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is a serious problem in petroleum producing communities. Crude and refined petroleum are accidentally and sometimes intentionally released into water from many sources, but the common sources are: normal off-shore operations of prospecting for and extracting crude oil; release of contaminated wash waters from ships and pipeline; and storage tank leak.
Effect of oil spills - the environmental effect of oil spills depends on (i) type of oil (2) amount released (3) distance of release from shore (4) time of year (5) weather condition (6) average water temperature (7) ocean current. Volatile organic compounds (i.e. hydrocarbons) immediately begin to kill aquatic life, resultant “tar-like globs” float on the surface and coat birds and coastlines, block breathing organs of aquatic animals and raise the temperature.
Methods of Cleaning Oil Spills
There are four common methods (out of many) for cleaning oil spills. They include: containment and recovery; dispersal; bio-remediation; and burning. Notice that these methods do not end-up polluting the water adversely (therefore, any technique that could seriously pollute the water is not encouraged).
1. Containment and recovering (Mechanical method) - This is usually the first measure used to attempt to clean up after an oil spill. Long, floating plastic or rubber barriers called booms are placed around the floating oil slick. These act as fence to contain the oil and prevent it from spreading or moving towards a shoreline. Once contained, some of the oil can be removed by various type of “skimmers.”
Vacuum skimmers work well in calm water and are used to suck the oil out of the water and into storage tanks. In choppy waters floating disk and rope skimmers can be passed through the oil. The oil sticks to these skimmers and is scrapped off later. Absorbent materials such as talc, straw and sawdust can also be added to the oil slick and then removed when they have soaked up some of the oil. Absorbent removal can work in choppy or fast moving water, but this method is slow and expensive.
2. Dispersal (Chemical method). Chemical dispersants are added to the spill to break up the oil slick into millions of small globs of oil - these are more easily dispersed and carried out to sea than a coherent slick. Rather than removing the oil, dispersants tend to spread the effect of oil spill over many different ecosystems.
3. Bio-remediation. Adding microbes (i.e., aerobic bacteria) and fertilizers to the affected areas is another method of cleaning up oil spills. This process work best when the oil has washed up on the shore, rather than in deep water situations. Notice that this method can best be used to clean farmlands affected by crude oil spillage.
4. Burning. This method involves the burning off of the layer of oil from the water. It spreads (i.e. disperses) the effect of pollution to wide areas, more than removing it.
5. Spraying with hot water - This method is used to clean the spills only when the oil has reached the beach (the oil will eventually reach the beach). Water at a high temperature (about 140oC) can be sprayed on the oil to remove it from the beach, and wash it back into the water. Once it returns to the water it can be scooped up by the booms mentioned above.
Note: - Use of detergents - detergents may also be used. This is because detergents break the oil into a sheen which can be broken down naturally. However, they have to be used as soon as possible because
when the oil comes in contact with sea water it changes chemically and physically.
Oil is made of many organic compounds. Some of these evaporate. What remains mixes with the sea water and becomes a brown, mousse - like substance. Detergents are useless at breaking it down at this state. In addition, detergents add much pollution to the water. For the above reasons detergents are not commonly used at cleaning oil spills.
- A combination of any of the methods discussed above can be used to clean- up oil spills.
- Most coastal systems recover from crude oil spills within 3 years, but from refined oil spills, recovery takes 10 years, with recovery time increasing as temperature decreases.
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