dispersant#Oil spill

Dispersants are mixtures of substances that are used to accelerate or facilitate the dispersion of oil spills in water. Thus, the oil is removed from the water surface, dispersed with correct application in relatively low concentrations in the water column and thus made available for oil- degrading microorganisms.

Composition

Dispersants consist of

• One or more surfactants which act as emulsifiers,
• A solvent and
• Stabilizers.

Generally contain at least two dispersing agents today surfactants with different HLB values ​​. The solvent comprises either or hydrocarbons is based on water-based and usually contains also alcohols, glycols or glycol ethers. The solvent allows the workability ( further dilution, spraying), and has great influence on the speed and completeness of the transport of the surfactants in the oil phase. It usually has the decisive impact on the ecotoxicity of a dispersant. Stabilizers are necessary to keep the dispersants long shelf life.

Application and results

Dispersants are applied directly to the oil, a dose corresponding to the film thickness is useful. Use of resources for application, depending on the extent of pollution and location of the installation site airplanes, ships or helicopters spraying or hand sprayers. Spread and thickness of oil spills at sea are recorded with specially equipped surveillance aircraft. The sinking of the Deepwater Horizon, a dispersant was brought to an oil discharge under water for use in 2010 for the first time.

For the actual dispersion of mechanical energy is also required. At sea it is applied by the wave energy so that the meaningful use a Mindestseegang is required. From ships but also otter boards can be used to a limited extent. In heavy seas, the use is also no longer makes sense, since the natural dispersion runs sufficiently fast. Other operating limits are water depth and exchange. Low water depths initially lead to higher oil and Dispergatorkonzentrationen, so that a higher toxic effect occurs. Where no adequate water exchange takes place, all of the oxygen can be consumed in water by the strong oxygen-depleting oil degradation. These factors are considered in Europe with the planning for oil spill response measures, yet another assessment of the circumstances of the individual case is always required in case of disaster, in which different consequences have to be weighed in the rule.

History

The first documented use of virtually identical even with industrial cleaners dispersants ( about 70 tons ) in 1966 with the sinking of Anne Mildred BROVIG by the Water and Shipping Authority Cuxhaven. Were first and last time more widely used these so-called first-generation dispersants at the wreck of the Torrey Canyon off Cornwall in 1967 with 117,000 tons of crude oil released. From 14,000 tons cleaner only 10,000 tons were used against 14,000 tons stranded oil. This use of very toxic agent led to extensive poisoning of marine life. The damage caused by the use were greater than they would have been by the oil. This led in the 1970s to develop the second generation of dispersants to the actual specific purpose of the oil spill, which was characterized by a greatly reduced toxicity. The ratio for oil in the application but was still 1:2 to 1:3. Developed by the end of the 1970s to the early 1990s, the third generation dispersants allow application with ratios 1:20 to 1:30 much longer periods of use inserted marine vessels and ultimately the most effective because of the large area coverage using aircraft. On ships to water- resources were first added in a ratio of 1:10 with sea water and then applied in the usual ratio. Highly viscous products are applied using specially developed spraying from aircraft in the undiluted state. As a successful example of the use of dispersants is considered the wreck of the Sea Empress in 1996 on the Welsh coast, where the amount of dispersed crude oil has tripled approximately opposite of exclusively natural dispersion with 446 tonnes of dispersant so that stranded from the released 72,000 tonnes of only about 4000 (about 40 % of the total amount evaporated, 1500 t were taken at sea).

Classification and approval

Second-generation dispersants are as type 1 still used. Type 2 and type 3 diluted referred undiluted dispersants applied to the third generation. Most products can be used either as Type 2 or Type 3 today. Require dispersants for use in most states an official authorization. In Europe this is demanded that its toxicity may not exceed that of the pollution to be controlled. The toxicity of the pollution must be also not significantly increased by mixing with the dispersant. In addition, the effectiveness is demonstrated.