Dispersants are chemicals that are sprayed especially on a surface oil slick. What dispersant does is to break down the oil into smaller droplets that are distributed or spread over a large volume of water which are more readily mix with the water. Dispersants do not reduce the amount of oil entering the environment, but push the effects of the spill underwater. Dispersant contain compounds such as surfactant that lowers the interfacial tension of molecules with both water-soluble and oil soluble component, which is been used in soap and detergent production.
While dispersants make the oil spill less visible, dispersants and dispersed oil under the ocean surface are hazardous for marine life.
Dispersants were being used in the BP oil spill to reduce the chance that the surface oil slick would reach shoreline habitats like marshes and mangroves or come into contact with animals at the surface. However, by mixing the oil below the water surface, dispersants increase the exposure of a wide array of marine life in the water and on the ocean floor to the spilled oil. Dispersants also decrease the ability to skim or absorb oil from the ocean surface.
Dispersant was used in an attempt to clean up the Exxon Valdez oil Spill in the year 1989, though its use was discontinued as there was not enough wave action to mix the dispersant with the oil in the water. Dispersant was also used on the Deepwater Horizon Spill at the Gulf of Mexico in 2010, recorded by The National Academies Press
CLASSIFICATION OF DISPERSANT
Dispersant are classified according to their generation and types
- The first generation of products, was similar to industrial cleaners and degreaser which contained components that where highly toxic to aquatic lives. First Generation Dispersants was introduced in the 1960’s and are no longer used in oil spill response
- Second generation dispersants, also called Type I dispersants, were majorly designed to treat oil spills at the sea by spraying dispersant from a boat. They contain a hydrocarbon solvent with a low or no aromatic content and also 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 the second generation/ Type I products.
TYPES OF DISPERSANT
1) Conventional Type
The conventional type of 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
Other Application of Dispersant.
Surface coating
In order to provide optimal performance, pigment particles must act independently of each other in the coating film and therefore must remain well dispersed throughout manufacture, storage, application, and film formation. Unfortunately, colloidal dispersions such as the pigment dispersions in liquid coatings are naturally unstable, and they must be stabilized against the flocculation that might occur.
Bio-dispersing
Dispersants are used to prevent formation of biofouling in industrial processes. It is also possible to disperse bacteria slime and increase the efficiency of biocides
Concrete
Dispersants are used in the mixing of sand, stone, cement and water to diminish the use of water and still exhibit the same slump (flow) property. This makes the concrete stronger and more resistant to water penetration.
Detergents
Dispersing is the major goal in the use of detergent, which the liquid bath is water. Detergents also are used as emulsifier in some applications. Laundry detergents eliminate dirt and grime, which naturally disperse.
Automotive
Automotive engine oil contain both detergents and dispersants. Metallic-based detergents prevent the accumulation of varnish like deposits on the cylinder walls,they also neutralize acids. Dispersants maintain contaminants in suspension.
Dispersants are also added to gasoline to prevent the buildup of sticky residues
Gypsum wallboard
A dispersant is added to the gypsum wallboard slurry to reduce the amount of water used. The lower water usage allows lower energy use to dry the wallboard.
Process industry
In the process industry, dispersing agents are added to process liquids to prevent unwanted deposit by keeping them finely dispersed.
Oil drilling
In oil drilling, dispersants aid in breaking up solid or liquid into fine particles or droplets into another water medium.
Factors that Determine the Quantity of Dispersant used are;
Type of oil in the spilled surface
Quantity of oil
Time the oil spill incident happened
Distance from the shore
Weather Condition
Marine environments and marine organism in the area of oil spill
Advantages of using Dispersant
- They can be used in stronger current and in rough seas; it removes the water from the surface, and reduces contamination of water birds and marine animals.
- It stops the carryover of oil by the wind to the shoreline and beaches.
- It is one of the quickest methods in fighting oil spillage. It restricts the formation of an oil-water emulsion.
- Dispersion does not produce wastes to be disposed.
- When dispersed, the pollutant is no longer drifted by the wind, and then follows the stream; therefore, when carried out upwind sensitive areas, dispersion contributes to reduce the amount of pollutant which would drift towards these locations.
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