Study Demonstrates How Natural Clay Particles Enhance Oil Dispersion and Biodegradation
– MAY 7, 2019
Scientists conducted laboratory experiments using an abundant natural clay material, kaolinite, modified with carbon derived from chitosan as an environmentally friendly alternative to chemical dispersants and visualized resulting phenomena at nanoscale detail. The modified clay particles attach to oil drops, which generates smaller clay-coated oil droplets (150 ± 50 μm) that do not coalesce or sink. The stabilized emulsions of clay-covered droplets provide oil-degrading microbes (Alcanivorax borkumensis) with a 5-times larger platform (compared to non-clay-coated droplets) upon which they anchor quickly and easily and produce copious amounts of biofilm and biosurfactant (extracellular polymeric substances or EPS). The subsequent biodegradation reduces hexadecane by 90% over the six-day experiment.
The researchers published their findings in ACS Sustainable Chemistry & Engineering: Engineered clays as sustainable oil dispersants in the presence of model hydrocarbon degrading bacteria: The role of bacterial sequestration and biofilm formation.
“The use of natural and sustainable materials as replacements for synthetic dispersants and their solvents has been a key issue in oil spill remediation,” said study author Vijay John. “While synthetic dispersant formulations are very effective in dispersing oil, there is considerable concern about their effects on hydrocarbon degrading bacteria and the possibility that they may inhibit the ability of bacteria to consume the oil.”
The team prepared emulsions of crude oil and particle suspensions containing kaolinite clay in synthetic seawater at a 1:30 oil phase-aqueous phase ratio. For biodegradation tests, the team inoculated microbes in 3 mL of synthetic seawater with oil added at a 1:100 v/v ratio.
John described cryogenic scanning electron microscopy (cryo-SEM) as a unique method for visualizing liquid-based systems at nanometer-scale resolutions and preserving their native state through vitrification. “Cryo-SEM allowed us to observe bacterial attachment onto clay-covered oil droplets, the sequestration of bacteria between clay layers, and the morphology of biofilm tendrils. The exquisite detail of imaging provides valuable insight into the mechanistic aspects of bacterial growth and oil degradation.”
John stated that there is no innate toxicity resulting from using these modified clays as natural dispersants and that the only toxicity would be a consequence of oil components. “Our study indicates that the natural system of clay dispersion and stabilization of oil droplets fully allows bacterial colonization, biosurfactant and biofilm generation, and oil consumption.”
The authors noted that the modified clay coating helps create a water-wetting surface on the oil droplet that may have implications for removing oil from beaches, preventing oiling of larger marine species and aquatic birds, and mitigating direct oil adsorption on shoreline plants.
Data are publicly available through the Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC) at doi:10.7266/N7QC020J.
By Nilde Maggie Dannreuther and Stephanie Ellis. Contact firstname.lastname@example.org with questions or comments.
This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to Tulane University, Louisiana State University, and Louisiana Tech University for their project The Design of Synergistic Dispersant and Herding Systems using Tubular Clay Structures and Gel Phase Materials.
The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit https://gulfresearchinitiative.org/.
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