Laboratory testing of dispersant effectiveness: The importance of oil-to-water ratio and settling time

Abstract

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.