Engineered Clays as Sustainable Oil Dispersants in the Presence of Model Hydrocarbon Degrading Bacteria: The Role of Bacterial Sequestration and Biofilm Formation

Particle stabilized emulsions provide an environmentally friendly alternative to the chemical dispersion of oil in the event of a spill over water. Mineral clay particles present in abundance in marine environments adsorb at oil water interfaces forming stable emulsion droplets. We describe the carbonization of these clays using the sustainable biopolymer, chitosan, to optimize wetting characteristics and generate extremely stable 150 mu m clay-armored droplets using a model crude (Anadarko). In addition to such droplet stabilization, the work is comprehensive in elucidating the microbial processes involved in oil biodegradation. Using a model alkane degrading organism Alcanivorax borkumensis acclimatized on n-hexadecane, the colonization of oil droplets and the growth of biofilm are clearly visualized through high-resolution cryo-scanning electron microscopy. The results indicate ubiquitous colonization of the organism on the surface and between platelets of the armored droplet with biofilm formation bridging these particle stabilized droplets. Such oil-mineral aggregates stay buoyant, although excess clay particles embedded in biofilm sediment carry out small amounts of entrapped oil. Biodegradation is monitored through the loss of hexadecane doped into the crude oil, and it is found that 90% of the hexadecane is lost over a 6-day experiment. These findings provide a comprehensive description of oil dispersion by mineral clay particles in the presence of marine oil-degrading bacterium, with the potential of developing technology for the mitigation of the environmental impacts of oil spills.