Oil spills are a very dangerous occurrence, for the marine ecosystem is affected and the marine life-forms’ existence gets unnecessarily threatened. Since exploration of oil from oceanic resources has become a must and oil spills end up occurring accidentally, as a result, it becomes important to employ various oil spill cleanup methods.
Oil is one of the most abundant pollutants in the oceans. About 3 million metric tons of oil contaminates the oceans annually. Oil spills vary in their severity and the extent of damage they cause. This can be attributed to variations in the oil type, the location of the spill, and the weather conditions present. The spread and behaviour of spilt oil in the seas is governed by a variety of chemical, physical and biological processes.
But irrespective of these, oil spills are a serious concern as they can inflict a lot of damage to the ecosystem. The effects are experienced not only in the area of the spill, but can also expand over vast regions to negatively impact shorelines and terrestrial wildlife thousands of metres away from the site of the spill.
Since the density of oil is lesser than water, it floats on the water surface when it leaks or spills (saltwater or freshwater). It is for this reason, that it is much easier to clean up an oil spill. It is easy to imagine the difficulty in cleaning up a spill if oil was denser than water, and as a result, formed a layer along the bottom of the seas instead of the surface!
Many major oil spills have taken place in recent years– the Exxon Valdez in 1989, the Prestige in 2002, and the Deepwater Horizon in 2010. Oil spills will continue to be a pressing problem and source of pollution as long as ships move most of the petroleum products around the world, and exploration of oil from oceanic resources is steadily on the rise.
Nevertheless, oil spills mostly end up occurring accidentally, and thus it becomes increasingly important to employ various cleanup methods for tacking the menace they could pose to the marine ecosystem.
There are different methodologies that can be adopted for the purpose of cleaning up oil spills. Some of the few important and commonly used methods can be explained as follows:
1. Using Oil Booms
The use of oil booms is a very simple and popular method of controlling oil spills. Equipment called containment booms acts like a fence to prevent the oil from further spreading or floating away. Booms float on the water surface and have three parts –
• A ‘freeboard’ is the part that rises above the water surface, containing the oil and preventing it from splashing over the top
• A ‘skirt’ is placed below the surface and keeps the oil from being squeezed under the booms and escaping
• A kind of cable or chain that connects the parts to strengthen and stabilize the boom.
Connected sections of the boom are placed around the area of the oil spill until it is totally surrounded and contained.
→ This method is Effective only when the oil is in one spot.
→ It works when the spill is accessible within a few hours of taking place, otherwise, the area of the spill becomes too large to manage
→ It cannot be successfully employed under rough sea waves, high wind velocities or fluctuating tides.
Related Read: Fighting Oil Spill on Ship
2. Using Skimmers
Once the oil has been confined by using oil booms, skimmers or oil scoops can be deployed onto boats to remove the contaminants from the water surface. Skimmers are machines specially designed to suck up the oil from the water surface like a vacuum cleaner. They are used to physically separate the oil from the water so that it can be collected and processed for re-use.
- Skimmers can be used to effectively recover most of the spilt oil, so it is economically viable.
- The presence of debris poses a major roadblock to this technique, as skimmers can get clogged easily.
3. Using Sorbents
Sorbents are materials that soak up liquids by either absorption (pulling in through pores) or adsorption (forming a layer on the surface). Both these properties make the process of clean-up much easier. Materials commonly used as oil sorbents are hay, peat moss, straw or vermiculite.
- The oil can be recovered, and this prevents wastage and further pollution.
- After the absorption, the sorbent materials must be effectively retrieved. This is a difficult task and may prove to be worse if ignored.
- Sorbents after absorption become heavier (3 to 15 times their weight), and as a result, may sink, making them difficult to retrieve and also pose a risk to aquatic life in the sea bottom.
- They are most effective in small spills or to manage the leftover traces of a larger spill.
4. Burning In-situ
In this method, the oil floating on the surface is ignited to burn it off. This in-situ burning of oil can effectively remove up to 98% of an oil spill, which is more than most of the other methods.
According to Obi et al, (2008), “The minimum concentration (thickness) of the slick on the water surface for any measurable effectiveness of in-situ burning is 3mm. This is because it would be very difficult (and even nearly impossible) to ignite a layer which is not thick enough.
- The toxic fumes released from the burning can cause significant damage to the environment as well as marine life.
- The procedure works on spills that are relatively fresh before the oil spreads to a larger area and decreases in thickness.
5. Using Dispersants
When the spilled oil cannot be contained by using booms, the only option left is to accelerate the disintegration of oil. Dispersal agents, such as Corexit 9500, are chemicals that are sprayed upon the spill with the help of aircraft and boats, which aid the natural breakdown of oil components.
They allow the oil to chemically bond with water by increasing the surface area of each molecule. This ensures that the slick does not travel over the surface of the water, and is easier to degrade by microbes.
- It can effectively be used for spills over large areas.
- Use of dispersants can create tarballs. As the oil combines with water, it also gets mixed with sand and debris present in the water. This results in the formation of large tar balls floating on the surface of the water, which often find their way to the shores.
- The toxicity of dispersants can affect marine organisms, especially the non-mobile ones such as corals and seagrass.
Related Read: Different Types of Dispersants Used in an Oil Spill
6. Hot Water and High-Pressure Washing
This procedure is mainly used in situations where the oil is inaccessible to methods of mechanical removal such as using booms and skimmers. It is used to dislodge the trapped and weathered oil from locations which are generally inaccessible to machinery.
Water heaters are used to heat up water to around 170°C, which is then sprayed by hand with high-pressure wands or nozzles. The oil is thus flushed to the water surface, which can be collected with skimmers or sorbents.
- The released oil must be immediately and adequately recovered to prevent any further contamination.
- Organisms falling in the direct spray zone have a high chance of being adversely affected by the hot water.
Related Read: What is Ship Oil Pollution Emergency Plan (SOPEP)?
7. Using Manual Labour
As the name suggests, the method requires hand-held tools and manual labour to clean up the contaminants. It involves the use of manual means like hands, rakes, shovels etc. to clean the surface oil and oily debris and place them in special containers to be removed from the shoreline.
Sometimes, mechanized equipment may be employed for providing any additional help and reach out to any inaccessible areas.
- This method is applicable only for cleaning up the slick in shorelines.
- The process is more economically viable, as unskilled workers with minimal training can be employed for the process
- Apart from being labour intensive, this process is also time-consuming.
- The use of heavy machinery can inflict damage upon shorelines, so they should be avoided as much as possible.
Bioremediation refers to the use of specific microorganisms to remove any toxic or harmful substances. There are various classes of bacteria, fungi, archaea and algae that degrade petroleum products by metabolizing and breaking them into simpler and non-toxic molecules (mostly fatty acids and carbon dioxide). Sometimes, reagents and fertilizers may be added to the area. These phosphorus-based and nitrogen-based fertilizers provide adequate nutrients to the microbes so that they are able to grow and multiply quickly.
This process is generally not used when the spill has happened in the deep seas and is gradually put into action once the oil starts to approach the shoreline.
- It is a time taking procedure and may even take years, so quicker solutions like using booms and skimmers or sorbents may be used if any urgent action is required.
- The fertilizers have an equally high chance of aiding the growth of unwanted algae, which consume much of the available oxygen and cut off sunlight from going to the deeper water levels. This can negatively impact marine life, and prove to be counter-productive.
Related Read: What is An Oil Spill Kit?
9. Chemical Stabilisation of oil by Elastomizers
Right after an oil spill, the immediate concern is to prevent the oil from spreading and contaminating the adjacent areas. While mechanical methods like using oil booms effectively contain the oil, they have certain limitations to their use.
Quite recently, experts have been using compounds like ‘Elastol’, which is basically poly iso-butylene (PIB) in a white powdered form, to confine oil spills. The compound gelatinizes or solidifies the oil on the water surface and thus keeps it from spreading or escaping. The gelatin is easy to retrieve, and this makes the process highly efficient.
- It is a quick action method, with typical reaction times of 15-40 minutes.
- While PIB is non-toxic and commonly found in foodstuffs, the gelatin may pose a risk of entangling or suffocating the aquatic animals.
10. Natural Recovery
The simplest method of dealing with the oil spill cleanup operation is to make use of the vagaries of nature like the sun, the wind, the weather, tides, or naturally occurring microbes. It is used in certain cases when the shoreline is too remote or inaccessible, or the environmental impact of cleaning up a spill could potentially far outweigh the benefits.
Due to the constancy of these elements, the oil generally evaporates or is broken down into simpler components.
- It is one of the most cost-effective methods.
- It is a highly time consuming and unreliable process and thus needs constant and close monitoring. It should not be confused with ‘sitting down and doing nothing’.
A pivotal factor in cleaning up an oil spill is the location where it has happened. Most of the oil spills take place far out in the sea, so they are generally left to naturally decompose in the environment. As they get closer to the shores, we gradually begin to treat them.
The treatments follow a general rule: (All distances measured from the shoreline)
- 200 nautical miles and beyond – No treatment is used, unless the case is very severe.
- Between 20 and 200 nautical miles, booms and skimmers may be used.
- Between 20 and 10 nautical miles, dispersants are used.
- For areas very close to the shoreline, biological agents are used.
These are only general rules and can be altered based on the type of oil that has been spilt and the prevailing weather conditions. No two oil spill cases are the same, so each one is evaluated individually based on its own merit.
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