Environmentally friendly approach to clean oil spills

Dr. Neil Canter, Contributing Editor | TLT Tech Beat March 2017

A newly developed modified sawdust is effective even in Arctic waters.

KEY CONCEPTS
• Potential oil exploration in the Arctic Ocean has caused researchers to seek an environmentally friendly, cold-water method for cleaning up oil spills.
• Modifying sawdust with vegetable fatty acids produces an environmentally friendly material that can absorb up to five times its weight in oil.
• This material can be used on land in an industrial setting.

THE CONTINUING CONCERN with how to deal with oil spills is leading to research exploring new approaches. In a past TLT article, a Janus fabric coated with a single multifunctional polymer was found to be very effective in removing oil from emulsions (1). Depending upon the environment, a specific functional group in the polymer rises to the top of the coating to first break the emulsion and then isolate the oil droplets. 

One strategy needing further exploration is finding an environmentally friendly method for cleaning up oil spills. This is a particularly important issue in a remote location such as the Arctic Ocean. George Bonheyo, senior research scientist at the Pacific Northwest National Laboratory (PNNL) and professor of bioengineering at the Gene and Linda Voiland School of Chemical Engineering and Bioengineering at Washington State University in Pullman, Wash., says, “With the ice retreating in the Arctic Ocean, further oil exploration and production will be occurring that will require better oil spill response methods that are effective in the icy, cold waters present in this region.”

In looking to find a solution, Bonheyo initially established a renewable strategy and wanted a material that readily absorbed oil. The direction that Bonheyo took was to evaluate the potential for using sawdust. He says, “We found that sawdust is a good carrier for microbes in bioremediation applications. Sawdust stabilizes the microbes and absorbs their toxins.”

Sawdust consists of cellulose, hemicellulose and lignin. While this material is not water soluble, it needs to be made more hydrophobic and less dense. The latter issue is important because the oil spill agent must float on seawater to be effective.

A new approach has been developed to convert sawdust into a material suitable for absorbing oil spills.

MODIFIED SAWDUST
Bonheyo and his colleagues have modified sawdust to make the material more hydrophobic and less dense so that it can absorb oil and remain on the surface of salt water for at least four months. He says, “We determined that sawdust can be modified by reacting the material with vegetable fatty acids at elevated temperatures.”

Bonheyo’s reasoning is that oil has a broad molecular distribution so a sawdust modified with a broad range of fatty acids is best able to absorb it. He says, “The inspiration for making the sawdust hydrophobic stems from work we did to develop superhydrobic coatings that act as anti-biofouling surfaces.”

The fatty acids are incorporated into sawdust by reacting with the hydroxyl groups present in the lignin. The resulting material is less dense than seawater and is able to hold oil on the surface of the water for a long period of time. Thermogravimetric analysis was used to determine the degree of esterification in the modified sawdust.

The efficacy of the modified sawdust was ascertained by adding the material to seawater in a customized shipping container that can be cooled down to as low as -15 C (5 F). Testing at that temperature is particularly useful because ice slush can form on the surface of the water. Bonheyo indicated that the hydrophobic nature of the modified sawdust enabled the material to prevent ice from forming on its surface. 

Figure 3 shows an image of how the modified sawdust is added to water for testing.


Figure 3. Sawdust modified with vegetable fatty acids can effectively absorb oil floating on water and may become an environmentally friendly option for cleaning up oil spills. (Figure courtesy of the Pacific Northwest National Laboratory.)

Several tests were run to assess the performance of the modified sawdust. Bonheyo says, “We evaluated the buoyancy of the material and found that it does not sink into the water. No emulsion is formed either with seawater or with distilled water.”

Modified sawdust also was smeared on a glass slide to determine the material’s contact angle. Bonheyo says, “We found the contact angle to be greater than 115 degrees.”

Oil absorption capacity showed that the modified sawdust can absorb up to five times its weight in oil. Burn efficiency also was evaluated because this is a rapid and efficient way to dispose of the oil in the harsh environment of the Arctic Ocean before it can cause greater harm. Bonheyo says, “An efficient burn will remove 90% of the oil leaving a small amount of tarry residue that is enriched in large poly-aromatic hydrocarbons (e.g., asphaltene) that can be difficult to remove.” Burn tests were performed at PNNL’s Marine Sciences Laboratory in Sequim, Wash., and at the U.S. Coast Guard and Naval Research Laboratory’s Joint Maritime Test Facility (JTMF) in Mobile, Ala. 

The modified sawdust also can be used on land in an industrial setting. Bonheyo says, “The most effective way to use the modified sawdust may be to add bacteria and fungus to the material to facilitate the decomposition of the oil. Water should be added to accelerate microbial activity. Byproducts of microbe metabolism are readily absorbed by the modified sawdust.”

Bonheyo recommends the use of aerobic microbes and believes the modified sawdust can be safely landfilled. The researchers will continue analyzing the properties of the modified sawdust and are hoping that the U.S. government will be interested in evaluating the material in the future. 

The research was funded by the Bureau of Safety and Environmental Enforcement. 

Additional information can be found in a press release at the following website: www.pnnl.gov/news/release.aspx?id=4333 or by contacting Bonheyo at george.bonheyo@pnnl.gov. 

REFERENCE
1. Canter, N. (2017), “Separation of oil from emulsions,” TLT, 73 (2), pp. 14-15.


Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. Ideas for Tech Beat can be submitted to him at neilcanter@comcast.net.