Formation Of Oil-mineral Aggregates Research Articles

Formation and sedimentation of oil-mineral aggregates in the presence of chemical dispersant.

The formation and sedimentation of oil-mineral aggregates (OMAs) is the major method to transport spilled oil to the seafloor. In this study, the formation and sedimentation experiments of OMA using montmorillonite and four crude oils were performed in a wave tank in the presence of chemical dispersant. Most of the formed OMAs were droplet OMAs, and single droplet OMA would aggregate into multiple ones under the action of the dispersant. The size of the oil droplets trapped in the OMA increased with time and was larger for the oil with higher viscosity. The sinking velocities of OMAs formed in this study were between 100-1200 μm s-1 and they were positively correlated with their diameter. The density of OMA was of the same order as that of the crude oil that formed them. An increase in the dispersant dosage could promote the formation of OMAs. The oil content in OMAs was higher for the denser oil in the presence of a dispersant. The maximum oil trapping efficiency of OMAs was 48.05%. This study provides fundamental data on the formation kinetics of OMAs.

An OMA-SIM Approach to Study OMA Kinetics for the Cleanup of Marine Oil Spill

Breaking waves can break oil slicks into fine droplets and entrain them in the water column. An interesting hypothesis has emerged in recent years that oil droplets and mineral fines may form Oil-Mineral Aggregates (OMAs) and enhance oil dispersion in aquatic environments. The present research investigated physical processes of marine oil spills, including oil slick breakup, the formation of OMAs, and oil/OMAs vertical mixing. In this study, a modeling approach is developed for simulating the formation and vertical mixing of oil droplets and OMAs, namely Oil Droplet and OMAs Simulation (OMA-SIM). This integrated modeling tool combines the oil vertical mixing model and density-based OMAs formation model to examine the dispersion of oil droplets and OMAs. The OMA-SIM is validated using data obtained from a mesoscale wave tank experimental study. Simulation results show that the energy dissipation rate of breaking waves is the predominant factor affecting the concentration and particle size of formed oil droplets and OMAs. It also confirms that oil viscosity has a significant influence on dispersed oil concentration. High temperature, low oil viscosity, together with more formed OMAs lead to a higher concentration of dissolved oil. Other findings based on the validated OMA-SIM approach include that: the dispersants reduce oil/water interfacial tension and decrease the size of oil droplets and OMAs, and the application of mineral fines facilitates the formation of OMAs. This study indicates that the OMA-SIM is an effective modeling tool for examining the vertical dispersion of spilled oil with or without the use of dispersant and other green particle materials like mineral fines under breaking waves.

Settling of dilbit-derived oil-mineral aggregates (OMAs) & transport parameters for oil spill modelling

The size and settling velocity of oil-mineral aggregates (OMAs) derived from diluted bitumen are primary constituents in predictive models for evaluating the potential fate of oil spilled in the aquatic environment. A series of low sediment concentration (15mg·L−1), colder water (<10°C) wave tank experiments designed to measure variability in these parameters in naturally-formed OMAs in response the presence or absence of chemical dispersant are discussed. Corresponding lab experiments revealed settling velocities of artificially formed OMAs on the order of 0.1–0.4mm·s−1. High-resolution imagery of settling particles were analyzed for particle size, density and settling velocity. In situ formation of OMAs in the wave tank was unsuccessful. Possible effects of chemical dispersant on natural sediment flocculation, the size of suspended oil droplets and clearance rates of suspended particles are discussed.

Effects of weathering on the dispersion of crude oil through oil-mineral aggregation

Crude oil that is inadvertently spilled in the marine environment can interact with suspended sediment to form oil-mineral aggregates (OMA). Researchers have identified OMA formation as a natural method of oil dispersion, and have sought ways to enhance this process for oil spill remediation. Currently there is a lack of understanding of how the weathering of oil will affect the formation of OMA due to a lack of published data on this relationship. Based on literature, we identified two conflicting hypotheses: OMA formation 1) increases with weathering as a result of increased asphaltene and polar compound content; or 2) decreases with weathering as a result of increased viscosity. While it is indeed true that the viscosity and the relative amount of polar compounds will increase with weathering, their net effects on OMA formation is unclear. Controlled laboratory experiments were carried out to systematically test these two conflicting hypotheses. Experimental results using light, intermediate, and heavy crude oils, each at five weathering stages, show a decrease in OMA formation as oil weathers.

In Situ Oil Spill Countermeasures in Ice-Infested Waters: A Modeling Study of the Fate/Behaviours of Spilled Oil

ABSTRACT The expansion of offshore oil and gas and marine transport activities in the Arctic have raised the level of risk for an oil spill to occur in the Arctic region. Existing technologies for oil spill cleanup in ice-covered conditions are limited and there is a need for improved oil spill countermeasures for use under Arctic conditions. A recent field study has assessed a proposed oil spill response technique in ice-infested waters based on the application of fine minerals in a slurry with mixing by propeller-wash to promote the formation of oil-mineral aggregates (OMA). While it was verified in the experimental study that the dispersion was enhanced and mineral fine additions promoted habitat recovery by enhancing both the rate and extent of oil biodegradation, limited monitoring data provide little insights on the fate of dispersed oil after the response. To help understand the oil transport process following mineral treatment in ice-covered conditions, mathematical modeling was used in this study to simulate the transport of OMA and calculate the mass balances of the spilled oil. To study the effects of ice and minerals on the fate and transport, the result was compared with scenarios without ice and without the addition of mineral fines. The results show general agreement between the modeling results and field observations, and further confirm the effectiveness and potential for using mineral treatment as a new oil spill counter-measure technology. This technique offers several operational advantages for use under Arctic conditions, including reduced number of personnel required for its application, lack of need for waste disposal sites, and cost effectiveness.

Influence of Seasonal Variability of Lower Mississippi River Discharge, Temperature, Suspended Sediments, and Salinity on Oil‐Mineral Aggregate Formation

Under certain conditions, oil droplets that have separated from the main oil slick may become coated by suspended sediments forming oil-mineral aggregates (OMAs). The formation of these aggregates depends on suspended particulate characteristics, temperature, salinity, mixing energy, droplet size and number, and oil properties. The OMAs do not re-coalesce with the slick and tend not to adhere to surfaces, potentially evading surface cleanup measures, enhancing opportunity for biodegradation and reducing shoreline oiling. Potential OMA formation was quantified during four distinct states of the Lower Mississippi River during a typical year using empirical relationships from laboratory and field studies for three common oils and different combinations of discharge, temperature, suspended sediments, and salinity. The largest potential OMA formation for the two lighter oils, up to 36% of the total release volume, was in the winter and spring, when high sediment availability promotes formation. For the denser, high-viscosity oil, the peak potential OMA formation, 9% of the release volume, occurred in the summer, when the salinity was higher. These results provide some evidence that, depending on environmental and spill characteristics, the formation of OMAs could be an important, but unaccounted for, process in the fate and transport of oils released in the Lower Mississippi River and should be included in oil spill dispersion models and post-spill site assessment and remediation actions.

Field Trials ofin-situOil Spill Countermeasures in Ice-Infested Waters

An oil spill response technique in ice-infested waters based on the application of fine minerals in a slurry with mixing by propeller-wash to promote the formation of oilmineral aggregates (OMA) has been proposed. This process promotes the physical dispersion of mineral-fine stabilized oil droplets into the water column that support higher rates of oil degradation by natural bacteria. To validate the operational effectiveness of this technique a controlled oil spill experiment was conducted from a Canadian Coast Guard ice-breaker in the St. Lawrence Estuary (offshore of Matane, Quebec, Canada). Following the release of the test crude oil and the application of experimental treatments, time-series changes in oil concentrations were monitored to quantify dispersion effectiveness. Field samples were also recovered for laboratory microcosm studies on the biodegradation of petroleum hydrocarbons by monitoring CO2 production and the depletion of specific hydrocarbon components. Detailed chemical analysis (GC/MS with hopane normalization) from these studies showed that more than 60% of the total petroleum hydrocarbon, 75-88% of total alkanes, and 55-65% total PAHs, were degraded after 56 days of incubation at 0.5 o C. The alkylated PAH was degraded to a greater extent following the addition of mineral fines. This technique offers several operational advantages as a spill countermeasure for use under Arctic conditions such as reduced numbers of personnel required for its application, no need for waste disposal sites, and cost effectiveness.

Investigation of OMA formation and the effect of minerals

Oil–mineral-aggregates (OMA) have been shown to be effective in oil spills cleanup. Experimental work was carried out to study the effects of physical–chemical properties of natural minerals and chemically modified minerals on OMA formation and oil removal. The results showed that the hydrophobicity, particle sizes and specific surface of minerals played an important role in OMA formation. Appropriate hydrophobicity of minerals can enhance the formation of OMA. The surface property of minerals can also influence the shape of OMA. Spherical mineral–oil aggregates were frequently formed with hydrophilic minerals while irregular shaped OMA were observed with hydrophobic minerals. The sizes of OMA also increased when the minerals changed from hydrophilic to hydrophobic. The effects of dispersant and mixing energy were also carefully studied. The results showed that dispersant were a dominant factor. When dispersant was applied, effects of other factors became minimal.

EFFECTS OF CHEMICAL DISPERSANTS AND MINERAL FINES ON PARTITIONING OF PETROLEUM HYDROCARBONS IN NATURAL SEAWATER

ABSTRACT The interaction of chemical dispersants and suspended sediments with crude oil influences the fate and transport of oil spills in coastal waters. Recent wave tank studies have shown that dispersants facilitate the dissipation of oil droplets into the water column and reduces the particle size distribution of oil-mineral aggregates (OMAs). In this work, baffled flasks were used to carry out a controlled laboratory experimental study to define the effects of chemical dispersants and mineral fines on the partitioning of crude oil, major fractions of oil, and petroleum hydrocarbons from the surface to the bulk water column and the sediment phases. The dissolved and dispersed oil in the aqueous phase and OMA was characterized using an Ultraviolet Fluorescence Spectroscopy (UVFS). The distribution of major fractions of crude oil (the alkanes, aromatics, resins, and asphaltenes) was analyzed by thin layer chromatography coupled to flame ionized detection (TLC/FID); aliphatic and aromatic hydrocarbons were analyzed by gas chromatography and mass spectrometry (GC/MS). The results suggest that chemical dispersants enhanced the transfer of oil from the surface to the water column as dispersed oil, and promoted the formation of oil-mineral aggregates in the water column. Interaction of chemically dispersed oil with suspended particular materials needs to be considered in order to accurately assess the environmental risk associated with chemical oil dispersant use in particle-rich nearshore and esturine waters. The results from this study indicate that there is not necessarily an increase in sedimentation of oil in particle rich water when dispersants are applied.

BIODEGRADATION AT A LAND-FARMING SITE AT 14,000 FEET IN THE HIGH BOLIVIAN ALTIPLANO

ABSTRACT Approximately 30,000 m3 of contaminated soil recovered from cleanup operations after a 29,000 barrel oil spill in the Desaguadero River (January 2000) was stored in temporary pits. Waste disposal plans explored several options for final disposal, including incineration and land farming. Initial concerns about the ability to landfarm the contaminated soil centered on the biodegradation potential at altitudes of 14,000 ft (4,300 m) and in a region with seasonally low day and nighttime temperatures. The Bolivian Altiplano has a semiarid climate where daily fluctuations of 15°C in temperature are common while average temperatures range between −6 C (July) and 21.0°C (November). The technical experts at the Bolivian Ministry of Sustainable Development were reluctant to grant permission for Land Farming to be used at high altitude and instead insisted that all the contaminated soil be sent by truck across Bolivia to lower altitudes where the proposed a Land Farm was to be created. As an operational response a series of experiments was set up to demonstrate that indeed Land Farming was possible at high altitude. This paper presents the results of these experiments but it should be clearly noted that the testes were conducted under operational conditions without the rigour normally found in laboratory or scientific experiments. Results showed that it was not only possible to deplete the total petroleum hydrocarbon (TPH) content from 40,000 ppm to below 1,000 ppm required by Bolivian law, but that it also could be completed within 4 months under specific technical conditions of the biodegradation process. Previous studies documented the formation of oil-mineral aggregates (OMAs) in the contaminated soils from the Rio Desaguadero spill1. We hypothesized that OMA formation and presence of aluminum polysilicate would provide an effective combination to increase the biodegradability of the soils under specific control conditions. This paper explains the high-altitude biodegradation process and the results of monitoring tests from the land farming under operational field conditions. ©2004 Transredes S.A. All Rights Reserved.

A COMPREHENSIVE NUMERICAL APPROACH TO PREDICT OIL-MINERAL AGGREGATE (OMA) FORMATION FOLLOWING OIL SPILLS IN AQUATIC ENVIRONMENTS

ABSTRACT Aggregation between suspended sediment grains and oil droplets, which leads to the formation of agglomerates commonly referred to as Oil-Mineral Aggregates (OMA), is widely acknowledged as a natural process that enhances dispersion of spilled oil in aquatic environments. A comprehensive numerical approach is developed to predict the contribution of OMA formation to the dispersal of spilled oil. The model comprises four modules to calculate maximum size of oil droplets, to predict formation of oil droplets from a slick, to predict formation of sediment floc, and to calculate density of oil-sediment flocs. The inputs of the model are environmental conditions, oil properties and concentration and grain-size distribution of suspended sediments. Sensitivity analysis performed using five crude oils covering a range of viscosities from 8 10−3 to 68 10−3 kg/ms, a kinetic energy dissipation rate from 10−3 to 102 m2/s3, a sediment grain size of 3 μm and a sediment concentration of 250 mg/l showed that formation of OMA is strongly dependent on the oil-water interfacial tension and the kinetic energy dissipation rate. Under breaking wave conditions, the contribution of OMA formation to the dispersal of spilled oil varies between 31 and 97 % depending on characteristics of the individual test oils, in particular oil-water interfacial tension. Results show also that OMA formation is enhanced when the Weber number approaches a value of 0.05.

Mechanisms of Crude Oil–Mineral Interactions

The formation of oil–mineral aggregates (OMA) in water is initiated by a variety of physical and chemical factors that are not readily amenable to differentiation in the field or in the laboratory. This study illustrates a method that may be used to isolate the limiting parameter responsible for the formation and stabilization of OMA based on the microstructure and sedimentation characteristics of the aggregates. A flocculation index based on the sedimentation behavior of a sheared crude oil–mineral–water mixture was used to quantify the degree of interaction of oil and minerals in water. The degree of crude oil–mineral interaction was found to be dependent on the viscosity of the crude oil and the type of mineral present. Hydrophilic quartz and kaolinite interact more strongly with low-viscosity oils than with high-viscosity oils, whereas calcite (an oleophilic mineral) interacts strongly with crude oils irrespective of their viscosities. It was observed that the water chemistry must favor flocculation before the minerals can effectively stabilize oil–mineral flocs. In a fresh water analogue, quartz and kaolin interact more strongly with crude oils than montmorillonite but the reverse is true in seawater. Calcite flocculates crude oils in fresh or seawater more strongly than the hydrophilic minerals tested. In all the minerals tested, the degree of oil–mineral interaction increases and then plateaus as mixing energy is increased. Confocal laser images of the oil–mineral structures reveal two types of OMA. In low-viscosity oils with hydrophilic minerals, negatively buoyant flocs comprising minerals stabilizing oil droplets in a water-continuous phase are predominant. OMA with calcite show mineral-stabilized oil droplets and mineral-rich positively buoyant oil-continuous phase.

Anaerobic Biodegradation of Vegetable Oil Spills

ABSTRACT Vegetable oil spills are common in the United States and Canada. Although vegetable oils usually are not toxic in the classic sense, at least not to the extent normally associated with crude oil and refined petroleum products, they can cause severe harmful effects in contaminated ecosystems. Since most of the adverse environmental effects of vegetable oils appear to be a result of the presence of the oil on the water surface, on shoreline sediments, or (in emulsified form) in the water column, a prudent spill response is to remove floating and suspended oil from the contaminated water body as quickly as possible. The goal of this research is to investigate a response alternative that is based on sedimentation of floating and suspended oil followed by anaerobic biodegradation in the sediments. The authors' research demonstrates that sedimentation of floating oil by formation of oil-mineral aggregates (OMAs) is possible, and that the interaction between oil and dry clay is crucial to the successful formation of negatively buoyant floes. The rate and extent of vegetable oil biodegradation under methanogenic and iron-reducing conditions in freshwater sediments have also been investigated. Anaerobic biodegradation of vegetable oil occurred in all sediments that were examined, including sediments from a river, a lake, and a wetland. Carbon and electron balances indicate that anaerobic mineralization of the added vegetable oil was complete.

PRELIMINARY FINDINGS OF OIL-SOLIDS INTERACTION IN EIGHT ALASKAN RIVERS

ABSTRACT The formation of oil-mineral aggregates in rivers with high concentrations of suspended solids could be an important mechanism for transferring oil from a surface slick into the water column. Seven glacier-fed rivers in south-central Alaska were sampled three times in the summer of 1999 and tested to see how suspended solids in the water would interact with crude oil. Oil-mineral aggregates formed with all samples, which lead to the conclusion that similar oil-solids interaction should occur if oil is spilled into other glacier-fed rivers. The amount of oil associated with the solids after mixing was roughly proportional to the concentration of suspended solids in the samples. The oil-loading results ranged between 0.01 and 0.45 g oil/g solid, with most of the measurements falling between 0.03 and 0.24 g oil/g solid. The average loading for all tests was 0.13 g oil/g solid, which is consistent with the findings of a similar study done in 1998 on the Yukon River. This result indicates that the suspended solids in the streams studied—especially the larger Yukon, Copper, and Lowe Rivers—have a large oil-holding capacity and would be capable of scavenging a considerable volume of oil. The exact quantity would depend on several factors, including the volume and dimensions of the slick, concentration of suspended solids, and current velocity of the river. Historical data on stream flow, suspended-solids concentration, and particle-size distribution were gathered and used in conjunction with the laboratory oil-solids interaction results to identify the times of the year when such interaction could occur to a significant degree. This data indicated that oil-mineral aggregates are expected to form in all rivers tested, with the most significant periods being during the summer months.