(454a) Evaluation of the Cactus Based-Mucilage As an Alternative Natural Dispersant on Toxicity, Effectiveness, and Surface Tension of Oil-in-Water Emulsion

Authors: 
Guo, F., University of South Florida
Stebbins, D. M. L., University of South Florida
Peng, T., University of South Florida
Zhao, W., University of South Florida
Falahat, R., University of South Florida
Thomas, S., University of South Florida
Toomey, R., University of South Florida
Alcantar, N., University of South Florida
Cactus based-mucilage has the advantage of being biodegradable and can be obtained through sustainable agriculture. This functional natural surfactant was extracted from the Opuntia ficus indica cactus plant, and the extraction process yielded two types of mucilage: the non-gelling extract (NE) and the gelling extract (GE). The properties of the cactus plant-based mucilage were studied on the toxicity, surface tension, droplet size and stability of dispersed crude oil in water emulsions (O/W emulsions). The toxicity of the mucilage and conventional dispersants (Corexit 9500A) were evaluated by a standard EPA toxicity test using Daphnia magna colonies exposed to both NE and GE mucilage extracts 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 2000 mg/L. The LC50 of Corexit 9500A was below 2 mg/L, which is moderately toxic to the Daphnia magna colonies. Cactus mucilage extracts and conventional dispersants has been evaluated by testing the surface tension and measuring the droplet size of O/W emulsions under different concentrations, including three concentrations of oil (3, 6, 30% v/v) and several dispersant to oil ratios (1:1, 1:3, 1:10). Synthetic seawater and surrogate oil from BP were used. The results of the dispersion obtained using mucilage extracts were compared with using Corexit 9500A. The surface tensions of emulsions with cactus mucilage were similar as with Corexit 9500A. The average droplet size in the systems with cactus mucilage (1.5% of NE has generated 5 µm droplets) were smaller when compared with the systems using the Corexit 9500A (1.5% of Corixit 9500A has formed 6.2 µm droplets). Smaller droplet size implies higher emulsion stability, and may improve the biodegradation of oil. An improved laboratory dispersant testing protocol developed by EPA, baffled flask test, was performed to measure the dispersion effectiveness at DOR 1:20, 1:50, and 1:100. The effectiveness of DOR at 1:20 and 1:50 were around 35%. Cactus mucilage is readily available through sustainable agriculture, it is inexpensive to extract, and has exhibited a long shelf live. 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.
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