V.I.Vaver Interdistrict Committee for Nature Protection and Natural Resources, Nizhnevartovsk
Causes and consequences of oil spills
Over the past three decades, 2.5 billion tons of oil have been produced in the Nizhnevartovsk region.
In accordance with the approach adopted in the sixties to the development of oil fields in Western Siberia, which presupposed their development mainly on a rotational basis and intensive development, the development of oil fields was carried out at minimal cost, with the expectation of short-term operation. At the same time, no one counted on the environmental safety of the facilities under construction, and attempts by designers and heads of oil and gas production departments to increase the technological reliability of pipelines by making them more expensive were thwarted by the expertise of the Ministry of Petroleum Industry.
The first ruptures of in-field oil pipelines, accompanied by spills of significant volumes of oil, were not long in coming, and due to the accelerated increase in oil water cut, after 5-6 years of operation, massive ruptures of oil-gathering network pipes began.
Some of the oil spilled in accessible places was pumped out; oil spills in the immediate vicinity of production facilities were simply covered with sand. Most of the spills remained abandoned or burned out. And each case of burning of spilled oil was accompanied by the release into the atmosphere of a significant amount of soot containing carcinogenic substances such as 2,4-benzo(a)pyrene. Light fractions of oil, including carcinogenic aromatic hydrocarbons, evaporating from the surface of spills in the summer, intensively pollute the atmospheric air. Soot emissions from oil burning and hydrocarbons evaporating from spills pollute the air not only in the territory of oil fields, but also make a significant contribution to air pollution in populated areas.
Residual oil, remaining at the spill site, constantly seeps into the soil waters and creates a threat of oil pollution of underground aquifers, which are the source of water supply to populated areas of the Nizhnevartovsk region. Signs of oil pollution of aquifers have already been noted on the territory of the Samotlor field. Gradually migrating, oil pollution spreads over areas that sometimes significantly exceed the area of primary pollution.
A significant part of the spilled oil with flood and storm waters rolls into watercourses, polluting the water with oil products. According to the Nizhnevartovsk special inspection of state environmental control, the content of petroleum products in the waters of the Ob and Vakh rivers in 1996 ranged from 1.7 to 2.3 MPC. Oil that gets into water bodies, losing its light fractions due to weathering, goes to the bottom, where, under conditions of oxygen deficiency, it remains for a long time, undergoing extremely slow biodegradation. Thus, sunken and buried oil in soil embankments becomes a constant source of pollution of groundwater and surface water bodies.
The overall toxicity of oil is generally low. At the same time, individual components of oil and its biodegradation products, mainly polyaromatic and polycyclic compounds, are characterized by mutagenicity, carcinogenic properties and teratogenicity. And the consequences of their impact on living organisms, including humans, can manifest themselves after many years and in subsequent generations. The manifestations of this effect are very diverse and can be expressed in a decrease in immunity, the development of allergies and cancer, an increase in the incidence of congenital deformities, etc. The greatest danger in this case is genetic disorders.
Green plants, fungi and microorganisms that develop in soils and bottom sediments of water bodies, containing even traces of oil, accumulate and concentrate heavy metals, radionuclides, carcinogenic substances and genetic poisons in their tissues and transmit them along the food chain to higher organisms with corresponding consequences.
Thus, oil pollution of natural environments poses a long-term threat to the health of the region's population. And it is no coincidence that the residents of Nizhnevartovsk, according to the state system “Environment-Health”, have recorded an excess of the average Russian incidence of malignant neoplasms by 2-3 times. In general, the health status of the population of Nizhnevartovsk is assessed as critical.
Scale of the disaster
Since the early nineties, massive work began to eliminate oil contamination of land. However, the increase in the area of land flooded with oil due to the increasing accident rate of pipes exceeded and exceeds the area of at least partially reclaimed land. At the beginning of 1997, the accumulated fund of oil-contaminated lands, according to clearly underestimated reporting data from oil producing enterprises, amounted to 2,314 hectares.
Today, oil spills in the oil fields of Western Siberia have become a disaster. Of the 20.2 thousand km of infield pipelines built in the Nizhnevartovsk region, 3.4 thousand km (16.6%) are almost completely worn out and require immediate replacement. Due to the lack of funds at enterprises for the reconstruction of pipelines, the stock of worn-out pipes is increasing, which inevitably leads to a progressive increase in the number of accidents and, accordingly, to an annual increase in the area of land flooded with oil.
According to reports from oil producing enterprises, in 1996 alone, 1,543 accidents on in-field pipelines were registered in the Nizhnevartovsk region, as a result of which 424.3 tons of oil and 607.0 tons of highly mineralized formation water were spilled. At the same time, 42.43 hectares of land were contaminated with oil.
According to minimal expert estimates, only in case of accidents in 1996 in the region, the area of land contaminated with oil should be at least 300 hectares, and the volume of oil spilled on the relief should be 30 thousand tons, from which technically no more than 18-25 thousand tons. According to forestry enterprises, as a result of only two accidents in 1996, 6.2 hectares of forests were contaminated with oil and highly mineralized formation water.
Under these conditions, eliminating the consequences of numerous accidents and reclamation of the vast accumulated and constantly emerging fund of oil-contaminated lands becomes a priority task.
Goals and real possibilities of reclamation
In common practice, reclamation means restoring the original fertility of previously disturbed lands. This is the ultimate goal of any reclamation work.
Reclamation of lands contaminated with oil and heavy petroleum products involves reducing their content in soil and water to biologically safe concentrations. However, the magnitude of these concentrations has not yet been established due to the complex and variable chemical composition of oil and is unlikely to be established unambiguously. Oils from different fields and even different layers of the same field differ significantly in chemical composition. And since the main danger is posed by carcinogenic and mutagenic substances contained in oil in variable and very small concentrations, which practically do not affect the productivity of the first generations of green plants, by which land fertility is usually assessed, the task of establishing a biologically safe level of oil pollution is extremely difficult.
The growth and reproduction of many types of green plants is possible with an oil content in the soil of up to several percent (depending on the type of soil). And for some oil-tolerant plants, such as cattail, oil is a growth promoter, as seen in some old oil spills. But the accumulation of mutagens and carcinogens in plants makes these plants dangerous for higher forms of life.
Therefore, it becomes obvious that the growth of green plants cannot serve as a true criterion for the rehabilitation of oil-contaminated lands and only indicates a decrease in the concentration of oil in the soil below phytotoxicity limits, which are different for different plant species and soil types.
In the case of oil contamination of land, we must clearly understand that quickly achieving the true goal of reclamation - ensuring the biological safety of contaminated land and the biomass developing on it - within a timeframe acceptable to production workers is only possible with the complete removal of contaminated soil from the spill site and replacing it with clean fertile soil.
In real production conditions, the actual goal of carrying out reclamation work is only to reduce the content of oil and petroleum products in the soil to a conditional limit, at which the development, growth and reproduction of green plants is possible, and to achieve a general design cover of the “reclaimed” land with plants that is close to the original one (see Table ).
Achieving this goal is quite possible in 1-5 years. In fact, this is just the initial stage of reclamation, during which further self-purification of the soil is possible to a biologically safe level with the participation of green plants and soil microflora. And this will take not years, but decades.
That is why, even after the fertility of the reclaimed lands has been restored, they should not be used for growing food and fodder plants. On these lands you cannot cut hay or graze livestock, you cannot pick mushrooms and berries. You should also not fish in oil-polluted waters. The only criterion for removing these restrictions may be the results of special physicochemical and toxicological studies of the soil, the plants growing on it and the inhabitants of reclaimed oil-contaminated reservoirs.
Unfortunately, almost all current regulatory documents regulating reclamation work and acceptance of reclaimed land do not take into account the danger of accumulation of toxic products of oxidation and biodegradation of spilled oil in the soil and the biomass that reproduces in it. In accordance with modern practice of reclamation work, soils and drilling waste with the content of petroleum products given in the table are considered to be sufficiently safe. And, although the requirements of the most stringent of the regulatory documents provide for the prohibition of the use of land reclaimed after oil pollution for collecting berries, mushrooms, haymaking, growing food and animal feed until the concentration of hazardous substances is reduced below the MPC level, in practice this provision is never implemented by anyone .
How to reclaim land contaminated with oil
Preparatory work. In the first stages of oil spill response, the main task is to localize the contaminated area to prevent the spread of the oil slick and collect the maximum possible amount of spilled oil. These works must be carried out immediately after the accident. And the more thoroughly they are carried out, the more favorable the prognosis for the reclamation results.
Since the majority of oil and oil product spills in world practice occurred during accidents of oil tankers, methods for localizing and collecting spilled oil on water surfaces have been most fully developed.
To localize oil spills on the water surface, various types of booms produced by many foreign companies are used. Unfortunately, the list of booms produced in Russia is limited to quickly installed rubber-fabric barriers "Uzh" and booms of the "Anaconda" type. Some small enterprises produce simple but reliable booms of the “BN” series and others. When installing booms, you should immediately organize the pumping of oil that accumulates in front of the boom, preventing its accumulation in significant quantities.
Since it is easiest to pump out spilled oil from the surface of the water, drainage (oil collection) ditches are installed on dry lands within localized areas of land, directed towards natural or specially opened depressions (catching pits), partially filled with water. Devices are installed in these depressions to pump out the oil that collects in them.
To increase the completeness of land cleanup, after pumping out the main volume of spilled oil, it is advisable to use the method of washing the soil from residual oil with jets of water, driving the spilled oil into a drainage ditch or directly into depressions in the relief. The efficiency of washing increases significantly when surfactants (surfactants) decomposed by soil microflora are added to the water in concentrations of 0.02-0.5%. It is especially useful to use a cleaning technique using a surfactant to clean grass or shrubs from oil.
To collect oil from the surface of the water in reservoirs, relief depressions, and in catch pits, floating oil intake suction devices are used - skimmers, drum and disk oil skimmers, mass-produced, mainly by foreign companies. To collect oil from the surface of the water, it is promising to use dynamic oil skimmers-accumulators of the “ND” series, operating in automatic mode and ensuring that there is no leakage of oil under booms. Currently, these oil skimmers are manufactured in single copies by TTC Sibirneft LLP (Nizhnevartovsk).
A number of domestic and foreign enterprises have developed and offer consumers absorbent mats for collecting oil from the surface of water and soil. The best examples of such mats can absorb up to 40 kg of oil per 1 m2 and, after squeezing the collected oil out of them, can be reused 12-15 times. It is rational to use them for collecting small spots of spilled oil and for “finish cleaning” of oil after pumping out the bulk of it using other methods. In this case, the maximum possible completeness of oil collection is achieved. In Russia, such mats with an absorption capacity of up to 15 kg of oil per 1 kg of mat (with a density of about 1 kg/m2) are offered by Ecoservice (Tomsk) and Echtech (Tomsk).
Some companies offer powdered and granular sorbents of various types that absorb spilled oil. But mechanical devices for collecting and recycling oil-saturated sorbents have not yet been created and produced on an industrial scale, and their mass use in extensive spills characteristic of the fields of Western Siberia is unpromising.
Reclamation works. After collecting the spilled oil, part of it remains sorbed on the soil and vegetation debris. It partially erodes, and over longer periods it becomes partially or completely bituminized, covering the soil with a dense crust. Oil spilled on the surface of reservoirs ends up at the bottom of the reservoir after a year due to sorption on solid particles, as well as due to an increase in density.
The first stage of reclamation of oil-contaminated lands is the cleaning of soils and soils from oil and oil products.
A fairly detailed description of the recommended methods and techniques for cleaning and recycling oil-containing soils and waste is given in the report of the working group of the international association of oil companies and oil industry enterprises "E&P Forum". To eliminate oil contamination of land, it is recommended to completely remove the contaminated soil followed by its cleaning. For purification, extraction of oil with liquid CO 2 or organic solvents is recommended, and, in the presence of favorable conditions, biochemical decomposition of oil hydrocarbons by soil microflora. Biochemical methods for cleaning up soil collected from spills include field irrigation, composting, or simply spreading oil-containing waste on the soil followed by self-purification.
The simplest of the methods listed is to spread the contaminated waste over the soil in a thin layer, followed by periodic plowing for mixing and aeration. The decomposition of hydrocarbons occurs under the influence of natural soil microflora. To intensify decomposition and prevent leaching and migration of contaminants, water and auxiliary substances - fertilizers, sorbents, etc. can be added to the soil mixed with waste. In one area, spreading is carried out once to avoid the accumulation of organic matter and heavy metals in the soil. This method is recommended for the removal of spent drilling fluids containing low hydrocarbons and salts.
The design of irrigation fields differs from the previous method only in that in the same area, spreading with subsequent plowing is carried out repeatedly. In dry times, watering is carried out.
Areas for spreading and constructing irrigation fields are selected in such a way as to exclude the possibility of contamination spreading beyond the boundaries of the area designated for this purpose.
Composting of oily waste can be used where there are relatively high concentrations of hydrocarbons and other biodegradable substances. To increase porosity, waste to be destroyed is mixed with filler - wood chips, straw, etc. - after which they are mixed with soil containing microorganisms. Agricultural waste can be added to the mixture to increase water-holding capacity, as well as mineral fertilizers and microelements. The mixture is placed on trays or in pallets with a mesh bottom or in piles up to 1 m high, periodically mixed and moistened. Using this method, the hydrocarbon content of the compost can be reduced from 10% to a fraction of a percent in 4-8 weeks.
For the preliminary purification of large quantities of collected soil and oil sludge from oil, various types of centrifugal devices are widely used, which make it possible to separate commercial oil from the soil and sludge and achieve a residual oil content in soils of no more than 8%.
Unfortunately, given the scale of oil spills in Western Siberia, these methods are in most cases practically inapplicable due to the high cost of work or are applicable in very limited quantities. However, such methods may be useful in cleaning up oil-contaminated sludge pits and small areas with high pollution intensity.
Microbiological land cleaning. When significant areas of land and water bodies are contaminated, the most acceptable method of cleaning land and water is the method that is widely used in world and domestic practice, using microbiological decomposition of oil at the spill site, followed by self-overgrowing of the cleaned land or sowing of perennial grasses.
This method is quite simple to implement and consists of carrying out a number of agrotechnical measures on contaminated lands aimed at activating soil oil-oxidizing microorganisms that have the ability to use oil hydrocarbons as the only source of nutrition, ultimately oxidizing them to CO 2 and water. The primary oxidation of oil to organic acids, alcohols, ketones and aldehydes is ensured precisely by hydrocarbon-oxidizing microorganisms, which are described quite fully in the review. At subsequent stages of destruction of the products of primary oxidation of oil, other physiological groups of soil microorganisms, protozoa and algae, which usually live in soil and water bodies, are also involved in the process. Considering the complex composition of oils and the unequal ability of different groups of hydrocarbon-oxidizing microorganisms to assimilate various components of oil, it is necessary to ensure that oil is exposed to a possibly more complex community of microorganisms.
Fortunately, all the necessary microorganisms are present in the microbial communities that have developed in soils and surface waters in areas of oil fields. These communities are especially active in areas that are constantly, but not heavily polluted with oil products, and in old, but not particularly massive oil spills. We examined more than 20 areas contaminated with oil at the Samotlor field. Very active multispecies communities of oil-oxidizing microorganisms were found at all sites.
The only exceptions may be areas that have never previously been contaminated with oil and petroleum products. But even in these cases, up to 103 cells/g of hydrocarbon-oxidizing bacteria were found in soil and water samples. True, their species composition was not diverse and was represented mainly by representatives of the genus Pseudomonas. Accordingly, their activity turned out to be relatively low. However, even in this case, when favorable conditions are created, very active microbiocenoses develop over time. Thus, in the overwhelming majority of cases characteristic of Western Siberian oil fields, the microorganisms necessary for the rapid destruction of spilled oil are already contained in the soil and water bodies. Their numbers may be low, but as a result of the reclamation measures carried out - the application of fertilizers, etc. - within a few days it increases from single cells per gram of soil or water to values of the order of 10 12 - 10 15 cells/g. And only in some cases, in the conditions of the short Siberian summer, in order to speed up the process of cleaning the soil from oil, is it justified to introduce bacterial preparations based on cultures of highly active strains of hydrocarbon-oxidizing microorganisms produced by a number of enterprises onto reclaimed areas.
Among the domestic ones, the most widely known preparations are “Putidoil” based on the bacteria Pseudomonas putida isolated from oil-contaminated soils of the Samotlor field, “Devoroil” based on the yeast Candida, “Bioprin”, as well as preparations of the “Biodestructor” group: “Leader” based on Rhodococcus sp. S-1213 and "Valentis" based on Acinetobacter valentis, recommended for purification of soil and water from oil, C 8 -C 40 paraffins, diesel fuel, raffinates, oils, aromatic hydrocarbons (phenol, benzene, toluene), boiler fuel. In recent years, the range of microbiological preparations approved for use by the State Sanitary and Epidemiological Supervision Authority and offered for sale has been increasing.
A very promising direction is the development of microbial preparations of hydrocarbon-oxidizing microorganisms immobilized on solid substrates capable of sorbing oil.
If it is necessary to quickly eliminate oil contamination of limited areas of land, it is advisable to use enzyme preparations that do not contain living cells, but retain intact fragments of the enzyme systems of hydrocarbon-oxidizing microorganisms that quickly destroy oil hydrocarbons. As a rule, these preparations contain numerous additives - vitamins, microelements, etc., which stimulate the accelerated development of soil microflora, which destroys the products of the primary oxidation of petroleum products by enzyme additives. As examples of such drugs, the domestic drug “Belvitamil”, proposed by NPF “MITEK” (Ufa), based on activated sludge of biochemical production, containing enzyme systems of Candida yeast, vitamins and microelements necessary to accelerate the development of indigenous microflora, can be mentioned. Domestic preparations containing enzyme systems of hydrocarbon-oxidizing bacteria immobilized on the surface of a solid sorbent have been developed, but have not yet found widespread use. Unfortunately, these drugs are very expensive.
In any case, when using indigenous microbial communities or when introducing microbial preparations, it is necessary to create in the cleaned environment optimal conditions for the development and active functioning of hydrocarbon-oxidizing microflora:
- supply of oxygen to the zone of microbial activity;
- the presence in the cleaned environment of easily digestible water-soluble minerals, primarily potassium, nitrogen and phosphorus;
- maintaining the acidity and humidity of the cleaned environment within limits that ensure the vital activity of microorganisms and sufficient activity of enzyme systems.
The main efforts when carrying out reclamation work should be aimed at ensuring these conditions. And, as a rule, it is enough to carry out the usual agricultural practices, agrochemical and agrotechnical measures.
When choosing specific forms of mineral nitrogen fertilizers, it should be taken into account that the microorganisms contained in the preparations of the “Biodestructor” series, when nitrate nitrogen is added, sharply reduce hydrocarbon-oxidizing activity. Considering that microorganisms of the genera Acinetobacter and Rhodococcus are widely represented in natural microbial communities and play a significant role in the processes of soil purification from petroleum products under natural conditions, the issue of using nitrate forms of nitrogen fertilizers should be approached with caution. It is advisable to give preference to non-nitrate forms of mineral fertilizers.
The actual dosages of fertilizers (in terms of K, P and N), recommended by us for application to reclaimed areas during their initial processing, are: nitrogen from 14 to 35 kg/ha, potassium from 11 to 27 kg/ha and phosphorus from 5 to 12 kg/ha for every 5 cm of soil plowing depth. When applying fertilizers to water-filled depressions, barns and oil-polluted lakes, for every 1000 m 3 of water it is advisable to add at least 28 kg of nitrogen, 22 kg of potassium and 10 kg of phosphorus. These dosages provide concentrations of K, N and P in the soil solution 5 times lower than those used in the preparation of mineral nutrient media for the isolation and accumulation of hydrocarbon-oxidizing bacteria (HCB). But, taking into account that high rates of development of URD are ensured even with a tenfold dilution of nutrient media, the use of such dosages is quite justified. As our practice shows, the best results are achieved when applying the calculated amount of mineral fertilizers in fractional doses, in 2 - 3 doses at intervals of 3 - 7 days. When first applied, the dose of fertilizer should be 10-20% of the calculated amount. This achieves a mild adaptation of the native soil microflora to an increase in the content of assimilable mineral substances in the environment.
The pH values of soil and water that are optimal for the development of hydrocarbon-oxidizing microorganisms lie in the range of 6.5-7.5. In real conditions, oil-oxidizing microorganisms develop well and retain sufficient activity when the pH of the environment decreases to 5.0. Some types of oil-oxidizing microorganisms (for example, yeast) are resistant to pH decreases to 3.5 and below. But the speed and completeness of the microflora's use of oil hydrocarbons is sharply reduced.
During microbiological oxidation of oil under conditions of oxygen deficiency, accumulation of organic acids occurs, accompanied by a decrease in pH.
Preliminary control of soil and water acidity is necessary at each site subject to reclamation. When the pH of soil water or soil is below 5.0 - 5.5, it is recommended to add deoxidizers - limestone or dolomite flour, or chalk. Application rates for deoxidizers are taken in accordance with normal agricultural practices. An overdose of carbonate materials does not lead to undesirable consequences. And the excess deoxidizing agent at the time of application is consumed as the oil breaks down and carboxylic acids form, preventing subsequent acidification of the soil. The resulting calcium salts of carboxylic acids are absorbed by soil microorganisms more easily than free acids. It should also be taken into account that in case of surface contamination of waterlogged soils with oil, zeolite, dolomite and limestone flour absorb spilled oil well and at the same time play the role of collectors on the surface of which microorganisms develop more intensively.
An absolutely necessary condition for ensuring the process of microbiological purification of soils and water from oil and petroleum products is aeration of zones of active activity of microorganisms by any available method.
Under natural conditions, the zone in which processes of accelerated biodegradation of oil occur is limited to the surface layer of soil accessible to the penetration of oxygen and aerated surface water. The presence of continuous layers of oil on the surface of soil and water greatly limits the aeration zone and the greater the thickness of the layer, the viscosity and the degree of weathering of the oil spilled on the surface of the contaminated area. If there are continuous layers or a crust of oil on the surface more than 2-3 mm thick, it is destroyed at a more or less noticeable speed only in the surface layer and only when it is periodically moistened by precipitation. That is why preliminary collection of oil from the spill surface can become a decisive factor determining the effectiveness of the entire complex of reclamation works. And if spilled oil penetrates into the soil, additional measures should be taken to ensure aeration of its entire thickness.
The most common method of aerating oil-contaminated soil is to loosen it by milling or plowing it to the full depth of oil penetration. In this case, the effect of reducing the concentration of oil in the soil is achieved by mixing oil-contaminated soil with uncontaminated or less contaminated soil from the underlying layers.
In case of surface contamination with oil of waterlogged soils or the water surface of swamps, hollows, small swamp lakes, etc., to accelerate the destruction of oil, the method of irrigating the surface of the reclaimed area with aerated water can be used. In this case, on the periphery of the site in the direction of natural drainage, a depression in the ground is selected or a small pit is dug with an excavator, 1.5-2 m deep, flooded with groundwater. If necessary, shallow collector grooves (furrows) are installed to ensure the flow of water and oil from the surface of the site into this recess. Nozzle or jet garden water sprinklers are installed on the site, used for watering park lawns. The sprinklers are positioned in such a way that the entire territory of the reclaimed area is irrigated with water, and they are connected by a system of flexible hoses made of oil-resistant material to a water pump that draws water from the excavation. A system designed in this way ensures continuous or periodic irrigation of the entire surface of the area with aerated water, which significantly accelerates the microbiological oxidation of oil. In this case, mineral fertilizers can not be distributed over the entire area, but placed in this depression, which greatly simplifies the work and ensures uniform distribution of fertilizers.
A dense layer of weathered oil can be destroyed on the eve of reclamation work by the caterpillar tracks of swamp vehicles or (after freezing of the soil) by the tracks of a heavy tractor. In small areas, oil crusts can be destroyed manually, using walk-behind tractors or hand tools - rakes, hoes, etc.
In small closed reservoirs covered with a layer of oil, water aeration can be ensured by installing floating aerators of the AP-24 type in the reservoir, manufactured by the New Technologies company (Nizhnevartovsk), which are small-sized turbine mixers with an electric drive, mounted on floats, ensuring the capture of atmospheric air and its intensive dispersion in the water of the reservoir.
In cases where oil is detected in bottom sediments, in addition to forced aeration of the water, it is recommended to periodically loosen the bottom sediments in the reservoir by repeatedly dragging along the bottom of the reservoir using ropes of conventional toothed harrows.
Phytorecultivation. After reducing the content of petroleum products in the soil in the reclaimed areas to values that provide the possibility of growth and reproduction of the most oil-resistant green plants, phytoremediation of contaminated lands begins.
Under natural conditions, after preliminary collection of spilled oil with a low degree of residual soil contamination, the spontaneous colonization of pioneer plant species that are most resistant to oil pollution begins by the end of the first year of reclamation, even without preliminary loosening of the soil. With an average degree of pollution, the area is overgrown with grasses usually within 3-7 years. And the entire process of soil self-purification with the restoration of natural plant communities continues for 80-100 years.
To speed up the process of grass development and, accordingly, delivery of the reclaimed area to the customer, they resort to sowing grass. In heavily contaminated areas, with vegetation completely dead by the time reclamation work begins, sowing grasses by 3 to 5 years reduces the time it takes for the areas to be populated by green plants.
Of course, the species composition of grass mixtures will be very different from the species composition of vegetation in neighboring areas. But in the future, as the soil self-purifies, the grass mixture will be replaced by a community of plants characteristic of a given landscape. However, this process is lengthy and not always possible, since changes in the structure and composition of the soil that occur during the reclamation of heavily contaminated soils can be irreversible.
For phytoremediation of oil-contaminated lands, the most available seeds of annual and perennial grasses are used, preferably cereals, which have a developed root system and increased resistance to oil pollution of the soil. In this case, one should prefer grass seeds that are characteristic of local swamp and forest-swamp ecosystems and are well adapted to local soil and climatic conditions. The choice of seeds for specific plants depends on the landscape features of the land being reclaimed. Typically, seed mixtures containing at least 3 types of herbs are used. In dry areas, the seed mixture must include creeping clover, and in flooded swamps, broad-leaved cattail. The seeds of these grasses (except cattail and Langsdorff's reed grass) are produced by a number of seed farms. You will have to harvest cattail seeds yourself. True, in the conditions of the forest-swamp complexes of Western Siberia this is not a problem.
It should be noted that there are often cases when, even after the most complete elimination of oil pollution, restoration of grass cover on the site is impossible due to the salinization of the land by highly mineralized reservoir water spilling along with oil (usually the sodium chloride type with a total mineralization of 13 - 25 g/l) . When the chloride content in the soil is more than 0.2%, a pronounced inhibition of the growth of most grasses is observed. At 0.3-0.35%, the overall projective grass cover is reduced by 1.5-2 times. When the chloride content in the soil solution increases to 1% or more, the development of most types of grass is impossible. In such cases, the area must be reclaimed and washed repeatedly with running water until the concentration of salts in the soil decreases. An example of the technology for desalinization of such lands is given in. Special measures for land reclamation and desalinization must be carried out only after oil contamination of the site has been eliminated.
After sowing, long-term observations of grass growth should be carried out on the site. Upon achieving a stable (within a year) standard general design coverage of the site, its reclamation is considered complete, and the site can be presented for delivery. Further self-cleaning of the soil on the site will occur spontaneously for many years. At the same time, the reclaimed area must be marked with signs and signs prohibiting the picking of berries, mushrooms, haymaking, and the cultivation of food and animal feed. Removal of these restrictions is possible only after conducting special studies confirming the environmental safety of soils and vegetation on the site, which is the achievement of the ultimate goal of reclamation of oil-contaminated lands.
Conclusion
Recently, large-scale work has been carried out on the territory of oil fields to eliminate oil spills and reclaim oil-contaminated lands. In the Nizhnevartovsk region alone, 251.2 hectares of contaminated land were reclaimed in 1995, and 366 hectares of contaminated land in 1996. However, the pace and quality of reclamation are clearly insufficient.
As shown by surveys of reclaimed lands in the Nefteyugansk and Nizhnevartovsk regions, carried out by order of the Nizhnevartovsk Interdistrict and Khanty-Mansiysk District Committees for Environmental Protection by specialists from the Tyumen Forestry Experimental Station, the quality of land reclamation is unsatisfactory.
The main reason for this situation is low technological discipline and numerous errors, as well as deliberate simplifications of the technology of reclamation work.
The most serious and dangerous mistake made during land reclamation is backfilling spilled oil with imported soil - sand or peat. At the same time, spilled oil is removed from the process of microbiological oxidation, and the site “reclaimed” in this way becomes a source of constant pollution of ground and groundwater for many decades.
The second most important serious mistake is the use of bacterial preparations without agricultural cultivation of the land. Preparations of hydrocarbon-oxidizing bacteria with mineral fertilizers sprayed over the surface of contaminated areas with relatively weak surface contamination actually clean the soil surface from oil and promote self-overgrowing of treated areas with grasses. However, oil that penetrates deep into the soil remains undecomposed. And with a clear cosmetic effect in the first months after “reclamation”, after 1-2 years, due to hydrophobization of the fertile soil layer by oil migrating to the surface, the initially developed vegetation completely or partially dies. And the site, in fact, remains unreclaimed, despite the costs incurred. Such methods of “reclamation” are prohibited by the Nizhnevartovsk Committee for Environmental Protection.
The most common misconception, reflected in the practice of reclamation of oil-contaminated lands, is the belief that once applied, even large doses of mineral fertilizers provide high activity of oil-oxidizing microflora throughout the entire period of reclamation work.
A significant mistake is also assessing the effectiveness of reclamation work by the intensity of grass growth on them during the first year, since leaving significant amounts of oil in the subsurface layers of the soil at depths of 15-50 cm will inevitably lead to the death of vegetation (except cattail and some other grasses) through 1-2 years. And contamination of soil and groundwater by oil components will continue. Thus, none of the goals of reclamation work will be achieved with obvious external well-being at the time of completion of the work.
In conclusion, it should be noted that there is an urgent need to create an experimental site on the territory of the Nizhnevartovsk region for testing the equipment and technology of reclamation work proposed for implementation. Only proven technologies can be recommended for large-scale land reclamation work in oil fields.
The implementation of this idea will significantly improve the state of affairs with the reclamation of oil-contaminated lands in the specific climatic-geographical and landscape conditions of oil fields in Western Siberia.
Literature
- State of the environment and natural resources in the Nizhnevartovsk region // Yearbook 1996 / Ed. V.I.Vavera. Nizhnevartovsk, 1997. Issue. 1.
- Current state of the territory in the area of activity of PA "Nizhnevartovskneftegaz": Work report / L.V. Mikhailova et al. Tyumen, 1993.
- V.I.Vaver. On the problems of assessing environmental damage during oil field pipeline accidents // Materials of the district meeting
The invention relates to the restoration of oil-contaminated lands. The method of reclamation of oil-contaminated lands involves applying material to the surface of oil-contaminated lands. The material used is spent proppant in the form of balls with a density of more than 10 3 kg/m 3, which push through oil-contaminated soil. The implementation of this method makes it possible to increase the efficiency of reclamation of oil-contaminated lands, as well as to dispose of waste from the oil and gas industry.
The invention relates to the field of ecology and can be used in the restoration of oil-contaminated lands.
There is a known method for the reclamation of disturbed soils (RU 2044434 C1), which is a prototype of the proposed method, including laying an organic substrate obtained from dehydrated silt and bark on the reclaimed soil surface. After laying, the compost is covered with a layer of sand or soil on top.
The disadvantage of this method is the need to use sand or soil, which increases the material costs of using the technology.
The purpose of the proposed method is to increase the efficiency of the process of reclamation of oil-contaminated lands, as well as the disposal of waste from the oil and gas industry.
Oil and gas industry waste refers to material used in hydraulic fracturing. This material has a round shape in the form of balls with a density of more than 10 3 kg/m 3.
The most suitable material is spent proppant, which can be presented in the form of either aluminosilicate or silicate material. After hydraulic fracturing, part of the proppant is released to the surface and forms waste, which is stored on the surface of well pads.
The proposed method for reclamation of oil-contaminated land is to take balls with a density of more than 10 3 kg/m 3 and apply them to the surface of oil-contaminated land using known equipment.
The balls push through the oil film, forming many holes, which ensures the flow of air and moisture into the soil, which accelerates the proliferation of native microorganisms. As a result, oil pollution is degraded and disturbed lands are restored.
A method for reclamation of oil-contaminated lands, which consists in applying the material to the surface of oil-contaminated lands, characterized in that the material used is spent proppant in the form of balls with a density of more than 10 3 kg/m 3, which push through the oil-contaminated soil.
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The invention relates to the oil industry and ecology and can be used for cleaning and reclamation of soil contamination by oil and oil products on agricultural and industrial lands in the Far North using plants
Zubaidullin A.A.
As is known, most of the oil-contaminated lands available in the Nizhnevartovsk region are sphagnum raised bogs with a thick layer of peat deposits. And it is on these lands that the use of traditional reclamation technologies and conventional technical means, as modern practice shows, not only does not bring positive results, but in some cases even helps to slow down the natural processes of self-healing that have begun.
First of all, this is due to the underestimation of the natural features of these biotopes: their high water content, low-bearing capacity of the surface and, most importantly, the uniqueness of the soil and plant complex, which together create significant difficulties for the application of standard schemes for the reclamation of oil-contaminated lands.
Let us clarify that the word “reclamation” here means the entire range of work carried out in the disturbed area and includes: collection and neutralization of petroleum organic matter, restoration of soil fertility and creation of stable vegetation cover. The next most common reason for negative results in the remediation of all oil-contaminated areas without exception, including those located in raised bogs, is ignorance (out of ignorance, for mercantile and other reasons) of the stages of action of natural mechanisms of oil decomposition on the earth's surface. For our region, there are three main stages of natural destruction of oil on the earth’s surface (Figure 1):
Stage I - lasts on average 1.5 years. Physicochemical processes prevail here, including the penetration of oil deep into the soil, evaporation of light fractions, leaching, oxidation by atmospheric oxygen and photochemical decomposition of petroleum hydrocarbons. The concentration of oil in the soil during this period decreases by 40-50%.
Stage II - lasts 3-4 years after the end of the first. Here, oil decomposition occurs under the influence of soil hydrocarbon-oxidizing microorganisms, the number of which increases by 25 times. Methane-naphthenic fractions, which are the most toxic components of oil for plants and soil animals, are destroyed.
Stage III - begins 4.5-5 years after the oil spill and lasts until it is completely destroyed. The stage is characterized by microbiological decomposition of the remaining less toxic part of hydrocarbons and resinous-asphaltene components, which form continuous hard crusts on the contaminated surface - the so-called kirs. In fact, already at the very beginning of the stage, it is possible to restore some plant species that are resistant to increased oil content in the soil. But their appearance is prevented by kirs, which do not allow air to penetrate into the root layer of peat, causing a kind of suffocation of plants and soil animals. From a chemical point of view, the process of natural oil destruction ends completely in no less than 25 years, however, the toxic properties of oil disappear after 10-12 years, the products of its decomposition are partially included in the soil humus, partially dissolved and removed from the soil profile.
Own research conducted in the summer season of 1996. on the territory of the Vatinskoye oil field (JSC Slavneft-Megionneftegaz), confirmed the presence of stages of natural degradation of oil in contaminated areas of raised bogs. Observations were carried out in three similar areas, representing the biocenosis of a ridge-hollow raised bog, which were subject to oil pollution at different times: a relatively recent spill in 1994, an old one in 1989. and old - 1985 The timing of the accidents was selected taking into account the already indicated stages of physicochemical and microbiological destruction of petroleum hydrocarbons and the associated stages of self-healing of disturbed phytocenoses. However, the duration of each of them, as shown by a field survey, in the conditions of high peat bogs exceeds those given (for drained areas) by 1.5 - 2 times, which is due to the specifics of peat bog soils (low intrasoil temperatures, lack of oxygen and minerals).
Only taking into account all of the above can we correctly structure the course of the reclamation process, optimally engaging and using all existing natural self-purification mechanisms, and obtain a significant environmental and economic effect, if this term is appropriate in this case. This effect is achieved due to two indicators:
Significant reduction in the period of cleansing and restoration of disturbed areas to their original conditions;
Reducing the overall material costs for reclamation.
Now directly about the most typical mistakes made when carrying out reclamation work in oil-contaminated areas of swamps. Quite often you can see how the following measures are used in the first two years when cleaning up fresh oil spills:
1) backfilling of contaminated areas with sand and peat,
2) plowing or loosening the surface with agricultural implements (harrows, plows, etc.) and all-terrain vehicle tracks,
3) introduction of oil-oxidizing microorganisms.
Unfortunately, each of these activities is actually a waste of effort and money from an environmental point of view. Moreover, in most cases, nature is rendered a kind of “disservice”, as a result of which much more damage is caused to swamp ecosystems than directly from the oil spill itself.
Thus, the implementation of the first two measures leads only to a temporary beautification of the ugly landscape and the achievement of acceptable oil concentrations in the “upper” (imported or inverted underlying) layer of soil in accordance with the requirements of the environmental inspection. In fact, oil is buried and preserved in the underlying watered layers of peat, where low temperatures and a lack of free oxygen are observed. For example, when heavy tracked swamp vehicles such as GPL, Vityaz, etc. move across the oil-contaminated surface of a swamp, oil is squeezed out and buried in a peat deposit at a depth of up to 50 cm. And with the natural distribution of oil over the surface, an average of 5-10 centimeter layer of peat deposit. All this removes residual oil from the action of natural physicochemical decomposition mechanisms (atmospheric oxygen and sunlight) for several years, and therefore the overall restoration of stable soil and vegetation cover significantly slows down. At the same time, the existing vegetation cover is also completely destroyed (covered or torn off by caterpillars), which could survive on individual elevations and hummocks and be a source of vegetation spread on contaminated lands in subsequent years.
The use of oil-oxidizing microorganisms (bacteria) is also inappropriate at this stage, since most of them die due to the acute toxicity of freshly spilled oil. In addition, the processes of biodegradation primarily involve lighter fractions of oil (a kind of “cream”), which would otherwise quickly collapse under the influence of atmospheric oxygen and sunlight.
Thus, it is advisable to accelerate the natural processes of destruction of residual oil and thereby reduce the time required to restore the original vegetation cover only after one and a half to two years from the moment of the accident (at stages II and III).
However, this does not mean that fresh spills should not be dealt with. It’s just that all efforts must be directed towards reliable localization of the oil spill within the smallest possible area and collection of the maximum possible amount of oil. Modern technical means make it possible to collect up to 70%, and under favorable natural conditions, up to 90% of spilled oil.
In swamps, localization of spills is carried out, as a rule, either by creating a thick peat embankment along the perimeter of the spill (swamp vehicles of the "KART" type are used), or by tearing off guide trenches and furrows to a common receiving pit, or by installing mobile booms (the latter, unfortunately, is not practiced). Oil is collected using conventional pumping equipment and specialized oil skimmers. It is also effective in swamps to use backpack vacuum pumps, both domestic and imported, for collecting oil from inter-tussock depressions and other hard-to-reach places. The main condition should be minimal movement of equipment and people on the reclaimed surface, especially on preserved areas of living vegetation.
The most acceptable method for thoroughly collecting residual oil, according to our own experience in carrying out such work, is the method of forced washing of soil and vegetation from oil with water. This is achieved either by completely flooding the contaminated area for a short period, or by periodically sprinkling it with irrigation systems (motor pumps, forest fire engines). The effectiveness of oil cleanup work at a site is significantly increased by the use of permitted surfactants.
For small volumes of spilled oil, an effective measure is the use of sorbents, in particular peat mats (the holding capacity of 1 m2, depending on the manufacturing technology, ranges from 10 to 40 kg of oil with 12-15 times of use). Such mats are convenient for quick deployment on fresh spills and, most importantly, convenient for their subsequent collection for disposal, unlike loose types of sorbents. By the way, there are simple domestic technologies for mass production of such mats locally. The natural mineral vermiculite, which has significant reserves in our mountain Trans-Urals, also has unique sorption properties.
2.3 Methods of bioindication and biotesting of soils
Biodiagnostics of anthropogenic changes is a rapid analysis method and, in addition, provides a comprehensive assessment of the ecological state of the soil. There are many biological indicators that can be used to assess the condition of soils. The most important are the integral indicators of biological activity: toxicity, “respiration,” the amount of free amino acids and proteins. The intensity of soil respiration is an extremely variable value and depends on a large number of factors (temperature, humidity, state of the phytocenosis, etc.). To assess the environmental impact of pollution, it is necessary to compare data obtained at different sites under the closest possible conditions. Other indicators, for example, enzymatic activity, are also informative.
The entry of oil and petroleum products into the soil leads to a change in the activity of the main soil enzymes, which affects the exchange of nitrogen, phosphorus, carbon and sulfur (Kireeva, Novoselova et al., 2001). Persistent changes in the activity of certain soil enzymes can be used as diagnostic indicators of soil contamination with oil. A group of enzymes, collectively called soil ureases, is convenient for this purpose. Firstly, they are less susceptible to the influence of other environmental factors and, secondly, there is a clear dependence of their activity on the degree of soil pollution (Kireeva, Vodopyanov et al., 2001).
The use of microorganisms to assess the integral toxicity of soil and the creation on their basis of a comprehensive system of sensitive, reliable and economical biotests is a promising area of research. Many physiological groups of soil microorganisms exhibit sensitivity to petroleum hydrocarbons.
The total number of microorganisms, as a rule, quite clearly reflects the microbiological activity of the soil, the rate of decomposition of organic matter and the cycle of mineral elements. Based on this indicator, one can not only judge the degree of soil contamination with oil, but also its potential ability to recover, as well as the processes of oil decomposition in natural conditions and during the reclamation of contaminated soils (Kireeva, 1995).
Oil pollution can also contribute to the accumulation in the soil of microscopic fungi that cause plant diseases and phytotoxins (Kireeva, Kuzyakhmetov et al., 2003). The latter circumstance plays an important role in the development of measures for phytomelioration of oil-contaminated lands.
The direct impact of oil on vegetation is that plant growth slows down, the functions of photosynthesis and respiration are disrupted, various morphological disorders are observed, the root system, leaves, stems and reproductive organs are severely affected. Operational information on the phytotoxicity of contaminated soil can be obtained using plant seeds and seedlings as test objects. To make it easier to perform toxicity tests, seeds are selected according to size and speed of germination. The seeds of radishes, watercress, corn, and grains are often used. The test function includes indicators of seed germination, seedling density and time of emergence, and the rate of seedling elongation, the last of which is considered the most sensitive.
In natural ecosystems, soil invertebrates are widely used for monitoring at the species complex level (Trublaevich and Semenova, 1997).
A set of test objects from plant seeds, microorganisms, soil invertebrates and enzymes can be used either in full or in part, depending on the purpose of the research and the degree of oil contamination of the soil. If samples with soil springtails and enzyme activity provide a good quantitative characterization of soil toxicity at low and medium degrees of contamination, then microbiological tests are convenient for describing the state of heavily polluted, highly toxic soils (Kireeva, 1995).
3. Methods for restoring oil-contaminated soil ecosystems
Oil pollution differs from many other anthropogenic impacts in that it does not produce a gradual, but, as a rule, a “volley” load on the environment, causing a quick response. When assessing the consequences of such pollution, it is not always possible to say whether the ecosystem will return to a stable state or will be irreversibly degraded. In all activities related to the elimination of the consequences of pollution and the restoration of disturbed lands, it is necessary to proceed from the main principle: not to cause more harm to the ecosystem than that already caused by pollution. The essence of restoration of contaminated ecosystems is the maximum mobilization of the internal resources of the ecosystem to restore its original functions. Self-healing and reclamation are an inseparable biogeochemical process.
Natural self-purification of natural objects from oil pollution is a long process, especially in the conditions of Siberia where low temperatures persist for a long time. In this regard, the development of methods for cleaning soil from oil hydrocarbon pollution is one of the most important tasks in solving the problem of reducing anthropogenic impact on the environment.
Classification of methods for remediation of soils contaminated with oil and petroleum products
Land reclamation is a set of measures aimed at restoring the productivity and economic value of disturbed and contaminated lands. The task of reclamation is to reduce the content of petroleum products and other toxic substances associated with them to a safe level, to restore land productivity lost as a result of pollution (Reimers, 1990). Currently, a number of methods have been developed for eliminating oil contamination of soil, including mechanical, physicochemical, and biological methods (Table 3.1).
Table 3.1 - Methods for eliminating oil contamination of soil (Kolesnichenko, 2004).
|
Elimination methods |
Features of application |
|
|
Mechanical |
Decontamination, pumping out oil from tanks |
Primary measures in case of large spills in the presence of appropriate equipment and tanks (the problem of cleaning the soil when oil seeps into the ground is not solved) |
|
Soil replacement |
Transporting soil to a landfill for natural decomposition |
|
|
Physico-chemical |
Burning |
An emergency measure in case of threat of oil breakthrough into water sources. Depending on the type of oil and petroleum product, 50 to 70% of the spill is destroyed, the rest seeps into the soil. Due to insufficiently high temperatures, products of sublimation and incomplete oxidation of oil enter the atmosphere; After burning, the soil must be taken to a landfill |
|
Fire Prevention |
When flammable products are spilled in workshops, residential areas, or on highways, where fire is more dangerous than soil contamination; isolate the spill from above with fire-fighting foams or cover it with sorbents |
|
|
Soil flushing |
It is carried out in washing drums using surfactants; the washing waters are settled in waterproofed ponds or containers, where they are subsequently separated and purified |
|
|
Soil drainage |
A type of on-site soil washing using drainage systems; can be combined with the use of oil-degrading bacteria |
|
|
Solvent extraction |
Usually carried out in washing drums with volatile solvents, followed by distillation of their residues with steam. |
|
|
Spills on relatively hard surfaces (asphalt, concrete, compacted soil) are covered with sorbents to absorb oil products and reduce the fire hazard from spills of flammable products |
||
|
Thermal desorption |
It is carried out rarely if the appropriate equipment is available, it allows you to obtain useful products down to fuel oil fractions |
|
|
Biological |
Bioremediation |
Oil-degrading microorganisms are used. It is necessary to plow the crop into the soil. Periodic fertilizing with fertilizer solutions, restrictions on the depth of cultivation, soil temperature (above 15ºС), the process takes 2-3 seasons |
|
Phytoremediation |
Removing oil residues by sowing oil-resistant grasses (creeping clover, sorrel, sedge, etc.), which activate soil microflora, is the final stage of remediation of contaminated soils |
Until recently, the most common and cheapest method of eliminating oil pollution was simple burning. This method is ineffective and harmful for two reasons: 1) combustion is possible if the oil lies on the surface in a thick layer or is collected in storage tanks; soil or soil saturated with it will not burn; 2) in the place of burned petroleum products, soil productivity, as a rule, is not restored, and among the combustion products remaining in place or dispersed in the environment, many toxic, in particular carcinogenic, substances appear (Gritsenko, Akopova, 1997).
Cleaning soils and soils in special installations by pyrolysis or steam extraction is expensive and ineffective for large volumes of soil. Large excavations are required, as a result of which the natural landscape is disrupted, and after heat treatment, newly formed polycyclic aromatic hydrocarbons, a source of carcinogenic hazard, may remain in the cleaned soil (Pikovsky, 1993).
Digging slows down the processes of decomposition of petroleum hydrocarbons, leading to the formation of intrasoil flows of oil and formation fluid and contamination of groundwater. Storing contaminated soil creates pockets of secondary pollution.
High-quality removal of oil pollutants at high levels of pollution is often impossible without the use of various types of sorbents. Among the possible raw materials for the production of sorbents, the most attractive are natural organic raw materials and production waste of plant origin. Such raw materials include peat, sapropels, agricultural crop processing waste, etc. Based on such raw materials, for example, sorbents such as “Sorbest”, “RS”, “Lessorb”, etc. have been developed (Kolesnichenko, 2004).
There is a technology for cleaning soils and groundwater by washing them with surfactants. This method can remove up to 86% of oil and petroleum products. It is hardly advisable to use it on a large scale, since surfactants themselves pollute the environment and there will be a problem with their collection and disposal (Pikovsky, 1993).
Reclamation methods used in foreign and domestic practice can be divided into four groups: physical, physicochemical, chemical and biological.
Physical methods include mechanical removal of oil-contaminated and bituminized soil layers containing more than 5% carbon from petroleum products (Yakubov, 1989), collection of petroleum products from the surface using a hydraulic pump (Hinchel et al., 1988), mixing contaminated soils with clean soil to reduce oil content and petroleum products (Abduev, Askerov, 1979; Akhmedov et al., 1988; Ismailov, Pikovsky, 1988).
A number of authors propose to intensively aerate oil-contaminated soils using deep plowing, loosening, disking, and harrowing (Samosova et al., 1979; Anderson, Propadushchaya, 1979, Askerov, 1982; Oborin et al., 1988).
Balch Thomas (1993) proposes intensive collection of contaminated soil into covered piles 4 - 5 m high and up to 40 m wide, at the base of which there is a network of perforated pipes to supply hot air. As a result of diffusion, heated air picks up hydrocarbons and volatile organic compounds.
Hasler Anders (1989) considers the possibility of using cleaning methods by heating the soil to a temperature of 700°C or using a high-pressure water jet. Heimhard Hans-lürgen (1987) suggests using a high-pressure water-air jet. Weston Roy F. (1998), Matig J., Trbenbach G. (1991), Joseph E. Musul (1993) use soil heating technology, which evaporates moisture and organic matter. Jorgenson Torre M., Krizan Larry W et. al. (1991) developed a step-by-step technology for cleaning up oil-contaminated lands in Alaska. Before the soil froze, the oil was removed mechanically and by washing; in the summer of the following year, the soil was fertilized, aerated, and a certain humidity was created, which contributed to favorable conditions for the decomposition of oil. As a result of these measures, the content of oil hydrocarbons decreased by 94% from the initial level.
Physico-chemical methods involve the use of specially selected surfactants (dispersants, dispersants, etc.) and auxiliary substances that affect the change in the state and colloidal dispersed structure of suspended particles in the oil and water phases.
To clean large areas contaminated with harmful man-made compounds, it is proposed to use widespread natural sorbents of organic origin (peat, moss, black soil, coal), clays and clayey materials with a high absorption capacity in relation to pollutants.
Hasler Anders (1989) proposes burning contaminated soils with the simultaneous addition of binders; after heat treatment, the resulting conglomerate is used as a building material, and Rez D.H. (1993) uses Portland cement to neutralize liquid and solid hydrocarbons, while the hydrocarbon is isolated from contact with the environment.
Punt et al. (1991) propose the extraction of soil-polluting petroleum products with a distilled fraction of natural condensate and hexane, and Bulman et al. (1993) and Greiner D (1994) propose chemical saturation of the soil with oxygen to restore its biological activity. Hinchel R.E., Downey D.C. et al. (1998) showed the possibility of using water injection enriched with oxygen or containing hydrogen peroxide.
A major role in accelerating the decomposition of oil and oil products in the soil belongs to mineral and organic fertilizers (Samosova et al., 1979; Demidenko et al., 1983; Abzalov et al., 1988; Gainutdinov et al., 1988, Tishkina, 1990).
The use of nitrogen fertilizers is especially important, because In the soil, oil pollution introduces a large amount of C, sharply changing the C:N ratio. For the normal development of microorganisms, 1 part nitrogen requires 10 parts carbon, in dirty ones up to 400 - 420 (Odu, 1978).
The biological method is the most effective and environmentally friendly method for reclamation of oil-contaminated soils. They include the use of biological products and biostimulants for the degradation of oil and petroleum products.
In the decomposition of oil in soil, the main and decisive importance is the functional activity of the complex of soil microorganisms, which ensure complete mineralization of oil and oil products to carbon dioxide and water. The main contribution to this process is made by microorganisms that are capable of using hydrocarbons as the only source of organic matter and energy. The type of soil, its mineral and organic composition, humidity, aeration, and temperature also affect the rate of degradation of oil hydrocarbons. Based on the ability of microorganisms to use petroleum hydrocarbons and other xenobiotics, a method of biocorrection of pollution has been proposed, which includes the following approaches:
- 1) activation of the degrading ability of microflora, naturally contained in contaminated soil, by introducing nutrients, cometabolized substrates, oxygen - biostimulation;
- 2) introduction into contaminated soil of specialized microorganisms, previously isolated from various contaminated sources or genetically modified - biosupplementation.
Using a biological method based on the use of natural strains of microorganisms, within 3 years of reclamation it is possible to completely restore the fertility of oil-contaminated soils at a pollution level not exceeding 10-15% of crude oil by weight of the soil. In the case of higher concentrations of pollutants, it is advisable to combine bioremediation with physical and physicochemical treatment methods.
The species diversity of oil-oxidizing bacteria is great. Based on strains of various bacteria and their associations, very effective biological products have been created - Rhodotrin, Ekoil, Putidoil, etc.
The physicochemical and chemical methods discussed below are also simulating to a certain extent. Various food additives and surfactants (surfactants), yeast production waste, fish flour, whey, protein and vitamin plant waste, activated sludge, nitrogen, phosphorus and potassium mineral fertilizers, traditional manure and even, as studies have shown, also serve as biostimulating agents. ON THE. Kireeva, liquid wastewater from livestock complexes and other wastewater that is disposed of in agricultural irrigation fields.
The role of earthworms in the decomposition of oil is known. Kibardin et al. (1989) showed that earthworms ingest oil in the soil and make it available to microorganisms.
Sowing alfalfa and other legumes and grasses with a branched root system into oil-contaminated soil helps accelerate the decomposition of hydrocarbons (Aliev et al., 1977; Gudin, Syratt, 1975; Lee Eusiand, 1993). The positive impact of crops of agricultural plants, and in particular perennial grasses, is explained by the fact that with their developed root system they help improve the gas-air regime of contaminated soil, enrich the soil with nitrogen and biologically active compounds released by the root system into the soil during plant life. All this stimulates the growth of microorganisms and, accordingly, accelerates the decomposition of oil and petroleum products. In this regard, one cannot fail to take into account the ability of plants themselves to decompose various classes of petroleum hydrocarbons (Ugrekhelidze, 1976) or adsorb them (Cunningham Scott et al., 1995).
