JP3410346B2 - 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,
A mushroom-growing bed containing a lignin-degrading enzyme produced during the growth 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, after adding the mushroom-growing bed to the oil-contaminated soil, the carbon content (TC) and nitrogen of the oil-contaminated soil are added. The ratio (C / N ratio) to the amount (TN) is adjusted so that a new lignin-degrading enzyme is produced from the white-rot fungus.

Further, in the method for decomposing and removing oil-contaminated soil by microorganisms according to the present invention, the mushroom bed for growing mushrooms is a waste bacterial bed after the grown mushrooms are removed.

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, therefore, the mushroom-growing bed containing 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 lignin-degrading enzyme contained in the mushroom-growing bed exerts its degrading activity without competing with already decaying microorganisms and remains in the oil-contaminated soil. Promptly decomposes persistent hydrocarbons.

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, after adding the mushroom bed for mushroom growth to the oil-contaminated soil, the ratio (C / N ratio) of the carbon content (TC) to the nitrogen content (TN) of the oil-contaminated soil is added. ) 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 white-rot fungus in the oil-contaminated soil in addition to the first added lignin-degrading enzyme. It is possible to generate.

Mushroom types include shiitake mushrooms, maitake mushrooms, nameko mushrooms, oyster mushrooms, enoki mushrooms, beech mushrooms, tsukuritake mushrooms, and agaric mushrooms.

As a mushroom bed for growing mushrooms, as long as the lignin-degrading enzyme is produced from white-rot fungi, the mushroom culture substrate, the culture conditions and the growth stage are arbitrary. For example, the hyphae of white-rot fungi are sufficiently proliferated. The lignin-degrading enzyme can also be used in a sufficiently expressed state, and the mushroom may be in a stage where it has grown to some extent. In that case, it is possible to reuse the waste bacterial bed, which is a waste medium that was conventionally disposed of, for the purpose of decomposing and removing oil-contaminated soil.

[0021]

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 the amount of carbon (TC) to the amount of nitrogen (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 on, and eventually it hardly 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 fungal bed for mushroom growth containing a lignin-degrading enzyme produced during the growth process of white-rot fungus is separately prepared (step 102).

Such a mushroom bed for growing mushrooms can be prepared according to a method generally used for culturing and cultivating mushrooms to obtain a culture having lignin-degrading enzyme activity. When the hyphae of white-rot fungi are grown on a substrate, for example, a medium mainly composed of a mixture of sawdust and nutrient additives such as bran, first of all, the carbon source and nitrogen source etc. in the nutrient additives that are easy to use are used. However, when nutrients in nutrient additives are depleted, cellulase, hemicellulase, lignin-degrading enzyme, etc. are secreted outside the microbial cell in order to utilize persistent substrates such as sawdust. Nutrients such as carbon source and nitrogen source are taken out from the substrate to continue the growth.

It is sufficient for the mushroom bed for growing mushrooms that the lignin-degrading enzyme is sufficiently produced from the white-rot fungus, and it is independent of the extent of mushroom growth. Therefore, it can be used at various stages, such as those that have not grown due to mushrooms but the hyphae of white-rot fungi have progressed to a certain degree, or those that have grown to some extent with mushrooms, but recycling should be considered. For example, it is preferable to use a so-called spent fungus bed after mushrooms have grown sufficiently and have been picked for shipping.

If the lignin-degrading enzyme is sufficiently produced in the mushroom-growing bed, the bed is added to the oil-contaminated soil in consideration of the time when the indigenous bacteria in the oil-contaminated soil have sufficiently declined ( Step 103).

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 shown in FIG. Just make a decision.

When a mushroom-growing bed containing a lignin-degrading enzyme is added to the oil-contaminated soil where the indigenous bacteria have declined, the lignin-degrading enzyme does not compete with the already-decayed microorganisms for its degrading activity. The polycyclic aromatic hydrocarbons that are produced and remain in the oil-contaminated soil are decomposed as secondary decomposition.

Next, the carbon content (TC) and the nitrogen content (TN) of the oil-contaminated soil to which the mushroom-growing bed is added are set to, for example, 100 or more in terms of their ratio (C / N ratio). (Step 104). As a method of adjustment, if the carbon amount is small, for example, sawdust may be added.

In this way, due to the lack of nitrogen, the white-rot fungus newly produces a lignin-degrading enzyme in the oil-contaminated soil in addition to the lignin-degrading enzyme produced in the bed. 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, as the first step, the activity of decomposing indigenous bacteria is increased to make easily degradable hydrocarbons, namely 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 mushroom-growing bed containing a lignin-decomposing enzyme capable of decomposing hydrogen, that is, a polycyclic aromatic hydrocarbon, was added, such a lignin-decomposing enzyme can be decomposed by its decomposing activity without competing with indigenous bacteria. Polycyclic aromatic hydrocarbons can be decomposed.

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, hardly decomposable carbonization. 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.

In such a two-step decomposition and removal method, in the first step, indigenous bacteria naturally contained in the soil are
In the second stage, the lignin-degrading enzymes contained in the fungal beds for growing edible mushrooms are used to decompose hydrocarbons, so that the human body and the ecosystem can be decomposed during or after decomposition and removal. There is almost no possibility of adverse effects, and it can be said that this is a very safe decomposition and removal method.

Further, according to the present embodiment, after adding a mushroom-growing bed containing a lignin-degrading enzyme to oil-contaminated soil, the C / N ratio of the oil-contaminated soil is adjusted to, for example, 100 or more. Therefore, in addition to the lignin-degrading enzyme added first, a new lignin-degrading enzyme is newly produced by white-rot fungi in oil-contaminated soil and is a persistent hydrocarbon that remains in oil-contaminated soil. It becomes possible to decompose ring aromatic hydrocarbons more efficiently.

Further, according to the present embodiment, the waste fungus bed after picking the grown mushrooms is used as the mushroom growth fungus bed. It can be reused for the purpose of decomposition and removal.

In the present embodiment, after adding the mushroom-growing fungal bed to the oil-contaminated soil, the carbon content (TC) and nitrogen content (TN) of the oil-contaminated soil are determined by their ratio (C / C). N ratio) is, for example, 1
Although it was adjusted to be 00 or more (step 104), if the lignin-degrading enzyme contained in the mushroom-growing bed alone can sufficiently decompose the persistent hydrocarbon, The step of adjusting the C / N ratio may be omitted.

[0043]

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. .

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 is newly added in addition to the lignin-degrading enzyme contained in the mushroom-growing bed. Generated from white-rot fungi in oil-contaminated soil,
There is also an effect that it becomes possible to more efficiently decompose polycyclic aromatic hydrocarbons, which are persistent hydrocarbons remaining in oil-contaminated soil.

According to the method for decomposing and removing oil-contaminated soil by microorganisms according to the third aspect of the present invention, it is possible to reuse the waste bacterial bed that has been disposed of for the purpose of decomposing and removing oil-contaminated soil. It also has the effect of becoming.

[0046]

[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.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Genshiro Kawai 1-2-23 Nishikukata-cho, Kiryu-shi, Gunma Mori Sangyo Co., Ltd. (56) Reference JP-A-61-204095 (JP, A) JP-A-9 -10752 (JP, A) JP 9-234491 (JP, A) JP 7-236897 (JP, A) JP 9-501841 (JP, A) JP 6-505634 (JP, A) ) US Patent 5597730 (US, A) US Patent 5459065 (US, A) US Patent 5476788 (US, A) US Patent 4891320 (US, A) Takada Satoshi, White rot fungus that decomposes dioxin, BIO INDUSTRY, Japan, CMC Co., Ltd., October 12, 1997, Vol. 14, No. 10, p. 5-12 (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. Then, after the decline of the indigenous bacteria, a mushroom bed for growing mushrooms containing a lignin-degrading enzyme produced in the growth process of white-rot fungi is added to the oil-contaminated soil to remove oil-contaminated soil from microorganisms. Disassembly and removal method. 2. A ratio (C / N ratio) of carbon content (TC) and nitrogen content (TN) of the oil-contaminated soil after the mushroom-growing bed is added to the oil-contaminated soil. The method for decomposing and removing oil-contaminated soil by a microorganism according to claim 1, wherein the method is adjusted so that a new lignin-degrading enzyme is produced from the white-rot fungus. 3. The method for decomposing and removing oil-contaminated soil by microorganisms according to claim 1, wherein the fungal bed for growing mushrooms is a waste fungal bed after the grown mushrooms are removed.