Oil is an ancient fossil fuel that we use to heat our homes, generate electricity, and power much of our economy. But when oil accidentally spills into the sea, it can cause major problems. Oil spills can harm sea creatures, ruin a day at the beach and make seafood unsafe for consumption. It takes sound science to clean up the oil, measure the effects of pollution, and help the ocean recover.
Removing oil from seawater can be a daunting task. Oil has a lower specific gravity (0.79 to 0.84) than seawater (1.023 to 1.028) and therefore floats on seawater, making “skimming” one of the most effective “direct” methods of extracting crude oil from seawater remove.
Other methods have been developed, including using a dispersant to sink the oil, introducing “oil-eating” bacteria, and simply letting the oil break down through natural processes. In this article, we will discuss the most commonly used methods for cleaning up oil spills at sea.
Methods for Oil Spill Cleanup at Sea
1. Using Oil Booms
Did you know that a third of the world’s oil comes from offshore drilling? While most offshore rigs never encounter problems, occasionally damage to the structure or the drill bit itself results in oil spilling into the ocean.
In these cases, Oil booms can save the situation by capturing the oil. They consist of three main components: A freeboard to catch the oil rising above the water surface.
The second component is called a “skirt” placed under the freeboard below the water surface which acts as the barrier wall. Let’s not forget a chain or cable that connects the parts to strengthen and stabilize the boom.
Incidentally, the booms cannot be used everywhere. This device is suitable for removing oil spills from a single area. The more oil gets into the sea, the less effective the method is. Oil booms are also not suitable for areas with strong waves, winds and high tides. In summary, booms come in a variety of sizes as their use depends on the size of the spill.
2. Using Sorbents
The word Sorbent may sound unfamiliar. We explain its meaning to you. When the oil spills in the sea, two types of sorbents can be used to clean up the spill. The absorbents that soak up the oil and the adsorbents that don’t soak up the oil but instead form a layer on the surface.
Materials commonly used as oil sorbents are straw, corn cobs or peat moss. Their advantage is their organic nature. The downside is that they only hold 3 to 15 times their weight.
Synthetic materials, which can absorb 70 times their weight, are better sorbents. Researchers at Argonne National Lab have developed an even more effective material that can absorb up to 90 times its weight in 2017. Unlike natural sorbents, which can only be used once, this polyurethane foam “sponge” can be reused.
The sorbents, like the oil booms, also have several disadvantages, such as being difficult to retrieve. In the worst case, the sorbents could sink under their own weight and pose a hazard to aquatic life.
3. Using Skimming
Skimming is a process that removes oil from the sea surface before it reaches sensitive areas along a coastline. Sometimes, two boats will tow a collection boom, allowing oil to concentrate within the boom, where it is then picked up by a “skimmer.”
From whirring disks to floating drums, skimmers come in various designs but all basically work by removing the oil layer from the surface of the water. These devices attract oil to their surfaces before transferring it to a collection tank, often on a boat. Ideal conditions for skimming are during the day when the oil slick is thick and the ocean surface is fairly calm.
The success of a skimming operation is dependent on something known as the “encounter rate.” Much like a vacuum picks up dirt from your carpet, a skimmer has to come in direct contact with the oil in order to remove it from the surface and, even then, it will still pick up some water. That’s why responders will often refer to the volume of oil removed via skimming as gallons of an oil-water mixture.
4. Hot Water and High-Pressure Washing
This procedure is mainly used in situations where the oil is inaccessible to mechanical removal methods such as using booms and skimmers. It is used to dislodge the trapped and weathered oil from locations that are generally inaccessible to machinery.
Water heaters are used to heat water to around 170°C, 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.
5. In Situ Burning
In situ burning is the process of burning spilled oil where it is on the ocean (known as “in situ,” which is Latin for “on-site”). Similar to skimming, two boats will often tow a fire-retardant collection boom to concentrate enough oil to burn. Burning is sometimes also used in treating oiled marshes.
Ideal conditions for in situ burning are daylight with mild or offshore winds and flat seas. The success of burning oil is dependent on corralling a layer of oil thick enough to maintain a sustained burn. Any burn operation includes careful air monitoring to ensure smoke or residue resulting from the burn do not adversely impact people or wildlife.
Bioremediation refers to the use of specific microorganisms to remove any toxic or harmful substances. For example, various bacteria, fungi, archaea, and algae 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 for the microbes to grow and multiply quickly.
This process is generally not used when the spill has happened in the deep seas and is gradually implemented once the oil approaches the shoreline.
7. Chemical Dispersants
Releasing chemical dispersants, usually from a small plane or a response vessel, on an oil slick breaks down the oil into smaller droplets, allowing them to mix more easily into the water column. Smaller droplets of oil become more readily available to microbes that will eat them and break them down into less harmful compounds.
However, using dispersants has its drawbacks, shifting potential impacts to the marine life living in the water column and on the seafloor. Because of this, the decision to chemically disperse oil into the water column is never made lightly. This decision is often made so that much less oil stays at the surface, where it could affect birds and wildlife at the ocean surface and drift onto vulnerable coastal habitat like beaches, wetlands, and tidal flats.
Ideal conditions for chemical dispersion are daylight with mild winds and moderate seas. Chemical dispersion is never done close to the shore, in shallow waters, near coastal communities, or when there is a potential for winds to carry the chemical spray away from its intended target.
Natural dispersion can and does occur when waves at the ocean surface have enough turbulent energy to allow surface oil to mix into the water column. Applying chemical dispersants can expedite this process when there is an imminent threat associated with allowing the oil to stay on the surface.
What are the largest marine oil spills in American history?
There are three oil spills that stand out in American history, each of which was the largest oil spill into American waterways at the time. In 1969, a blowout on an offshore platform off the coast of Santa Barbara, California, spilled over four million gallons of oil. In 1989, the Exxon Valdez oil tanker ran aground in the Prince William Sound in Alaska, spilling over 11 million gallons of oil.
The largest marine oil spill in all of U.S. history was the Deepwater Horizon spill. On April 20, 2010, an explosion occurred on the Deepwater Horizon drilling platform in the Gulf of Mexico, killing 11 people.
Before it was capped three months later, approximately 134 million gallons of oil had spilled into the ocean. That is equivalent to the volume of over 200 Olympic-sized swimming pools. An $8.8 billion settlement for restoration was reached in 2016, and restoration is still continuing today.