Dispersed Oil Concentrations Research Articles

Impact of salinity on coagulation and dissolved air flotation treatment for oil and gas produced water

Produced water is a major wastewater stream in the oil and gas industry which typically consists of dispersed and dissolved oils, and high levels of salinity. Despite concerns that dissolved aromatics in produced water may be detrimental to marine life, discharge regulations and treatment technologies for produced water largely focus on dispersed oil and grease removal. The purpose of this research project was to investigate coagulation with ferric chloride (FeCl3) and dissolved air flotation (DAF) at bench-scale for the removal of both dispersed and dissolved oils from synthetic and offshore produced water samples, with a specific focus on the impact of salinity on the coagulation process. Coagulation and DAF treatment of the produced water samples achieved high removals of dispersed oil and grease, but had limited impact on dissolved aromatics. The coagulation process in the saline produced water samples reduced dispersed oil and grease concentrations from 100 mg/L to below North American discharge limits (i.e. 30 mg/L in Canada, 29 mg/L in the USA) under all conditions tested, while the effectiveness of coagulation treatment in the fresh water synthetic samples was highly dependent on coagulation pH.

Bench-scale investigation of an integrated adsorption–coagulation–dissolved air flotation process for produced water treatment

In oil and gas extraction operations, water from the hydrocarbon reservoir is brought to the surface along with the oil or gas. This “produced water” contains organics which may be free, dispersed, or dissolved in the water. While certain dissolved compounds may contribute to environmental risk from produced water, current North American discharge regulations only address the dispersed fraction of oil and grease (29mg/L in the US, 30mg/L in Canada). The purpose of this research was to investigate, at bench scale, chemical coagulation with ferric chloride (FeCl3) and adsorption with organoclay (OC) in a completely stirred tank reactor (CSTR) configuration as pre-treatment for dissolved air flotation (DAF) for the removal of dissolved and dispersed oils from produced water. The integrated process was evaluated and compared to the individual processes of coagulation-DAF, adsorption-DAF and DAF without pre-treatment for the removal of dispersed oil, naphthalene and phenol from synthetic produced water. Concentrations of dispersed oil in clarified water were reduced, from an initial concentration of 100mg/L, to concentrations as low as 10±1.6mg/L after coagulation with FeCl3 (FeCl3-DAF), 15±1.2mg/L after adsorption with OC (OC-DAF), and 7±1.4mg/L after the integrated process (OC-FeCl3-DAF). From an initial naphthalene concentration of 1mg/L, both the adsorption (OC-DAF) and integrated process (OC-FeCl3) achieved clarified naphthalene concentrations of 0.11±0.01mg/L, representing a significant improvement over the 0.53±0.03mg/L achieved by coagulation treatment (FeCl3-DAF). However, none of the processes evaluated in this study were found to be effective for phenol removal.

Lab tests on the biodegradation of chemically dispersed oil should consider the rapid dilution that occurs at sea

Most crude oils spread on open water to an average thickness as low as 0.1mm. The application of dispersants enhances the transport of oil as small droplets into the water column, and when combined with the turbulence of 1m waves will quickly entrain oil into the top 1m of the water column, where it rapidly dilutes to concentrations less than 100ppm. In less than 24h, the dispersed oil is expected to mix into the top 10m of the water column and be diluted to concentrations well below 10ppm, with dilution continuing as time proceeds. Over the multiple weeks that biodegradation takes place, dispersed oil concentrations are expected to be below 1ppm. Measurements from spills and wave basin studies support these calculations. Published laboratory studies focused on the quantification of contaminant biodegradation rates have used concentrations orders of magnitude greater than this, as it was necessary to ensure the concentrations of hydrocarbons and other chemicals were higher than the detection limits of chemical analysis. However, current analytical methods can quantify individual alkanes and PAHs (and their alkyl homologues) at ppb and ppm levels. To simulate marine biodegradation of dispersed oil at dilute concentrations commonly encountered in the field, laboratory studies should be conducted at similarly low hydrocarbon concentrations.

Estimating sub-surface dispersed oil concentration using acoustic backscatter response

The recent Deepwater Horizon disaster resulted in a dispersed oil plume at an approximate depth of 1000m. Several methods were used to characterize this plume with respect to concentration and spatial extent including surface supported sampling and autonomous underwater vehicles with in situ instrument payloads. Additionally, echo sounders were used to track the plume location, demonstrating the potential for remote detection using acoustic backscatter (ABS). This study evaluated use of an Acoustic Doppler Current Profiler (ADCP) to quantitatively detect oil-droplet suspensions from the ABS response in a controlled laboratory setting. Results from this study showed log-linear ABS responses to oil-droplet volume concentration. However, the inability to reproduce ABS response factors suggests the difficultly in developing meaningful calibration factors for quantitative field analysis. Evaluation of theoretical ABS intensity derived from the particle size distribution provided insight regarding method sensitivity in the presence of interfering ambient particles.

Ingestion and defecation of dispersed oil droplets by pelagic tunicates

Subsurface plumes of small, stable dispersed oil droplets are a feature of oil spills treated with dispersants. The doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea), a zooplankton species abundant in the Gulf of Mexico, was observed to ingest dispersed oil droplets (1 – 30 mm in diameter), produced by vigorous mixing of a dispersant with crude oil. Oil droplets were first observed in the doliolid stomach, followed by appearance in the fecal pellets formed within the doliolid. Released fecal pellets had numerous oil droplets. Concentrations of ingested oil droplets in doliolids, exposed to high droplet concentrations (17 000 droplets/mL), increased from 800 to 5300 droplets/doliolid after 4 and 24 h, respectively. At a lower concentration (1200 droplets/mL), the ingested droplet concentration after 12 h was 450 droplets/doliolid. Fecal pellets were an important route for the elimination of oil droplets. Oil droplet concentrations in fecal pellets were 85 droplets/ fecal pellet and 10 droplets/fecal pellet at high and low concentrations of dispersed oil, respectively. A calculation of the amount of oil in doliolid fecal pellets, based on doliolid concentrations, their fecal production rates and oil concentration in the fecal pellets, indicated that 200 mg oil/m 3 -day could be carried to the

Effects of different concentrations of crude oil on first feeding larvae of Atlantic herring ( Clupea harengus)

Studies have shown that exposure to Polycyclic Aromatic Hydrocarbons (PAHs) and other oil related components alter normal fish larvae development and can cause increased mortality in early life stages. Modelling of results from controlled laboratory exposure experiments will help relate typical oil exposure parameters (biomarkers) to field observations and are valuable tools for oil exposure monitoring and risk assessment. Post yolk sack larval stages of Atlantic herring were exposed to different concentrations of dispersed Arctic crude oil. The selected nominal concentrations were 0.015, 0.040, 0.060, 0.250 and 0.750 mg l − 1 raw dispersed oil (0.129, 0.373, 0.496, 2.486 and 6.019 μg l − 1 Total Polycyclic Aromatic Hydrocarbons (TPAH) respectively), and control seawater in flow through systems. The larvae were exposed for 12 days and daily mortality recorded in all treatments. Thereafter, the larvae were transported to two large (300 l) rearing tanks, one for control/trace oil and one for oil exposed larvae. The larvae were allowed to recover for 8 weeks after exposure, and mortality and morphological factors then assessed, giving preliminary information on recovery of Atlantic herring larvae after oil exposure. Throughout the testing period, there was a general trend for higher mortality of herring larvae in the oil exposure concentrations than in control, and significantly higher mortality was found in all oil concentrations than in the control after 12 days. We did not detect a clear dose related mortality for our test concentrations, except for the highest concentration. There was no difference found in mortality rates of the herring larvae from either the oil or control/trace oil batch during the recovery phase during the following 60 days. Morphological observations of the herring larvae after 2 months recovery in clean seawater showed that the oil exposed larvae had morphological features that could be described as deformities, and growth was found to be significantly impaired for the oil exposed group when compared to the control/trace oil group.

DISCOBIOL Program: Investigation of Dispersant Use in Coastal and Estuarine

ABSTRACT Dispersants are known to be an appropriate solution for offshore spill response when dilution conditions are high and dispersed oil concentrations will decrease rapidly below levels that c...

Tracking Oil Dispersion in the Gulf of Mexico by Fluorescence Intensity (FI) and the Fluorescence Intensity Ratio (FIR)

Abstract Ultraviolet fluorescence (UVF) spectroscopy has been utilized to generate excitation-emission matrices (EEM) of thirteen reference oils (with viscosities ranging from 4 to 14,470 cP) and MC 252 source oil from the 2010 spill in the Gulf of Mexico. All of the oils were dispersed in seawater shaken in baffled flasks. The reference oils were dispersed at relatively high concentrations (650–836 ppm) by physical mixing or by using the chemical dispersant Corexit 9500 in combination with mixing. The matrices were reduced down to fluorescence intensity ratios (FIRs) obtained from two emission peaks at 340 and 445nm (with excitation fixed at 280nm), and the ratios compared to dispersed oil concentration. When oil concentrations were expressed as dispersion efficiencies, low FIRs (of less than 3 – 4) were associated with high dispersion efficiencies (greater than 40%) while FIRs greater than 3 – 4 were characteristic of oils dispersed with efficiencies of 20% or less. When the same dispersion techniques w...

Transcriptional effects on glutathione S-transferases in first feeding Atlantic cod ( Gadus morhua) larvae exposed to crude oil

Polycyclic aromatic hydrocarbons (PAHs) and other oil compounds are known to induce stress and impact health of marine organisms. Water-soluble fractions of oil contain components known to induce glutathione S-transferases (GSTs), one of the major classes of phase II detoxifying enzymes present in essentially all eukaryotic organisms. In this study, the transcriptional responses of six GSTs (GST pi, GST mu, GST omega, GST theta, GSY zeta and GST kappa) were examined in early larvae of Atlantic cod Gadus morhua exposed to five concentrations of dispersed oil (containing oil droplets and water-soluble fraction) and water-soluble fractions (WSF) of oil. When Atlantic cod larvae were exposed to WSF (containing 1.31 ± 0.31 μg ∑PAH/L for 4 days), expression of GSTM3 and GSTO1 was significantly increased, whereas no differences in GST expression were observed in larvae exposed to a corresponding 50% lower amount of dispersed oil (containing 0.36 ± 0.10 μg ∑PAH/L for 4 days). The study suggest that although the oil clearly had severe negative effects on the larvae (i.e. concentration-dependent lethality and growth reduction), only minor effects on GST transcription could be observed using RNA obtained from pooled whole-larvae homogenates. This result indicates that the expression of these important detoxification enzymes is only moderately inducible at such an early developmental stage either reflecting low tolerance of cod larvae to dispersed oil or alternatively that using whole-larvae homogenates may have masked tissue-specific mRNA induction.

A Multivariate Analysis on the Influence of Indigenous Crude Oil Components on the Quality of Produced Water. Comparison Between Bench and Rig Scale Experiments

A matrix of 30 crude oils have been analyzed to investigate if there is any correlation between the physiochemical properties of the crude oils and the quality of the produced water. As an approach to study produced water quality, oil. and brine water (3.5 wt%) have been mixed together, and transmission profiles from the separation process have been investigated by means of Turbiscan LAb. The Turbiscan LAb enables the study of stability of colloidal dispersions without any dilution or modification of the sample. The oil-in-water emulsions (30:70) were made by mixing oil and water at low speed to be sure that they separate within a short period of time. Drop size distributions were investigated for all crude oil emulsions by using a Coulter Counter (COULTER Multisizer II). The correlations between transmission profiles and crude oil characteristics were made by using principal component analysis (PCA), a method that helps visualize the most important information contained in a data set and find combinations of variables that describe major trends. A Vortoil K-liner hydrocyclone connected to a mixing rig has been used to separate oil and water in larger scale experiments. The objective with these experiments was to compare the results with separation experiments done at bench scale. Six crude oils have been investigated at the separation rig, and both droplet size distribution and dispersed oil concentration have been performed. The main conclusions from this work are that Turbiscan LAb is a suitable technique to study the separation of oil-in-water with good reproducibility. The results from the multivariate data analysis show that the crude oils group according to if they are light or heavy and according to if they get high or low transmission. From the larger scale experiments it has been shown that the droplet sizes, oil/water density differential, and viscosity have a significant impact on separation efficiency.

Enzymatic and cellular responses in relation to body burden of PAHs in bivalve molluscs: A case study with chronic levels of North Sea and Barents Sea dispersed oil

Mytilus edulis and Chlamys islandica were exposed to nominal dispersed crude oil concentrations in the range 0.015–0.25mg/l for one month. Five biomarkers (enzymatic and cellular responses) were analysed together with bioaccumulation of PAHs at the end of exposure. In both species, PAH tissue residues reflected the exposure concentration measured in the water and lipophylicity determined the bioaccumulation levels. Oil caused biomarker responses in both species but more significant alterations in exposed C. islandica were observed. The relationships between exposure levels and enzymatic responses were apparently complex. The integrated biomarker response related against the exposure levels was U-shaped in both species and no correlation with total PAH body burden was found. For the monitoring of chronic offshore discharges, dose- and time-related events should be evaluated in the selection of biomarkers to apply. From this study, cellular damages appear more fitted than enzymatic responses, transient and more complex to interpret.

Fast start performance in golden grey mullet Liza aurata exposed to sub-lethal concentrations of dispersed oil

Fast start performance in golden grey mullet Liza aurata exposed to sub-lethal concentrations of dispersed oil

Immune function in the Arctic Scallop, Chlamys islandica, following dispersed oil exposure

With the current expansion of offshore oil activities in Arctic regions, there is an urgent need to establish the potential effects of oil-related compounds on Arctic organisms. As susceptibility to growth, disease and survival is determined partly by the condition of an organism's immune system, measurement of endpoints linked to the latter system provide important early warning signals of the sub-lethal effects of exposure to contaminants. This study assessed the impact of dispersed oil exposure on immune endpoints in the Arctic Scallop Chlamys islandica, using a combination of cellular and humoral biological responses. Laboratory exposures of C. islandica to sub-lethal dispersed oil concentrations (0.06 and 0.25 mg l −1) were conducted over 15 days, followed by a 7-day recovery period in clean, filtered seawater. Cellular endpoints were significantly altered following dispersed oil exposure: haemocyte counts ( P < 0.01) and protein levels ( P < 0.01) were significantly elevated, whilst cell membrane stability ( P < 0.001) and phagocytosis ( P < 0.01) demonstrated a significant reduction. Whilst these results indicate alteration in the immune endpoints measured, this appears to be reversible upon removal of the contaminant stress. However, the impact of long-term continuous exposure and high-level acute exposure to oil is still unknown, and may have consequences for disease resistance and hence survival.

DISPERSED OIL TRANSPORT MODELING CALIBRATED BY FIELD-COLLECTED DATA MEASURING FLUORESCEIN DYE DISPERSION

ABSTRACT Oil-spill fate and transport modeling may be used to evaluate water column hydrocarbon concentrations, potential exposure to organisms, and impacts of oil spills with and without dispersant use. Important inputs to transport modeling for such analyses are current velocities and turbulent dispersion coefficients. Fluorescein dye studies off San Diego, California, were used to calibrate an oil transport model by hindcasting movement and dispersion of dye. The oil spill model was then used to predict subsurface hydrocarbon concentrations and potential water column impacts if oil were to be dispersed into the water column under similar conditions. Field-collected data included surface currents calculated from high-frequency radar data (HF-Radar), near-surface currents from drifter measurements drogued at several depths (1m, 2m, 4m or 5m), dye concentrations measured by fluorescence, spreading and dye intensity measurements based on aerial photography, and water density profiles from CTD casts. As the dye plume quickly extended throughout an upper mixed layer (7–15m), the horizontal dye movements were better indicated by the drifters drogued to a depth near the middle of that layer than the HF-Radar, which measured surface (∼top 50 cm) currents (including wind drift). Diffusion rates were estimated based on dye spreading measured by aerial photography and fluorescence-depth profiles. The model used these data as inputs, modeling of wind-forced surface water turbulence and drift as a function of wind speed and direction (based on published results of fluid dynamics studies), and Stokes law for droplet rise/sinking rates, to predict oil transport and dispersion rates within the water column. Use of such diffusion rate data in an oil fate model can provide estimates of likely dispersed oil concentrations under similar conditions, which may be used to evaluate potential impacts on water column biota. However, other conditions with different patterns of current shear (due to background currents, tidal currents, and wind stress) should be examined before these results can be generalized.

OIL DROPLET SIZE DISTRIBUTION AS A FUNCTION OF ENERGY DISSIPATION RATE IN AN EXPERIMENTAL WAVE TANK

ABSTRACT The U.S. National Research Council (NRC) Committee on Understanding Oil Spill Dispersants: Efficacy and Effects (2005) identified two factors that require further investigation in chemical oil dispersant efficacy studies: 1) quantification of mixing energy at sea as energy dissipation rate and 2) dispersed particle size distribution. To fully evaluate the significance of these factors, a wave tank facility was designed and constructed to conduct controlled oil dispersion studies. A factorial experimental design was used to study the dispersant effectiveness as a function of energy dissipation rate for two oils and two dispersants under three different wave conditions, namely regular non-breaking waves, spilling breakers, and plunging breakers. The oils tested were weathered MESA and fresh ANS crude. The dispersants tested were Corexit 9500 and SPC 1000 plus water for no-dispersant control. The wave tank surface energy dissipatation rates of the three waves were determined to be 0.005, 0.1, and 1 m2/s3, respectively. The dispersed oil concentrations and droplet size distribution, measured by in-situ laser diffraction, were compared to quantify the chemical dispersant effectiveness as a function of energy dissipation rate. The results indicate that high energy dissipation rate of breaking waves enhanced chemical dispersant effectiveness by significantly increasing dispersed oil concentration and reducing droplet sizes in the water column (p &amp;lt;0.05). The presence of dispersants and breaking waves stimulated the oil dispersion kinetics. The findings of this research are expected to provide guidance to disperant application on oil spill responses.

ULTRAVIOLET FLUORESCENCE SPECTROSCOPY (UVFS): A NEW MEANS OF DETERMINING THE EFFECT OF CHEMICAL DISPERSANTS ON OIL SPILLS

ABSTRACT Crude oils dispersed in seawater produce distinct emission spectra when exposed to ultraviolet (UV) light. The spectra can be used to estimate how effectively oil is dispersed by chemical methods. Oil dispersants (such as Corexit 9500) have a pronounced effect on water-based UV spectra, strongly enhancing emission at 445 nm. This enhancement of fluorescence over the 455 nm bandwidth is the result of dispersant breaking up higher molecular weight (&amp;gt;3 ring) polycyclic aromatic hydrocarbons (PAHs) into stable suspensions of small droplets. Ultraviolet fluorescence spectroscopy (UVFS) has been tested as a rapid analytical tool in the laboratory and in a wave tank designed to investigate the response of crude oils to dispersants and a range of energy dissipation rates. The results obtained with UVFS are consistent with standard chemical analyses, confirming that the method can be employed as a rapid, quantitative measure of dispersed oil concentration. Given that higher molecular weight PAHs are associated with many of the persistent toxic effects of crude oils on marine organisms, UVFS may also prove to be a useful tool for tracking these fractions during dispersed oil toxicity assays.

Assessment of chemical dispersant effectiveness in a wave tank under regular non-breaking and breaking wave conditions

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.

Biodegradability of dispersed crude oil at two different temperatures

Laboratory experiments were initiated to study the biodegradability of oil after dispersants were applied. Two experiments were conducted, one at 20 °C and the other at 5 °C. In both experiments, only the dispersed oil fraction was investigated. Each experiment required treatment flasks containing 3.5% artificial seawater and crude oil previously dispersed by either Corexit 9500 or JD2000 at a dispersant-to-oil ratio of 1:25. Two different concentrations of dispersed oil were prepared, the dispersed oil then transferred to shake flasks, which were inoculated with a bacterial culture and shaken on a rotary shaker at 200 rpm for several weeks. Periodically, triplicate flasks were removed and sacrificed to determine the residual oil concentration remaining at that time. Oil compositional analysis was performed by gas chromatography/mass spectrometry (GC/MS) to quantify the biodegradability. Dispersed oil biodegraded rapidly at 20 °C and less rapidly at 5 °C, in line with the hypothesis that the ultimate fate of dispersed oil in the sea is rapid loss by biodegradation.

EVALUATION OF DISPERSANTS FOR USE IN THE AZERBAIJAN REGION OF THE CASPIAN SEA

ABSTRACT Open marine water (salinity 30–35°/00) is the environment where dispersants are used most frequently in oil spill response. In the Azerbaijan sector of the Caspian Sea, offshore oil and gas reserves are being developed in areas where salinity ranges from 10 to 12 °loo. Because salinity can affect dispersant efficacy and toxicity, the effectiveness and aquatic toxicity of six commercially available dispersants were tested using Azerbaijan crude oil, Caspian species and 12°/oo seawater. Effectiveness for the dispersants tested with Chirag crude oil and Caspian seawater ranged from 72% to 86%, using USEPA's baffled flask method. Dispersant toxicities were in the ranges: diatom (Chaetoceros tenuissimus) 72 hr EC50 (effective concentrations inhibiting growth rate by 50%) 18 to &amp;gt; 100 mg/l; copepod (Calanipeda aquae dulcis) 48 hr LC50 (effective concentration for immobilizing 50% test organisms) 12 to 49 mg/l; amphipod (Pontogammarus maeoticus) 48 hr LC50 (concentration lethal to 50% test organisms) 50 to &amp;gt; 100 mg/l. For dispersant use, the key toxicity concern is that of dispersed oil, not dispersant. Aquatic toxicity was determined for water—accommodated fractions (WAFs) of Chirag crude in Caspian seawater. Toxicity results for the WAFs were: diatom 72 hr EC50 &amp;gt; 10,000 mg/l nominal; copepod 48 hr LC50 3.9 mg/l; amphipod 48 hr LC50 &amp;gt;15 mg/l. Chirag crude was mixed with dispersant at 20:1 oil: dispersant ratio and resulting WAFs were tested for toxicity. Results were: diatom 72 hr EC50 &amp;lt; 18 to 208 mg/l nominal; copepod 48 hr LC50 2.1 to 37 mg/l; amphipod 48 hr LC50 20 to 89 mg/l. Dispersant and dispersed oil toxicity for Caspian species are similar to published toxicity data for marine species tested at typical ocean salinity. Prolonged exposure (24 to 96hrs.) to constant concentrations of dispersant or dispersed oil used in laboratory tests may overestimate potential field toxicity, where dilution and mixing can decrease concentrations to low ppm's within hours of application. Dispersant use decisions for any Caspian Sea oil spills will focus on net environmental benefits of moving oil into the water column where it can be quickly diluted compared to potentially greater impacts from oil reaching nearshore environments.

Using a New Dispersed Oil Model to Support Ecological Risk Assessment

ABSTRACT A new model is being used to support dispersant Ecological Risk Assessment (ERA) workshops. User-driven output includes trajectory maps for both chemically dispersed and undispersed oil, and concentration isopleths reported by depth and over time. To help make toxicological sense of the output, oil concentration isopleths were nominally fixed at concentrations and exposure times of concern developed by consensus during past ERA workshops. Two No. 6 fuel spill scenarios, each with alternative outcomes (not dispersed vs 80% dispersed) were developed, one in open ocean water (10,000 bbls spill), and the other in an estuary (2000 bbls spill). Plume epicenter maximum dispersed oil concentrations peaked in the range of 10–20 ppm but decreased within 24 hours to 1–2 ppm or less. Average concentrations in the most contaminated portions of the dispersion area never exceeded 3 ppm in either scenario. Plankton in a small (&amp;lt; 25%) fraction of the open ocean plume were at moderate risk at 24 hours. These effects must be compared to those of the non-dispersion alternative, which could impact wildlife and shorelines.