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.

Evaluating Chemical Dispersant Efficacy in an Experimental Wave Tank: 2—Significant Factors Determining In Situ Oil Droplet Size Distribution

“…Fingas et al (1989) showed that the dispersant effectiveness values were relatively constant over the OWR ranging from 1:1,000 to 1:120,000, but had a large variation when the ratio was 1:500 or smaller. In that study, however, the effect of OWR, in the range from 1:4,000 to 1:120,000, was evaluated in a recirculation-flow cylinder, which had no control over resurfacing and=or settling of the dispersed oil.…”

“…In dispersant effectiveness testing, it is important for the testing system to have hydrodynamics and dilution [commonly expressed as oil-to-water ratio (OWR)] approach field conditions (Fingas et al, 1989;NRC, 2005). Fingas et al (1989) showed that the dispersant effectiveness values were relatively constant over the OWR ranging from 1:1,000 to 1:120,000, but had a large variation when the ratio was 1:500 or smaller.…”

Oil spill treating agents

“…Comparative studies revealed that the test results from different apparatus are not highly correlated, and often the effectiveness rank is not correlated [44]. The effect of the settling time and oil/water ratio are important in determining the final effectiveness value.…”

Testing the Effectiveness of Spill-Treating Agents: Laboratory Test Development and Initial Results

“…6 A recent study by the present author has shown that lack of correlation is primarily a function of settling time allowed between the time that the energy is no longer applied and the time that the water sample is taken from the apparatus. 7 Another important factor is the oil-to-water ratio used in the apparatus. When these two parameters are adjusted to be the same and to larger values, test results from most apparatus are similar.…”