Dissolution rate coefficients for surface slicks on rivers

The aqueous concentrations of oils, fuels and solvents resulting from riverine spills are highly dependent upon the dissolution rate coefficients, on which there is little information available. The water-film mass transfer rate coefficient was measured for the dissolution of a hexane slick in a stirred cylinder and in an oscillating grid chamber. In both devices, the turbulence was generated beneath the oil-water interface, similar to the bed-generated turbulence in rivers. The liquid-film coefficient was also measured during reaeration studies, conducted without a surface slick under the same conditions. In comparing the coefficients measured with a slick and without, the presence of the surface slick was found to have minimal impact on the water-film mass transfer coefficient after indexing properly with the Schmidt number. Thus, the dissolution rate coefficient for any compound can be easily predicted from the reaeration rate coefficient for a given river reach. Additionally, no scale effects were detected between the between the 4 L stirred cylinder and the 87 L oscillating grid chamber.