Kenneth Lee

Formation and Characterization of Oil–Mineral Aggregates

Abstract Oil associates with fine mineral particles in an aqueous medium not only as molecules adsorbed onto mineral surfaces, but also as a discrete phase to form microscopic oil–mineral aggregates (OMA). As it promotes the dispersion of stranded oil, this process is now believed to be instrumental in the natural recovery of oiled shorelines and in the efficacy of spill countermeasure techniques such as surf-washing (relocation of oiled sediment into the zone of wave action). To predict the fate of residual oil following spills and the effectiveness of such countermeasures, an improved understanding of the nature and properties of OMA and of the factors influencing their formation is required. Laboratory protocols and microscopical methods have been refined for the detection and classification of OMA. Three OMA types have been identified: droplet, solid and flake aggregates. Droplet aggregates are oil droplets (usually a few μm in diameter) surrounded by individual or flocculated mineral particles. Solid aggregates are mixed oil and mineral bodies of various shapes (scale of tens of μm). Flake aggregates are thin sheets that can reach the mm size range in which mineral and oil are arranged in an ordered configuration. The parameters controlling the quantity, type and size of OMA include mineral type and surface properties, quantity, viscosity and composition of the oil, and oil/mineral ratio. It is also evident that water turbulence (i.e. breaking waves, strong flood currents) greatly enhances OMA formation. Once formed, OMA appear to be very stable structures the buoyancy of which depends on the ratio of oil to mineral in each individual aggregate. OMA being on average less dense than mineral-only aggregates and even buoyant, they will be kept in suspension longer and be dispersed further than unoiled sediment. Mineral particles in OMA act as a surfactant preventing the oil from recoalescing. As OMA formation increases the surface to volume ratio of spilled oil, it prolongs and enhances oil weathering processes such as dissolution, evaporation and biodegradation.

Removal of Oil from the Sea Surface through Particulate Interactions: Review and Prospectus

Abstract The fate of oil spilled in coastal zones depends in large part on the interactions with environmental factors existing within a short time of the spill event. In addition to weathering which produces changes in the chemistry of the hydrocarbon stock, physical interactions between oil and suspended particulate matter (SPM), both organic and inorganic, play a role in determining the dispersal and sedimentation rates of the spill. This in turn affects the degradation rate of the oil. This paper provides a comprehensive literature review of the role of oil–particle interactions in removal of petroleum hydrocarbons from the sea surface and provides estimates of the degree to which SPM may augment the deposition of oil. Both field and laboratory observations have shown widely varying rates of oil removal due to particulate interactions. The discussion covers the interaction between oil weathering, injection, sinking, adsorption, microbial processes, flocculation and ingestion by zooplankton, which all contribute to packaging oil and SPM into settling aggregates.

Oil–Particle Interactions in Aquatic Environments: Influence on the Transport, Fate, Effect and Remediation of Oil Spills

Abstract During the last decade, there has been a growing interest in the natural interaction between spilled oil and particles in aquatic environments due to recognition of its influence on residual oil persistence. Both organic (e.g. phytoplankton, fecal pellets) and inorganic particles (e.g. mineral fines) have been implicated in the transport of oil from surface waters to the benthic environment. In particular, the formation of oil–mineral aggregates (OMA) has been shown to contribute to the removal of stranded oil from low-energy, intertidal environments. This natural self-cleaning process is attributed to the reduction in oil adhesion when oil droplets become stabilized by their interaction with mineral fines. Increasing knowledge of this process has fostered the development and evaluation of oil spill countermeasure strategies based on the promotion of oil–particle interactions. To validate and optimize the application of these techniques, an international research effort is now focused on the mechanism and factors, which influence the rate and extent of OMA formation and the significance of OMA formation on the persistence and biological effects of residual oil in the environment. In addition to providing guidance for the application of remedial treatments based on the enhancement of OMA formation, these studies have improved our ability to predict natural rates of recovery following spill events.

Interaction of oil and mineral fines on shorelines: review and assessment

The interaction of fine mineral particles with stranded oil in an aqueous medium reduces the adhesion of the oil to solid surfaces, such as sediments or bedrock. The net result is the formation of stable, micron-sized, oil droplets that disperse into the water column. In turn, the increase in surface area makes the oil more available for biodegradation. This interaction, referred to as oil-mineral aggregate (OMA) formation, can explain how oiled shorelines are cleaned naturally in the absence of wave action in very sheltered coastal environments. OMA formation also plays an important role in the efficacy of shoreline treatment techniques, such as physical mixing and sediment relocation that move oiled sediments into the zone of wave action to promote the interaction between oil and mineral fines. Successful application of these shoreline treatment options has been demonstrated at two spill events (the Tampa Bay response in Florida and the Sea Empress operation in Wales) and at a controlled oil spill experiment in the field (the 1997 Svalbard ITOSS program). Sediment relocation harnesses the hydraulic action of waves so that the processes of fine-particle interaction and physical abrasion usually occur in tandem on open coasts. There has been no evidence of significant detrimental side-effects of residual oil in pelagic or benthic environments associated with the use of these treatment options to enhance rates of dispersion and oil biodegradation.

Oil–Mineral Aggregate Formation on Oiled Beaches: Natural Attenuation and Sediment Relocation

Abstract The significance of oil–mineral aggregate (OMA) formation on the effectiveness of the in situ shoreline treatment options of natural attenuation (natural recovery) and sediment relocation (surf washing) was examined during field trials on two mixed-sediment (sand and pebble) beaches experimentally oiled with IF-30 oil. At both sites, the amount of oil remaining in the experimental plots was dramatically reduced within five days after sediment relocation treatments. Time-series microscopy and image analysis of breaker-zone water samples demonstrate that OMA formation occurred naturally on the oiled beaches at both sites and was accelerated by the sediment relocation procedure. Lower concentrations of OMA in the breaker zone at Site 3 are attributed to the higher wave-energy levels at this site that presumably facilitated more rapid OMA dispersion. The granulometry and mineralogy of beach sediment and of subtidal sediment trap samples indicate that the material settling in nearshore waters originated from the relocated sediment and that a portion of the finer sediment was probably transported out of the study region before settling. Gas chromatography/mass spectrometry analysis demonstrated that a significant fraction of the oil dispersed into nearshore waters and sediments by interaction with mineral fines was biodegraded. The fact that little or no residual oil was found stranded on the shore in areas adjacent to the experimental plots and that only small amounts of oil were found in nearshore subtidal sediments and sediment trap samples suggests that a large fraction of the oil lost from the experimental plots may have been dispersed in the form of relatively buoyant OMA.

Characteristics of oil droplets stabilized by mineral particles: Effects of oil type and temperature

Abstract The relative influence of oil type and temperature on the characteristics of oil droplets stabilized by mineral particles (oil–mineral aggregates––OMA) was studied in the laboratory. OMA were generated by shaking eight different oils under two temperatures with natural mineral fines in seawater at a pre-defined energy level. Shape, mean and maximum sizes, size distribution and concentration of oil droplets forming negatively buoyant OMA were measured by image analysis using epi-fluorescence microscopy. Results showed that oil droplets are, on average, spherical regardless of oil composition and temperature. Non-spherical “elongated” oil droplets form more at 20 °C than at 0 °C. Droplet shape and size were not correlated to oil viscosity. The concentration of oil droplets decreased rapidly with oil viscosity, temperature and asphaltenes–resins content (ARC). When normalized with ARC, mass concentration of oil droplets correlates well with oil viscosity, regardless of experimental temperature. A model was proposed to calculate mass of oil dispersed by OMA as a function of oil viscosity and ARC. Size distributions of oil droplets follow similar trends, but their magnitudes depend on oil type and temperature. A function was derived that describes all the data when size distributions were presented in a normalized form N / N t = f ( D / D 50 ), where N is number of droplets of diameter D , N t is the total number of droplets and D 50 the mean size of the droplets.

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.

CHARACTERIZATION OF OIL-MINERAL AGGREGATES

ABSTRACT Oil associates with fine mineral particles in an aqueous medium not only as molecules adsorbed on mineral surfaces, but also as a discrete phase to form microscopic oil-mineral aggregates ...

PARTICLE SIZE ANALYSIS OF DISPERSED OIL AND OIL‐MINERAL AGGREGATES WITH AN AUTOMATED ULTRAVIOLET EPI‐FLUORESCENCE MICROSCOPY SYSTEM

Abstract This paper describes recent advances in microscopic analysis for quantitative measurement of oil droplets. Integration of a microscope with bright‐field and ultraviolet epi‐fluorescence illumination (excitation wavelengths 340–380 nm; emission wavelengths 400–430 nm) fitted with a computer‐controlled motorized stage, a high resolution digital camera, and new image‐analysis software, enables automatic acquisition of multiple images and facilitates efficient counting and sizing of oil droplets. Laboratory experiments were conducted with this system to investigate the size distribution of chemically dispersed oil droplets and oil‐mineral aggregates in baffled flasks that have been developed for testing chemical dispersant effectiveness. Image acquisition and data processing methods were developed to illustrate the size distribution of chemically dispersed oil droplets, as a function of energy dissipation rate in the baffled flasks, and the time‐dependent change of the morphology and size distribution of oil‐mineral aggregates. As a quantitative analytical tool, epi‐fluorescence microscopy shows promise for application in research on oil spill response technologies, such as evaluating the effectiveness of chemical dispersant and characterizing the natural interaction between oil and mineral fines and other suspended particulate matters.

Monitoring Dispersed Oil Droplet Size Distribution at the Gulf of Mexico Deepwater Horizon Spill Site

ABSTRACT In response to the Deepwater Horizon oil spill in the Gulf of Mexico, at-sea monitoring of dispersed oil was conducted to support the spill response operation, particularly for the verification and tracking of any sub-sea plumes identified by model prediction. This paper describes the methodology that has been developed for the analysis of small particle concentrations (SPC) in the field associated with dispersed oil. The dispersed oil droplet size distribution from the field samples was analyzed by using a laser in situ scattering and transmissometry system (LISST-100X, Sequoia Scientific Inc. Seattle, WA) system set up in the laboratory on the research vessels. The samples collected from the surface and water column were transferred into a full-path mixing chamber of the LISST-100X to perform particle size distribution analysis. Small particle (d ≤ 70μm) concentrations were monitored to verify the surface and subsurface presence of dispersed oil, and to track the size and movement of the subsur...