gh PURIFICATION OF OIL-CONTAMINATED AREAS

The oil and oil products are the most frequent biosphere contaminators. The oil-contaminated soil is purified with the help of special microbes, which decompose the oil. The soil is normally covered with leaves which, along with oil, make nutrient medium for microorganisms. The scientists have not come to the consensus yet on the impact of plants on the oil decomposition by microbes. The scientists of the Lomonosov Moscow State University and the Institute of Microbiology, Russian Academy of Sciences, have undertaken the research. They have come to the conclusion that for efficient purification of the oil contaminated soil, the latter is required to contain more oxygen and less leaves.

The researches used Rhodococcus bacteria, evolved from the oil- contaminated soil, these bacteria decompose oil efficiently. If the soil contains the plant cellulose, bacteria turn this matter into glucose and consume it. In the laboratory environment the Rhodococcus bacteria grow up on the nutrient medium containing one of the oil components - hexadecane. Adding different amounts of glucose to the medium, the scientists have found out that the glucose concentration influences the oil decomposition.

In the oil-contaminated soil microorganisms are slowly growing and gradually decomposing hydrocarbons. However, if leaves cover the soil densely the situation changes, as leaves are the source of nourishing glucose. At first the bacteria are growing very fast, processing oil and cellulose rapidly and increasing the glucose content of the soil. Eventually the glucose amount grows to such an extent that the Rhodococcus bacteria fail to oxidize all of it, this fact resulting in the soil accumulating the glucose. The laws of biochemistry are unchangeable: if the oxygen amount is insufficient in the soil, the excess glucose is not oxidized by the microorganisms, instead it gets fermented, the butyric acid being the product of this reaction. The butyric acid is a very unfavorable substance. It inhibits the oil-consuming microorganisms activity, they cease decomposing oil, and all purification processes stop. The scientists have discovered that the critical glucose concentration makes up 4 milligrams per gram of soil.

On top of that, the excess of glucose hinders the seed germination. In this case the soil 'swells up' and smells of butyric acid. If the glucose concentration in the soil exceeds 6 milligrams per gram of soil, seeds would not germinate (the researchers have experimented on the watercress seeds). The butyric acid is a volatile substance, in the experiments it disappeared from the soil within eight days and after that the seeds restored the germinating capacity.

The researchers have come to the conclusion that purification of the oil-contaminated soil requires elimination of the conditions favorable for fermentation. It means that there should be enough oxygen in the soil, and very few sources of glucose, i.e. dry grass and fallen leaves. The practical conclusion is that the oil-contaminated areas should be cleared of leaves and grass, and the soil should be loosened.

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