Fate of surface spills of cold lake blend diluted bitumen treated with dispersant and mineral fines in a wave tank

Abstract

Cold Lake Blend (CLB) diluted bitumen (dilbit) was used to evaluate the fate and transport of preweathered (6.2% w/w) dilbit under environmental conditions both in spring (seawater temperature 8.5°C±1.3°C and salinity 27.7±1.6 practical salinity units [psu]) and in summer (seawater temperature 17.0°C±2.6°C and salinity 26.8±2.4 psu). The following oil spill treatments were considered: no treatment, dispersant alone, mineral fines (MF) alone, and dispersant+MF. The aim was to determine their influences on the fate of spilled CLB at sea. When dispersant alone was used, the highest dispersion effectiveness (DE) was noted, and DE ranged from 45% to 59% under the selected environmental conditions. With no treatment and treatment of MF alone, CLB DE was insufficient under tested conditions. Total petroleum hydrocarbon (TPH) concentration in the water column was highest for the dispersant alone, followed by that of dispersant+MF. TPH concentration for the dispersant alone increased abruptly with time. Droplet size distribution (DSD) resulting from dispersant alone had a unimodal shape, which was different than previously observed when conventional oils were treated with the dispersant. Cases of dispersant+MF were thus characterized by a broader DSD compared with dispersant only and a gradual increase in TPH concentration. This suggests that MF could be used with dispersant as a means to control the release of toxic compounds into the water column and for better engineering the response.