OIL SPILL CLEANUP

Introduction to Oil spill cleanup, cont.

II. Recovery of oil

Once an oil spill has been contained, efforts to remove the oil from the water can begin. Three different types of equipment/materials are commonly used to recover oil from the waters surface and shorelines; skimmer, adsorbents, and absorbents.

Oil Spill Cleanup Skimmers

A skimmer is a device for the recovery of spilled oil from the waters surface. Skimmers may be self propelled and may be used from shore or operated from vessels. The efficiency of skimmers depends on the weather conditions. In moderately rough or choppy water, skimmers tend to recover more water than oil. Three types of skimmers -weir, oleophilic, and suction - are described below. Each type offers advantages and drawbacks, depending on the type of oil being cleaned up, the condition of the sea during cleanup efforts, and the presence of ice or debris in the water.

Oleophilic (oil attracting) skimmers use belts, disks, drums or continuous mop chains of Oleophilic materials to blot the oil from the waters surface. The oil is then squeezed out or scraped off into a recovery tank. Oleophilic skimmers have the advantage of flexibility, allowing them to be used effectively on spills of any thickness. Some types, such as chain or rope-mop skimmers, work well on water that is choked with debris or rough ice.

A suction skimmer operates like a household vacuum cleaner. Oil is sucked up though wide floating heads and pumped into storage tanks. Although suction skimmers are generally very efficient, they are vulnerable to becoming clogged by debris and require constant skilled observation. Suction skimmers operate best on smooth water where oil has collected against a boom or barrier.

Oil Spill Cleanup Sorbents (Adsorbents/Absorbents)

Sorbents are materials that soak up liquids. They can be used to recover oil through the mechanisms of absorption and adsorption, or both. Absorbents allow oil to penetrate into pore spaces in the material they are made of, while adsorbents attract oil to their surfaces but do not allow it to penetrate into the material. To be useful in combating water born oil spill cleanups, sorbents need to be oleophilic and hydrophobic (water repellent). Although they may be used as the sole cleanup method in small spills, sorbents are most often used to remove the final traces of oil, or in areas that cannot be reached with skimmers. Once sorbents have been used to recover oil, they must be removed from the water and properly disposed of on land or cleaned for reuse. Any oil that is removed from the sorbent materials must also be disposed of or recycled.

Sorbents can be divided into three basic categories: natural organic, natural inorganic and synthetic. Natural organic sorbents include peatmoss, straw, hay, sawdust, ground corncobs, feathers, and other carbon-based products. They are relatively inexpensive and generally readily available.

Organic sorbents can soak up 3 to 15 times their weight in oil, but they do present some disadvantages. Some organic sorbents tend to soak up water as well as oil, causing them to sink. Many organic sorbents are loose particles, such as sawdust, and are difficult to collect after they are spread on the water.
Natural inorganic sorbents include clay, perlite, vermiculite, glass, wool, sand, and volcanic ash. They can absorb from 4 to 20 times their weight in oil. Inorganic substances, like organic substances, are inexpensive and readily available. Most organic materials can only be used on land and are not adaptable to water use for and oil spill cleanup.

Synthetic sorbents include man-made materials that are similar to plastics, such as polyurethane, polyethylene, polypropylene, and nylon fibers. Most synthetic sorbents can absorb as much as 70 times their weight in oil. Synthetic sorbents that cannot be cleaned after used can present difficulties because they must be stored temporarily until they can be disposed of properly. They are best suited to absorb lighter viscosity oils that can perpetrate or wick into its fiber.

The following characteristics must be considered when choosing sorbent for oil spill cleanups:

Rate of Absorption or Adsorption - The rate of absorption varies with the thickness or viscosity of the oil.
    Light oils are soaked up more quickly than heavy ones. Adsorbents must provide maximum surface
    area to be effective for heavier oils.

Oil retention-the weight of recovered oil can cause a sorbent structure to sag and deform. When it is
    lifted out of the water, it can release oil that is trapped in its pores. During recovery of absorbent
    materials, lighter, less viscous oil is lost through the pores more easily those heavier more viscous oils.
    The more viscous oils tend to adhere to the surface more then absorbing into the material.

Ease of application-sorbents may be applied to spills manually or mechanically, using blowers or fans.
    Many natural organic sorbents that exist as loose materials such as clay and vermiculite are dusty, and
    difficult to apply in windy conditions, and are potentially hazardous if inhaled.

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