Evaluating the efficiency of using dispersant in dealing with oil pollution at sea ارزيابي ميزان كارايي استفاده از مواد ديسپرسنت در عمليات مقابله با آلودگيهاي نفتي- Maryam Rasooli-Atran Group

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Dispersants are products used in oil spill response to enhance natural dispersant  microbial degradation, a naturally occurring process where microorganisms remove oil from the environment. All environments contain naturally occurring microbes that feed on and break down crude oil. Dispersants aid the microbial degradation by forming tiny oil droplets, typically less than the size of a period on this page (<100 microns), making them more available for microbial degradation. Wind, current, wave action, or other forms of turbulence help both this process and the rapid dilution of the dispersed oil.

The increased surface area of these very small oil droplets in relation to their volume makes the oil much easier for the petroleum-degrading microorganisms to consume. The reason for using dispersants, either on floating oil or by subsea application, is the same: to minimize the overall ecological and socio-economic damage, by preventing the released oil from drifting into near shore or coastal habitats and onto the shore.

Dispersant use on floating oil breaks the surface slick into many small oil droplets that are dispersed, rapidly diluted and subsequently biodegraded in the upper layer of the water column. Subsea dispersant use aims to prevent the oil released subsea from reaching the sea surface by dispersing the oil into the water close to the release. This provides a major health and safety benefit by greatly reducing the exposure of personnel responding near the release site to volatile organic compounds (VOCs).

Adding dispersant to the released oil and gas subsea causes a greater proportion of the released oil to break into small oil droplets that will be dispersed, diluted and biodegraded in the water column, unlike the larger oil droplets that will float up to the sea surface. The surfactants in the dispersant greatly reduce the oil/water interfacial tension that exists between oil and water and this permits the turbulence associated with a subsea oil and gas release to convert a greater proportion of the released oil into small oil droplets.

The potential toxicity of existing chemical dispersants on the marine environment has motivated the search for environmentally friendly dispersants with excellent dispersion ability

                Keywords: Dispersant, Seawater, oil spill, response, biodegradability, marine life

 Introduction

Dispersants are chemical agents or biological products used to mitigate the petroleum hydrocarbon contamination in case of accidental oil spills at sea. They break spilled oil into small droplets that are transferred from the sea surface to the water column.Their dispersion by waves and wind action and the natural degradation process by bacteria may prevent serious damage to coastal are as and marine life.

The aim of dispersants’ use is to facilitate the dispersion of spilled oil in the water column, thus preventing oil from reaching the shorelines. Today’s products are less damaging for the environment than the toxic solvents used in earlier spills, but their toxicity is still not negligible, especially when products are used in large quantities

In recent years, the use of dispersant has been an issue of renewed attention within the EU countries and some have established national policies to authorise products’ use at sea. The approval procedures differ among the EU countries: most countries require an ecotoxicological assessment of dispersants products (France, Greece, Italy, Norway,Spain),

but only in the United Kingdom dispersant toxicity is tested on a mixture of chemically dispersed oil and it is compared to that of mechanically dispersed oil Most of the studies are related to short-term (≤ 96 h) biological effects of dispersants and fewdata are available on long-term toxicity on marine organisms.

The 2010 Deepwater Horizon (DWH) oil spill released an estimated 731 million liters of crude oil into the Gulf of Mexico. Inresponse to the incident, approximately 7.9 million liters of chemical dispersants Corexit EC9500A (6.8 million liters) and Corexit 9527A (1.1 million liters) were applied on the sea surface and at the wellhead.

Classification of Dispersants

Dispersants are classed according to their generation and type

  • The first generation of products, introduced in the 1960’s, was similar to industrial cleaners and degreaser with high aquatic toxicity. First Generation Dispersants are no longer used in oil spill response
  • Second generation dispersants, also called Type I dispersants, were explicitly designed to treat oil spills at sea by spraying from a boat. They contain a hydrocarbon solvent with a low or no aromatic content and typically 15 to 25% surfactant.
  • These Generation dispersants are intended to be applied undiluted
  • Third generation dispersants contain a blend of two or more surfactants with glycol and light petroleum distillate solvents. The most common surfactants used are non-ionic and anionic. The concentration of surfactant with the solvent lies between 25% and 65% and tends to be higher than with Type I products

Types of Oil dispersants

There are two major types of dispersant

1) Conventional type

The conventional type dispersants are the mixture of non-aromatic hydrocarbons solvents & mostly used for shoreline clean up. They are used undiluted at the time of application, and the quantity of dosage of this type of dispersant is kept between the range of 30-100% / oil spill quantity.

2) Concentrate type

A concentrated dispersant is more popular because it is much easier to handle and deal with concentrated products. This dispersant consists of the mixture of oxygenates like glycol and non-aromatic hydrocarbon.

They can be used after diluting, but the latest concentrated dispersants (3rd generation) can be used undiluted from the ship as well as from aircrafts. The dosage of concentrated dispersants drastically reduces to 5-15 % of dispersant/oil quantity.

Different Oil Dispersing Products

BIODISPERS: Formerly known as PETROBIODISPERS is an Oil Dispersant manufactured by Petrochemical America Corporation. It is a Non-flammable dispersant, with an effectiveness of approximately 51% and 63% of Prudhoe Bay Crude and South Louisiana Crude respectively.

The most effective method of application is by aircraft, fireboat monitors or similar apparatus. The shelf life of the product is unlimited if kept in a closed container. The solvent dispersant is Water, and the Surface-Active Agent is kept Confidential by the Company.

DISPERSIT SPC 1000: Also known as SEACARE is manufactured by U.S. Polychemical Corporation. It is a Non-flammable, Non-hazardous and possesses an unlimited shelf life if kept in a closed container. SEACARE uses non-petroleum based solvents, and Surface Active Agents are anionic and non-ionic.

The product has a significant effect on fresh and brackish water. Well suited mode of application is either by aerial spraying or by boat spraying.

Nokomis 3-AA and 3-F4: Developed by Mar-Len Supply, Inc. in 1971, Nokomis 3-AA is water based colloid and can be applied through spray nozzles on workboats or ships in such a way so that the propeller helps in mixing the product into the water for the maximum outcome.

It is a biodegradable and non-polluting cleaner, which requires no special handling procedures. It has a shelf life of 15 years or more, if stored correctly and is also considered to be Non-hazardous. The overall effectiveness is 65% and should be applied undiluted.

Later, a new product Nokomis 3-F4 was developed with the same physical and chemical properties other than its viscosity. Increased viscosity increases the chance that the full product will reach the water surface.

SAF-RON GOLD: Manufactured by Sustainable Environmental Technologies, Inc., Atlanta, this oil dispersant has an average effectiveness of 69% and has an unlimited shelf life when kept in a closed container. It can be applied to either a boat or an aircraft. It is non-flammable and is used in diluted form.

MARE CLEAN 200: Formerly known as MARE CLEAN 505, it is manufactured by Ichinen Chemicals Co., Ltd, Tokyo. It is a solvent-based dispersant with solvents as Paraffinic hydrocarbons and the mixture of sorbitan fatty acid esters, polysorbates, and polyoxyethylene fatty acid esters as Surface Active Agent.

The Average effectiveness is 74% and is non-flammable. Though the performance of MARE CLEAN 200 is not affected by water salinity, at temperatures below 40°F or in case of a substantial crude oil spill, MARE CLEAN 200 should not be used without dilution.

NEOS AB3000: A product of NEOS Company Limited, it has a shelf life of five years and should be kept away from open flames, as it is flammable. With an average effectiveness of 55%, it is useful in fresh as well as brackish water.

Along with crude and residual heavy oil, NEOS AB3000 is also effective at controlling volatile emissions from the oil. It is a Hydrocarbon based Solvent and Non-Ionic and Cationic surfactants as Surface Active Agent.

SEA BRAT 4: It is a non-toxic, non-flammable, non-pathogenic oil dispersant manufactured by B.R.A.T. Microbial Products Inc. For efficient dispersion, the affected area should be sprayed with a high-pressure pump with a pressure of 80 psi and 100 psi.

It has propylene glycol as solvent and surfactants as Surface Active Agent. The average effectiveness of the dispersant is 57%, and it possesses a shelf life of an indefinite time when stored properly.

It has propylene glycol as solvent and surfactants as Surface Active Agent. The average effectiveness of the dispersant is 57%, and it possesses a shelf life of an indefinite time when stored properly.

JD-2000: Manufactured by GlobeMark Resources Ltd., Texas, this product shows an outstanding performance than its competitors. It is free of phosphates, aromatic chlorinated solvents, branched ethoxylated alcohols, and hydrotreated distillates.

It shows an average effectiveness of 69%. JD-2000 is considered to be the least toxic among other available Oil Dispersants. With a shelf life of 1 year in an open container, it is proven to decrease mortality rates and increase photosynthesis of plants contaminated with oil.

Special Mention- COREXIT 9500 and 9527: Nalco Holding Company, associated with British Petroleum and Exxon produced a product line of Oil Dispersants, which was named as COREXIT. It is applied either by spraying from ships or by aerial spraying directly onto the Oil Slick. 2-Butoxyethanol and a proprietary organic sulfonate with a small concentration of propylene glycol are the main components of Corexit 9527.

The production of Corexit 9527 was discontinued in 2002 as the main component of the product has caused cancer and infertility in animals, and long-term exposure caused respiratory, nervous system, liver, kidney and blood disorders in Human Beings.

Detail and concentration of all the components are not being revealed to the public, as NALCO considers such information as a trade secret. These two were the mainly used Oil Dispersant by British Petroleum in the Deepwater Horizon Spill, 2010.

2.Dispersent approval

Dispersant product approval describes the process and criteria which a product has to fulfil for being approved for use according tonational rules, and thus be in principle acceptable for use in national waters. It has to be noted that this product approval is distinct from a dispersant use authorisation, which refers to specific conditions (where, when, under what circumstances) or a specific event where an approved product is actually authorised

Different approaches for product approval in Europe were established in France, the United Kingdom, and Norway. The objectives are similar: approve efficient products with low toxicity. However, tests and approval criteria could not be harmonized in the past. Dispersants of the latest generation generally are more efficient and less toxic to aquatic organisms than the former products.

With modern dispersants,the concern of toxic effects has thus shifted from the products themselves to the toxicity of the dispersed oil. Testing dispersants with all kinds of mineral oils within an approval procedure is not feasible. The UK therefore went for a standardised “typical” mineral oil type whereas in France, only toxicity of the dispersant alone is tested.

French experts argue that information on toxic effects of the dispersed oil are not indispensable for approval and would be better integrated in the NEBA as they depend on the specific type of oil spilled. It was concluded that the different approval procedures in France and in the UK did not result in approvals of significantly different dispersant products. A number of products are accepted under both approaches and are thus covered by stocks offered by the EMSA for European use.

3.Laboratory Effectiveness Tests

Bench-scale testing continues to be widely used to evaluate the performance of dispersants and the physical and chemical mechanisms of oil dispersion.A major disadvantage is that it is difficult to scale the results of these tests to predict performance in the field. Several factors that are difficult to extrapolate include energy regimes, dilution due to advection, and turbulent diffusion.

Bench-scale tests are very useful for determining the effectiveness of various dispersant oil combinations, salinity, temperature effects, effects of oil composition, and effects of oil weathering. It has been noted that many of the current tests are too energetic, for they yield results well above those obtained in older field tests.

Effectiveness remains a major issue associated with oil spill dispersants. It is important to recognize that many factors influence dispersant effectiveness, including oil composition, sea energy, state of oil weathering, type of dispersant used and the amount applied, temperature, and salinity of the water. The most important of these factors is the composition of the oil, followed closely by

sea energy and the amount of dispersant applied. Effectiveness issues are confounded by the fact that various tests show highly different results depending on how they are constructed and operated. Detailed scientific examination of most effectiveness tests shows major deficiencies.

Emphasis should be on real results from real spills. Tank testing continued at high levels during the review time period. Tank testing technology still lags the many recommendations put forward by the NAS committee and others. Since these recommendations were not followed, reviews of these particular tests were not given here. Analytical means continues to be a major concern for effectiveness testing. It is

very clear that only careful GC/MS techniques produce a correct result answer Few analytical methods can be used outdoors or in field situations. Very early in the field testing program, fluorometers were used. Studies then show that because the amount and distribution of PAHs, the target compound for fluorometers,change with time during the course of a chemical dispersion event,a fluorometer can never be truly “calibrated” for a particular oil and dispersant combination.

The invalid colorimetric analytical method also continues to be used in a few cases for laboratory tests.

4. Environment-friendly Oil Spill Dispersant

Since 1960s, the international community started the research and development of chemical oil spill dispersant.

In 1967, a great volume of oil spill dispersant was used to handle the spilled oil from the Torrey Canyon oil spill

accident; due to its high toxicity, the oil spill dispersant severely damaged the marine ecological environment.

Hence, many scholars began to focus on the researches of low-toxic oil spill dispersant. For the first generation of products, the major component is anionic surfactant and the major solvent light aromatic hydrocarbon; for the second generation, the major component is nonionic surfactant with lower toxicity (mainly ether surfactant);

for the third generation of concentrated products, its D-sorbite, fatty acid, and other raw materialscome from agricultural and sideline products, and the solvent is polyethylene glycol so that the oil spill dispersant products are much less toxic. Generally speaking, the oil spill dispersant products have undergone three development stages by types of surfactant and solventText describing, say, the experimental observations, the experimental conditions etc. typically would follow the introduction.

Here we use this part of the paper to give an example of a table within the text, together with recommended spacing before and after: In view of this situation, we launched the research on new efficient environment-friendly oil spill dispersant by starting with the international exploration focus-biosurfactant and its application. Firstly, we chose and cultured high-yielding strains of biosurfactant in addition to sampling bed mud and water body.

After fermenting these strains, we extracted biosurfactant with high emulsification performance. According to the main assessment indicators such as emulsification rate, biotoxicity and biodegradability, and through designed orthogonal experiment,we determined the oil spill dispersant formula dominated by biosurfactant.Currently, the test over the efficient environment-friendly oil spill dispersant developed by us performed by

the North China Sea Environmental Monitoring Center, State Oceanic Administration shows that its performance indicators meet relevant national standards. This oil spill dispersant can be used in oil spill accidents by domestic offshore oil platforms, ports and vessels and has a very promising application prospect.

Another way to make dispersants more environmentally friendly is by making them more efficient so that less of them are needed to clean up a spill. One group of researchers from C-MEDs is trying to do just that by using naturally-occurring clay particles made up of tiny hollowed-out tubes.

With a diameter of about 20 nanometers (1/1000th the size of a human hair), each tube is filled with the soap-like component of dispersants. When added to a spill, they attach to the interface of oil and water and then release the dispersant into the water slowly, similar to time-release medicines that gradually provide relief over a period of time. Perhaps counterintuitively, this method may require less dispersant overall.

When using faster-working dispersants like Corexit, workers apply large quantities to ensure that it reaches all of the spilled oil before washing away. The clay particle dispersant, however, will stick with the oil and water interface for a longer time, ensuring that dispersant is released in the correct area.

5.Conclusions

The basic nature of dispersants, like any other surfactant, is the resulting product, or the dispersion in the water column is not stable and over time the dispersed oil will resurface to an oil slick. This is the ultimate stable state. The half-lives of oil spill dispersions are estimated to vary between 12 to 24 hours.The prime motivation for using dispersants is to reduce the impact of oil on shorelines.

To accomplish this reduction, the dispersant application must be highly successful and effectiveness high. As some oil would come ashore and much would resurface within a few hours, there is much discussion on what effectiveness is required to significantly reduce the shoreline impact.

A major issue that remains is the actual effectiveness during spills so that these values can be used in estimates for assessment and models.The second motivation for using dispersants is to reduce the impact on birds and mammals on the water surface. As the NAS committee on dispersants notes, little or no research on this matter has been carried out since the 1980s. The benefits or deleterious effects of using dispersants to reduce impacts on wildlife still remain unknown.

The third motivation for using dispersants is to promote the biodegradation of oil in the water column. The effect of dispersants on biodegradation is still a matter of discussion. There are a number of contradictory papers stating that dispersants inhibit biodegradation, whereas others indicate that dispersants have little effect on biodegradation.

The most recent papers, however, confirm that the surfactants in some of the current dispersant formulations can either inhibit or leave biodegradation unaffected.No recent study has shown that dispersants clearly enhanced biodegradation.Furthermore, there are issues about the biodegradability of the surfactant themselves, and this fact can confound many tests of dispersed oil biodegradation.

As the NAS committee pointed out, older tests that may have shown enhanced biodegradation with dispersants were flawed in that they were conducted under high nutrient conditions and in times that were not representative of oceanic conditions.1 An important issue that is rarely discussed is that oil-degrading bacteria largely live on the water surface,where they would feed on similar natural hydrocarbons in the absence of spills.

Another serious question is that of timescale. Biodegradation takes place over weeks, months, and years compared to dispersion half-lives of 12 to 36 hours

Dispersants are chemical agents (similar to soaps and detergents) that help break up an oil slick into very small droplets, which dilute throughout the water. While this does not remove the spilled material, smaller oil particles are more easily biodegraded and it provides a measure of protection for sensitive habitats threatened by a surface slick. Dispersants are sprayed onto spills by specially equipped boats or planes.

All environments contain naturally occurring microbes that feed on and break down crude oil. Dispersants aid biodegradation by forming tiny oil droplets, typically less the size of a period on this page (<100 microns), making them more available for microbial degradation. Wind, current, wave action, or other forms of turbulence helps this process.

The increased surface area of these very small oil droplets makes the oil much easier for the petroleum-degrading microorganisms to consume. Subsea dispersant injection is a novel technique that was used during the Deepwater Horizon oil spill response effort. This technique played an important role in not only protecting the environment but also the health and safety of workers in vessels attempting to contain the well. Industry plans to incorporate this tool in response strategies for deepwater wells.

To support its use, API and its industry companies have developed a large-scale, multiple-year Subsea Dispersant Program to conduct controlled experiments. The Program will study the effectiveness of subsea injection over a range of conditions, the effects of dispersed oil on deepwater marine environments, numerical modeling upgrade needs that are necessary to better predict the fate of oil treated with dispersant and released from a deepwater well, and monitoring tools that could be used to determine the effectiveness of subsea injection during an event.

Lessons learned from operational teams of the Deepwater Horizon response incident regarding targeting and application capabilities suggest that there were many complications to dispersant use that surrounded application. A project team formed to review dispersant surface application techniques and processes in order to validate safety margins and promote the use of as little dispersant as necessary to disperse the oil.

Acknowledgments

This paper was scientifically an financially supported by Ports and Maritime Organization (PMO)

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