A Roundup of Oil Spill Cleanup Methods

Fossil fuels continue to be the leading source of energy worldwide. Cleaner renewable energy sources such as solar and wind chip away at this lead, but as of 2018, 54 percent of the total worldwide energy supply still comes from oil or natural gas. Therefore, exploration and extraction of oil and gas continues.

Even though drilling and transportation for oil and gas have become safer, the risk of disaster remains. In 2020, oil spills occurred in Russia and Mauritius. After the Deepwater Horizon oil spill in 2010, experts noted that there had been little progress in oil spill cleanup technologies since the Exxon Valdez spill two decades earlier, putting the blame on a lack of investment into research by the big oil companies. Current methodologies are either inefficient (booms and skimmers) or cause even further damage to the environment (dispersants and in situ burning)

Where big oil is not offering innovation, university researchers and small start-ups are taking up the slack.

An MIT invention, Seaswarm employs a conveyor belt of a thin oleophilic (attracts oil) and hydrophobic (repels water) nanowire mesh powered by photovoltaic cells. The belt serves a dual function: to propel itself and to absorb oil up to 20 times its own weight. It works most effectively in a “swarm,” guided by GPS for a well-organized cleanup of a spill site.

Researchers at North Carolina State University have designed a seafaring Roomba, a 3D-printed solar-powered robot that can absorb oil as it autonomously navigates the oceans in search of oil spills. A built-in pump is activated when the sensor detects any oil in the water. This mixture then passes through the oleophilic and hydrophobic nanomaterial, made from tree leaves, thus recovering the oil and releasing clean water back into the ocean.

Another option, on an even smaller scale, is a swarm of microscopic submarines that propel themselves thanks to the presence of an inner layer of hydrogen peroxide that reacts with water to form bubbles of oxygen and water. The tiny robots are coated with superhydrophobic alkanethiol, which causes oil to be absorbed by adhesion to a long chain of self-assembled monolayers (SAMs).

The Deepwater Horizon spill led to the $1.4 million Wendy Schmidt Oil Cleanup XCHALLENGE, which provided an incentive for everyone in the field of oil cleanup to present ground-breaking solutions. The proposed technology had to meet or exceed the exacting criteria of recovering oil on the sea surface at the oil recovery rate (ORR) of over 2,500 gallons per minute (GPM) with an oil recovery efficiency (ORE) of more than 70 percent. This compares to an industry standard of 1,100 GPM. The winner was Elastec, with an ORR of 4,760 gallons per minute and an ORE of 89.5 percent. Elastec patented a Grooved Disc skimming technology that takes advantage of plastic being oleophilic and hydrophobic. The skimmer has 64 grooved plastic discs, arranged in rows, with a scraper along the top that removes the oil into a trough, separating it from the water. It is particularly suitable for quickly removing oil during an event like a tanker spill.

Elastec skimmer at the Oil Cleanup XChallenge. (Video courtesy of Elastec.)

Another noteworthy contender at the event was a device called “Otter skimmer” by PPR Alaska. The device is a towable skimmer that can easily be set up locally and is able to reach OREs of up to 99 percent—the highest efficiency achieved at the challenge. The skimmer employs two floating arms that form a V shape and channel floating oil into the separator via a pipe. Oil and water then separate due to a vacuum being applied by a pump through the pipe above. An open tank float valve (essentially a ball that floats at the oil-water interface, which is on the water but submerged in oil) closes the pipe above as all the oil is extracted, leaving the water behind. The pump is then turned off, which removes the vacuum, and the resulting clean water can be discharged back into the sea via the bottom one-way valve.

There are also the high-speed skimming boats by Extreme Spill Technology that can operate in waves higher than 1.5 m and also in broken ice— conditions in which traditional booms and skimmers become ineffective. The machines can also travel much faster and do not clog as easily as traditional skimmers. The method for these machines has been successfully demonstrated for the Chinese and the Canadian Coast Guards.

Research is underway to develop materials that can be used to soak up both surface and subsurface oil and then be wrung-out for reuse. One option, known as the Oleo Sponge, has been developed at Argonne National Laboratory. Researchers were able to create complicated nanostructures of hard metal atoms that absorb oil and leave water behind. A thin layer of these metal oxides can be built into common polyurethane foam found in furniture and home insulation.

Researchers at Northwestern University have developed a highly porous smart sponge that can selectively absorb 30 times its weight in oil. The oleophilic, hydrophobic and magnetic (OHM) compound is a nanocomposite coating of magnetic nanostructures and a carbon-based substrate that can convert even household sponges into smart “OHM sponges.”

Another variety, called an aerogel, has been developed by researchers at Case Western Reserve University and is named AeroClay. The aerogel is made by mixing clay with a polymer and water in a blender, which is then freeze-dried. The air fills the gaps left by the loss of water. The resulting material is super light, composed of about 96 percent air, 2 percent polymer and 2 percent clay, and can be manufactured in any form such as grains, sheets or blocks.

At Pennsylvania State University, a new polyolefin-based petroleum super-absorbent (Petro-SAP) has been patented that can effectively transform a maritime oil spill into a floating solid oil-containing gel. The material, known as Petrogel, has a high absorption capacity: up to 40 times its weight with low molecular weight hydrocarbons and refined oil products. It is also very buoyant, making it ready for collection and refining as regular crude oil, resulting in no waste in natural resources and no disposal issues.

In all the cases, oil recovered from the sponges can be recycled, which provides another cost- and environment-friendly feature. Additionally, the sponges can be brought into service in the remediation of harbors and ports, helping remove any hydrocarbons present in the water.

One of the main strategies for mitigating the Deepwater Horizon oil spill was the use of dispersants, known to not degrade easily and to cause damage to the environment. To address this, MIT researchers have filed patents for water-repellent ferrous nanoparticles that can be mixed with an oil plume. With this method, the oil becomes magnetic and can thus be separated by using magnets to pull the oil out of the water. The oil can then be reused by magnetically removing the nanoparticles from the oil, helping to recoup the cost of cleanup.

Scientists at Bristol University have come up with a similar solution by creating soap composed of rich iron salts dissolved in water. They accomplished this by dissolving iron in a range of inert surfactant materials composed of chloride and bromide ions, which creates metallic cores within the soap particles. The magnetic properties allow the cores, with the oil, to be recovered by applying a magnetic force.

Nature itself may provide us with a defense against oil spills through microbes that thrive in the oil-rich waters. Scientists investigating the bacteria that feed on ingredients in crude oil and natural gas have singled out the Alcanivorax borkumensis, a rod-shaped bacterium that creates enzymes that turn hydrocarbon molecules into fuel. Its genome was mapped at the German Research Center for Biotechnology. A team from University of Quebec found the bacteria will break up 80 percent of various crude oil components and theorizes that it can be genetically modified to break up even more. 

Experiments conducted in Norway by Kallak Torvstrøfabrikk revealed that simple 100 percent organic peat moss is an excellent oil absorbent. It can be scattered directly at the site of the spill, where the oil will be encapsulated in the moss, and water cannot penetrate it. Best of all, it can be easily removed afterward from the ocean surface. The technology is being presented as Kallak Absorbent and was deemed a success against a 2009 oil spill off the coast of Norway.

Scientists at Technical University Dresden, in cooperation with the Universities of Rostock and Leipzig have developed oil binding wood chips (BioBind technology) that can achieve oil absorption of up to 92 percent–well suited for small to medium-sized oil spills of approximately 5 to 50 tons. Like the Kallak Absorbent, these wood chips can be easily dispersed and gathered.

A Canadian company, Encore3, is not only looking to sustainably produce cleanup kits, but is also helping an endangered species. Encore3 has discovered that seed pod fibers of the milkweed plant—a plant native to North America—are naturally hydrophobic and have a cylindrical shape, which increases oil absorption. The company claims that each kit can absorb 53 gallons of oil at 0.06 GPM, double the rate of existing cleanup materials. Encore3 has contracted local farmers to grow this crop on a large scale without the use of pesticides or fertilizers—therefore posing no threat to the declining population of Monarch butterflies that, in their caterpillar state, rely on the milkweed as their main source of food.

Fearing a decline in the tourism industry due to reef damage from the Mauritius oil spill, locals donated their hair to make oil absorbent sacks. Human and dog hair is a good absorbent of oil, as verified by the University of Technology Sydney (UTS). Hair swept up from salons and dog groomers was found to be more successful than synthetic fibers at sweeping up spills. Fur and hair felted mats were easy to apply and remove oil from spills.