DISPERSANT EFFECTIVENESS ON OIL SPILLS – EMPIRICAL CORRELATIONS

Abstract

ABSTRACT When a dispersant is applied to an oil slick, its effectiveness in dispersing the spilled oil depends on various factors such as oil properties, wave mixing energy, temperature of both oil and water, and salinity of the water. Estuaries represent water with varying salinities. In this study three salinity values in the range of 10–34 ppt were investigated, representing potential salinities found in typical estuaries. Three oils were chosen to represent light refined oil, light crude oil and medium crude oil. Each oil was tested at three weathering levels to represent maximum, medium and zero weathering. Two dispersants were chosen for evaluation. A modified trypsinizing flask termed the ‘Baffled Flask’ was used for conducting the experimental runs. A full factorial experiment was conducted for each oil to investigate the effect of salinity (3 levels), temperature (6 levels), oil weathering (3 levels) and mixing energy (150, 200, and 250 rpm) on dispersant effectiveness. Each experiment was replicated four times in order to evaluate the accuracy of the test. Statistical analyses of the experimental data were performed separately for each of the three oils three times (with or without dispersant). Viscosity of the three oils at the different temperatures and weathering conditions were determined. An empirical correlation of the viscosity for each of the three oils was then obtained. A linear regression model incorporating the viscosity correlations to represent temperature and weathering, the other remaining main factors (salinity and flask speed) and second order interactions among the factors was developed and was found to accurately represent the experimental data. The empirical approach to the interaction between the dispersant and oil slick developed could provide a useful or practical approach for including dispersants in a model to assess the impact of dispersant usage on oil spills.