The effect of water salinity on the effectiveness of oil dispersants

A comparative evaluation of the effectiveness of the industrially produced oil spill dispersants (Finasol OSR 52 (France), Slickgone NS and Slickgone EW (United Kingdom)) was carried out. The effectiveness of dispersants was assessed using three samples of domestic crude oil with different physical and chemical properties (extra light, heavy, and bituminous oil) in water samples of various salinity. 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) was used for evaluation. The low-energy technique was chosen to determine conditionally lower limits of the dispersant effectiveness. Comparative tests were carried out at the highest dispersant-to-oil ratio 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 0, 5, 10, 20, and 35‰. It is shown that the dispersants are poorly effective in dispersing the considered oil samples at water salinity 35‰. A general trend of increasing the dispersant effectiveness with a decrease in water salinity is demonstrated. It is shown that all tested dispersants are not suitable for application in the studied range of water salinity in the event of spill of the bituminous oil with a high content of asphaltenes and polar compounds. For all dispersants, the limits of their application are determined depending on the salinity of water. The effectiveness value equal to 45 % legally approved in the USA and Mexico was taken as a threshold value. The revealed lack of the dispersant versality necessitates preliminary experimental testing using a sample of spilled oil under climatic and hydrochemical conditions corresponding to the potential area of their application.

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