JP4423061B2 - Decomposition method of oil in soil - Google Patents

Description

  The present invention relates to a method for degrading oil in soil, in which bacteria are grown in soil containing an oil component to decompose the oil component.

  Conventionally, when a microorganism is grown to decompose an oil component in soil containing an aromatic hydrocarbon (PAH) that is an oil component, for example, a low-molecular oil component of a 4-ring PAH or less (4-ring or less PAH) Can be decomposed relatively easily by many microorganisms, but oil components of 5-cyclic PAH or higher (5-ring or higher PAH) are difficult to decompose and remain in the soil without being decomposed ( There is no appropriate patent document that mentions such problems).

The inventors of the present invention have repeatedly studied and experimented on the decomposition of microorganisms with respect to oil components of five-ring PAH or more, and found that sulfate-reducing bacteria are effective in degrading resins or asphaltenes that are oil components of five-ring PAH or more. I came to know that there was.

The present invention is based on this new finding, and its purpose is to grow microorganisms and effectively decompose them even in soil containing resin or asphaltene , which is an oil component higher than pentacyclic PAH. It is to provide a method for decomposing oil in soil.

The first characteristic feature of the present invention, by adding sulfuric acid or sulfate to the soil containing the resin or asphaltenes is an oil component of 5 or more rings aromatic hydrocarbons, pH 4 to the sulfate-reducing bacteria in anaerobic conditions In an environment of pH 9 and grown at a temperature of 10 ° C. to 38 ° C. , the sulfate-reducing bacterium reduces the molecular weight of the aromatic hydrocarbons having 5 or more rings to aromatic hydrocarbons having 3 or less rings, Thereafter, the aromatic hydrocarbons having 3 or less rings are decomposed by aerobic bacteria under aerobic conditions.

According to the first characteristic configuration of the present invention, sulfate-reducing bacteria are added under anaerobic conditions by adding sulfuric acid or sulfate to soil containing resin or asphaltene which is an oil component of five or more aromatic hydrocarbons. As it grows, the sulfate-reducing bacteria decompose the high molecular weight oil component to lower the molecular weight, as is apparent from the experimental results described later. More specifically, oil components of 5-cyclic PAH or more (5-ring or more PAH) that have been conventionally impossible to be decomposed by microorganisms, such as resins and asphaltenes, are tricyclic PAH or less (3-ring or less PAH) is reduced in molecular weight.
And after that, the aerobic bacteria under aerobic conditions further decomposes the oil component whose molecular weight has been reduced to less than tricyclic PAH, and finally decomposes the oil component contained in the soil. I can .

At that time, according to the first characteristic configuration of the present invention, since the sulfate-reducing bacteria are grown in an environment of pH 4 to pH 9, the growth of the sulfate-reducing bacteria is promoted, and within a relatively short period of time, 5 An oil component of cyclic PAH or higher can be reduced to a molecular weight of tricyclic PAH or lower, and it is particularly effective and preferable to grow in an environment of pH 5 to pH 7.

Further, according to the first characterizing feature of the present invention, since grown at a temperature of 10 ° C. to 38 DEG ° C. The sulfate reducing bacteria, the growth of sulfate-reducing bacteria is promoted, among relatively short period In addition, it is possible to reduce the molecular weight of an oil component of 5 cyclic PAH or higher to 3 cyclic PAH or lower, and it is particularly effective and preferable to grow at a temperature of 25 ° C. to 38 ° C.

A second characteristic configuration of the present invention is that the sulfate-reducing bacteria are grown under a sulfate ion concentration of 5 mM to 20 mM.

According to the second characteristic configuration of the present invention, since the sulfate-reducing bacteria are grown under a sulfate ion concentration of 5 mM to 20 mM, the concentration is not very toxic, and the growth-promoting effect of the sulfate-reducing bacteria can be achieved. In particular, it is more effective and preferable to grow under a sulfate ion concentration of about 10 mM.

An embodiment of the method for decomposing oil in soil according to the present invention will be described.
In particular, the present invention adds sulfuric acid or sulfate to soil containing aromatic hydrocarbons (PAH) as an oil component to grow sulfate-reducing bacteria under anaerobic conditions, and then favors them under aerobic conditions. This is a method of degrading oil in soil, which is degraded by aerobic bacteria, and its effects have been confirmed through various experiments, so the main experiments and the results will be mentioned.

First, the apparatus used in the experiment will be described. As shown in FIG. 1, a glass filter funnel containing a soil S containing an oil component as a sample is used as a sample container 1 and a cylinder containing a solution L as a medium. A mold-bottom separable flask (capacity 1 L) was used as the solution tank 2, and the solution L in the solution tank 2 was circulated and supplied to the sample container 1 by the pump 3.
The sample container 1 has a double structure equipped with a water jacket 4, and in order to ensure the porosity of the sample soil S and avoid clogging, the sample soil S and glass beads having a diameter of 2 mm are in a weight ratio of 1: 1. 300 g of the mixture was put into the sample container 1 and covered with a silicon stopper.
In the solution tank 2, a stirrer 5 for stirring the solution L is disposed, and the outer side of the sample container 1 is covered with aluminum foil and shielded from light in consideration of the influence of light.

[Experimental example]
An oil component decomposition experiment was conducted using the apparatus shown in FIG.
In addition, the soil S containing resin and asphaltenes, which are oil components of 5-cyclic PAH or higher (5-ring or higher PAH), is used as a sample, and the sulfate ion concentration is 5 mM to 20 mM, more preferably about 10 mM as the solution L. The solution L is used, and the solution L is adjusted to pH 4 to pH 9, more preferably pH 5 to pH 7, and warm water is supplied to the water jacket 4 so that the inside of the sample container 1 is 10 ° C. to 38 ° C., preferably 25 ° C. It was kept at ˜38 ° C., more preferably at approximately 35 ° C., under anoxic conditions. Then, the oil component concentrations were measured 57 days, 143 days and 248 days after the start of the decomposition treatment, respectively, and the results are shown in FIG.

In FIG. 2, the horizontal axis indicates the number of days elapsed, and the vertical axis indicates the carbon concentration (mg) per gram of soil. From this experimental result, the resin and asphaltene components are reduced by about 50% after 248 days. It was found that the aromatic component, which is a lower molecular weight PAH, increased and the carbon concentration hardly changed as a whole.
Next, the sample soil S after 248 days is spread on a tray, and water is supplied to such an extent that the sample soil S is not dried and soaked in water, and stirred once a week for the sample soil S. The result of measuring the oil component after 56 days after supplying air is shown in the right end of FIG. According to this, the aromatic component was reduced by about 76%, and the carbon concentration was also reduced by about 62% as a whole.

[Comparative Example 1]
In order to compare with the above experimental example, a comparative experiment was performed using the same apparatus.
In addition, except that water was used as the solution L, all comparative experiments were performed under the same conditions as the experimental examples. That is, the soil S containing resin and asphaltenes was used as a sample, hot water was supplied to the water jacket 4 to maintain the inside of the sample container 1 at approximately 35 ° C., and left under oxygen-free conditions. The oil component concentrations were measured 57 days, 143 days and 248 days after the start of the comparative experiment, respectively, and the results are shown in FIG.
From the experimental results shown in FIG. 3, it was found that the concentration of the oil component hardly changed even after 248 days.

[Comparative Example 2]
As a precaution, a comparative experiment was also performed under aerobic conditions.
That is, a soil S containing resin and asphaltenes is used as a sample, the sample soil S is spread on a tray, and water is supplied to the extent that the sample soil S is not dried and immersed in water, once a week. The air was supplied to the sample soil S with stirring at a ratio of ≦, and the oil component was measured after 56 days. The result is shown in FIG.
From the experimental results shown in FIG. 4, it was found that the carbon component decomposed by about 42% as a whole, but most of the carbon components were decomposed by the aromatic component, and the resin and asphaltenes component were hardly decomposed.

From the above experimental examples and comparative examples 1 and 2, sulfate ions (sulfuric acid or sulfate) are added to the soil containing the resin and asphaltenes as oil components to grow sulfate-reducing bacteria under anaerobic conditions, Decomposition with aerobic bacteria under aerobic conditions ensures that the resin and asphaltene components were not decomposed only under anaerobic conditions without addition of sulfate ions or only under aerobic conditions. It was clarified that the oil component in soil was effectively removed .

Schematic diagram of the equipment used for the experiment Chart showing experimental results Chart showing results of Comparative Example 1 Chart showing results of Comparative Example 2

DESCRIPTION OF SYMBOLS 1 Sample container 2 Solution tank 3 Pump 4 Water jacket 5 Stirring apparatus L Solution (medium)
S Sample soil

Claims (2)

5 by adding sulfuric acid or sulfate to the soil containing the resin or asphaltenes is an oil component of the ring or aromatic hydrocarbons, the sulfate reducing bacteria in the environment of pH4~pH9 under anaerobic conditions, and, 10 ° C. Growing at a temperature of ˜38 ° C., the sulfate-reducing bacterium reduces the molecular weight of the aromatic hydrocarbons having 5 or more rings to aromatic hydrocarbons having 3 or less rings, and then aerobic bacteria under aerobic conditions The method for decomposing oil in soil for decomposing the aromatic hydrocarbons having 3 or less rings by the above method. The method for decomposing oil in soil according to claim 1, wherein the sulfate-reducing bacteria are grown under a sulfate ion concentration of 5 mM to 20 mM.

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