and absorb oil without absorbing water. Removes all hydrocarbons and saves time, labor and disposal cost.
- Dispersants
Dispersant is a major remediation method after oil spills.
a. How dispersant work?
Dispersants are chemicals that promote the formation of tiny oil droplets, and delay the reformation of slicks. They contain surfactants and/or solvent compounds.
Picture 14: Function of Surfactants
After an oil spill, oil droplets break down because of waves and currents during the dispersion process. Water and oil droplets then combined to a water-in-oil emulsion, which has high viscosity. The balance between natural dispersion and emulsification is set up.
Dispersants can alter this kind of natural balance, inhibit emulsion formation and promote oil dispersion. Thus they can remove the spilled oil from the water surface and reduce the impact to environment, especially to the shoreline and sensitive habitats.
b. The effectiveness of dispersants depends on several factors.
1) Oil properties: Dispersant have little effect on very viscous, floating oils. When oil weathers, its properties change. With the passage of time, oil slicks become less and less dispersible.
2) Environmental conditions: For example, Water temperature. In general, low temperatures will make oils more viscous and have some minor effects on dispersant effectiveness. Dispersants work best in warm water. Dispersants are sensitive to low salinity.
3) Spraying or aircraft/ship operations. Dispersants are applied by spraying equipment mounted on boats of various sizes, small fixed wing aircraft and helicopters. For large incidents, bigger fixed wing aircraft can be used.
Picture 16b: Spraying by small fixed wing aircraft
Picture 16a: Spraying by HelicopterPicture 15: Mechanism of Dispersants Remediation
Picture 16c: Spraying by Ship
c. Advantage of dispersant
1) Dispersants can rapidly treat large area of spilled oil, especially through application of dispersant from aircraft. This method can also handle spills occur in remote areas. They are their key advantages over other methods. The benefit of the appropriate use of dispersants was clearly demonstrated during the response to the 'SEA EMPRESS' incident in 1996. In this case, chemical dispersants prevented at least 17,000 tonnes of crude oil from hitting the environmentally sensitive coastline of southwest Wales.
2) Dispersants can be more effective as compared to other techniques in extremely harsh weather conditions, i.e. strong winds or currents.
Picture 17: Some 120 tons of dispersant was used to treat slicks in severe weather on the Shetland Isles, Scotland, 1993.
3) Dispersants assist the biodegradation of the oil by increasing exposure to bacteria and oxygen. And the biological processes further break the oil droplets to accelerate the dispersion and dilution.
4) Dispersed oil droplets can associate with suspended sediment, reducing risk of contamination of marine habitats and wildlife.
d. Limitations of dispersants
1) Dispersants and/or dispersed oil are toxic and may have long-term fate and effects on environment. Dispersants promote the biodegradation process and make the oil more available to organisms and enter the marine food chain. It will cause lethal or harmful effects on planktonic plants, animals, and fishes.
2) Dispersants may not be as effective as other response techniques since they are affected greatly by environmental condition. In the famous Exxon Valdez oil spill in 1989, a trial dispersant was conducted, but was discontinued eventually, because there was not enough wave action to mix the dispersant with the oil in the water.
3) Dispersant spraying was ineffective on some crude oil and all heavy fuel oil spilled because of their high viscosity.e. Types of dispersants
1) ‘Type 1 dispersants’---Low toxicity dispersants. This kind of dispersants is based on hydrocarbon solvents with between 15 and 25% surfactant. They are of relatively low effectiveness and need to be used at very high treatment rates.
2) ‘Type 2 dispersants’---More efficient dispersants using a higher surfactant content. The higher viscosity of these dispersants made them difficult to apply using certain existing spraying mechanisms, but this was later overcome by substituting some of the solvent with seawater.
3) ‘Type 3 dispersants’--- Higher performance dispersants using blends of different surfactant types. Most modern dispersants can be sprayed from aircraft, and from boats and ships.
f. Prospect of future dispersants: Scientists are devoted into develop more advanced dispersants. The goal is to improve the effectiveness of dispersants for heavy and weathered oil and to develop dispersants with less toxic and long-term cumulative effects are the main emphasis of future development.
In-situ burning of oil is defined as the controlled burning of an oil spill on the water’s surface. Burning requires minimal equipment although some specialized equipment and training is required. Because the oil is gasified during combustion, the need for physical collection, storage and transport of recovered product is reduced but can cause air pollution to a great extent. At times, burning also leaves a toxic residue on the surface of water, causing more pollution rather than removing it from the natural environment.
Picture 18: In-situ burning of oil when the oil still floating on the surface.
As bioremediation requires oxygen, this process can only take place at the oil-water interface. Other factors that may slow bioremediation are concentrations of contaminants being so high they are toxic to microbes, unfavorable moisture and temperature. Altering environmental conditions, adding nutrients or additional microbes and stimulating microorganisms with electric charges can increase microbe activity and bioremediation.
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