Comparative Testing of Corexit EC9500A, Finasol OSR52, Accell Clean DWD, and ZI 400 at Ohmsett in a Simulated Arctic Environment

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Courtesy of OHMSETT

The Bureau of Safety and Environmental Enforcement (BSEE) recently conducted independent dispersant effectiveness testing. Several products were tested under simulated arctic conditions at Ohmsett. The test program was conducted to better understand the effectiveness of various dispersants under the test conditions and compare the products. The results will assist BSEE and its federal partners in their decision making in regards to the various dispersants being considered by the oil spill response organizations (OSROs) for use on the U.S. Outer Continental Shelf.

Four dispersants were selected from the Environmental Protection Agency’s (EPA) National Contingency Plan (NCP) Product Schedule and were tested on an Alaskan crude oil. They include Corexit EC9500A, Finasol OSR 52, Accell Clean DWD, and ZI 400. To capture operational effectiveness issues, the dispersants were applied to a surface slick using Ohmsett’s spray bar, which simulated a system similar to a boat spraying system.

Data collected included dispersant effectiveness (DE) based on the volume of the surface slick which remained after the test as compared to the volume dispersed into the water column and particle size distribution of the oil droplets dispersed at 1 meter and 2 meters below the water surface. Particle size distribution was captured using two LISST-100x instruments from Sequoia Scientific. The instruments allowed researchers to quantify the performance of each dispersant. Oil concentration, paired with particle size distribution, showed how much oil was dispersed into the water column and the size of the water droplets that were created. For this test program, droplets sizes of 70 microns (µm) or smaller were considered to be fully dispersed because they are assumed to stay suspended in the water column whereas the larger droplets may resurface and coalesce into a new slick.

The performance of the products was quantified and compared to each other based on DE and the droplet size of dispersed oil. Corexit EC9500A performed very well in this study as compared to the other dispersants, producing the highest average DE, the most improvement in dispersion compared to the tests with untreated oil, and the smallest median droplet size. Finasol OSR 52 demonstrated a performance close to that of Corexit, producing the second highest average DE, and a median droplet size only slightly larger than Corexit. The average DE for Accell fell between that of Finasol and ZI 400, as did the median droplet size. ZI 400 performed poorly relative to the other products tested.

In addition to providing performance data of the products in pseudo-field conditions, operational performance was captured as a general discussion about the ease of use, limitations, and concerns about the products in the environment simulated by the test conditions. BSEE intends to use the results of these tests to provide both OSROs and BSEE with information for their decision making processes.

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