(326b) Novel and Natural Oil Spill Dispersant Based on the Cactus-Mucilage

Authors: 
Guo, F., University of South Florida
Thomas, S., University of South Florida
Toomey, R., University of South Florida
Alcantar, N., University of South Florida
Dispersing the crude oil is a rapid response method for oil spills in the open sea. However, the application of extremely high amounts of chemical dispersants could be detrimental to marine life and the environment. Functional surfactants from natural materials have the advantages of being biodegradable, non-toxic, and can be obtained through sustainable agriculture. In this research, a functional natural surfactant was used to stimulate the dispersion process of oil in water. The compound was extracted from the Opuntia ficus indica cactus plant. The properties of the non-gelling cactus plant-based mucilage (NE) were studied on the surface tension, droplet size and stability of oil-in-water (O/W) emulsions, toxicity, and dispersion effectiveness. Synthetic seawater and the surrogate oil from BP were used. Surface tension test was used to quantify the variation of surface tension of the O/W emulsion with the application of cactus mucilage and conventional dispersants (COREXIT® EC9500A). The factors and the levels of each factor were as follows: DOR (mg/mg) (control, 1:200, 1:100, 1:50, and 1:20), Volume ratio of oil (3 and 6% v/v). We observed that the application of NE reduced the surface tensions of the O/W emulsions. We also directly measured the surface tensions of the O/W emulsion and found a proportional relationship between DORs and surface tensions at the lower volume ratio of oil (3% v/v). The results of the dispersion obtained using mucilage extracts were compared with using COREXIT® EC9500A. The surface tensions of emulsions with cactus mucilage were similar as that with COREXIT® EC9500A. The average droplet size in the systems with cactus mucilage (1.5% of NE has generated 5 µm droplets) were smaller compared with that of COREXIT® EC9500A (1.5% of COREXIT® EC9500A has formed 6.2 µm droplets). Smaller droplet size implies higher emulsion stability and may improve the biodegradation of oil. The baffled flask test was conducted to determine the influence of three environmental factors with cactus mucilage on oil dispersion. The percentage effectiveness of the dispersion was the response variable for this experiment. The factors and the levels of each factor were as follows: DOR (mg/mg) (control, 1:200, 1:100, 1:75, 1:50, 1:35, and 1:20), salinity of the synthetic seawater (10 and 35 PSU), and mixing speed (150, 200, and 250 rpm). The results showed that the dispersion effectiveness increased as the DOR increased. There was also a proportional relationship between DORs and the dispersion effectiveness. The increasing of the amount of cactus mucilage caused a reduction of the surface tension of O/W emulsion which made it easier to form the oil droplets. The cactus mucilage performed better at a lower salinity. When the mixing speed increased from 150 to 250 rpm, the dispersion effectiveness increased significantly. Mixing energy significantly enhanced the dispersion process with NE. The toxicity of the mucilage and conventional dispersants (COREXIT® EC9500A) were evaluated by a standard EPA toxicity test using Daphnia magna colonies exposed to NE mucilage solution in concentrations ranging from 0 to 2000 mg/L for 48 hours. It has shown that mucilage can be classified as practically non-toxic to the Daphnia magna colonies with a LC50 above 500 mg/L, while the LC50 of COREXIT® EC9500A was below 2 mg/L, which is moderately toxic to the Daphnia magna colonies. Therefore, cactus mucilage can be an alternative technology to mitigate the damage that oil may cause to the aquatic ecosystem and minimize undesired effects associated with the use of synthetic dispersants in oil spills.