Influence of Water Salinity on Effectiveness of Oil Dispersants

This article describes a comparative evaluation of effectiveness of certain commercial dispersants (Finasol OSR 52 (France) and Slickgone NS and Slickgone EW (Great Britain)) for spill response of three crude oils produced in Russia and characterized by different physicochemical properties (extra light, heavy, and bituminous) in waters of various salinity. The evaluation has been based on an adapted version of ASTM F2059-17 “Standard Test Method for Laboratory Oil Spill Dispersant Effectiveness Using the Swirling Flask” (the so called SFT test). The conventional lower limits of dispersant effectiveness have been determined using a low energy procedure. Comparative tests of dispersant effectiveness have been performed at the highest dispersant-to-oil ratio of 1 : 10 allowed in the Russian Federation (according to STO 318.4.02-2005 “Rules of Dispersant Application for Oil Spill Response”), water temperature 20°C, and water salinity of 0, 5, 10, 20, and 35‰. It has been revealed that the considered dispersants have low effectiveness for dispersion of the tested oil samples at water salinity of 35‰. A general trend of increase in dispersant effectiveness with decrease in water salinity is demonstrated. It has been established that all considered dispersants are not suitable for application throughout the analyzed salinity range in the case of spill of bituminous oil with high content of asphaltenes and polar compounds. The limits of dispersant application have been determined for all dispersants as a function of water salinity. The effectiveness of 45%, legally validated in the United States and Mexico, has been selected as the threshold value. It has been proved that, as a consequence of nonuniversality of dispersant action, it is recommended to carry out preliminary experimental examination of their effectiveness using a sample of spilled oil under climatic and hydrochemical conditions corresponding to the potential region of application.