Formation and Fate of Oil-Particle Aggregates in Cold Freshwater
, Abdulrhman Alali . 2020
Oil spills in marine environments have been comprehensively studied, while oil spills in freshwaters, which occur frequently, have received less attention. With an increase in the transport of crude oils in North America’s freshwater environments, specific research on this topic is necessary, particularly for cold freshwater. This research aims to elucidate the mechanism of coagulation and formation of oil particle aggregates (OPAs) in freshwater and to provide parameters for predictive modeling purposes. To achieve these aims, three specific tasks are conducted: (1) Experimentally investigate the interaction of clay particles with oil, in response to changes in the type and concentration of oil and sediment, water temperature, and mixing intensity; (2) Measure variability in the particle size distribution of the formed OPAs to generate comprehensive experimental data that can be used as a reference for inputs to numerical models for the fate and transport of oil in cold freshwater systems; and (3) Employ a mechanistic OPA aggregation model (A-DROP), in conjunction with experimental data, to better understand the mechanisms of OPA formation under a range of conditions.
Standard jar mixing tests are used with three oils, distinguished by different viscosities, along with two different commonly used clays, kaolinite and bentonite. The experimental data show that using oils with different viscosities leads to the formation of different sizes of OPAs. The size of the OPAs when using kaolinite clay with oil I (0.0073 Pa. s) was between 20 μm to 400 μm, and a few OPAs had diameters greater than 400 μm. For oil II (0.0131 Pa. s)) and oil III (0.1038 Pa. s) (highest viscosity), the particle size of the OPAs was between 20 μm to 220 μm, and 20 μm to 180 μm, respectively. For bentonite clay, the OPA particle size distribution was between 20 μm to 800 μm for oil I, 20 μm to 600 μm for oil II, and 20 μm to 140 μm for oil III. Based on these results, higher-viscosity oil does not tend to form larger aggregates in a freshwater environment. In contrast, lower-viscosity oil tends to form a wider size range of OPAs and also forms larger aggregates. Also, the experimental data show that using different types of sediments forms different structures of OPAs. For example, when using kaolinite clay, most of the formed OPAs were droplet OPAs, while for bentonite clay, solid and flake OPAs were abundant. This appears to be a result of the different physical and chemical properties of each clay.
Other factors tested include mixing intensity and water temperature. Results show that mixing intensity plays a vital role in the formation of OPAs. By increasing the mixing intensity, a larger number of smaller oil droplets will form. Thus, the collisions between the oil globules and sediment particles increase as well, and larger OPAs are formed. For all the oils, higher temperatures seem to help in forming larger OPAs, possibly because the oils can become less viscous. The results show that as the water temperature increases, the size of OPAs increases.
Based on the comparison between the results from the experimental data and the A-DROP model, we found inconsistent comparisons between the A-DROP model and experimental data. Certain trends were produced by the model, but overall improvements in understanding the A-DROP model or in providing more accurate input values are needed before better comparisons with experimental results will be achieved.
The findings of this research give a better understanding of how oils interact with clay particles in lakes or rivers and the relative importance of different mechanisms involved in the formation of OPAs. By knowing this information, a user can track oil spills more quickly, which can allow a faster response for cleanup.
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Oil spills in marine environments have been comprehensively studied, while oil spills in freshwaters, which occur frequently, have received less attention. With an increase in the transport of…