Effects of chemical dispersants and mineral fines on crude oil dispersion in a wave tank under breaking waves (original) (raw)
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Spill Science & Technology Bulletin, 2002
When spilled in the environment, especially in coastal systems such as estuaries, oil frequently interacts with fine mineral particles to form aggregates. This phenomenon may be enhanced in the case of chemical dispersion and influence the behavior and fate of the pollutant in the environment. Understanding this process will help decide whether chemical dispersion is a good oil clean-up option in a particular environment. This study investigated the formation of oil-mineral aggregates (OMA) when the oil was chemically dispersed, focussing on the size distribution of these structures. Results of laboratory experiments show that aggregate size is correlated to its relative composition in oil and clay, and that for a given concentration of mineral, the average size presents a maximum. Other highlights include the influence of oil type and salinity on the clay concentration corresponding to maximum size. The behavior of a particular oil as OMA depends on the size and buoyancy of its aggregates which will vary with the local of salinity, suspended mineral l oad and hydrodynamics conditions. Guyomarch et al. Final MS for SS&TB Vol. 8 (Lee) 11.6.02, Champ, Pages 2 of 2 .
Environmental Engineering Science, 2009
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 mm (from 122 to 86 mm) by plunging breaking conditions. Volume mean diameters were decreased by 92 mm (from 153 to 61 mm) and 37 mm (from 153 to 116 mm), 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.
When three or more high and low energy substrates are mixed, wetting order can significantly affect the behavior of the mixture. We analyzed the phase distribution of fresh floating Louisiana crude oil into dispersed, settled and floating phases depending on the exposure sequence to Corexit 9500A (disper-sant) and granular materials. In the experiments artificial sea water at salinity 34‰ was used. Limestone (2.00e0.300 mm) and quartz sand (0.300e0.075 mm) were used as the natural granular materials. Dispersant Corexit 9500A increased the amount of dispersed oil up to 33.76 ± 7.04%. Addition of granular materials after the dispersant increased dispersion of oil to 47.96 ± 1.96%. When solid particles were applied on the floating oil before the dispersant, oil was captured as oil-particle aggregates and removed from the floating layer. However, dispersant addition led to partial release of the captured oil, removing it from the aggregated form to the dispersed and floating phases. There was no visible oil aggregation with the granular materials when quartz or limestone was at the bottom of the flask before the addition of oil and dispersant. The results show that granular materials can be effective when applied from the surface for aggregating or dispersing oil. However, the granular materials in the sediments are not effective neither for aggregating nor dispersing floating oil.
International Oil Spill Conference Proceedings, 1981
Dispersant use is a factor that may partly determine the fate and effects of spilled oil. A series of quantitative field experiments has been initiated to simulate conditions following nearshore treatment of a floating oil slick or following the cleaning of a spill stranded on the shore. The basic experimental design is a series of treatments (Forties or Nigerian crude oil, BP 1100WD dispersant, or oil plus dispersant) applied to sets of experimental plots in a range of intertidal and subtidal communities. Biological recording includes frequency and density measurements of plants and animals, and hydrocarbon analysis is by capillary gas liquid chromatography and computerised gas chrornatography–mass spectrometry. Additionally, the effects of dispersant on the movement and fate of oil in different types of sediment is being investigated using a laboratory sediment column and controllable temperature seawater system. The columns have been successfully used in the modeling of low-energ...
Marine Pollution Bulletin, 2014
The interaction of dispersed oil droplets with large diameter suspended particulate materials (SPM) has been little studied. In the current study, particle size, oil characteristics and chemical dispersant significantly influence the adsorption of oil droplets to SPM in seawater. Sediments with a smaller particulate size (clay) approaching that of the oil droplets (2-20 µm) adsorbed more oil per gram than sediments with large particle size (sand). Heavier, more polar oils with a high asphaltene content adsorbed more efficiently to SPM than lighter, less polar oils. A decrease in the smaller, more water soluble oil components in the sediment adsorbed oil was observed for all oil types. Addition of chemical dispersant decreased the adsorption of oil droplets to suspended carbonate sand in an exponential-like manner. No change in the relative distribution of compounds adsorbed to the sediment was observed, indicating dispersants do not alter the dissolution of compounds from oil droplets.
Wave Tank Studies on Formation and Transport of OMA from the Chemically Dispersed Oil
NATO Science for Peace and Security Series C: Environmental Security, 2008
Current chemical dispersant effectiveness tests for product selection are commonly performed with bench-scale testing apparatus. However, for the assessment of oil dispersant effectiveness under real sea state conditions, test protocols are required to have hydrodynamic conditions closer to the natural environment, including transport and dilution effects. To achieve this goal, Fisheries and Oceans Canada and the US Environmental Protection Agency (EPA) designed and constructed a wave tank system to study chemical dispersant effectiveness under controlled mixing energy conditions (regular non-breaking, spilling breaking, and plunging breaking waves). Quantification of oil dispersant effectiveness was based on observed changes in dispersed oil concentrations and oil-droplet size distribution. The study results quantitatively demonstrated that total dispersed oil concentration and breakup kinetics of oil droplets in the water column were strongly dependent on the presence of chemical dispersants and the influence of breaking waves. These data on the effectiveness of dispersants as a function of sea state will have significant implications in the drafting of future operational guidelines for dispersant use at sea.
2008
Current chemical dispersant effectiveness tests for product selection are commonly performed with bench-scale testing apparatus. However, for the assessment of oil dispersant effectiveness under real sea state conditions, test protocols are required to have hydrodynamic conditions closer to the natural environment, including transport and dilution effects. To achieve this goal, Fisheries and Oceans Canada and the US Environmental Protection Agency (EPA) designed and constructed a wave tank system to study chemical dispersant effectiveness under controlled mixing energy conditions (regular non-breaking, spilling breaking, and plunging breaking waves). Quantification of oil dispersant effectiveness was based on observed changes in dispersed oil concentrations and oil-droplet size distribution. The study results quantitatively demonstrated that total dispersed oil concentration and breakup kinetics of oil droplets in the water column were strongly dependent on the presence of chemical dispersants and the influence of breaking waves. These data on the effectiveness of dispersants as a function of sea state will have significant implications in the drafting of future operational guidelines for dispersant use at sea.
International Oil Spill Conference Proceedings, 2008
As it is well established that application of chemical dispersant to oil slicks enhances the concentration of oil droplets and reduces their size, chemical dispersants are expected to enhance oil sedimentation if applied in coastal waters rich in suspended particulate matter (SPM) and if flocculation between chemically dispersed oil and SPM, which leads to formation of oil-SPM aggregates (OSAs), occurs readily. New laboratory experiments were conducted to establish a quantitative understanding of the process and to verify this hypothesis. This paper presents findings from experiments conducted using Standard Reference Material 1941b prepared by the National Institute of Standards and Technology, Arabian Medium, Alaska North Slope and South Louisiana crude oils, and Corexit 9500 and Corexit 9527 chemical dispersants. Results showed that OSAs do form with chemically dispersed oil. Oil sedimentation increases with sediment concentration and reach a maximum at a sediment-to-oil ratio of...
Dispersion of crude oil in seawater: The role of synthetic surfactants
Oil and Chemical Pollution, 1986
Over the last two decades, the use of chemical dispersants as a countermeasure to oil spills at sea has become accepted worldwide. The recent development of more efficient and less toxic dispersants has renewed interest for basic studies on dispersant improvement and on the fate of dispersed oil in seawater. This work reports interfacial tensions and the effectiveness in oil dispersion of many synthetic, commercially available surfactan ts when used alone and in various blends. The results are discussed in terms of the local structure of the oil-water interface. The maximum efficiency is reached when the surfactant molecules have a structure compatibility and can form stable arrangements at the interface. An improved knowledge of interfacial phenomena responsible for the oil dispersion helps in formulating better dispersants by guiding a judicious combination of surfactants in appropriate proportions.