JP3412674B2 - Decomposition and removal of oil-contaminated soil by microorganisms - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for decomposing and removing oil-contaminated soil by microorganisms.

[0002]

2. Description of the Related Art Recently, a technique called so-called bioremediation, which decomposes pollutants by microorganisms to render them harmless, has been attracting attention.

[0003] Bioremediation is a method of degrading pollutants by making use of the ability of degrading microorganisms such as bacteria and fungi to render them harmless. -By adjusting the environment such as nutrition and aeration to improve the activity of microorganisms, the pollutants can be decomposed more efficiently than in the natural state.

Since such bioremediation does not use any chemicals like physical treatment or chemical treatment, it is low in cost and high in safety, and it is expected that its application range will be further expanded in the future.

[0005]

When, for example, purifying soil contaminated with crude oil by bioremediation, various hydrocarbon compounds having 5 to 40 carbon atoms, which are the main components of crude oil, are Depending on the type of structure, it is roughly divided into so-called aliphatic hydrocarbons such as paraffin-based and olefin-based ones and aromatic hydrocarbons, and easily degradable hydrocarbons such as aliphatic hydrocarbons and aromatic hydrocarbons with a relatively simple structure. Hydrogen can be decomposed relatively easily by bacteria contained in the soil.

[0006] On the other hand, persistent hydrocarbons such as polycyclic aromatic hydrocarbons having a complicated structure cannot be decomposed by such soil fungi, and the polycyclic aromatic hydrocarbons cannot be decomposed. Degradable special selection (screening)
Even if you use these bacteria, they usually compete with soil bacteria,
There was a problem that it declined without being able to exert its original decomposition action.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for decomposing and removing oil-contaminated soil by a microorganism capable of decomposing and removing polycyclic aromatic hydrocarbons.

[0008]

In order to achieve the above object, the method for decomposing and removing oil-contaminated soil by microorganisms according to the present invention is naturally contained in oil-contaminated soil as described in claim 1. For the oil-contaminated soil, at least nutrition, aeration, moisture and temperature are controlled for a predetermined period so that the decomposition activity of indigenous bacteria is increased, and the easily degradable hydrocarbons in the oil-contaminated soil are decomposed and consumed to cause the indigenous soil. It is judged that the fungus has declined based on the time when the oil content in the oil-contaminated soil is monitored and their content hardly decreases, and after the decline of the indigenous bacteria,
The lignin-degrading enzyme produced during the growth process of white-rot fungi is added to the oil-contaminated soil.

Further, in the method for decomposing and removing oil-contaminated soil by microorganisms according to the present invention, the lignin-degrading enzyme is added to the oil-contaminated soil together with the white-rot fungus and its carrier, and the carbon content (T The ratio (C / N) of —C) to the amount of nitrogen (TN) is adjusted so that a new lignin-degrading enzyme is produced from the white-rot fungus.

Further, the method for decomposing and removing oil-contaminated soil by the microorganisms according to the present invention, as described in claim 3, so that the decomposition activity of indigenous bacteria naturally contained in the oil-contaminated soil is enhanced. For the polluted soil, at least nutrition, aeration, moisture and temperature are controlled for a predetermined period, and it is shown that the indigenous bacteria have declined due to the decomposition and consumption of easily degradable hydrocarbons in the oil-contaminated soil. The oil content of the oil is monitored and judged based on the time when the content of the oil hardly decreases. After the indigenous bacteria have declined, the white-rot fungus and its carrier are added to the oil-contaminated soil, The ratio (C / N ratio) of the amount of carbon (TC) to the amount of nitrogen (TN) of the contaminated soil is adjusted so that a lignin-degrading enzyme is produced from the white-rot fungus.

In the method for decomposing and removing oil-contaminated soil by microorganisms according to the first aspect of the present invention, first, for oil-contaminated soil containing oil, decomposition of indigenous bacteria naturally contained in the oil-contaminated soil is decomposed. Control at least nutrition, aeration, moisture and temperature for a period of time to increase activity.

The oil mainly contains so-called aliphatic hydrocarbons such as paraffinic and olefinic hydrocarbons and aromatic hydrocarbons. If the decomposition activity of microorganisms is increased as described above, these Of these, easily decomposable hydrocarbons, that is, most of aliphatic hydrocarbons and aromatic hydrocarbons having a relatively simple structure are decomposed and removed by the action of microorganisms in oil-contaminated soil. This is called primary decomposition.

Next, when the primary decomposition proceeds and the easily decomposable hydrocarbon is consumed, the energy source, which is the source of the activity, is deficient from the viewpoint of the microorganism, so that the microorganism gradually grows. to decline.

At this stage, the lignin-degrading enzyme produced during the growth process of the white-rot fungus is added to the oil-contaminated soil.

In this way, the added lignin-degrading enzyme exerts its degrading activity without competing with the already depleted microorganisms and removes the persistent hydrocarbons remaining in the oil-contaminated soil. Decomposes quickly.

As indigenous bacteria, bacteria such as Pseudomonas and Rhodococcus can be used.

The refractory hydrocarbon is a polycyclic aromatic hydrocarbon having a plurality of benzene rings, and the polycyclic aromatic hydrocarbon has three or more benzene rings, such as phenanthrene and pyrene. Contains substances of Further, the easily decomposable hydrocarbon means an aromatic hydrocarbon excluding the aliphatic hydrocarbon and the above-mentioned hardly decomposable hydrocarbon.

Here, the lignin-degrading enzyme is added to the oil-contaminated soil together with the white-rot fungus and its carrier, and the ratio of carbon content (TC) to nitrogen content (TN) of the oil-contaminated soil is added. If the (C / N ratio) is adjusted so that a new lignin-degrading enzyme is produced from the white-rot fungus, a new lignin-degrading enzyme is added to the oil-contaminated soil in addition to the lignin-degrading enzyme added first. It is possible to generate from white rot fungus.

Also in the method for decomposing and removing oil-contaminated soil by microorganisms according to the invention of claim 3, as in the invention of claim 1,
First, the oil-contaminated soil containing oil is primarily decomposed.

Next, white rot fungus and its carrier are added to the oil-contaminated soil, and the ratio (C / N ratio) of carbon content (TC) to nitrogen content (TN) of the oil-contaminated soil is added. ) Is adjusted so that a lignin-degrading enzyme is produced from the white-rot fungus.

In this way, the lignin-degrading enzyme produced in the oil-contaminated soil exerts its degrading activity without competing with the already-decayed microorganisms, and remains in the oil-contaminated soil. Rapidly decomposes hydrocarbons.

The description of the microorganism and the polycyclic aromatic hydrocarbon is the same as that of the invention of claim 1, and therefore the description thereof is omitted here.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the method for decomposing and removing oil-contaminated soil by microorganisms according to the present invention will be described below with reference to the accompanying drawings. It should be noted that parts and the like which are substantially the same as those of the conventional technique are designated by the same reference numerals and the description thereof will be omitted.

(First Embodiment) FIG. 1 is a flow chart showing the procedure of a method for decomposing and removing oil-contaminated soil by microorganisms according to the first embodiment. As can be seen in the figure, in the method for decomposing and removing according to the present embodiment, first, for oil-contaminated soil containing oil, nutrition is given for a predetermined period so that the decomposition activity of microorganisms present in the oil-contaminated soil is increased. , Ventilation, moisture, temperature, etc. are managed (step 101).

As the microorganism, it is preferable to use the indigenous bacteria naturally contained in the oil-contaminated soil.

Here, the ratio (C / N ratio) of carbon content (TC) to nitrogen content (TN) of the oil-contaminated soil is about 10 to 50,
In particular, sawdust, nitrogen fertilizer, etc. are appropriately added so as to maintain around 20. By setting the C / N ratio in this way, it is possible to keep good the decomposition activity of microorganisms in oil-contaminated soil, in this embodiment, indigenous bacteria.

When the C / N ratio is set in this way to enhance the decomposition activity of indigenous bacteria, easily degradable hydrocarbons in the oil contained in the oil-contaminated soil, that is, paraffin-based, olefin-based, etc. Aliphatic hydrocarbons and aromatic hydrocarbons having a relatively simple structure are efficiently decomposed and removed by indigenous bacteria.

FIG. 2 is a graph showing how hydrocarbons in oil-contaminated soil decrease due to the decomposition action of indigenous bacteria.

However, as can be seen from the figure, the rate of decrease of hydrocarbons in the oil-contaminated soil gradually decreases as time goes by, and almost never decreases. This is because easily decomposable hydrocarbons, such as aliphatic hydrocarbons that can be decomposed by indigenous bacteria and aromatic hydrocarbons with a simple structure, are consumed up by decomposition, and in the oil-contaminated soil it is a persistent hydrocarbon. This means that only certain polycyclic aromatic hydrocarbons remain.

In such a state, the energy source, which is the source of the activity, is deficient from the viewpoint of the indigenous bacteria, so that the indigenous bacteria gradually decline.

On the other hand, a wood which is appropriately finely divided into sawdust, chips, flakes, etc. is used as a carrier, and a white-rot fungus, which is a kind of basidiomycete (mushroom), is added to the carrier together with a nutrient medium. Are propagated separately (step 10
2).

In this way, the white-rot fungus grows with nutrients such as bran and nitrogen fertilizer contained in the nutrient medium, but the degree of growth gradually decreases, and eventually the white-rot fungus hardly grows. This is because the nitrogen-based nutrients contained in the nutrient medium are depleted. In such a state, the white-rot fungus decomposes the lignin in the carrier (wood) to extract the energy source, and the lignin-degrading enzyme is used. To generate itself.

Therefore, when the indigenous bacteria in the oil-contaminated soil have sufficiently diminished, the lignin-degrading enzyme produced in the process of the growth of the white-rot fungus as described above, together with the white-rot fungus and its carrier, are added to the oil-contaminated soil. (Step 10)
3).

Whether or not the indigenous bacteria have sufficiently declined is monitored based on the time when the oil content in the oil-contaminated soil is monitored using, for example, a graph as shown in FIG. Just make a decision.

When a lignin-degrading enzyme is added to the oil-contaminated soil in which the indigenous bacteria have declined, the lignin-degrading enzyme exerts its degrading activity without competing with the already-decayed microorganisms, and the The remaining polycyclic aromatic hydrocarbons are decomposed and removed, so to speak, as secondary decomposition.

Next, the carbon content (TC) and the nitrogen content (TN) of the oil-contaminated soil to which the lignin-degrading enzyme, the white-rot fungus and its carrier were added were calculated as the ratio (C / N ratio). So for example 1
The value is adjusted to be 00 or more (step 104). As a method of adjustment, if the carbon amount is small, for example, sawdust may be added.

In this way, in addition to the lignin-degrading enzyme added first, another lignin-degrading enzyme is newly generated from the white-rot fungus in the oil-contaminated soil. Then, the polycyclic aromatic hydrocarbons, which are persistent hydrocarbons remaining in the oil-contaminated soil, are decomposed more efficiently.

As described above, according to the method for decomposing and removing oil-contaminated soil by microorganisms according to the present embodiment, first, in the first step, the activity of decomposing indigenous bacteria is increased to make easily degradable hydrocarbons, that is, fats. Group 2 hydrocarbons and aromatic hydrocarbons with a simple structure are decomposed and removed, and then the second stage is the persistent carbonization in anticipation of the decline of indigenous bacteria due to the depletion of easily degradable hydrocarbons that are the target of indigenous bacteria decomposition. Since a lignin degrading enzyme capable of degrading hydrogen, that is, a polycyclic aromatic hydrocarbon was added, such a lignin degrading enzyme decomposes the polycyclic aromatic hydrocarbon by its degrading activity without competing with indigenous bacteria. be able to.

That is, by adopting such a two-step decomposition and removal method, it becomes possible to decompose and remove almost all the hydrocarbons contained in the oil-contaminated soil, and as in the conventional case, it is difficult to decompose carbon. It is possible to avoid a situation in which only polycyclic aromatic hydrocarbons that are hydrogen remain in the oil-contaminated soil without being decomposed.

Further, according to this embodiment, after the lignin-degrading enzyme is added to the oil-contaminated soil together with the white-rot fungus and its carrier, the C / N ratio of the oil-contaminated soil is adjusted to, for example, 100 or more. Therefore, another lignin-degrading enzyme different from the first added lignin-degrading enzyme was newly generated from white-rot fungi in oil-contaminated soil, and it is a polycyclic ring that is a persistent hydrocarbon that remains in oil-contaminated soil. It becomes possible to decompose aromatic hydrocarbons more efficiently.

In this embodiment, the lignin-degrading enzyme is added to the oil-contaminated soil together with the white-rot fungus and its carrier. However, even if only the lignin-degrading enzyme is extracted and added to the oil-contaminated soil. Good. In such a configuration, the C / N of the oil-contaminated soil after the addition of the lignin-degrading enzyme
No adjustment of the ratio is necessary.

Even when the lignin-degrading enzyme is added to the oil-contaminated soil together with the white-rot fungus and its carrier,
If the hardly-degradable hydrocarbon can be sufficiently decomposed only by the lignin-degrading enzyme added first, the subsequent step of adjusting the C / N ratio to the oil-contaminated soil may be omitted.

Further, in the present embodiment, the lignin-degrading enzyme generated during the growth process of the white-rot fungus is added to the oil-contaminated soil where the primary decomposition has been completed.
As shown in Fig. 3, when the indigenous bacteria of the oil-contaminated soil have declined, the white-rot fungus and its carrier are added to the oil-contaminated soil (step 112), and then the carbon content (T -
C) and the amount of nitrogen (TN) may be adjusted so that the C / N ratio is, for example, 100 or more (step 1).
13).

In such a construction, a lignin-degrading enzyme is generated from the white-rot fungus in the process of growing the white-rot fungus in the oil-contaminated soil. Then, the lignin-degrading enzyme decomposes polycyclic aromatic hydrocarbons, which are persistent hydrocarbons remaining in oil-contaminated soil.

Therefore, also in this modification, the lignin-degrading enzyme generated in the oil-contaminated soil where the primary decomposition is completed can decompose polycyclic aromatic hydrocarbons by its decomposition activity without competing with indigenous bacteria. It will be possible. By adopting such a two-step decomposition and removal method, it becomes possible to decompose and remove almost all the hydrocarbons contained in the oil-contaminated soil, and as in the past, it is a persistent hydrocarbon. It is possible to avoid a situation in which only polycyclic aromatic hydrocarbons remain in oil-contaminated soil without being decomposed.

Since step 111 is the same as step 101 described in the above embodiment,
The description is omitted here.

[0047]

As described above, according to the method for decomposing and removing oil-contaminated soil by the microorganism of the present invention according to claim 1, a lignin-degrading enzyme capable of decomposing and removing hardly decomposable hydrocarbons,
It becomes possible to exert its decomposition activity without competing with indigenous bacteria, and it is possible to avoid the situation where only persistent hydrocarbons are not decomposed and remain in oil-contaminated soil as in the past. .

Further, according to the method for decomposing and removing oil-contaminated soil by microorganisms of the present invention according to claim 2, another lignin-degrading enzyme different from the first added lignin-degrading enzyme is newly added in the oil-contaminated soil. There is also an effect that it is possible to more efficiently decompose polycyclic aromatic hydrocarbons, which are hard-to-decompose hydrocarbons that are generated from white-rot fungi and remain in oil-contaminated soil.

According to the method for decomposing and removing oil-contaminated soil by microorganisms of the present invention according to claim 3, the lignin degrading enzyme capable of decomposing and removing persistent hydrocarbons is decomposed without competing with indigenous bacteria. It becomes possible to exert the activity, and it is possible to avoid the situation that only the hardly-decomposable hydrocarbon remains in the oil-contaminated soil without being decomposed as in the conventional case.

[0050]

[Brief description of drawings]

FIG. 1 is a flowchart showing a procedure of a method for decomposing and removing oil-contaminated soil by microorganisms according to the present embodiment.

FIG. 2 is a graph showing the action of the method for decomposing and removing oil-contaminated soil by microorganisms according to the present embodiment.

FIG. 3 is a flowchart showing a procedure of a method for decomposing and removing oil-contaminated soil by microorganisms according to a modification.

Continuation of the front page (56) Reference JP-A-61-204095 (JP, A) JP-A-9-10752 (JP, A) JP-A-9-234491 (JP, A) JP-A-7-236897 (JP , A) Special Table 9-501841 (JP, A) Special Table 6-505634 (JP, A) US Patent 5597730 (US, A) US Patent 5459065 (US, A) US Patent 5476788 (US, A) US Patent 4891320 (US, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B09C 1/10 ZAB

Claims (3)

(57) [Claims] 1. The oil-contaminated soil is controlled for at least nutrition, aeration, moisture and temperature for a predetermined period so that the decomposition activity of indigenous bacteria naturally contained in the oil-contaminated soil is enhanced. Judgment based on the time when the oil content in the oil-contaminated soil was monitored and the content of the oil-degraded hydrocarbons in the contaminated soil was decomposed and consumed and the indigenous bacteria declined. A method for decomposing and removing oil-contaminated soil by microorganisms, which comprises adding a lignin-degrading enzyme produced in the process of growth of white-rot fungus to the oil-contaminated soil after the indigenous bacteria have declined. 2. The lignin-degrading enzyme is added to the oil-contaminated soil together with the white-rot fungus and its carrier, and the ratio of carbon content (TC) to nitrogen content (TN) of the oil-contaminated soil ( C /
The method for decomposing and removing oil-contaminated soil by microorganisms according to claim 1, wherein the N ratio) is adjusted so that a new lignin-degrading enzyme is produced from the white-rot fungus. 3. The oil-contaminated soil is controlled by controlling at least nutrition, aeration, moisture and temperature for a predetermined period so that the decomposition activity of indigenous bacteria naturally contained in the oil-contaminated soil is enhanced. Judgment based on the time when the oil content in the oil-contaminated soil was monitored and the content of the oil-degraded hydrocarbons in the contaminated soil was decomposed and consumed and the indigenous bacteria declined. Then, after the indigenous bacteria have declined, white-rot fungus and its carrier are added to the oil-contaminated soil to obtain a ratio (C-C) of the carbon content (TC) to the nitrogen content (TN) of the oil-contaminated soil. / N ratio)
Is adjusted so that a lignin-degrading enzyme is produced from the white-rot fungus, and a method for degrading and removing oil-contaminated soil by microorganisms.