BG65778B1 - Method for bioremediation of soils - Google Patents

Abstract

The invention relates to a method for bioremediation of soil contaminated with hydrocarbon waste, in particular petroleum and petroleum products. It is based on the ability of the local soil microflora to actively develop under co-metabolic conditions, where non-growth substrates are oxidized conjugationally with organic compounds, which in turn serve as growth substrates for the soil microflora.The proposed combination of operations according to the invention leads to significant acceleration of the process of biodegradation of the oil products, whereat for a period of one month 88 to 95 percent oxidation of the pollutant is achieved.

Description

Technical field

The invention relates to a method for bioremediation of soils contaminated with hydrocarbon wastes, in particular oil and petroleum products.

BACKGROUND OF THE INVENTION

It is known that the main factors influencing the process of bioremediation of soil contaminated with hydrocarbon wastes with the participation of local soil microflora are the presence of water, the concentration of pollutants and their ability to form stable emulsions, temperature, oxygen access, acidity. , as well as the salinity of the medium and the presence of nitrogen and phosphorus inorganic salts. On this basis, different approaches have been developed for the recovery of contaminated soils, namely:

According to a number of patent documents, specialized microbial crops are used to enrich the soil with a view to decomposing hydrocarbon pollutants based on their biological activity. For example, according to WO 2000/056668, the concentration of oil in various media is reduced by the use of butane-digesting microorganisms in the presence of oxygen. Microorganisms such as Pseudomonas, Variovorax, Nocardia, Comamonas, Acidovorax, Rhodococcus, Chryseobacterium, Comamonas, Rhodococcus, Aureobacterium, Micrococcus, Aeromonas and others have been proposed as alkane-absorbing microorganisms.

Another type of approach is based on the preparation of specialized microbial cultures and their combination with plantations. Thus, RU 2181640 provides for biological remediation of soils contaminated with oil and petroleum products by means of a biological preparation consisting of several micro-organisms, a grass mixture and a plant growth regulator.

European Patent Application EP 1008396 offers remediation of soils contaminated with oil and petroleum products through combined mechanical, physical and chemical treatment. In particular, the proposed method involves mixing contaminated soil with thermally-fractionated graphite, adding water and separating the sorbent that rises to the surface with the petroleum products adsorbed thereon.

Another approach for bioremediation involves the use of a suspension of microorganisms based on the local soil microflora and their supplemental feeding with nitrogen and phosphorus salts in order to stimulate their biological activity in order to degrade the pollutants. Thus, RU 2062669 describes a method for the elimination of hydrocarbon contamination of soil by aeration of contaminated soil, the introduction of a microbial suspension of microorganisms and the introduction of mineral salts of nitrogen and phosphorus. In the case of the preparation of the microbial suspension, a community of micro-organisms, taken from the well with oil-contaminated soil, is used.

SUMMARY OF THE INVENTION

In essence, the invention is a method of bioremediation of soils contaminated with hydrocarbon wastes, in particular oil and petroleum products. It is based on the ability of the local soil microflora to actively develop in metabolic conditions, when non-growth substrates are neatly oxidized with organic compounds, which in turn serve as growth substrates for the soil microflora. In particular, the method is based on the ability of the local soil microflora to oxidize petroleum hydrocarbons in the presence of carbohydrates as a sometabolite at a concentration that acts stimulating the synthesis of the enzymes responsible for the transformation of the petroleum hydrocarbons.

The bioremediation of soils, according to the method, is carried out by a sequence of operations, which includes homogenization of contaminated soil, introduction of a sometabolite and solution of inorganic salts with subsequent aeration and moistening of the soil at observance of temperature limits from 15 to 30 ° C. D-glucose is used as a metabolite,

65778 Bl a nitrogen and phosphorus fertilizers, in particular potassium nitrate (KNO ₃ ) and bibasic potassium phosphate (CNDP) are used as a source of inorganic salts.

The method provides two embodiments whereby the bioremediation of soils with contamination below and about 10% of the pollutant by soil weight is carried out at the site of contamination (in situ), and the bioremediation of soils with contamination over 10% by weight of the soil, yes is purified on a specially designed site (ex situ).

Regardless of whether the soil substrate is treated on-site or outside the contamination zone, the amount of D-glucose introduced is such that during the co-oxidation process, the ratio of Dpucose to oil or oil products is maintained at 1: 2, respectively. Nitrogen and phosphorus fertilizers are introduced in the form of a 0.012% aqueous solution in compliance with a ratio of 4: 1, respectively. The solution is introduced in an amount amounting to 5 to 6% of the volume of contaminated soil, and its additional moistening is carried out with 2.53% of water. Aeration of the soil is carried out by plowing before the start of treatment and 3-4 days after the introduction of sametabolite and fertilizers.

The method according to the invention enables the stimulation of the activity of local soil microflora with respect to the biodegradation of oil of both light and heavy type; the proposed combination of components involved in the process alters the mechanism of degradation of the petroleum, with aromatic compounds and paraffins being preferably oxidized in light-type oil, and in iso-alkanes, benzene and poly-aromatic compounds being preferably broken down in heavy-duty oil. The proposed combination of operations according to the invention leads to a significant acceleration of the process of biodegradation of petroleum products, with 88 to 95% oxidation of the pollutant achieved over a period of one month.

Examples of carrying out the invention

The invention is illustrated by the following non-limiting embodiments.

Example 1. In situ bioremediation of soil

In the extraction of rock salt from the Mirkovo field by underground leaching through deep wells, in the latter, a certain amount of insolvent is pumped according to technology dating from 1954. Light fractions from the distillation of oil - oil, gas oil, are used as the solvent. therefore, many oil spills have been identified as a result of accidents and repairs. Studies of averaged soil samples show that in 24 well areas, the values of petroleum products in contaminated soils exceed 5000 mg / kg dry soil and in some cases are in the order of 44000 mg / kg. In order to solve such an environmental problem, proceed to the treatment of the relevant section of oil-contaminated soil as follows.

The soil in a 10 x ^{2 section} with a petroleum concentration of 103.5 g / kg dry soil is purified at the site of contamination. For this purpose, it is first subjected to homogenization. During the first week, 40015% D-glucose solution is introduced into contaminated soil once. Subsequently, 250 l of a 0.012% potassium nitrate solution (KNO ₃ ) and bibasic potassium phosphate (K ₂ HPO ₄ ) are added, followed by aeration by manual loosening. In the second week, the same quantities of D-glucose solutions and nitrogen and phosphorus fertilizers are re-introduced once with subsequent aeration. During the next, third week, the amount of D-glucose introduced is reduced - 350 1 5% D-glucose solution is introduced without fertilizer solution being introduced, but after aeration water is irrigated according to with atmospheric conditions to reach more than 20% soil moisture. During the fourth week, the treatment from the previous one was repeated (Scheme 1).

After completion of the 4-week treatment cycle, averaged soil samples were taken according to BDS 17.4.5.01-85 to determine the content of petroleum hydrocarbons in them. The results show over 95% degradation of petroleum products.

Example 2. Ex situ soil bioremediation

Soil with contamination of more than 10% of oil is recovered from the spill site and forced

65778 Bl on a specially designed site 10 m ² in size. The latter shall be concreted and properly insulated so as to prevent contamination of groundwater aquifers. The maximum height of the soil layer after homogenisation and leveling should be 0.70 t. The site is surrounded by ditches, which will not allow the arbitrary transfusion of water from them in case of greater waterlogging of the treated soil and to drain such waters to the drainage system, so that the oil be captured and collected without the risk of new pollution.

This type of bioremediation avoids the possibility of contamination of groundwater and surface water. the process control capability is significantly higher and even allows for automation, and the water returns to the soil for fresh humidity.

To this end, in the first week, 400 1 12% D-glucose solution was introduced into the pre-homogenized soil with a contaminant of the order of 244.9 g / kg dry soil. Subsequently, 250 l of a 0.012% potassium nitrate solution (KNO ₃ ) and bibasic potassium phosphate (K ₂ HPO ₄ ) are added, followed by aeration by manual loosening. In the second week, the same quantities of D-glucose solutions and nitrogen and phosphorus fertilizers are re-introduced once with subsequent aeration. In the next third week, 350 1 5% solution of Dpokoza is introduced without the fertilizer solution being introduced, but at the same time after aeration irrigation is carried out with water in accordance with atmospheric conditions to reach more than 20 % soil moisture. During the fourth week, the treatment from the previous week was repeated (Scheme 1).

After completion of the 4-week treatment cycle, averaged soil samples were taken according to BDS 17.4.5.01-85 to determine the content of petroleum hydrocarbons in them. The results show over 88% oil degradation.

Claims (5)

Claims 1. A method for bioremediation of soils contaminated with hydrocarbon wastes, in particular oil and petroleum products, by aeration and with the participation of local soil microflora in the presence of nitrogen and phosphorus salts, characterized in that it involves homogenizing the soil, introducing D-Pococcosis and solution of inorganic salts, followed by aeration and humidification. A soil bioremediation method according to claim 1, characterized in that the amount of D-glucose introduced into the pollutant is in the ratio of 1: 2. A soil bioremediation method according to claim 1, characterized in that nitrogen and phosphorus fertilizers in the ratio of 4: 1 are used as a source of inorganic salts. A soil bioremediation method according to claim 4, characterized in that the nitrogen and phosphorus fertilizers are introduced in the form of a 0.012% aqueous solution. 5. A soil bioremediation method according to claim 4, characterized in that the solution of nitrogen and phosphorus fertilizers is introduced in an amount of from 5 to 6% by volume of the contaminated soil.