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№ 6 (June 2012)

Rehabilitation of Contaminated Soil and Water with Biodegradable Sorbents

   Increasingly common oil contamination of soil and water causes extensive damage to the environment. Rehabilitation, one of the most important environmental measures, is aimed at restoring the fertility of contaminated soil.

By Pavel Ivasishin. Deputy General Director of OSH, Process Safety and Environmental Science, YUGRAGASPERERABOTKA LLC

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   Application of sphagnum-based biological sorption technologies has been producing excellent results in this area.

The Causes of Oil Contamination

   An oil spill can occur throughout the technologic chain – production, transportation and storage, refining and application. Often, contamination may be due to the physical wear and tear of equipment or because of its mechanical failure. Trunk and infield oil pipelines dominate the list of oil contingencies. Here, the vast majority of accidents are due to the corrosion of equipment and poor quality of construction and assembly work; only minor part can be attributed to a factory defect or operational error.

   Russia’s environmental legislation requires, in the shortest time, containment and elimination of crude oil and oil products spills and reduction of residual hydrocarbons in the environment to an acceptable level. Rehabilitation of the soil fully or partially infertile due to oil spills is obligatory. After all the work is done, rehabilitated soil, adjacent areas and water zones should form optimal environmentally balanced sustainable landscape. RF Resolution “On urgent measures to prevent and eliminate oil and oil products spills” states that every facility must develop an oil spills contingency plan (OSCP). However, in practice, most companies have neither OSCP nor technical equipment and materials to remove contamination.

Methods for Oil Spill Containment and Elimination

   Mechanical methods of containment and elimination of oil spills facilitate collection of hydrocarbons from the soil and water surfaces using specialized instruments and devices. In this case large volume of hydrocarbons gets absorbed into the soil, rendering impossible the option for mechanical collection. With the development of science and technology companies started to use physico-chemical and biological methods along with mechanical methods.
Physico-chemical methods for spills elimination are based on the use of oil sorption materials. Depending on the mechanism of oil absorption, such materials can be divided into adsorbents and absorbents. In turn, each of these varies by the origin, dispersion, oil capacity, floatability, moisture capacity, and other indicators. Today, both inorganic and organic sorbents of either natural or synthetic origin are used. Many sorbents are universal – they can absorb quite a wide range of oil products. Recently, the choice of spill contingency tools increasingly leans towards sorbents capable of absorbing oil and oil products and decomposing the material into simple and harmless substances – carbon dioxide and water. In this case the process of oil products biodegradation is completed using natural microorganisms. To accelerate oil products biodegradation along with the sorbents the companies can apply bio-products that contain colonies of various microorganisms – biodestructors of oil.

Rehabilitation of Soil and Reservoirs with Biodegradable Sorbents

   Oil spill can destroy flora and fauna, cause mutation of microorganisms living in soil and in water. Restoration of vegetation in contaminated soils is slowed down or altogether stopped.

   Rehabilitation of contaminated soil is paramount for any oil contingency plan. Rehabilitation is required for 95.9% of the contaminated soil. Each year, the area of contaminated soil requiring rehabilitation grows by 10,000 hectares.
It is worth recalling a recent example, when on 25 April 2012 more than 300 tons of oil products contaminated Angara River after the illegal tie-in into the pipeline of “Pribaikalie” facility of Federal State Reserve Agency. The leak has been eliminated but the concentration of hydrocarbons in the spill area is 20-120 times higher than normal (depending on the distance from the contamination source), reports Russia’s environmental watchdog (Rosprirodnadzor).

   Good indicators of rehabilitation for contaminated areas are achieved through the use of absorbents using a modified sphagnum moss peat. The modification is based on the finding that after high-temperature processing the peat changes its properties from hydrophilic to hydrophobic and oleophilic. The humic component works as a catalyst for autochthonous biocenose, boosting its activity and amplifying its interaction with hydrocarbons. After hydrocarbon biodegradation, a peat capsule goes into a hydrophilic state and begins to absorb water, just as in ordinary natural conditions, becoming a useful component for both soil and water.

   In order to confirm the effectiveness of water-surface absorbent based on a modified sphagnum moss peat, one of the environmental analytical labs ran relevant trials. The trials identified key indicators of the absorbent: bulk density, oil capacity, floatability, and tested the oil sorbing ability of the absorbent for the water surface. The tests also helped to define the scale for absorbent-based water purification in case with oil. Measurements by fluorimetric method showed that after using the sorbent, the average residual content of oil dissolved in water, as obtained by triangulation, is 0.086 mg/l (0.094; 0.073; 0.091). This is fully consistent with MPC for water facilities of domestic, cultural and drinking use: the maximum oil content of 0.3 mg/l, polysulphide oil – 0.1*.

   The specialists of the Department of Industrial Ecology at Gubkin’s oil&gas state university under the lead of the department head Professor S. Meshcheryakov studied in detail the influence of peat absorbent on oil contaminated soil. The experiment conducted in the department lab over seven months period has shown that application of absorbent based on modified sphagnum moss peat during rehabilitation of oil-contaminated soils results in significantly lower hydrocarbon content, reduction of toxic levels to the background values and the almost complete reduction in plant growth inhibition. This means that the use of absorbent based on modified sphagnum moss peat in a short time normalizes ecological situation on the location of the oil spill.

   Two weeks after the start of the experiment, two samples with sorbent in the proportion of oil/absorbent 1:1 and 4:1 with complex granular fertilizers showed reduction of hydrocarbon content by 73% and 67% respectively, after 6 months – by 94.3% and 94% respectively (Fig. 1). Other samples for the same two-week period showed 15-47% improvement, with gradually slower reduction of hydrocarbons content in the samples without the absorbent. According to the norms of Khanty-Mansy Autonomy, tests on samples with sorbent in proportion to oil 1:1 and 1:4 enable usage of absorbent on soil with these parameters. To evaluate the soil rehabilitation from a biological point of view, a number of additional studies was conducted on the influence of the sorbent based on modified sphagnum moss peat on the process of soil rehabilitation.

   Study of the Soil Toxicity Levels. In the early stages of the experiment, the toxicity of soil reached a high level. After 3 months, toxicity level approached zero in all the samples that used a modified sphagnum moss sorbent (Fig. 2).

Soil Microbiocenosis Activity

   Inhibition of the soil microbiocenosis was observed during the entire experiment in all samples. The exception is the sample, where the absorbent dose is the highest (proportion to oil 1:1). Samples with proportion of oil and absorbent at 4:1, 2:1 and 4:1 with fertilizers may be considered satisfactory at the final stage of the experiment, where inhibition slightly exceeds the permitted value of 30% (Fig. 3).

Phytocenotic Indicators

   Study of phytocenotic indicators of cereals showed the soil toxicity in all of the experimental samples. Soil toxicity in samples with absorbent is less pronounced. All plants involved in the experiment (wheat, oat, radish and grass) showed pronounced inhibition of the root system due to the soil toxicity. Wheat grain was the most sensitive to oil pollution. Aboveground part of plants is also inhibited. Inhibition slightly decreased as more absorbent applied to the contaminated soil (proportion with the oil 2:1 and 1:1).

   Comprehensive studies showed best performance results in two samples: the first – with a moderate dose of absorbent based on the modified sphagnum moss peat (the ratio to oil 4:1) on the fertilizer background; the second – with a maximum dose of the same absorbent (the ratio to oil 1:1) (Fig. 4).
Biological studies revealed that, despite the reduction of hydrocarbons level in oil-polluted soil without absorbent application, full-scale plant life cannot be guaranteed.

   In order to evaluate the effectiveness of rehabilitation with the absorbent, the lab conducted research on the possibility of biodegradation of oil contamination and drilling slurry. The results showed that oil content in test samples fell by 78%. Oil products level in the test samples continued to decline, reaching the maximum permissible concentrations level after 100 days (See the Table).
High clearing rates of contaminated soils and waters with sorbent based on modified sphagnum moss peat constituted a ground for its introduction into the standard oil/products and drilling slurry contingency procedure for soil and water next to the largest companies. An example is given by use of the absorbent on contaminated soil one of the companies in the Khanty-Mansiysk Autonomy. Before applying the absorbent, oil product content in soil reached 28%. 45 days after sorbent application, oil product content fell 20% to 5.8%, lower than the Khanty-Mansiysk MPC level (6%) (see the picture).

   Soil rehabilitation considered completed after the establishment of dense and sustainable grass; the concentration of residual oil with oil oxidation rate over 90% should stay at below 8.0% site average in organic soil and 1.5% in mineral and mixed soils.

   Examination of the entire experiment in the development suggests that with biodegradable sorbents the rehabilitation of oil-contaminated soils is faster and more efficient. Also, biodegradable sorbents have a positive impact on the development of plants in contaminated soils. Especially good results were shown by the sorbent based on the modified sphagnum moss peat.

   The sorbent helps to normalize the environment in the oil contingency zone, both on the soil and water. Experts only have to scatter it on the oil spill location and leave for a while. Its use accelerates the process of rehabilitation of soil and water contaminated with oil and drilling slurry and is justified from economic as well as environmental point of view, as confirmed by the experiments.

1. RF Government Resolution of 21.08.00 No. 613 “On urgent measures to prevent and eliminate oil and oil products spills” (revision of 15.04.02 No. 240).
2. Order of the Ministry of Natural Resources “On improving the oil contingency operations» No. 144, 2003.
3. Report on the results of research at the Department of Industrial Ecology of Gubkin’s oil&gas state university “The influence of peat absorbent on oil spill contingencies” Moscow, 2008.
4. GN about MPC of the chemicals for water facilities of domestic, cultural and drinking use from 04.03.98 as amended on 15.06.03.a

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