Dispersant To Oil Ratio Research Articles

A Novel Biosurfactant-Based Oil Spill Response Dispersant for Efficient Application under Temperate and Arctic Conditions.

Synthetic oil spill dispersants have become essential in offshore oil spill response strategies. However, their use raises significant concerns regarding toxicity to phyto- and zooplankton and other marine organisms, especially in isolated and vulnerable areas such as the Arctic and shorelines. Sustainable alternatives may be developed by replacing the major active components of commercial dispersants with their natural counterparts. During this study, interfacial properties of different types of glycolipid-based biosurfactants (rhamnolipids, mannosylerythritol lipids, and trehalose lipids) were explored in a crude oil-seawater system. The best-performing biosurfactant was further mixed with different nontoxic components of Corexit 9500A, and the interfacial properties of the most promising dispersant blend were further explored with various types of crude oils, weathered oil, bunker, and diesel fuel in natural seawater. Our findings indicate that the most efficient dispersant formulation was achieved when mannosylerythritol lipids (MELs) were mixed with Tween 80 (T). The MELs-T dispersant blend significantly reduced the interfacial tension (IFT) of various crude oils in seawater with results comparable to those obtained with Corexit 9500A. Importantly, no leaching or desorption of MELs-T components from the crude oil-water interface was observed. Furthermore, for weathered and more viscous asphaltenic bunker fuel oil, IFT results with the MELs-T dispersant blend surpassed those obtained with Corexit 9500A. This dispersant blend also demonstrated effectiveness at different dosages (dispersant-to-oil ratio (DOR)) and under various temperature conditions. The efficacy of the MELs-T dispersant was further confirmed by standard baffled flask tests (BFTs) and Mackay-Nadeau-Steelman (MNS) tests. Overall, our study provides promising data for the development of effective biobased dispersants, particularly in the context of petroleum exploitation in subsea resources and transportation in the Arctic.

Aggregation, toxicity, and biodegradability study of an ionic liquid-based formulation for effective oil spill remediation

Chemical dispersants are extensively used for marine oil spill remediation. However, the increased toxicity and low biodegradability of these dispersants restrict their employment in the marine environment. Hence, in this work, we have developed an eco-friendly formulation composed of an ionic liquid,1-butyl-3-methylimidazolium lauroyl sarcosinate [BMIM][Lausar] and sorbitan monooleate (Span) 80. Micellar and interfacial parameters, dispersion effectiveness, as well as the toxicity and biodegradability of the developed formulation were investigated. Micellar properties confirmed a high degree of synergism among the surfactant molecules and the formation of stable micelle. The dispersion effectiveness, at dispersant-to-oil ratio (DOR) of 1:25 (v/v), against three crude oils (Arab, Ratawi, and Doba) was assessed. We achieved a dispersion effectiveness of 68.49%, 74.05%, and 83.43% for Ratawi, Doba, and Arab crude oil, respectively, using a 70:30 (w/w) ratio of Span 80 to [BMIM][Lausar]. Furthermore, the results obtained from optical microscopy and particle size analysis (PSA) indicated that the oil droplet size decreased with higher DOR. Additionally, acute toxicity experiments were conducted on zebrafish (Danio rerio) using the developed formulation, confirming its non-toxic behavior, with LC50 values of 800 mg/L after 96 h. The formulation also exhibited high biodegradability, with only 25.01% of the original quantity remaining after 28 days. Hence, these results suggest that the new formulation has the potential to be a highly effective and environmentally friendly dispersant for oil spill remediation.

Impact of mixing energy and dispersant dosage on oil dispersion and sedimentation with microplastics in the marine environment

Recently, the fate of spilled oil in the presence of microplastics (MPs) in the sea has attracted attention of researchers. Merey crude oil and polyethylene terephthalate (PET) were used as the experimental materials in this study. The effects of mixing energy and dispersant dosage on oil dispersion and sedimentation in the presence of MPs in the water column were investigated by laboratory experiments simulating actual sea conditions. The increase of mixing energy showed a promoting effect on oil dispersion. When the oscillation frequency increased from 140 rpm to 180 rpm, the oil dispersion efficiency (ODE) ranged from 2.1 %–3.7 % to 17.4 %–30.8 %, and the volumetric mean diameter (VMD) of the suspended oil droplets/MPs-oil agglomerates (MOA) decreased from 99.9–131.4 μm to 76.6–88.2 μm after 2 h oscillation. The application of chemical dispersant led to an increase in both the quantity and size of the formed sunken MPs-oil-dispersant agglomerates (MODA). At the dispersant-to-oil ratio (DOR) of 1:5, the ODE declined from 77.7 % to 62.6 % when the MPs concentration increased from 0 to 150 mg/L, while the oil sinking efficiency (OSE) rose from 3.4 % to 15.6 % when the MPs increased from 25 to 150 mg/L; the maximum size of the sunken MODA reached 13.0 mm, and the total volume of the MODA formed per unit volume oil reached 389.7 μL/mL oil at the MPs concentration of 150 mg/L. Meanwhile, the results showed that the presence of MPs inhibited the oil dispersion by increasing the oil-water interfacial tension. The outcomes of this work may provide assistance in predicting the transport of spilled oil and developing emergency measures.

Enhanced Oil Spill Remediation Using Environmentally Asymmetric Dicationic Ionic Liquids: Synthesis, Characterization, and Evaluation

The disastrous consequences for society—economically, environmentally, and socially—caused by oil spills encouraged us to treat this problem. The target of this work is to synthesize new amphiphilic dicationic ionic liquids (Ia, Ib, and Ic) and evaluate them spectroscopically and gravimetrically as potential oil spill dispersants at different temperatures to cover cold and warm areas. The synthesized ILs were well characterized by different tools for analysis of their surface activity and thermal stability. Ia, Ib, and Ic showed good dispersion effects, which were recorded to be 5.32, 20.45, and 33.61% for Ia, Ib, and Ic, respectively, at 10 °C and 12.28, 52.55, and 66.80% for Ia, Ib, and Ic, respectively, at 30 °C with a dispersant-to-oil ratio (DOR) of 0.8:10 (wt.%). Acute toxicity tests were elucidated against Nile tilapia and Oreochromis niloticus fish and confirmed their slight toxicity by determining a LC50 value greater than 100 ppm after 96 h, which recorded 13.25, 17.75, and 37.5 mg/L for Ia, Ib, and Ic, respectively. Overall, the new synthesized ILs can be represented as sustainable materials for toxic chemicals to disperse oil spills.

Effect of Oil Properties on the Generation of Nano-Aerosols During Bubble Bursting Through Crude Oil-Dispersant Slicks.

This study examines the effect of dispersant and oil properties on the aerosolization of fresh and weathered surface crude oil slicks by bursting of a plume of ∼0.7 mm bubbles. A scanning mobility particle sizer measures the size distribution of aerosols in the 20-400 nm range in a clean air chamber. The 500-μm-thick slicks contain oils with varying origin, viscosity, interfacial tension, and weathering state. Test are performed with and without premixed dispersant (Corexit 9500A), which reduces the oil-seawater interfacial tension by 2 orders of magnitude at a dispersant-to-oil ratio (DOR) of 1:25. When compared to aerosolization in clean seawater, the nano-aerosol concentration decreases for slicks without dispersant but increases by 27%-351% upon introduction of dispersant. For most cases, the airborne nanodroplet concentration increases with decreasing Capillary or Morton numbers as well as the ratio of the so-called inner to thermal length scales. To explain the airborne nanodroplet generation in an oil-dispersant mixture, we show that prior to bubble injection, even minimal agitation of the interface causes generation of a subsurface cloud of nanodroplets that diffuses away from the interface. This process appears to be caused by thermal capillary instability when the interfacial tension is low enough to increase the thermal length scale to a few nanometers.

Surface active ionic liquid and Tween-80 blend as an effective dispersant for crude oil spill remediation

Chemical oil spill dispersants are toxic to the marine environment, spurring a search for environmentally friendly dispersant formulations. We have formulated an oil spill dispersant composed of two biocompatible surfactants, Tween 80 (T) and surface-active ionic liquid (SAIL), [BMIM] [Lausar] (1-butyl-3-methylimidazolium lauroyl sarcosinate). Various micellar, interfacial, and thermodynamic properties of Tween 80 and ionic liquid (T/IL) blends were studied. The T/IL blends were solubilized in simulated seawater, and their oil (light Arab crude oil) dispersion effectiveness was determined by the baffled flask test. A synergistic interaction was observed between T and IL, such that a blend is effective as an oil dispersant, but neither is effective on its own. The stability of crude oil droplets was maximized at a 40/60 (w/w) of T/IL. The dispersion effectiveness at this specific ratio was found to be 81.19%, with a dispersant to oil ratio (DOR) of 1:25 (volume). The size and size distribution of dispersed oil droplets at function of DOR were investigated using optical microscopy and particle size analyzer. The results showed that the sizes of oil droplets decreased with DOR. We conclude that T/IL blends have unique properties which make them viable alternatives for oil spill remediation.

Characterizing Dispersion Effectiveness at Varying Salinities

ABSTRACT Chemical dispersant formulations typically provide maximum oil dispersion in waters between 30–40 ppt (parts per thousand) salt content, which encompasses typical ocean salinity (~34 ppt). As a result, most laboratory studies of oil dispersion effectiveness (DE) are conducted at low to average ocean salinity. Ocean salinity can vary locally from below 20 ppt during ice and snow melt, to extremely high (over 100 ppt) during freeze up periods or within natural brine pools in deeper waters. In this study, the influence of salinity on DE was evaluated using the baffled flask test (BFT) at a dispersant-to-oil ratio (DOR) of 1:25. Benchtop experiments were conducted with Alaskan North Slope (ANS) crude oil in the presence or absence of chemical dispersant at 5 and 25°C and varying salinities (0.2 to 125 ppt). In addition to DE as determined by BFT, oil droplet size distribution (DSD) and fluorescence intensity was measured via a LISST-100X particle size analyzer (Sequoia Scientific, Inc., Bellevue, WA) and ECO fluorometer (Sea Bird - WET Labs, Inc.; Philomath, OR), respectively. Results indicate that in the presence of dispersant, maximum DE occurred at 25ppt, and decreases above and below this salinity. Concentration of small droplets (<10 μm) was twice as high at 35ppt than at the other salinities in the presence of dispersant at 25°C. Treatments without dispersant did not vary significantly as a function of salinity. Flume tank experiments over a range of salinities support the lab scale results of DSD. These results provide a more comprehensive picture pertaining to the influence of salinity on dispersant usage at high salinities.

The effect of pressure variation on droplet size distribution of dispersed oil under simulated deep-water conditions

Droplet size distribution of dispersed oil in deep-water is critical to the transport and biodegradation of spilled oil in deep-sea. Few studies have focused on the effects of pressure on chemically dispersed oil through experiments. This study thus simulated how the crude oil homogenously pre-dispersed by Corexit 9500A using baffled flasks would behave after being exposed to deep-water conditions. Key factors included dispersant-to-oil ratio (DOR), mixing energy (energy dissipation rate and Kolmogorov microscale), and pressure (up to 150 bar). The variations of pressure were demonstrated to have insignificant effects on the size distribution of pre-dispersed oil. Both the average and medium droplet sizes were correlated negatively with DOR and mixing energy in an established model with a p-value ≤ 0.0011. The log-normal and log-logistic distributions provided a reasonable fit to simulate the droplet size distribution. The two parameters of log-logistic distribution were dependent on DOR and mixing energy with a p-value < 0.005. The results would be valuable to advance the understanding of the behaviours and trajectories of chemically dispersed oil under deep-water conditions. The research helped provide more scientific evidence to improve the understanding of dispersed oil behaviours under high pressure and support deep-sea oil spill research and potential extension of the existing results from shallow water to deep water conditions.

Impact of dispersant on crude oil content of airborne fine particulate matter emitted from seawater after an oil spill

Inhalation of PM2.5, particles with an aerodynamic diameter <2.5 μm, from sea spray after crude oil spills could present serious health concerns. The addition of dispersants to effectively spread the crude oil throughout the water column has been practiced in recent years. Here, we investigated the possibility of an increase in the toxic content of fine PM after adding dispersant. A laboratory setup consisted of a vertical tank filled with seawater, 31.5 L airspace for aerosol sampling, and a bubble generating nozzle that aerosolized the oily droplets. Four different cases were studied: no slick, 0.5-mm-thick slick of pure crude oil (MC252 surrogate), dispersant (Corexit 9500A) mixed with crude oil at dispersant to oil ratio (DOR) 1:25, and DOR 1:100. The resulting airborne droplets were sampled for gravimetric and chemical analyses through development of a gas chromatography and mass spectrometry technique. Also, PM2.5 particles were size-fractioned into 13 size bins covering <60 nm to 12.1 μm using a low-pressure cascade impactor.The highest PM2.5 concentration (20.83 ± 5.21 μg/m3) was released from a slick of DOR 1:25, 8.83× greater than the case with pure crude oil. The average ratio of crude oil content from the slick of DOR 1:25 to the case with pure crude oil was 2.37 (1.83 vs 0.77 μg/m3) that decreased to 1.17 (0.90 vs 0.77 μg/m3) at DOR 1:100. For particles <220 nm, the resultant crude oil concentrations were 0.64 and 0.29 μg/m3 at DOR 1:25 and 1:100, both higher than 0.11 μg/m3 from the slick of pure crude oil.

Optimization and Performance Test of Oil Spill Dispersant at Bioremediation of Contaminated Soil with Heavy Oil by Bioslurry Technique

Petroleum industry activities produce waste such as petroleum hydrocarbons which damage to the soil environment due to changes in soil physical, chemical and biological properties. Oil Spill Dispersant (OSD) is a product that can break down waste of oil into small parts so that it can be dispersed naturally. Laboratory experiments aimed to find out optimize and performance test of OSD in the process of bioremediation with using bio-slurry technique on contaminated soil with heavy oil was carried out at Laboratory of Surfactant and Bio-energy Research Center (SBRC), Research and Community Service Institute of Bogor Agricultural University on January - August 2018 using contaminated soil with heavy oil. The experiment used Response Surface Method (RSM) with two factors, namely the incubation time factor (X1) and the Dispersant to oil ratio (DOR) (X2). The observed variables were soil Total Petroleum Hydrocarbons (TPH), pH, total microbes, and Chemical Oxygen Demand (COD) at soil solution. The results showed that the treatment of incubation time and its combination with DOR significantly reduced soil TPH, increased soil acidity, and increased soil total B. megaterium, but did not significantly affect on COD in soil solutions. Optimization of OSD with RSM showed that the higher DOR of OSD and the longer the incubation time, the higher also the rate of biodegradation of TPH. The optimum conditions were reached at DOR of 1.16:1 and incubation time of 7 days which were able to degrade soil TPH of 54.30%. The optimum conditions of soil pH (8.825) was reached at DOR of 1:1 and incubation time of 5 days, as well as the optimum conditions of B. megaterium (8.35 log CFU g-1) was reached at DOR of 0.86:1 and incubation time of 7 days. Oil spill dispersant (OSD) increased COD in soil solution in both uncontaminated and contaminated soils with heavy oil.

Dispersant Enhances Hydrocarbon Degradation and Alters the Structure of Metabolically Active Microbial Communities in Shallow Seawater From the Northeastern Gulf of Mexico.

Dispersant application is a primary emergency oil spill response strategy and yet the efficacy and unintended consequences of this approach in marine ecosystems remain controversial. To address these uncertainties, ex situ incubations were conducted to quantify the impact of dispersant on petroleum hydrocarbon (PHC) biodegradation rates and microbial community structure at as close as realistically possible to approximated in situ conditions [2 ppm v/v oil with or without dispersant, at a dispersant to oil ratio (DOR) of 1:15] in surface seawater. Biodegradation rates were not substantially affected by dispersant application at low mixing conditions, while under completely dispersed conditions, biodegradation was substantially enhanced, decreasing the overall half-life of total PHC compounds from 15.4 to 8.8 days. While microbial respiration and growth were not substantially altered by dispersant treatment, RNA analysis revealed that dispersant application resulted in pronounced changes to the composition of metabolically active microbial communities, and the abundance of nitrogen-fixing prokaryotes, as determined by qPCR of nitrogenase (nifH) genes, showed a large increase. While the Gammaproteobacteria were enriched in all treatments, the Betaproteobacteria and different families of Alphaproteobacteria predominated in the oil and dispersant treatment, respectively. Results show that mixing conditions regulate the efficacy of dispersant application in an oil slick, and the quantitative increase in the nitrogen-fixing microbial community indicates a selection pressure for nitrogen fixation in response to a readily biodegradable, nitrogen-poor substrate.

Investigation of choline based ionic liquids as an oil spill dispersant

Chemical dispersants are universally used to overcome oil spill damages. However, the toxicity related with chemical dispersants minimizes its usage as oil spill dispersants. Thus, the employment of biodegradable and environmental benign dispersants in marine environment is much needed. In this research, the capability of choline myristate [Cho][Myr] and choline oleate [Cho][Ol] were investigated to be used as oil spill dispersants. Results reported in this study illustrates that by combining these two amphiphilies, an effective dispersion is achieved. A maximum dispersion of 71 % was achieved by combining [Cho][Myr] and [Cho][Ol] with an optimal ratio of 60:40 (w/w). The dispersant to oil ratio (DOR) was 1:10 (v/v) at this optimal combination. Further, by increasing the DOR the effectiveness increases and about 78% dispersion is achieved at 1:1 (v/v). Moreover, the blend of [Cho][Myr] and [Cho][Ol] at 60:40 (w/w) ratio formed a stable emulsion than its single components.

Dispersion of crude oil by choline based ionic liquids

The employment of chemical dispersants for oil spills is a universally accepted response option. However, the toxicity associated with chemical dispersant restricts its usage in marine environments. The toxicity of these dipersants can be minimized by utilizing biodegradable and enviromentally benign surfactants. In addition, the use of water in their formulation further reduces its toxicity. In this study, the ability of choline based Ionic Liquids (choline laurate and choline oleate) solubilized in water to disperse crude oil were analyzed. Results presented in this study showed that an effective dispersant is obtained by combining these two amphiphilies. For maximum dispersion, the optimal choline laurate and choline oleate ratio used is 50:50 (w/w). The dispersion efficiency of 67% was achieved by employing this optimal combination with dispersant to oil ratio (DOR) of 1:10 (v/v). The interfacial activity of the combined system was also investigated and it was observed that the interfacial activity of the combined system is greater than individual components.The results presented in this study suggests that the blend of choline laurate and choline oleate could potentially replace the conventional toxic oil spill dispersants.

Kinerja Oil Spill Dispersant Dalam Proses Bioremediasi Tanah Tercemar Minyak Bumi (Studi Kasus Tanah Tercemar Minyak Bumi Lapangan XYZ)

Oil spill dispersant (OSD) is a surfactant product that serves as dispersant. OSD has been widely used and proven to be effective in oil spills both in the sea and in the land. The OSD-SBRC (Surfactant and Bioenergy Research Center) IPB was produced from palm oil, while the commercial product of OSD S200 was made from LAS (Linear Alkyl Benzene Sulfonate) based from petroleum. Application of OSD in bioremediation testing occurred on petroleum contaminated soil from the field with initial total petroleum hydrocarbon of 6-10%. The treatment of dispersant to oil ratio (DOR) was at 0.5:1 and 1:1. The contaminated soil was added with Pseudomonas aeruginosa and fertilizers (Urea and SP36) to support bacterial growth. The environmental soil conditions during the bioremediation process were observed as pH, moisture content, and temperature. The OSD performance in bioremediation process was measured as TPH (Total Petroleum Hydrocarbon) and TPC (Total Plate Count). The results showed that pH, moisture content and temperature levels were at optimum condition for bacterial growth to optimally degrade the hydrocarbon. The result of TPC value showed that treatment with the addition of OSD S200 caused inhibition of microbial growth P. aeruginosa bacteria. The TPH measurements showed that treatment with OSD SBRC with DOR (0.5:1) was able to degrade hydrocarbons up to 89.62%. The bioremediation process using OSD-SBRC was better than OSD S200.Keywords: bioremediation, hydrocarbon, OSD, surfactant­

Hydrodynamics of oil jets without and with dispersant: Experimental and numerical characterization

In this paper, we present the analysis of an underwater horizontal oil jet experimental measurement and Computational Fluid Dynamics (CFD) using the Reynolds Averaged Navier Stokes (RANS) equations. Two oil subsurface releases were conducted: one with crude oil and another with crude oil premixed with dispersant at the dispersant to oil ratio (DOR) of 1:20. The jet profile was captured by a camera at moderate resolution, and the instantaneous velocity was measured by a Vectrino Profiler. The velocity components, turbulence kinetic energy, and turbulence dissipation rate from the experiment agreed well with those from the CFD simulation using the k-epsilon turbulence model. The spread angle of the jet was found to be around 21° and 24° from the experiment measurement, for oil without dispersant and oil with dispersant, respectively. The latter is close to the angle of miscible jets at 23°. The jet profile of oil with dispersant had a smaller buoyancy than that without dispersant, which is probably due to the large water entrainment for the oil with dispersant jet. The cross sections of the jet for both cases gradually became flattened with distance, as the plume turned upward.

Oil plume simulations: Tracking oil droplet size distribution and fluorescence within high-pressure release jets

ABSTRACT Optical measurements have been used during oil spill response for more than three decades to determine oil presence in slicks and plumes. Oil surveillance approaches range from simple (human eyeball) to the sophisticated (sensors on AUVs, aircraft, satellites). In situ fluorometers and particle size analyzers were deployed during the Deepwater Horizon (DWH) Gulf of Mexico oil spill to track shallow and deep subsea plumes. Uncertainties regarding instrument specifications and capabilities during DWH necessitated performance testing of sensors exposed to simulated, dispersed oil plumes. Seventy-two wave tank experiments were conducted at the Bedford Institute of Oceanography. Simulated were oil releases with varying parameters such as oil release rate, oil temperature (reservoir temp ~ 80 °C), water temperature (&amp;lt;8 °C and &amp;gt;15 °C), oil type, dispersant type (Corexit 9500 and Finasol OSR52) and dispersant to oil ratio (DOR). Plumes of Alaskan North Slope Crude (ANS), South Louisiana Crude (SLC) and IFO-120 oils were tracked using in situ fluorescence, droplet size distribution (DSD), total petroleum hydrocarbons (TPH) and benzene-toluene-ethylbenzene-xylene (BTEX). For the lighter SLC, bimodal droplet size with mean diameter &amp;lt; 70 μm was achieved for 1:20 and 1:100 DOR, regardless of water temperature. Similarly, the medium ANS crude exhibited mean droplet diameter &amp;lt;70 μm, but was bimodal only for the 1:20 treatment. Bimodal distribution was not achieved with the heavy IFO, but droplet &amp;lt; 70 μm were observed for 1:20 warm waters, indicating poor dispersibility of the high viscosity oil even for jet releases. Results offer valuable information on the behavior and dispersibility of oils over a range of viscosity, DOR and environmental conditions. Findings have implications for fate and transport models, where DSD, chemistry and fluorescence are all impacted by release variables. This research was supported by the Bureau of Safety and Environmental Enforcement.

Comparative Study to Determine the Biodegradability of Dispersants at Environmentally Relevant Concentrations

ABSTRACTChemical dispersant agents reduce the interfacial tension between oil and water, and increase the surface area to volume ratio of oil droplets thus facilitating the biodegradation of spilled oil. Dispersants are composed of surface active molecules known as surfactants and various commercial products contain Dioctyl Sulfosuccinate (DOSS) as the active surfactant ingredient. Since previous laboratory studies were conducted at oil and dispersant concentrations significantly higher (~0.7 g/L oil with Dispersant to Oil Ratio (DOR) of 1:25) than those typically found in field conditions, experiments were conducted at low levels of oil and dispersant (28 μg/L oil with DOR of 1:25) in order to determine the degradation trends at environmentally relevant concentrations. Experiments were conducted using two crude oils (Alaskan North Slope (ANS) and Endicott) and two dispersant products (Corexit 9500 and Finasol OSR 52) to study the biodegradation of dispersants and dispersed oil and oil alone samples were used as controls. Two oil degrading cultures, isolated from the surface (meso) and deep sea (cryo) of the Gulf of Mexico, were enriched on crude oil at 25 and 5 °C and were used as the inocula. The biodegradation experiments were performed at 5 °C for 56 days and at 25 °C for 48 days using sterile GP2 artificial seawater as the media. The time series concentration of DOSS, the primary surfactant in the dispersants was monitored using LC-MS/MS in addition to the oil concentration which was measured using GC-MS/MS. Although the initial concentration of DOSS in Finasol OSR 52 was 20% higher than in Corexit 9500, over 95% of the anionic surfactant fraction was metabolized for both types of dispersant products by the end of the experiment at 25 °C while it persisted at 5 °C. The effect of dispersant and oil type on microbial community structure was also analyzed using PCR analysis. Results indicated that the abundance of Thalassospira correlated well with hydrocarbon degradation trends. The results from this study significantly expands on our understanding of biodegradation of DOSS, dispersed, and non-dispersed oil and also provides information regarding bacterial community composition.

Effect of Corexit 9500A on Mississippi Canyon crude oil weathering patterns using artificial and natural seawater.

During the 2010 Deepwater Horizon oil well blowout in the Northern Gulf of Mexico (GoM), the application of 6.97 million litres of chemical dispersants was used at the well-head and on the sea surface to promote oil degradation and weathering of the Mississippi Canyon 252 (MC252) crude oil. Chemical dispersants encourage microbial degradation by increasing the surface area of the spilled oil, which also increases its bioavailability. However, the net beneficial effects of using chemical dispersants on spilled oil and their effects on weathering are not completely elucidated in contemporary literature. The use of simulated environmental conditions in replicate laboratory microcosm weathering experiments were employed to study the weathering of oil and the effects of dispersants on oil weathering. Fresh MC252 oil was evaporatively weathered 40% by-weight to approximate the composition of oil seen in surface slicks during the 2010 spill. This surface oil was then well mixed with two types of seawater, autoclaved artificial seawater, the abiotic control, and Gulf of Mexico seawater, the biotic experiment. Four different weathering combinations were tested: 10 mg of oil mixed in 150 ml artificial seawater (OAS) or natural (i.e., GoM) seawater (ON) and 10 mg of oil with dispersant mixed with 150 ml of artificial seawater (OASD) or natural (i.e., GoM) seawater (OND). For the treatments with dispersant (OASD and OND), the dispersant-to-oil ratio (DoR) was 1:20. The experiment was carried out over 28 days with replicates that were sacrificed on Days 0, 0.5, 3, 7, 14, 21 and 28. For the OAS and OASD treatments, abiotic weathering (i.e., evaporation) dominated the weathering process. However, the ON and OND treatments showed a dramatic and rapid decrease in total concentrations of both alkanes and aromatics with biodegradation dominating the weathering process. Further, there were no identifiable differences in the observed weathering patterns between microcosms using oil or oil treated with dispersant. In the biotic weathering microcosms, the relative degree of individual polycyclic aromatic hydrocarbon (PAH) depletion decreases with an increase in rings and within a homolog series (increased alkylation). The n-C17/pristane and n-C18/phytane ratios rapidly decreased compared to the abiotic weathering experiments. The C2-dibenzothiophenes (DBT)/C2-phenanthrenes (D2/P2) and C3-DBTs/C3-phenanthrenes (D3/P3) ratios initially remained constant during the early stages of weathering and then increased with time showing preferential weathering of the sulfur containing compounds compared to similar sized PAH compounds. These ratios in the abiotic microcosms remained constant over 28 days. Additionally, twenty-four quantitative MC252 oil biomarker ratios were evaluated to determine if their usefulness as oil source-fingerprinting tools were compromised after significant weathering and dispersant augmentation.

Combined Experimental and Molecular Simulation Investigation of the Individual Effects of Corexit Surfactants on the Aerosolization of Oil Spill Matter.

We report laboratory aerosolization experiments and classical molecular dynamics (MD) simulations, with the objective of investigating the individual effects of the two Corexit surfactants Span 80 (nonionic) and dioctyl sodium sulfosuccinate (DOSS, ionic), on the aerosolization of oil spill matter to the atmosphere. Our simulation results show that Span 80, DOSS, and the oil alkanes n-pentadecane (C15) and n-triacontane (C30) exhibit deep free energy minima at the air/seawater interface. C15 and C30 exhibit deeper free energy minima at the interface when Span 80 is present, as compared to the situation when DOSS or no surfactants are at the interface. These results suggest that Span 80 makes these oil hydrocarbons more likely to be adsorbed at the surface of seawater droplets and carried out to the atmosphere, relative to DOSS or to the situation where no surfactants are present. These simulation trends are in qualitative agreement with our experimental observations in a bubble-column setup, where larger amounts of oil hydrocarbons are ejected when Span 80 is mixed with oil and injected into the column, as compared to when DOSS is used. Our simulations also indicate that Span 80 has a larger thermodynamic incentive than DOSS to move from the seawater phase and into the air/seawater interface. This observation is also in qualitative agreement with our experimental measurements, which indicate that Span 80 is ejected in larger quantities than DOSS. Our simulations also suggest that DOSS predominantly adopts a perpendicular orientation with respect to the air/seawater interface at a dispersant to oil ratio (DOR) of 1:20, but has a slight preference to lie parallel to the interfaces at a DOR = 1:5; in both cases, DOSS molecules have their tails wide open and stretched. In contrast, Span 80 has a slight preference to align parallel to the interfaces with a coiled conformation at both DOR values.

Modeling Subsurface Dispersant Applications for Response Planning and Preparation

ABSTRACTThe increase in oil and gas development activity at increasing water depths has highlighted the need for modeling tools to evaluate the unique aspects of accidental deepwater releases, one aspect being the need to assess the impact of subsurface dispersant application to a deepwater blowout. In response to this need, the effect of subsurface dispersant application has been implemented within RPS ASA's blowout model OILMAPDeep. OILMAPDeep was developed to simulate deepwater blowout releases; it predicts the evolution and characteristics of the subsurface plume and estimates the oil droplet size distribution associated with the release. The droplet size distribution dictates the vertical transport of oil within the water column, and impacts the relative volume anticipated to either surface or remain trapped in the water column. Droplet sizes are primarily a function of the energy of the release and the oil-water interfacial tension. The energy of the release is characterized by a reference velocity, typically the exit velocity, and the oil-water interfacial tension as a function of the oil properties. Dispersants mixed with oil reduce the oil-water interfacial tension, which in turn reduces the droplet sizes associated with treated releases serving to delay or eliminate surfacing oil. The present model implementation takes advantage of recent studies that have quantitatively assessed the relationship between the dispersant to oil ratio and surface tension.Here we present a background of the OILMAPDeep module, the governing physical processes of droplet formation, and the relationship between dispersant-to-oil ratio (DOR) and droplet size formation as characterized in the model. A description of the model implementation including model inputs and outputs are provided. Furthermore a set of scenarios are presented that demonstrate the model's capabilities for planning and preparing response activities in the event of a potential oil well blowout. This paper shows how the implementation of subsurface dispersant application within OILMAPDeep provides an effective means of evaluating potential response activities associated with subsurface dispersant application to a deepwater blowout. This includes evaluating the effect of subsurface dispersant application on droplet size distribution, and the ultimate impact on the timing, location and the relative volume of surfacing oil.