Dispersant To Oil Ratio Research Articles

Dispersion of Louisiana crude oil in salt water environment by Corexit 9500A in the presence of natural coastal materials

Effectiveness of Corexit 9500A for dispersing Louisiana crude oil was evaluated in salt water solutions containing natural materials in relation to salinity and dispersant-to-oil ratio (DOR). Experimental results showed that both salinity and DOR had significant effects on dispersion of Louisiana crude oil in the presence of different natural materials. The natural materials added to the salt water solutions included sea sand (South Beach, Miami, Florida), red mangrove leaves (Rhizophora mangle), seaweed (Sargassum natans), and sea grass (Halodule wrightii). Dispersant effectiveness (amount of oil dispersed into the water) was reduced significantly with increasing salinity with the minimum effectiveness observed in the salinity range between 30 and 50 ppt in all aqueous samples containing natural materials. When significant amounts of floating oil were present, the partially submerged natural materials enhanced the transfer of oil into the water column, which improved the dispersion effectiveness. However, dispersant effectiveness was significantly reduced when the amount of floating oil was relatively small and could not be released back to the water column. Surface tension may not be an adequate parameter for monitoring the effectiveness of dispersants in salt water environment. When distilled water was used (i.e., zero salinity), surface tension was significantly reduced with increasing dispersant concentration. However, there was no clear trend in the surface tension of the salt water solutions (17–51 ppt) containing crude oil and natural materials with increasing dispersant concentration.

Production and characterization of microbial biosurfactants for potential use in oil-spill remediation

Two biosurfactants, surfactin and fatty acyl-glutamate, were produced from genetically-modified strains of Bacillus subtilis on 2% glucose and mineral salts media in shake-flasks and bioreactors. Biosurfactant synthesis ceased when the main carbohydrate source was completely depleted. Surfactin titers were ∼30-fold higher than fatty acyl-glutamate in the same medium. When bacteria were grown in large aerated bioreactors, biosurfactants mostly partitioned to the foam fraction, which was recovered. Dispersion effectiveness of surfactin and fatty acyl-glutamate was evaluated by measuring the critical micelle concentration (CMC) and dispersant-to-oil ratio (DOR). The CMC values for surfactin and fatty acyl-glutamate in double deionized distilled water were 0.015 and 0.10g/L, respectively. However, CMC values were higher, 0.02 and 0.4g/L for surfactin and fatty acyl-glutamate, respectively, in 12 parts per trillion (ppt) Instant Ocean® sea salt, which has been partly attributed to saline-induced conformational changes in the solvated ionic species of the biosurfactants. The DORs for surfactin and fatty acyl-glutamate were 1:96 and 1:12, respectively, in water. In Instant Ocean® solutions containing 12ppt sea salt, these decreased to 1:30 and 1:4, respectively, suggesting reduction in oil dispersing efficiency of both surfactants in saline. Surfactant toxicities were assessed using the Gulf killifish, Fundulus grandis, which is common in estuarine habitats of the Gulf of Mexico. Surfactin was 10-fold more toxic than fatty acyl-glutamate. A commercial surfactant, sodium laurel sulfate, had intermediate toxicity. Raising the salinity from 5 to 25ppt increased the toxicity of all three surfactants; however, the increase was the lowest for fatty acyl-glutamate.

DETERMINATION OF THE LIMITING OIL VISCOSITY FOR CHEMICAL DISPERSION AT SEA

ABSTRACT Many previous studies using laboratory test methods have shown that the ability to disperse spilled oils depends on several factors including: spilled oil properties (and how these change with oil weathering), the mixing energy, and the dispersant-to-oil ratio (DOR). There appears to be a ‘limiting oil viscosity’ value that, when exceeded, causes a sharp reduction in the effectiveness of a dispersant. The results obtained in laboratory tests are relative and not absolute, and it has therefore proved very difficult to correlate dispersant effectiveness results from these laboratory tests with dispersant performance at sea. A series of small-scale dispersant tests were conducted at sea in the English Channel in June 2003. Several small test slicks of residual fuel oils of different viscosity grades were laid on the sea and immediately sprayed with different dispersants at different DORs. Observers used a simple ranking system to visually assess the degree of dispersion that occurred when a cresting wave passed through an area of the dispersant-treated oil. Collation of the results showed that there were obvious and consistent differences in the degree of effectiveness observed with different combinations of oil viscosity, dispersant and treatment rate.

Dispersant Effectiveness on Heavy Fuel Oil and Crude Oil in New Zealand

ABSTRACT The New Zealand (NZ) Maritime Safety Authority (MSA) recently identified seven crude oils and nine IFO-380 heavy fuel oils used or transported in NZ waters that had a high relative risk of being spilt. To determine the relative effectiveness of dispersants stocked by the MSA (Corexit 9527, Slickgone LTSW, Gamlen OSD LT, and Tergo R40) on the oils, effectiveness was tested using the Warren Spring Laboratory (WSL) LR 448 protocol. All testing was on fresh (unweathered) oil at 15°C, at a dispersant to oil ratio (DOR) of 1:25. Effective dispersion was considered to be equivalent to a WSL test result of ≥15%, as proposed in the work of Lunel & Davies (1996). Overall, the seven crude oils tested could be dispersed with MSA stocked dispersants; Corexit 9527 and Slickgone LTSW dispersing the greatest volume of oil, while Gamlen OSD LT and Tergo R40 were effective on the widest range of oils. For the nine IFO-380 heavy fuel oils, dispersant effectiveness was generally lower than for crude oils, and two oils could not be dispersed. Corexit 9527 was the most effective dispersant and worked on the widest range of fuel oils. Slickgone LTSW, Gamlen OSD LT, and Tergo R40 were less effective and worked on a smaller range of fuel oils. To assess whether other dispersants not currently stocked by the MSA offered a significantly improved capacity, two high performance products (Corexit 9500 and Slickgone EW) were tested on the same oils, and across a range of temperatures and DORs. Laboratory results showed that Corexit 9500 and Slickgone EW were significantly more effective on both the crude oils and the IFO-380 heavy fuel oils than existing MSA dispersant stocks. While the results of this study provide a good indication of the relative effectiveness of different dispersants, they do not indicate absolute levels of effectiveness, and field experiments are needed to define how laboratory effectiveness translates to effectiveness in the field.

Behavior of a chemically dispersed oil in a wetland environment

An experiment was conducted at a wetland research facility, investigating the behavior and effects of chemically dispersed oil (CDO) using an oil-spill dispersant. The research site is located on the San Jacinto River near Houston, TX. The replicated treatments included oiled control, “high-dose” CDO (1:10 dispersant-to-oil ratio (DOR)), “low-dose” CDO (1:20 DOR), as well as an unoiled control. Known amounts of oil or dispersed oil were added to the respective plots. Sediment samples were taken over a 99-day period using a 5-cm-diameter coring device. The GC/MS results for both “total target saturate hydrocarbons” and “total target aromatic hydrocarbons” were plotted over time and data were modeled using nonlinear regression. The overall (including abiotic and biotic) petroleum loss rates for the dispersed-oil treatments were not statistically different when compared to the oiled control. However, the initial concentrations for the dispersed-oil treatments were statically lower (95% confidence) than for the oiled control. From this, it can be inferred that the dispersed oil was more prone to flush off the sediments, as was visually observed. Biodegradation rates were also determined for all treatments; it was concluded that there were no differences when comparing each dispersed-oil treatment to the oiled control. The sediments from each plot were also analyzed for microbial population numbers (most-probable-number) and acute toxicity (Microtox ® 100% Test). Statistical analyses for both sets of data found no significant differences for the dispersed-oil treatments when compared to the oiled control.

MODIFICATION OF THE DISPERSANT COREXIT®9500 FOR USE IN FRESHWATER

ABSTRACT Recent inland spills in Latin America have generated interest in dispersant use for freshwater oil spills. However, oil spill dispersants primarily are formulated for use in marine waters. Dispersants that are designed for saltwater use show reduced effectiveness when applied in freshwater. The effectiveness of COREXIT® 9500 in low salinity waters varies with the type of oil, the dispersant-to-oil ratio (DOR), and other factors. The effectiveness of COREXIT® 9500 can decrease markedly at salinities of 15 ppt or less. The authors observed an increase in effectiveness of COREXIT® 9500 in freshwater when the dispersant was blended with an inorganic, divalent salt, such as calcium chloride, prior to use (patent pending). COREXIT® 9500* refers here to the blend of the salt and dispersant. The Exxon Dispersant Effectiveness Test (EXDET) was used to evaluate dispersant performance in deionized water and in river water samples from Rio de la Plata, Argentina. COREXIT® 9500 showed 22% effectiveness on Alaska North Slope (ANS) crude oil in deionized water, a value indicative of poor effectiveness. Depending on the amount of calcium chloride added, COREXIT® 9500* showed up to 63% effectiveness on ANS crude oil in deionized water, which indicates good effectiveness. The effectiveness of COREXIT® 9500* and COREXIT® 9500 was compared for three additional crude oils both in deionized water and in river water. In all cases, the effectiveness of COREXIT® 9500 was lower compared with COREXIT® 9500*.