Laboratory effectiveness tests have been developed for four classes of spill treating agents: solidifiers, demulsifying agents, surface-washing agents, and dispersants. Many of the currently available treating agents in these four categories have been tested for effectiveness. These results are presented. Solidifiers or gelling agents change liquid oil to a solid. Tests show that these require a large amount of agent to solidify oil, ranging from 16 percent by weight to over 200 percent. Demoussifiers or emulsion breakers are used to prevent or reverse the formation of water-in-oil emulsions. A newly developed effectiveness test shows that only one product is highly effective. However, many products will work, but require large amounts of spill treating agent. Surfactant-containing materials are of two types, surface-washing agents and dispersants. Testing has shown that an agent that is a good dispersant is conversely a poor surface-washing agent, and vice versa. Tests of surface washing agents show that only a few agents have effectiveness of 25 to 40 percent, where this effectiveness is defined as the percentage of oil removed from a test surface. Extensive work has been done on dispersant testing and comparison of laboratory tests. All laboratory tests will yield the same effectiveness value if the oil-to-water ratio is about 1:1,000 or greater, and if a settling time of 10 or more minutes is employed. Extensive results using the “swirling flask” testare reported. Heavy oils show effectiveness values of about 1 percent, medium crudes of about 10 percent, light crude oils of about 30 percent, and very light oils of about 90 percent.
Laboratory tests and apparatus for oil spill dispersant effectiveness were the subject of the present study. A review of previous work shows that test results from different apparatus are not highly correlated, and often the rank of effectiveness is also not correlated. The effect of two experimental parameters—settling time and oil-to-water ratio—are examined in this study and found to be very important in determining final effectiveness value. Four apparatus—the swirling flask, the flowing column, the Labofina, and the Mackay—are used with 3 dispersants and 16 oils to examine effectiveness values when the oil-to-water ratio is the same (1:1,200) and when the settling time is maintained at the same value (10 minutes) in all apparatus. The effectiveness values resulting from the four devices are nearly identical after values from the more energetic devices are corrected for natural dispersion. Our conclusions are that the most important parameters of laboratory dispersant testing are settling time and oil-to-water ratio. Energy is less important than previously thought and is important only to the extent that when high energy is applied to an oil-dispersant system, dispersion is increased by an amount related to the oil's natural dispersibility.
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