The effects of mixing energy on water column oil

Abstract

The rate at which an oil spill spreads will determine the extent of contamination and toxic effects that affect the environment. When spilled at sea, oil first forms a slick that is then broken into smaller oil droplets due to physical dispersion caused by a combination of wind, currents and wave action. A series of laboratory experiments were conducted to determine how oil partitions into the aqueous phase when subjected to mixing energies common to estuaries. In the experiment, an oil/water system was mixed in a reactor and sampled after 48 h. Three experimental runs were performed for eight increasing mixing energies: 0 s⁻¹, 2.6 s⁻¹, 7.4 s⁻¹, 10.8 s⁻¹, 13.4 s⁻¹, 14.6 s⁻¹, 15.6 s⁻¹ and 20.4 s⁻¹. GC-MS was used to analyze the samples for the presence and concentration of several PAH parent compounds and their constituents, while a Coulter Counter was used to determine size and volume distributions of the entrained petroleum colloids in the water column. The volume of entrained petroleum colloids increased significantly between 0 s⁻¹ and 2.6 s⁻¹; further increases in energy showed no correlation to volume of entrained petroleum colloids. A liquid-liquid partition coefficient (K[d]) was estimated for several of the PAHs analyzed. The estimated K[d] values were at least one order of magnitude higher than K[ow] values reported for the same PAHs suggesting that the mixing energy did contribute to a colloidal phenomenon. Although no correlation was found between the increased mixing energies and oil entrainment, the formation of colloids did play a significant role in determining the concentration of PAHs in the aqueous phase. Further studies are needed to determine at what point a correlation develops between the mixing energy and the volume of entrained petroleum colloids.