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by Maria MARKAROVA, Cand. Sc. (BioL), Senior Researcher of the Institute of Biology of the Komi Research Center, Ural Department of the Russian Academy of Sciences

How to cope with the consequences of oil spills?

This is a stiff task, particularly, in the Far North. That is why for over ten years the research center of the RAS Ural Department has been studying the damaged landscapes trying to assess the efficiency of various technologies of land recultivation and the self-cleaning capacity of biocenoses. This is how it became possible to collect a workable set of hydrocarbon oxidizing microorganisms and on this basis obtain a biopreparation ("Universal") commercially tested in the Republic of Komi, in the Perm and Tyumen regions.

For the Republic of Komi, as well as for other regions of Russia, where "black gold" is extracted, oil spills present a serious problem. Suffice it to say that in 1994 when, because of a trunk pipeline break in the Usinsk district, about 200 thousand tons of oil came to be spilled over. This event was even entered in the Guinness Book of Records. Over 70 hectares (175 acres) of land was polluted and damaged mechanically; most of the damaged territory lay in the area of peat bogs and swamps. Pollutant concentration reached 600 to 850 mg/g, and the depth of soil stratum impregnation ranged 30 to 150 cm.

It should be stressed that local soils are characterized by a high sensitivity to any kind of technogenic effects. Decomposition of organic matter takes place slowly because of low pH values (3.5 to 4.5 on the average), low efficiency of biologically active horizons and also due to the short period of above-zero temperatures (2 to 2.5 months) and extensive bogging. In addition, peat bogs display a very high sorption capacity, which compounds the problem of high-viscosity oil mining in the north of the Komi Republic. To solve this problem solely by mechanical techniques is hardly possible: we just get rid of surface pollution only. Therefore biochemical techniques attain particular importance for they "trigger" a mechanism of natural oil oxidation*.

Today the use of oil-decomposing biological preparations is a widespread method of polluted soil recultivation. They eliminate the toxic effect of oil on the natural microbe community, help purify soils from hydrocarbons and their intermediate decomposition products, including water-soluble ones. Alternative biological cleaning techniques, like soil loosening and fertilizer, are efficient in the North only in areas with a moderate degree of pollution, where the self-cleaning potential is rather high anyway. At severely damaged objects agroengineering methods make it possible to reduce the content of hydrocarbons by


See: I. Borzenkov, "Nature's Protective Forces", Science in Russia, No. 5 - 6, 1993. - Ed.

стр. 30


The oil content dynamics in soil and water. The first year of the biological remediation experiment with "Universal".

15 to 20 percent in one a season, biological preparations - by 40 percent, while the combination of these two approaches improves this indicator 60 to 80 percent.

Many research workers have come to the following conclusion: the most efficient way of combating oil spills is to use preparations whose microbial strains have been obtained in similar soil-climatic conditions and with a similar composition of hydrocarbon pollution. Therefore, the formula of the "Universal" product developed at our institute contains bacteria taken from polluted soils of Usinsk and Ukhtinsk districts of the Republic of Komi and oil fields of the Tyumen Region. It should be noted that the working set collected by us numbers more than 200 bacterial and yeast strains which prefer an oil-containing substrate. However, to date only 12 species have been up to toxicological expert examination which, in various combinations (depending on pollution specifics), are used within the "Universal" product. The most effective compositions are being licensed now. Among microorganisms currently in use are the well-known alkanotrophs added to other oil-oxidizing products: of the Pseudomonas, Rhodococcus, Agrobacterium and Arhtrobacter genera. The little studied Variovorax, Kurthia, Rhodotorula and other genera are employed as well.

OPTIMAL COMPOSITIONS

To estimate how well oil products are decomposed by such species as Pseudomonas, Rhodococcus, Variovorax and Rhodotorula (both in pure and mixed cultures) various substrates for their growth were taken: the "light" naphthene-methane oil substrate (Nizhnevartovsk field) and the "heavy" one, with a high content of resins and paraffins (Usinsk field), and also pure n-alkanes (paraffins) with the carbon chain from 12 to 22 atoms long. As shown by laboratory experiments there was a 55 to 95-percent decrease in the total mass of hydrocarbons contained in oil as compared with the initial level. However, the entire pattern of microbiological treatment can be assessed only with respect to the oil fractional composition. The point is that in the fields of the Usinsk district the concentration of hydrocarbons ranges 65 to 85 percent. The remaining 35 to 15 percent is under heterocyclic compounds. As for the light oil cuts of the Nizhnevartovsk field, its hydrocarbon portion may be as high as 98 percent.

The Pseudomonas group of microorganisms "works" better with hydrocarbons, while the Variovorax and Rhodotorula - with heterocyclic compounds more resistant to destruction. As a result, such compounds begin converting to a water-soluble phase already on the third day whereupon the combination of Rhodococcus and Pseudomonas strains perform more efficiently.

The yeasts of the Rhodotorula genus are but seldom mentioned in the literature in connection with oil destruction. Our studies have shown that at some stages of the reclamation of ecological systems damaged by oil spills their oil-oxidizing activity is rather high. For example, strains separated from recently polluted top soils proved efficient in purifying the substrate from petrol and kerosene fractions. Thereupon they became active with respect to heavy paraffins, aromatic and polyaromatic hydrocarbons. And at later stages of the self-recovery of soil ecological systems they became implicated in the transforming of heterocyclic compounds. In places where oil spills were burnt up, we managed to select a number of strains capable of effective decomposition of such a xenobiotic as benz(a)pyrene.

The above information makes it possible to construct a provisional pattern of soil remediation. Thus, immediately

стр. 31


An oil-polluted area where the first commercial tests of the "Universal" biopreparation were carried out in June 1995.

The same area today. Projected grassing - 100 percent, the sedge-and-cotton grass community rehabilitated. Dwarf birch and willow are back to dry areas.

after oil pollution, when the percentage of the most toxic light fractions (toxic to most of the soil micro-flora) is rather high, treatment should be carried out by destructor strains of these compounds (Pseudomonas sp. and Rhodococcus sp.). Next, for the purpose of decomposing paraffins and high-molecular hydrocarbons use is made of such active strains as Rhodococcus sp. and Rhodotorula sp. Due to the growth of the oil oxidizing activity of the microflora there occurs an outburst in the formation of water-soluble hydrocarbon fractions, and these, given the high extent of bogging of the Usinsk district, may migrate outside the recultivated area. However, as mentioned previously, the same Pseudomonas sp. copes well enough; thus its strains are the best at this stage. The final stages of soil purification from oil are characterized by a decrease in total mass of hydrocarbons and increase in the amount of heterocyclic compounds, with Variovorax sp. and Rhodotorula sp. reactive to them. They are also capable of composite acting upon hydrocarbons.

The significance of the indigenous microflora should not be underestimated either as it becomes involved in the decomposition of oil compounds immediately after pollution. The use of the natural potential of soil along with the proper application of remedial preparations produces a good practical result. However, it would be naive to suppose that biological preparations are sufficient for combating oil spills. A complex of engineering and biotechnological methods is necessary, each assigned a specific role in soil and water purification from oil and products of oil decomposition; this is a guarantee of successful remedial effect as confirmed by many experiments which we have been conducting for over ten years including those carried out on a commercial scale. More than 400 hectares (1,000 acres) of land was recultivated throughout Russia. The "Universal" product had its acid test during the notorious Usinsk spill of 1994.

At that time we managed to clean a contaminated territory of about 4 hectares (10 acres). Under a 1-m layer of water there was peat impregnated with oil 50 to 80 cm deep. The degree of pollution was 450 to 750 mg/g. On this site we used our technologies of thorough purification of soil and water from oil and its components. As a result, the polluting agents were gradually withdrawn from the soil mass and then removed from the water surface. Next dissolved hydrocarbons were taken away from the subsurface layers. The hydrological conditions of the area were restored back to normal, and the additional treatment of the polluted soil was carried out. This work went on for two field seasons. A year after its termination the flora was rehabilitated in practical terms.

We should point to economic advantages of biopreparations: their cost did not exceed 7 to 10 percent of the total bill, while the overall effect in oil pollution reduction may be 50 to 80 percent.

SLUDGE TREATMENT

Treatment of sludge formed upon the mechanical removal of polluted soil is yet another formidable job in

стр. 32


Part of the reclaimed quarry.

reclaiming oil-contaminated territories. Sludge is accumulated for years. The concentration of oil in liquid sludge (slurry) exceeds 50 to 90 percent. Solid sludge is oil-polluted soil in which the level of pollution is not above 50 percent. The treatment of both solid and liquid sludge is to some extent interconnected, and the final objective of utilization is to bring back oil to the commodity turnover, obtain secondary feed (bitumen, asphalts, paraffins) and cope with soil purification and reclamation.

In our opinion utilization of solid sludge is a most problem area. Oil-containing soils stored in earthen containers are remarkable for an extremely low biological activity compared with soils of similar pollution levels. In addition, they consist of substrates of different grain-size composition and, accordingly, differ in sorption ability. Long storage contributes to adhesion of pollutants to soil particles, which compounds the cleansing job. Physicochemical transformation of oil provides for the concentration of high molecular weight compounds. Finally, periodic annealing of oil sludge stimulates the accumulation of high-toxic poly-aromatic hydrocarbons hardly amenable to destruction by biological methods.

With the aid of "Universal" we managed to move further in solving the problem. The work on utilizing oil sludge that we have done in cooperation with the Astarta and EkoAlians companies in the Usinsk and Ukhtinsk districts includes the separation of phases (oil-soil-water) and their subsequent purification. The extracted oil products are brought up to a marketable state. Water is purified from suspended matter by sedimentation and by means of biodegradation under intensive aeration to get rid of hydrocarbons dissolved in it. Upon the partial washout of pollutants the soil is carried to biological amelioration sites and brought up to normal characteristics with the use of the biopreparation, fertilizers and microelements. The proposed process pattern for the treatment of oil and gas-condensate sludge makes it possible, during one or two field seasons, to rehabilitate soil with a very high initial level of pollution without combustion of oil products in it-a very harmful procedure for the natural environment. In this case the waste of class 3 hazard is brought down to the low-toxicity class 4 and the practically safe class 5.

But what about the treated soil? Special conditions are needed for burial of a substrate, even if purified. And yet this problem can also be solved thanks to abandoned sand quarries which have not been overgrown and exposed to wind and water erosion for many years. In the Far North their reclamation is difficult due to the shortage of available organic substrate. True, in taiga woodland areas it is possible to organize peat mining. But not in open tundra plains and forest tundra, particularly, in regions with fragmentary or total permafrost, where such activities are considered environmentally hazardous. That's where the soil purified through solid oil sludge treatment comes in handy. Actually, by solving one environmental problem we coped with another one: building a biologically productive layer above dead quarries.

"Universal" is now produced on a commercial scale. Detailed instructions for its use are available for different types of soil, for different degrees and time of hydrocarbon pollution. Its variable composition has been taken into consideration as well. Recommendations and instructions are offered for the use of "Universal" in utilizing oil and gas-condensate waste. And in the Perm Region it is incorporated into the standard projects on comprehensive treatment of solid and liquid sludge of the same composition. Similar documents for the Republic of Komi are being prepared as well.


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Maria MARKAROVA, THE FAR NORTH: CLEANING Of SOIL FROM OIL // London: Libmonster (LIBMONSTER.COM). Updated: 27.09.2018. URL: https://libmonster.com/m/articles/view/THE-FAR-NORTH-CLEANING-Of-SOIL-FROM-OIL (date of access: 21.04.2021).

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