JP3520489B2 - Biodegradation evaluation method of contaminated soil and repair method of contaminated soil - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for evaluating biodegradation of contaminated soil for evaluating biodegradation of contaminated soil and a method for repairing contaminated soil to which the biodegradation evaluation method can be applied.

[0002]

2. Description of the Related Art In recent years, the number of cases in which urban soil is becoming contaminated is increasing, and in particular, soil contamination is often found due to land alteration such as reuse of a factory site. Regarding such urban soil pollution, a cumulative total of 1 since 1975 was found in a survey on the implementation status of soil pollution countermeasures in 1992.
77 cases are known, and the number of cases found has been increasing in recent years.

The causes of soil pollution are leakage due to damage to manufacturing facilities, improper landfill of waste on the factory premises before the enforcement of the Waste Disposal Law, improper handling of pollutant substances,
It is illegally dumped, etc., and by business, it is common in the chemical industry, electroplating industry, and electrical machinery manufacturing industry. Pollutants include heavy metals such as lead, hexavalent chromium, and mercury, and in recent years,
The increase of organochlorine compounds such as trichlorethylene and tetrachloroethylene is remarkable.

On the other hand, even in the United States, many leaks of stored materials from hazardous waste disposal sites and underground tanks have caused serious problems of soil pollution and groundwater pollution. Efforts are being made.

Under such circumstances, various contaminated soil restoration techniques have been proposed. Conventional restoration techniques include an incineration method, a solidification method, and a stabilization method. Recently, development of a restoration technology that effectively and economically cleans contaminated soil has attracted attention. Among them are various innovative methods for remediating contaminated soil such as extraction / purification, chemical decomposition, vacuum extraction, bioremediation and so on.

In particular, bioremediation, that is,
The method for remediating contaminated soil using the decomposition of organic pollutants by microorganisms has been attracting attention because it can be treated over a wide range and at low concentrations, and it can also be treated by physical and chemical treatments.

[0007]

However, such a method for repairing contaminated soil using microorganisms is still unsolved, especially when the organic pollutant contains a large amount of highly volatile substances such as gasoline. Have a problem. That is, when the organic pollutant contains a large amount of highly volatile substances, it is estimated that part of the organic pollutant is diffused into the atmosphere, and therefore the organic pollutant is decomposed by microorganisms. There was a problem that the amount could not be clearly detected and the degree of effect could not be grasped.

Therefore, in the conventional method for repairing contaminated soil using microorganisms, whether or not the microorganisms need to be replenished to the contaminated soil or the amount of the microorganisms to be replenished must be roughly estimated. Therefore, there is an inconvenience that the supply of microorganisms and the like must be performed inefficiently, and the estimation of the repair construction period of contaminated soil cannot be kept.

In view of the above circumstances, the present invention provides a biodegradation evaluation method for contaminated soil, which enables highly accurate detection of the amount of decomposition of organic pollutants by microorganisms, and efficient remediation of contaminated soil by microorganisms. The purpose of the present invention is to provide a method for repairing contaminated soil, which enables speeding up.

[0010]

[Means for Solving the Problems] In repairing organic contaminated soil, first, the presence of indigenous decomposing bacteria (that is, microorganisms) present in the contaminated soil is confirmed, and there is sufficient indigenous decomposing bacteria. In some cases, select a method (Biostimuration) to repair contaminated soil using indigenous degrading bacteria, and if there are not enough indigenous degrading bacteria or the activity is very low, It is efficient to select a method (Bioaugmentation) to replenish the contaminated soil by replenishing it.
The following first and second inventions are suitable for this selection. Therefore, in the biodegradation evaluation method of the contaminated soil of the first invention of the present invention, the contaminated soil and oxygen are enclosed under a closed system,
Either or both of the oxygen decrease amount and the carbon dioxide increase amount in the closed system are measured, and the amount of decomposition of the organic pollutant in the contaminated soil by the indigenous microorganisms is detected based on the measured value.

That is, the microorganism decomposes the organic pollutants in the contaminated soil and produces carbon dioxide while consuming oxygen. Therefore, by measuring either one or both of the oxygen decrease amount and the carbon dioxide increase amount, the amount of decomposition of the organic pollutants in the contaminated soil by the microorganism can be detected.

Further, since the polluted soil is arranged under a closed system, even if the organic pollutant contains a large amount of highly volatile substances such as gasoline, the polluted soil will not be discharged into the atmosphere. Dispersion from soil due to air dispersal is prevented.

Further, by arranging oxygen in a closed system, deficiency of oxygen is prevented.

The biodegradation evaluation method for contaminated soil according to the second invention of the present invention is characterized in that, in the first invention, microorganisms are supplemented in addition to the contaminated soil and oxygen under a closed system.

Thus, when there are not enough microorganisms indigenous to the contaminated soil, it is possible to detect the optimum microbial environment such as the type of microorganisms to be supplemented and the amount of supplementation. That is,
It is possible to appropriately supplement the contaminated soil with microorganisms depending on the contaminated soil.

A third aspect of the present invention is a method for repairing contaminated soil, which is a method for repairing contaminated soil having a soil remediation step of remediating contaminated soil with microorganisms, in which an optimum environment is detected before the soil remediation step. The optimum environment setting step is provided, and in the optimum environment setting step, at least the contaminated soil is sealed under the closed system, the change amount of the component concentration of the internal gas under the closed system is measured, and based on the measured value, the microorganisms are By using the biodegradation evaluation method of the contaminated soil to detect the amount of decomposition of organic pollutants in the contaminated soil according to, in this biodegradation evaluation method of the contaminated soil, by changing the environment under a closed system, for each environment The optimum environment for decomposing organic pollutants in contaminated soil is detected by detecting and comparing the amount of decomposed organic pollutants in contaminated soil. And adjusting the environment.

That is, it is possible to bring the environment of the contaminated soil closer to an environment suitable for the microorganisms to decompose the organic pollutants, and to enhance the decomposition efficiency of the organic pollutants by the microorganisms.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. The contaminated soil G shown in FIG. 5 is contaminated with the organic pollutant S, and one embodiment of the method for repairing the contaminated soil G for repairing such contaminated soil G will be described below.

Examples of the organic pollutants S include petroleum hydrocarbons such as gasoline, diesel fuel, fuel oil, and refinery sludge, and benzene, toluene, xylene, ethylbenzene, styrene and the like. Aromatic (BTEX) and polycyclic aromatics (PAH) such as naphthalene, phenanthrene, pyrene and benzopyrene
, Alcohols such as isopropanol, ethanol, ethylene glycol, t-butanol, carbohydrates, surfactants, ketones such as acetone and ethyl methyl ketone, phenols such as chlorophenol and PCP, PC
B, phthalic acid, and organic chlorine solvents such as methylene chloride and ethylene dichloride.

Now, the method for repairing contaminated soil according to the present embodiment comprises a soil repairing step for repairing the contaminated soil G by the microorganism B and an optimum environment setting step shown in FIG. 1 which is carried out before the soil repairing step. Is.

In the optimum environment setting step, first, as shown in FIG. 1, a large number of a part (about 10 grams in this embodiment) of the contaminated soil G to be repaired as shown in FIG. 5 is sampled. .

Next, the decomposition amount of the organic pollutant S in the sample G1 under various environments is detected using the following method for evaluating the biodegradation of contaminated soil.

First, each sample G1 is treated with pure oxygen O ₂
And a fixed amount of nutrient salt N, and sealed in a closed volume culture bottle 1 having a constant volume (300 ml in this embodiment) having a butyl rubber stopper 1a and placed under a closed system, and cultured under different environments as described below. To do.

The amount of pure oxygen O ₂ enclosed is larger than the amount of oxygen consumed by the microorganism B to decompose all the organic pollutants S in the sample G1.

In the standard closed culture bottle 1, only the sample G1, pure oxygen O ₂ and a fixed amount of nutrient salt N are enclosed.

In many other closed culture bottles 1, in addition to the sample G1, pure oxygen O ₂ and a fixed amount of nutrient salt N, the microorganism B is supplemented and enclosed. In this large number of closed culture bottles 1,
The amount of the microorganism B is changed stepwise, and the microorganism B is changed.
, And the microbial environment is changed according to the type 1 closed culture bottle 1, the second type closed culture bottle 1, the third type closed culture bottle 1 ,.

Further, a standard closed culture bottle 1, a first-type closed culture bottle 1, a second-type closed culture bottle 1, a third-type closed culture bottle 1, ... A large number of sets are provided as a first set, a second set, a third set, ....

Furthermore, the closed culture bottles 1 change the temperature environment and humidity environment under the closed system for each set.

The internal gas A of each closed culture bottle 1
To collect. To collect the internal gas A, a gas-tight syringe (not shown) that is an airtight extraction means is pierced through the butyl rubber stopper 1a of the closed culture bottle 1 and the tip is placed in the closed culture bottle 1. , The extraction can be performed without breaking the closed system.

The collected internal gas A is loaded into a gas chromatograph (not shown) capable of separating and quantitatively analyzing each component from a gas in which many kinds of components are mixed, and the internal gas A is analyzed by the gas chromatograph. The oxygen concentration and the carbon dioxide concentration of are detected and recorded as initial values. Further, the concentration may be grasped by a gas detection tube for detecting the oxygen concentration and the dioxide concentration in a closed container such as the closed culture bottle 1 or other method.

[0031] During the culture, as shown by the following chemical formula, microorganism B while consuming oxygen O _2, to decompose the organic contaminants S in the contaminated soil G, to produce carbon dioxide CO _2. The following formula shows the case where the organic pollutant S is benzene. _{C 6 H 6 + 7.5O 2 →} 6CO 2 + 3H 2 O

When a fixed period of time has passed after the start of culture, the internal gas A in each closed culture bottle 1 is sampled again, and its oxygen concentration and carbon dioxide concentration are detected. Then, the oxygen reduction amount and the carbon dioxide increase amount of the internal gas A are measured for each closed culture bottle 1 based on the oxygen concentration and the carbon dioxide concentration and their initial values.

Since the decrease in oxygen O ₂ and the increase in carbon dioxide CO ₂ are caused by the decomposition of the organic pollutant S by the microorganism B, the oxygen decrease amount and the carbon dioxide increase amount are measured based on the measured values. The decomposition amount of the organic pollutant S in the sample G1 can be detected for each closed culture bottle 1.

As described above, in the biodegradation evaluation method for contaminated soil according to the present embodiment, since the sample G1 is arranged in a closed system, the organic pollutant S in the sample G1 is volatilized from gasoline or the like. Even when a large amount of highly probable substance is contained, it is possible to prevent the organic pollutant S from disappearing from the sample G1 due to vaporization into the atmosphere.

Further, by sufficiently disposing oxygen O ₂ in a closed system, deficiency of oxygen O ₂ is prevented.

Therefore, even when the organic pollutant S contains a large amount of highly volatile substances, the oxygen decrease amount and the carbon dioxide increase amount can be measured with high accuracy, and the organic pollutant S The amount of decomposition can be detected with high accuracy.

Next, of those closed culture bottles 1, the one with the largest decomposition amount is selected, and the microorganism environment in the closed culture bottle 1 is set as the optimum environment, and the microorganisms in this closed culture bottle 1 are selected. The contaminated soil G of FIG.
The amount of supplement of the microorganism B suitable for is detected. The supply amount of the microorganism B is the mass per unit mass of the contaminated soil G.

Further, the temperature environment and the humidity environment in the selected closed culture bottle 1 in FIG. 1 are detected as the optimum environment for decomposing the organic pollutant S in the contaminated soil G in FIG.

The details of the step of detecting the optimum environment will be described below based on an example performed assuming a contaminated soil G for an experiment. In this experiment, the sample G1 in FIG.
Kerosene was added as organic pollutant S to a concentration of 1% to a field soil having a dry weight of 10 grams which had been sieved with 2 mm, and urea and K ₂ were used as nutrient salts N in this sample G1. HPO ₄ is added so that the mass ratio with respect to the organic pollutant S is 10% and 1%. Further, the microorganism B is only naturally present in upland soil, and the oxygen concentration after culturing for 43 days is detected.

The amount of water, which is the amount of water W in the sample G1, is adjusted to a humidity of 40%, and the temperature is adjusted to 10 degrees Celsius as shown in FIG.
The oxygen concentration in each environment changed to 20 degrees, 30 degrees, 40 degrees, and 50 degrees is examined. In this experimental result, the amount of oxygen decrease is the largest in the environment where the temperature is 30 degrees, and thus the environment where the temperature is 30 degrees is detected as the optimum environment.

Further, FIG. 3 shows that in the above experiment, the temperature was fixed at about 30 ° C. and the water content of the sample G1 was set to 20% humidity and 3%.
The oxygen concentration in each environment changed to 0%, 40%, 50%, 70% is examined. According to this experimental result, the oxygen reduction amount is the largest in the environment in which the water content is 70% in humidity, and therefore, the environment in which the humidity is 70% is detected as the optimum environment.

As described above, in the optimum environment setting step, it is possible to detect the supply amount of the microorganism B suitable for the contaminated soil G shown in FIG. 5 and the optimum environment.

Therefore, in the soil remediation step, whether the contaminated soil G is supplemented with the microorganism B based on the optimal environment of the microbial environment detected in the optimal environment setting step, that is, based on the supplementation amount of the microorganism B. If it is determined that replenishment is necessary, the replenishment of the microorganism B to the contaminated soil G is performed so as to match the replenishment amount of the microorganism B detected in the optimum environment setting step.

The case where the microorganism B is not replenished is the case where the standard closed culture bottle 1 is selected as the one having the largest decomposition amount in the optimum environment setting step of FIG. In the expression culture bottle 1, since the microorganisms B other than the indigenous microorganisms B in the specimen G1 are not artificially supplied and enclosed, the indigenous microorganisms B of the contaminated soil G in FIG. It will be naturally present in an amount suitable for. Therefore, naturally, it is not necessary to supplement the microorganism B.

Further, in the soil remediation step, the microorganisms B set the environment of the contaminated soil G on the basis of the optimum environment of the temperature environment and the humidity environment detected in the optimum environment setting step.
Make an environment suitable for disassembling. To make the environment suitable for decomposition, for example, sprinkle water on the contaminated soil G so that the humidity (water content) of the contaminated soil G approaches the humidity of the optimum environment, or set the temperature of the contaminated soil G to the optimum environment. The contaminated soil G is shaded so as to approach the temperature of the contaminated soil G, and the temperature and humidity control equipment is provided so as to surround the contaminated soil G, and the temperature and the humidity of the contaminated soil G are constantly adjusted to the optimum environment temperature. ,
For example, keeping the humidity.

As described above, the microorganism B can be appropriately supplied to the contaminated soil G in accordance with the contaminated soil G, and the microorganism B decomposes the organic pollutant S in the environment of the contaminated soil G. Since it is possible to approach the environment suitable for the operation, the efficiency of decomposing the organic pollutant S by the microorganism B can be increased. Therefore, in the method for repairing contaminated soil according to the present embodiment, it is possible to improve the efficiency and speed of repairing the contaminated soil G by the microorganism B.

In the optimum environment setting step, the internal gas A of the closed culture bottle 1 shown in FIG. 1 is periodically sampled after the culture is started to determine the decomposition amount of the organic pollutant S in the sample G1. Detecting the change over time, based on this change in the amount of decomposition over time, the period during which the decomposition is efficiently performed is detected, and the period for the soil restoration process is determined based on this period. It is possible to improve the efficiency and speed of G restoration.

That is, FIG. 4 shows that the soils G polluted with different petroleum compounds in the experiments in FIGS. It is a graph which investigated the increase of carbon concentration over time. As the sample G1 in FIG. 1, a sample in which gasoline was added to the upland soil, a sample in which kerosene was added to the upland soil, and a sample in which light oil was added to the upland soil were added so that each had a concentration of 1%. There is.

According to the results of this experiment, as shown in FIG. 4, for example, kerosene had the largest oxygen decrease, and 43
The pure oxygen concentration decreased to 40% in a day. But,
After that, the change in the amount of oxygen reduction with time is slow. Therefore, if the period of the soil remediation process by the microorganism B in FIG. 5 and the timing of reintroduction of the microorganism B and the nutrient salt N are determined based on this 43-day period, the efficiency of remediating the contaminated soil G is improved. It is possible to increase the speed and speed.

In the biodegradation evaluation method for contaminated soil in the optimum environment setting process shown in FIG. 1, both the oxygen decrease amount and the carbon dioxide increase amount were detected, but either the oxygen decrease amount or the carbon dioxide increase amount was detected. It may be configured to detect one of them. Also,
For the decomposition of the organic pollutant S in the contaminated soil G, there are substances that are highly active under anaerobic conditions. In that case, instead of oxygen O ₂ in a closed container such as the closed culture bottle 1, It is also possible to use a gas such as nitrogen and evaluate under conditions without oxygen. In this case, the decomposition of the organic pollutant S can be evaluated by detecting the generation of methane and hydrogen in addition to carbon dioxide CO ₂ in the closed container.

In the optimum environment setting step,
The biodegradation evaluation method of the contaminated soil is performed by changing the type of the microbial group B, the type of the microbial group B is detected as one of the optimal microbial environments, and the microbial group B is used in the soil restoration process of FIG. You may add a structure.

Further, in the method for evaluating biodegradation of contaminated soil in FIG. 1, the type or amount of nutrient salt N is changed to detect nutrient salt N or its supplement amount as one of the optimal environment. In the soil remediation step, a configuration may be added in which the nutrient salt N is replenished by an appropriate replenishment amount.

In the biodegradation evaluation method for contaminated soil shown in FIG. 1, the hydrogen ion index (pH) of the sample G1 was changed to detect the hydrogen ion index as one of the optimum hydrogen ion environments. In the remediation step, a configuration may be added in which the contaminated soil G has an optimum hydrogen ion index.

[0054]

According to the biodegradation evaluation method for polluted soil of the first aspect of the present invention, the organic pollutant is a highly volatile substance such as gasoline by arranging the polluted soil in a closed system. Even when it contains a large amount of organic pollutants, it is possible to prevent the loss of organic pollutants from the soil due to air diffusion, and to prevent oxygen deficiency by arranging oxygen in a closed system. . Therefore, even if the organic pollutant contains a large amount of highly volatile substances, by measuring either or both of the oxygen decrease amount and the carbon dioxide increase amount, the organic pollutant in the contaminated soil can be measured. The amount of decomposition of can be detected with high accuracy.

According to the method for evaluating biodegradation of contaminated soil of the second aspect of the present invention, in addition to the above effects, it is possible to appropriately supplement the contaminated soil with microorganisms depending on the contaminated soil. Therefore, the microbial environment, which is one of the environments of contaminated soil, can be brought close to the optimum environment, and the efficiency and speed of repair of contaminated soil by microorganisms can be improved.

According to the method for repairing contaminated soil of the third aspect of the present invention, the environment of the contaminated soil is brought close to the environment suitable for the microorganisms to decompose the organic pollutants. The decomposition efficiency of can be increased. Therefore, the efficiency and speed of repair of contaminated soil by microorganisms can be further improved.

[Brief description of drawings]

FIG. 1 is a simplified diagram showing an embodiment of a biodegradation evaluation method for contaminated soil used in the optimum environment setting step of the method for repairing contaminated soil according to the present invention.

FIG. 2 is a graph showing the results of examining the effect of temperature on the biodegradation of petroleum compounds using the biodegradation evaluation method for contaminated soil in FIG.

FIG. 3 is a graph showing the results of examining the influence of water on the biodegradation of petroleum compounds using the biodegradation evaluation method for contaminated soil in FIG. 1.

[Fig. 4] Using the method for evaluating biodegradation of polluted soil in Fig. 1, biodegradation of polluted soil polluted with different petroleum compounds respectively, and comparing them, the decrease of oxygen concentration and the increase of carbon dioxide concentration were performed. It is a graph examined over time.

FIG. 5 is a simplified diagram showing an embodiment of a soil remediation step of the contaminated soil remediation method of the present invention.

[Explanation of symbols]

G ... contaminated soil G1 ... sample (contaminated soil) S ... organic pollutant B ... microorganism O ₂ ... oxygen

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-136633 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B09C 1/10 C12Q 1/04

Claims (3)

(57) [Claims] 1. A contaminated soil and oxygen are enclosed under a closed system,
Either or both of the oxygen decrease amount and the carbon dioxide increase amount in the closed system are measured, and the amount of decomposition of the organic pollutant in the contaminated soil by the indigenous microorganisms is detected based on the measured value. Evaluation method of biodegradation of contaminated soil. 2. The method for evaluating biodegradation of contaminated soil according to claim 1, wherein microorganisms are supplemented to the contaminated soil and the oxygen under the closed system. 3. A method for repairing contaminated soil, comprising a soil remediation step for remediating contaminated soil with microorganisms, wherein an optimal environment setting step for detecting an optimal environment is provided before the soil remediation step. In the process, at least the contaminated soil is enclosed under a closed system, the change amount of the component concentration of the internal gas under the closed system is measured, and based on this measurement value, the organic pollutants in the contaminated soil due to microorganisms Using a biodegradation evaluation method for contaminated soil that detects the amount of decomposition, in this biodegradation evaluation method for contaminated soil, the environment under the closed system is changed to change the organic pollutants in the contaminated soil for each environment. By detecting and comparing the amount of decomposition,
An optimum environment for decomposing organic pollutants in the contaminated soil is detected, and in the soil remediation step, the environment of the contaminated soil is adjusted based on the optimal environment. .