Oil Spill Dispersants Research Articles

Droplet size distributions in chemical dispersion of oil spills: Towards a mathematical model

The results of a series of chemical dispersion tests are presented, in which three crude oils (Gullfaks, Statfjord and Arabian heavy), each at 4 states of weathering, have been dispersed at 13°C with two dispersants (Finasol OSR-5 and OSR-12) using three laboratory tests (Warren Spring Rotating Flask — WSL test, Institute Français du Pétrole flow test — IFP test and MackayNadeau—Steelman — MNS test). Effectiveness and dispersed oil droplet size distributions in the different test methods have been studied and an attempt has been made to develop correlation or mathematical models of the chemical dispersion phenomena. This mathematical treatment helps to explain the reasons that the tests give different results, but it is concluded that, at present, our understanding of the basic dispersion phenomena is not sufficient to form a basis for a reliable model. Several modelling approaches are discussed in the hope that as further data and insights become available, reliable models may be developed to describe this complex process.

Effect of salinity on biodegradation of oil spill dispersants

Biochemical oxygen demand and riverwater biodegradation tests of oil spill dispersants were determined at three sodium chloride concentrations—0, 20, and 40 g/L—and at ambient temperature. Surfactant concentration was monitored by infra red spectroscopy. Results obtained indicated that microbial degradation of all the dispersants used in the study decreased with increasing salt concentration.

LABORATORY TESTING OF DISPERSANT EFFECTIVENESS: THE IMPORTANCE OF OIL-TO-WATER RATIO AND SETTLING TIME

ABSTRACT Laboratory tests and apparatus for oil spill dispersant effectiveness were the subject of the present study. A review of previous work shows that test results from different apparatus are not highly correlated, and often the rank of effectiveness is also not correlated. The effect of two experimental parameters—settling time and oil-to-water ratio—are examined in this study and found to be very important in determining final effectiveness value. Four apparatus—the swirling flask, the flowing column, the Labofina, and the Mackay—are used with 3 dispersants and 16 oils to examine effectiveness values when the oil-to-water ratio is the same (1:1,200) and when the settling time is maintained at the same value (10 minutes) in all apparatus. The effectiveness values resulting from the four devices are nearly identical after values from the more energetic devices are corrected for natural dispersion. Our conclusions are that the most important parameters of laboratory dispersant testing are settling time and oil-to-water ratio. Energy is less important than previously thought and is important only to the extent that when high energy is applied to an oil-dispersant system, dispersion is increased by an amount related to the oil's natural dispersibility.

STUDY OF OIL-IN-WATER DISPERSION USING A DYNAMIC TURBIDIMETER

ABSTRACT A new laboratory method using a turbidimetric technique has been developed to study basic oil-in-water dispersion processes and oil spill chemical dispersant effectiveness. A simple dynamic turbidimeter was interfaced to a microcomputer, and rates of oil dispersion and oil droplet resurfacing were recorded and correlated to experimental parameters such as oil-to-water ratio and dispersant-to-oil ratio. The new technique was found much more sensitive than classical effectiveness methods and experimental results were in excellent agreement with a mathematical model developed a few years ago to predict oil spill dispersant effectiveness. The method was also found very useful for studying dispersant formulation.

Microemulsion Performance Fluids

ABSTRACTMicroemulsions are thermodynamically stable mixtures of two immiscible fluids, such as oil and water, and one or more surfactants or cosurfactants. These systems have a rich micro-structure and phase behavior which can take the form of a variety of multi-phase and single phase oil- or watercontinuous or bicontinuous fluids with unique and useful properties. The thermodynamic stability, ultra-low interfacial tension, clarity, high solubilization capacity and high interfacial area suggest uses “performance fluids.” The relationship between surfactant ussetsru cfotur reth eansde the phase behavior and properties of microemulsions is the key to their design. Through the proper selection of surfactants, microemulsion phase continuity can be tailored for a variety of applications. Two such applications, coal freeze conditioning and oil spill dispersion, are described in this paper.

Real-time application of an oil spill movement prediction system

This paper deals with the prediction, in real time, of the motion of experimental oil slicks. The experiments were conducted during September 1983 offshore near Halifax on the east coast of Canada. The objectives of the experiments were (i) to determine the suitability of oil spill dispersants as countermeasures and (ii) the testing and verification of oil spill trajectory models and systems.

The effect of crude oil and oil spill chemicals on nitrogen fixation in the cyanobacteria Nostoc sp.

The effects of crude oil and three oil spill dispersants (Corexit 9600, 9550 and 7664) on nitrogenase activity in the cyanobacteria Nostoc sp. were examined. The addition of oil to Nostoc sp. cultures resulted in a catastrophic decline in nitrogenase activity with activity ceasing 7 h after treatment. The addition of a dispersant with the oil did not ameliorate this effect. Cultures exposed to high concentrations of dispersants showed lower rates on nitrogenase activity than untreated cultures. However, it is unlikely that dispersant concentrations of this magnitude would occur in the field. At the lowest concentration tested, which approximates the manufacturer's recommended application rate, the effects of the dispersant appear to be negligible.

The effects of oil spill chemicals on CO 2 assimilation by the fruticose lichen Cladina mitis

The effects of three oil spill dispersants (Corexit 9600, 9550 and 7664) on carbon fixation by the fruticose lichen Cladina mitis were examined in order to provide insights into the potential risks associated with dispersant use in and around freshwater systems. Cladina is a common plant of northern freshwater shoreline communities. Treatments with the undiluted dispersants inhibited rates of carbon fixation by 60% to 80% and bleached portions of the thalli when applied at doses less than 10 mg g −1 dry weight (approximately 2·5 mg cm −2 on an aerial basis). Since the recommended field application rates for the dispersants range from 0·2 to 3 mg cm −2, there is a distinct possibility that misapplication (direct spraying) may be detrimental to populations of Cladina. However, the inhibitory effects were not lethal in all cases and partial recovery of the lichens was noted within 3 weeks after treatment. The potential impact of dispersant use in freshwater systems on the shoreline plant communities is discussed in the light of our findings.

A study of chemicals to inhibit emulsification and promote dispersion of oil spills

As a result of a 2-year program involving bench-scale, small-scale, and mesoscale testing a new class of oil spill treating agents has been identified. These agents, called emulsion inhibitors, are highly oleophilic surfactants, which, when applied onto oil spills in very low concentrations, not only prevent mousse formation for significant periods of time but also cause a large reduction in oil-water interfacial tension. Both of these promote the dispersion of the oil into the water column. The best chemicals to effect these results were found to be surfactants normally sold as oil spill ‘demulsifiers’ (that is, surfactants that ‘break’ oil spill mousses once collected). The best of these, a European-manufactured product, was found to prevent emulsification at dosages as low as one part inhibitor to 20 000 part of fresh oil at 20°C. At dosages of the order of 1: 1000, at temperatures higher than 10°C, the chemical also results in significant and rapid dispersion of the oil. For very low temperatures or highly weathered oil the performance of the chemical falls off sharply.

The use of oil-spill dispersants: Some views from the UK

The current use of dispersants in the UK is reviewed, with a brief consideration of historical background and views on desirable future developments. Contrary to the practice in many countries, their early application is favoured in the UK, where weather conditions and the properties of the spilt oil are appropriate. Development work is being conducted into procedures for their more effective use and for the achievement of greater application rates from aircraft.

ECOLOGICAL EFFECTS OF OIL VERSUS OIL PLUS DISPERSANT ON THE LITTORAL ECOSYSTEM OF THE BALTIC SEA

ABSTRACT The effects of a North Sea oil with or without the addition of dispersant were studied in a model of the littoral ecosystem of the Baltic Sea. Experiments were carried out in six pools with a volume of 8 m3 each, with flowthrough seawater and an ecosystem of the shallow rocky Baltic archipelago. All major fauna and flora were transferred into the pools in normal numbers and proportions. Two of the pools were exposed to oil alone. The amount of oil was equivalent to 20 ppm assuming total mixture. Two other pools were exposed to the same amount of oil and an oil dispersant (Corexit 9550, Exxon), and two pools served as controls. The effects studied were those on abundance of heterotrophic bacteria, periphyton photosynthesis, growth of bladder wrack, phytoplankton growth, zooplankton abundance and diversity, benthic fauna, physiological responses of certain crustaceans and molluscs, and the growth of blue mussels. In addition, the total photosynthesis and respiration of the ecosystem was studied. Concentrations of oil in water and in blue mussels were monitored. The experiments showed that almost all the measured parameters were affected. When comparing the effects between the pools, several of the results indicated a stronger response for oil alone compared to oil and dispersant. This was particularly obvious when monitoring the total production and respiration of the ecosystems. The explanation may be that the ecosystems in the pools exposed to oil and dispersant were exposed less time compared to those in the pools where oil alone was added. The oil and dispersant mixture obviously left the system much faster due to the water exchange compared to the oil without dispersant. In the latter case the oil adhered to surfaces and detritus and thus tended to stay longer in the environment. These results may provide valuable information for decision makers faced with an oil spill in shallow waters and who have an option to use oil spill dispersant.

REAL TIME APPLICATION OF AN OIL SPILL MOTION PREDICTION SYSTEM

ABSTRACT This paper deals with the prediction in real time of the motion of experimental oil slicks. These slicks were the subject of an oil spill experiment organized by the joint Government/Industry Canadian Aerial Applications Task Force. These experiments offshore were conducted during September 1983 near Halifax on the east coast of Canada, at 44°30′ N, 63°00′ W. The primary objective of the experiments was to determine the suitability of oil spill dispersants as countermeasures. A secondary objective was the testing and verification of oil spill trajectory models and systems. The Atmospheric Environment Service (AES) participated in the experiments to test the capability of its oil spill motion prediction system in providing real time trajectory forecasts. The AES system resident on computer facilities at the Canadian Meteorological Centre in Montreal was accessed through standard telephone lines, with appropriate output products available on a computer terminal near the experiment site. The experiment consisted of three sets of spills. Each set had a control slick and a test slick. Sixteen barrels of crude oil were used in each spill. The test slicks were used to test the effectiveness of various dispersants, the control slicks were used to verify trajectory forecasts. The spill trajectories and oil weathering information obtained from the system during the experiments demonstrated the relative ease with which the system could handle the required input and provide timely forecasts. The accuracy of these forecast trajectories was confirmed by observations, and their utility was demonstrated by their application in the operational decision making process.

PLANS FOR INTEGRATING DISPERSANT USE IN CALIFORNIA

ABSTRACT Since the early 1970s both the effectiveness and efficiency of oil spill dispersants have been improved while the toxicity of these chemicals has been reduced. Although a large body of research has been published in the last five years which supports these claims, there has been little experience with the use of dispersants in the United States. This lack of experience has been created, in part, by a cumbersome dispersant approval process and the reluctance of spill responders to invest in dispersants and related application equipment. The Region IX Regional Response Team has identified four prerequisites for effective use of dispersants: informed decision-makers; a functional decision-making process; coordinated contingency plans; and effective, region-specific application capabilities. This paper explores the approach taken by government and industry to fulfill these prerequisites. The goal of these efforts, which include sponsoring workshops, implementing a dispersant application test program, and requiring specific dispersant contingency planning efforts, is to fully integrate dispersants into the oil spill control efforts of the region.

An assessment of the Mackay apparatus for testing oilspill dispersants

The successful use of chemical dispersants for treating oilspills requires advance information of product effectiveness, such information being necessary for stock piling in contingency planning. Many existing quality tests are unrepresentative of the conditions at sea. Here, a new method of testing oilspill dispersants is described and compared with a standard Warren Spring Laboratory test for effectiveness. Results show that, although similar in its ability to rank dispersants, the Mackay test could also prove useful for observational work on dispersant/oil/water mixtures and control of mousse formation.

The drop-weight interfacial tension method for predicting dispersant performance

The drop-weight test is an improved interfacial tension method for predicting the relative effectiveness of oil-spill dispersant products. The test is based on the relationship between the weight of a drop of oil detached from a capillary beneath a dispersant-in-seawater solution and the lowering of the interfacial tension between oil and water. A modified test procedure, based on measuring the time for a drop detachment rather than the weight, significantly reduces the test time and simplifies the apparatus. Another modification permits the determination of relative diffusion rates of dispersants through an oil column. Seventeen water-based dispersant products were evaluated with light Arabian crude oil and, in some cases, with No. 6 fuel oil using the modified procedures. The results were interpreted in terms of data reliability and compared with information obtained by a standard test.

Toxicity testing of oil spill dispersants in South Africa

Prior to 1981, manufacturers of oil spill dispersants wishing their products to carry the South African Bureau of Standards (S.A.B.S.) mark of approval or to conform to the applicable S.A.B.S. specification had to have the testing undertaken in the United Kingdom. A new test was introduced in the United Kingdom in 1975, and this and several other tests in use worldwide are reviewed. After consideration of the requirements of a dispersant toxicity test, the necessary modifications for the South African situation are detailed. Results show that the test is comparable with those in use overseas as regards licensing purposes, but there are still basic research problems on dispersant use to be overcome.

PERFORMANCE EVALUATION OF A NEW VERSATILE OIL SPILL DISPERSANT

ABSTRACT Several oil spill dispersants available since 1975 have successfully dispersed spills of light to medium oils. However, they generally have performed poorly on heavily weathered oil, low gravity viscous oils, waxy crudes, “chocolate mousse” emulsions, and any oil spilled in cold environments. Some also were not formulated for use on waters of low salinity. In many cases involving spills of low viscosity oils, the decision to use chemical treatment has been delayed until the oil is in a weathered state. Chemical treatment under any of these conditions requires that the active surfactants reach the oil/water interface with the aid of a penetrating hydrocarbon solvent. Such formulations lose effectiveness when diluted with water (as in boat spraying) and usually must be used undiluted at a high dosage. They also often are too low in viscosity and density to be sprayed efficiently by aircraft. This paper discusses the properties and performance of formulations which avoid the above oil viscosity and water salinity problems and offer, for the first time, opportunity for widespread chemical treatment of such spills by aerial spray from large aircraft.

Toxicity testing of oil slick dispersants in Hong Kong

In Hong Kong, the toxicity of oil spill dispersants was assessed in a preliminary screening test, based upon TD 50 values in samples of ten fish. Later, an improved test was introduced, based upon new procedures developed in the United Kingdom and modified to suit conditions in Hong Kong. Products approved elsewhere were usually, but not always, approved in Hong Kong. Further work is needed to relate the test results to oil-spill damage in local waters.

THE USE OF DISPERSANTS ON VISCOUS FUEL OILS AND WATER IN CRUDE OIL EMULSIONS

ABSTRACT The various factors affecting the performance of oil spill dispersants have been studied in the laboratory using a simple test to emulsify the oil in the water. The observations have been confirmed by spraying oil onto the sea followed by overspraying with dispersant. It was found that viscosity of the oil or mousse was the main limitation that influenced the droplet size distribution. Energy of agitation had a minor effect but there was no evidence that the “self-mix” dispersants required less energy for adequate dispersion.

THE LABORATORY DETERMINATION OF DISPERSANT EFFECTIVENESS: METHOD DEVELOPMENT AND RESULTS

ABSTRACT A research project is described in which a previously devised effectiveness test for chemical oil spill dispersants was further developed and standardized. The principle of the test is that known volumes of dispersant and crude oil are contacted on the surface of seawater in a laboratory-scale vessel in which there is a circulating air current that imparts a swirling wave action to the water. This flow geometry is believed to simulate ocean surface conditions better than tests that involve shaking, stirring, or pumping as turbulence-generating mechanisms. From the results of a series of tests at various dispersant-to-oil ratios, the ratios that affect the dispersion of 50 and 75 percent of the original amount of oil added to the water surface are calculated and used as an indication of dispersant effectiveness. The corresponding percent of the oil that remains dispersed after settling is also deduced. The results of a series of tests using two crude oils, Murban (light) and La Rosa (heavy), and 17 dispersants are presented. These results show a wide range in the dispersant-to-oil ratio necessary to achieve 50- to 75-percent dispersion. Five products failed to achieve 50-percent dispersion of both crude oils at a dispersant-to-oil ratio of 0.2, which is regarded as the practical upper limit of dispersant dosage. There was a group of highly effective dispersants requiring a dispersant-to-oil ratio of only 0.005 to 0.007 to accomplish 50-percent dispersion. The test method can discriminate between two dispersant products with effectivenesses which differ by approximately 10 percent. The implications of these experimental results are discussed.