Lakes of petroleum lifeless shores

Annual costs for purification and reclamation of soil contaminated with hydrocarbons amount to tens of milliards of dollars worldwide.

Production, storage, and transport of oil are accompanied by leakage of a vast amount of petroleum products. The oil products spread to large territories thus contaminating soil and subterranean water.

Today hundreds of millions tons of oil sludge, millions of cubic metres of oil-contaminated water are accumulated in Russia alone. Besides, there is a vast amount of soil contaminated with raw oil and oil products, which is hard to estimate.

Such large-scale contamination of soil, subterranean water, and seas can sooner or later result in an environmental catastrophe, if no countermeasures are taken in the nearest future.

The usual quota of raw oil and oil product losses in oil production and refinement comprises 1-2%, which in Russia amounts to ca. 5 million metric tons per year. According to the more pessimistic estimates, 1.5% of the total amount of liquid hydrocarbon fuel escapes into soil during oil refinement alone.

The soils around many of the oil refineries after tens of years of operation accumulated a huge amount of raw oil and oil products. Sometimes it means hundreds thousands tons. No wonder then that gasoline lakes are formed under most of the refineries, storage facilities, production cites, motor-transport depots, and airports.

For example, the soils near Groznyi in Chechen Republic (Russia) became one of the greatest man-made oil fields. The experts evaluate the amount of oil in this oil field as one million tons. According to certain estimates, the soils in Moscow Region (Russia) are contaminated with 37 thousand tons of oil products yearly.

Great depression

What are the consequences of such intensive contamination of soils with petroleum? First, the oil products penetrating the soil can interact with water-bearing strata and contaminate drinking water sources. Second, the structure of the soil itself degrades, its acidity increases, pathogenic microorganisms are accumulated in the soil (predominantly the pathogens of root rot). Degradation and depression of the soil microflora occurs, soil microbiocenosis and biocenosis as a whole is disrupted.

All this results in a catastrophic degradation of soil fecundity. This, in turn, leads to shrinking of the arable lands and decrease of their productivity. The quality of crops decreases. The total annual losses of Russian economy are estimated as hundreds of milliards roubles (tens of milliards dollars).

This is all the more hazardous since the recovery of fecundity of soils polluted with oil goes much slower than in case of other man-caused contaminants. Water penetrability of the soil changes drastically, water falls down to deeper strata, soil humidity decreases. This leads to the dying off of vegetation, which is one of the main components of the biocenosis.

Raw oil and oil products cause an almost complete depression of the functional activity of fauna and flora. Metabolism of most microorganisms is suppressed. Besides, oil penetrating the soil increases the total concentration of carbon that changes the carbon/nitrogen ratio. The relative lack of nitrogen requires application of greater quantities of nitrogen fertilisers.

The sources of hazard

The facilities of oil producing and oil refining industry are naturally the main sources of environment pollution with oil products. All the components of the biosphere in the oil-producing regions suffer the intensive impact leading to the derangement of ecosystem equilibrium.

A research expedition of the Lomonosov Moscow State University to the major oil-bearing regions of West Siberia and Central Volga Region has been organised recently. The main aim of the expedition was to study the environmental impact of the oil and gas production facilities.

The results obtained by the researchers have shown that oil-field development deranges the natural ecosystems to a very high degree. In particular, the analyses have shown that the soil in the location near a petroleum gas flare (especially within 100-300 metre wide ring) contains a considerable amount of organic carbon compounds.

Such compounds including soot, various petroleum derivatives and incomplete combustion products (like dioxins) lead to a catastrophic change of the vegetation.

Besides, petroleum industry is a typical source of wastewater and sludge polluted with mineral oil. The latter are formed during the construction of oil and gas wells, oil field development, oil refinement, treatment of petroleum-containing wastewater, cleaning of oil tanks and other equipment, and also during accidents.

For all the variety of techniques

Even nowadays remediation of soils and petroleum sludge is still performed with insufficient effect. The problem in general still remains unsolved despite all the efforts of most leading companies producing chemical equipment directed at development and perfection of purifying and regenerating equipment.

The worldwide first separation facilities for remediation of petroleum sludge were built in Russia at the refineries in Yaroslavl and Volgograd. The following conclusions have been made based on the experience of operating these facilities. The separators can be applied for purification of oil sludge.

However, the economical efficiency was very low, because the working cell of the installation had to be opened and cleaned after every 8 hours of operation. A gross engineering error was made in the development of this project: the sludge was loaded into the separator without any preliminary treatment and purification.

The application of separators is rational and economically efficient only at the last stage of petroleum sludge purification.

Because of the unsuccessful experience of separator application for petroleum sludge purification were discontinued, and 25 years later the technology came back to Russia via Western companies.

An installation for incinerating petroleum sludge, bottom deposits of slurry ponds and flotation foam was built at the oil refinery in Ufa (Russia) in 1971. Such installations were in operation till the beginning of the 1980s. However, this way of oil sludge disposal was also economically inefficient.

Apart from the losses of oil, additional fuel was spent for water evaporation and supporting the working temperature in the furnace. Other disadvantages of the installation were the absence of purification of smoke fumes (formed in the process of sludge incineration) from the nitrogen and sulphur oxides, and also the necessity of preliminary treatment of the sludge before incineration.

About the same time a Swedish company Alfa Laval developed an installation for oil sludge remediation. The purification process runs as follows. First the petroleum sludge is pumped into a reservoir where it is kept for several days for initial separation.

Then the separated water is discharged into the wastewater treatment system and the oil-containing fraction is directed to the Alfa-Laval installation. There it goes through a hydrocyclone and then into a two-phase centrifuge for separation from the heavy solid particles. Separation of oil from water is performed in a three-phase separator.

Unfortunately, the experience of operating this installation has shown that it can only purify only freshly formed petroleum sludge. It is absolutely unfit for separation of the bottom deposits of sludge pits. Besides, water at the output of the installation is still polluted with stable oil emulsions.

No treatment of the mechanical admixtures (soil) periodically removed from the separator is performed at all. Yet another drawback of this technology is the absence of chemical reagents-deemulsifiers, which can help to decompose the stable oil emulsions and reach higher purification degree.

Equipment for petroleum sludge remediation produced by the German Company KHD was installed in 1990 at the site of the Production Company Permnefteorgsintez. Equipment produced by the company Flottweg GmbH can be considered similar to that produced by KHD. The initial stage of purification, as in case of Alfa-Laval equipment, consists in pumping the sludge into a reservoir for preliminary separation.

Then the oil fraction from the reservoir is directed to a three-phase centrifuge. Centrifugal forces separate the sludge into three components: oil, water, and solid particles. To enhance the separation efficiency the sludge is treated with chemical reagents before it is loaded into the centrifuge.

The design of the KDH installation is simpler than that realised by Alfa Laval. However, it has a number of essential drawbacks. For example, the preliminary settling reservoir must ensure a high separation degree, so that concentration of petroleum in the sludge at the input of the installation is above 70%.

Otherwise the oil after purification would contain a high percentage of water. In contrast to the three-phase separator, the centrifuge does not allow automating the separation process. Besides, the KHD installation is also designed for separation of freshly formed petroleum sludge. Similar to the Alfa Laval equipment, it can not process the bottom deposits of sludge pits.

Belt filtering presses can in principle compete with the centrifuges. However, such equipment allows only separating soils from liquids. In this technology the processed soil still contains 20-30% of hydrocarbons.

The technologies for destruction of oil sludge using microbiological cultures became widely known in the beginning of 1990s. Specially developed microbial cultures are currently applied: Putidoil, Devoroil, etc. The essence of the process is the following: a huge quantity of microbial cultures is produced (propagated) in factories and transported to the application site either in sacks or mixed with liquids (and thus ready for use).

The polluted soil is excavated and spread over a specially prepared site so that soil layer thickness is within 20-30 cm. The evenly distributed soil is then sprayed with the water-based mixture containing microbial cultures. If the cultures are transported in dry form, then mixing them with water and nutrient solution and seasoning them for several hours is necessary before application.

The soil should be periodically ploughed and sprayed with additional quantities of water mixture containing microbial cultures. The processing of soil lasts 1-2 years. Often the treatment with microbial cultures is performed without excavating the polluted soil and spreading it uniformly over a specially prepared territory. In this case the duration of the treatment can exceed three years.

Note that the biodestruction technique is inefficient when concentration of hydrocarbons in soil exceeds 15%. In this case too large quantities of biological cultures are required. Metabolism of hydrocarbon-oxidising bacteria requires oxygen, therefore biodestruction of hydrocarbons is observed only in the upper layer of soil within 20 cm from the surface. Humidity of the processed soil should be no less than 75%.

Besides, the activity of the bacteria at temperatures below 10C is almost zero. To prevent the pollution of the treatment site, its surface should be protected with gasoline- and oil-resistant hermetic material before spreading the contaminated soil over it.

What even bogart failed to achieve

American Company Bogart environmental services has developed an original technique for separation of soils polluted with oil products. This company has several years successful experience of working in Kuwait on remediation of sandy soils from spilled oil.

During the first stage of this technique the soil is excavated and mounted into 10 metre high heaps. Part of the oil is squeezed from the soil by the sheer weight of the sand. Then the oil is purified with centrifuges. The remaining soil is mixed with water to reach 95% humidity and put into reservoirs for biological destruction of hydrocarbons.

The experts of the Company Bogart visited Krasnodar Region in 1994. They took samples of local soils and signed a co-operation agreement with the Krasnodar Regional Environmental Committee. However after having studied the soil samples the Company came to the conclusion that their technology is unsuitable for purification of chernozem soils characteristic for the Krasnodar Region. The chernozem soils contain a large quantity of light solid particles.

Application of the technology and equipment developed by the Bogart Company for purification of light soils encounters several difficulties. First, such soils are almost impossible to mount in compact heaps. Therefore the biological purification has to start while the soil still contains a lot of free oil. However, the microbiological technique is effective only for hydrocarbon concentration in soil below 15%.

Besides, the Bogart Company mixes the polluted soils with clear water to enhance the efficiency of oil biodestruction by bacterial cultures. Thus the drawbacks of this technology are the high water consumption rate and an essential increase of purification duration.

Microorganisms applied for biodestruction of hydrocarbon pollutants tend to accumulate hazardous chemical elements and substances. The number of microorganisms in the purified soil is proportional to the quantity of nutrient substance (i.e. hydrocarbons) in the polluted soil. So the greater mass of hydrocarbons is subjected to biodestruction, the greater is the surplus biomass in the soil after the process is completed. Bogart Company purifies soils with high concentration of hydrocarbons, and this causes accumulation of a greater quantity of hazardous substances in the bacterial cells. This is in itself can be dangerous for the environment.

In order to maintain the biodestruction process in biological purification of soil, vast amounts of biomass should be regularly applied to the processed soil. Therefore the purification sites are usually equipped with reactors for producing this biomass.

This implies costs for the nutrient solutions and additives required for propagation of bacteria. Ferments can be applied to reduce the total biomass necessary for biodestruction of hydrocarbons. However, this also leads to an essential increase of the technologys cost.

Note also that hydrogen-oxidising bacteria work effectively only when the ambient air temperature is above 10C. At lower temperatures the cells fall into anabiosis, therefore optimal climatic conditions are necessary for microbiological purification of oil-polluted soils.

So the soil purification process can extend to several years in the climate characteristic for Russia. Besides, no special machinery is used in Russia for harrowing the soil during biological remediation.

Besides, Bogart Company has practically no technology for removing dense viscous oil products or large objects: stones and debris from the treated soil.

The solution was close at hand

The experts of the Institute of Ecotechnologies developed a multi-stage technology for soil remediation. This technology combines various purification methods (extraction, mechanical, etc.). This allows removing oil products and also radionuclides, heptyl, and other chemical pollutants.

The installation developed and produced by the Institute has a modular design. Each module can fit in a standard 6 metre long container. This allows using this installation as a mobile plant for soil purification. The installation is shipped in three modules: soil purification module, analysis and control module, and power production module. Remediation cycle in this installation takes approximately 60 minutes. Two operators can control this plant during one shift.

The Institute has also developed an installation for collecting oil products, which can be used in temporary sheds or other locations where great amount of oil product was spilled or accumulated. The functional design of this installation is shown in a figure below.

Both installations have been successfully used at the Moscow oil refinery for several years.

The installation for pumping off of the oil products can be applied at the initial stage of soil remediation in case of high degree of oil pollution, and the modular installation can be used for additional purification.

The Institute provides equipment shipping, starting-up and adjustment of the installation, choosing and shipping deemulsifiers, warranty service, and maintenance staff training.

Andrei ILINICHEV,

Senior research associate of the

Institute of Ecotechnologies

Valerii CHERNONOZHKIN

Head of laboratory of the

Institute of Ecotechnologies

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