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

Abstract

Chemical dispersion is one of the most cost-effective options to remediate oil spill at open sea. Identifying significant factors that determine in situ droplet size distributions facilitates mechanistic understanding of dispersant effectiveness. In this work, in situ dispersed oil droplet size distributions were characterized during testing of chemical dispersant effectiveness of two dispersants (Corexit 9500 and SPC 1000) on two oils [Medium South American (MESA) and Alaska North Slope (ANS)] under three wave conditions (regular nonbreaking, spilling breaking, and plunging breaking waves) in an experimental wave tank. Results showed that physical dispersion generated monomodal lognormal oil droplet size distributions of larger median diameters, whereas chemical dispersion produced bi- or trimodal lognormal oil droplet size distributions of smaller median diameters over a wider range. Factorial analysis of variance (ANOVA) followed by Tukey's paired comparison statistical data analysis indicated that the volume mean diameters of dispersed oil droplets were reduced by 36 μm (from 122 to 86 μm) by plunging breaking conditions. Volume mean diameters were decreased by 92 μm (from 153 to 61 μm) and 37 μm (from 153 to 116 μm), respectively, by Corexit 9500 and SPC 1000. These results are useful in optimizing operational guidelines for dispersant use, and providing input for modeling transport, fate, and biological effects of dispersed oil.