JPH11179336A - Restoration method and apparatus for oil-contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for undergoing effective restoration treatment of oil-contaminated soil in a shorter time as compared with the conventional method by effectively starting up activity of an oil-decomposing microorganism in a soil pile. SOLUTION: Leachate containing native microorganisms and oil from a soil pile 1 is retained in a first reservoir tank 4 and a nourishment composition for the microorganisms is added and agitated to make oil-decomposing microorganisms grow and the leachate in the tank 4 is transferred to a second reservoir tank 6 and water or water containing oil is added and agitated to make the oil-decomposing microorganisms further grow and operation of adding water to the soil pile is repeated and oil contaminants in the soil pile 1 is decomposed by the microorganisms.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is directed to reducing oil-contaminated soil caused by leakage of crude oil, heavy oil, light oil, kerosene, gasoline, and other petroleum hydrocarbons by utilizing the oil-decomposing action of microbial decomposition activity. The present invention relates to a method for performing repair processing at a cost and an apparatus therefor.

[0002]

2. Description of the Related Art In recent years, among soil pollution in urban areas, which has become a social problem, the problem of leakage from underground tanks of gasoline and light oil has recently become more serious. In particular, it is said that in the process of unprofitable gas stations being arranged in the future, the era will have to be rehabilitated in a large amount of soil contaminated with petroleum hydrocarbons in these lands.

[0003] As one of the techniques for repairing such oil-contaminated soil, there is an incineration method. This method involves incineration of oil-contaminated soil in a dedicated kiln. However, with a processing capacity of about 100 tons per day per unit of current scale, not only is it impossible to cope with future large-scale processing in terms of capacity. It is said that there are many issues, especially in operation costs.

[0004] On the other hand, microbial repair treatment techniques are particularly advantageous in terms of cost, and various methods are being studied. This microbial repair method can be roughly divided into three forms. One is the land farming method, in which contaminated soil is spread over a large site like a field, watering and tilling are repeated, and the polluted oil is waited for to be naturally decomposed by microorganisms. It can be said that this method is not suitable for Japan where the land is small.

[0005] The second of the microbial restoration methods is a method called a soil pile method or a compost method. This method activates the activity of aerobic heterotrophic bacteria in the soil by creating a soil pile up to 2m to 3m in oil-contaminated soil and supplying air and nutrients for microbial growth to the inside. Then, the contaminated oil is decomposed and removed by microbial decomposition activity. This method has an advantage that it can be performed on a relatively small site as compared with the land farming method.

[0006] A third microbial remediation method is a slurry treatment method, in which microorganisms act on a fluidized oil-contaminated soil in a slurry state. Although this method is excellent in the speed of decomposition of the contaminated oil by microorganisms, it has a disadvantage that the treatment equipment becomes large.

[0007]

In the above-mentioned restoration method using the soil pile method, air is supplied to the soil pile, nutrient water or a microbial preparation is supplied, and the soil pile is mechanically turned back as required. Meanwhile, the contaminated oil is decomposed by microorganisms, and the leachate from the bottom of the soil pile is returned to the soil pile by adding new water. However, this soil pile method has the following problems.

[0008] First, regardless of whether a commercially available microbial preparation is used as a source of microorganisms or only indigenous microorganisms inhabiting the originally contaminated soil are decomposed, the effect of decomposing the oil is degraded. The disadvantage is that the period of restoration treatment becomes extremely long because microorganisms increase in every area of the soil pile and a certain long period is required until the oil decomposition rate in the whole area becomes significant. was there.

[0009] That is, the soil pile, which is an open system, is naturally a mixed microbial system, and since a large number of bacterial groups of a type suitable for its own soil environment inhabit, the nutrients such as nutrients are temporarily removed from the outside. The operation of replenishing the material alone does not necessarily mean that the target oil-decomposing microorganisms will immediately increase as the dominant species in all areas in the soil pile.

[0010] Even when microbial preparations are used, even if the microbial preparations are evenly planted in the soil pile, the explanted foreign microorganisms compete for survival with many indigenous microorganisms originally living in the soil. As it unfolds, its population only gradually increases thereafter. Therefore, no matter how high the microbial concentration of the microbial agent to be added, it is uncertain how soon it will start to grow in the soil pile to be treated, and the microorganisms that have been killed due to environmental incompatibility. Even exists. However, at present, there is no ideal microbial preparation for remediation of oil-contaminated soil, which adapts to all soils and rapidly adapts and grows.

In addition, after the oil component which is relatively easily decomposed in the oil-contaminated soil is decomposed by the microorganisms, the object of the decomposition by the microorganisms extends to the hardly decomposed oil component which has not been sufficiently decomposed by then. However, the decomposition rate of the hardly decomposable oil component was extremely slow in the conventional soil pile method.

[0012] Under such circumstances, in the conventional soil pile method, particularly in the case of repairing oil-contaminated soil having a scale of contamination of several percent or more due to heavy oil or the like, an effective oil decomposition action by microorganisms is applied to the soil. An extremely long restoration period was required, at least six months, including the time required to take root.

In order to shorten the restoration period, various improvements have been made in the method of supplying oxygen and nutrient composition to the soil pile. However, even with these improvement methods, fundamental improvement has not yet been achieved in terms of increasing the rate of oil-decomposing microorganisms to settle on the soil in the initial stage of the restoration treatment. In addition, in the process of shifting the decomposition target to the hardly decomposable oil component, it has not been realized to increase the rate of change in the composition of the microorganism species.

The present invention has been made in view of such a conventional situation,
Oil contamination that can efficiently activate oil-degrading microorganisms in soil piles and promote the decomposition of hard-to-decompose oil components, allowing oil-contaminated soil to be repaired more efficiently in a shorter time than before. An object of the present invention is to provide a soil repair method and an apparatus therefor.

[0015]

In order to achieve the above object, the present invention provides a method for remediating oil-contaminated soil, comprising recovering leachate containing oil and indigenous microorganisms from a soil pile and storing the leachate in a first water tank. Then, by adding the nutrient composition for microorganisms to the leachate in the first water tank and agitating the oil-decomposing microorganisms, the leachate in the first water tank is transferred to the second water tank, and then water or After the oil-decomposing microorganisms are further grown by adding oil-containing water and stirring, water in the second storage tank is poured into the soil pile, and the above operation is repeated to contaminate the soil pile with the contaminated oil in the soil pile. Is characterized by the following:

[0016] Further, an apparatus for repairing oil-contaminated soil according to the present invention comprises a leachate recovery facility for recovering leachate from a soil pile, and a microbial reservoir for storing leachate supplied from the leachate recovery facility. A first water tank provided with an inlet for the nutritional composition and stirring means, and a water or oil-containing water inlet and a stirring means for storing leachate supplied from the first water tank. It is characterized by comprising two water tanks and a water injection facility for injecting water in the second water tank into the soil pile.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention aims at setting up the activity of oil-decomposing microorganisms in a soil pile more efficiently than ever. That is, in the present invention, the indigenous microorganisms living in the oil-contaminated soil to be treated are taken out together with the leachate from the soil pile, and the microorganisms having the target oil-decomposing action are taken therefrom in a water tank provided separately from the soil pile. After growing in a short period of time, they are returned to the soil pile again.

[0018] Microorganisms, which can be said to be indigenous species that are easy to adapt to the environment, have been established in each of the oil-contaminated soils to be treated, according to their respective soil environments. Therefore,
Among those indigenous microorganisms, those having an oil-decomposing action are superior in environmental adaptability to oil-contaminated soil to be treated, as compared with foreign microorganisms added in the form of microbial preparations. For this reason, in the present invention, the indigenous microorganisms are cultured and propagated in the soil pile as described above, so that the activity of the oil-decomposing microorganisms can be efficiently started in the soil pile in a short period of time.

Next, the present invention will be described in detail with reference to FIG. Oil contaminated soil excavated from the pollution site is piled up to form a soil pile 1, and leachate from the soil pile 1 is collected and collected by a leachate recovery facility such as a waterproof sheet 2 and a pit 3 laid under the soil pile 1. This leachate contains various indigenous microorganisms derived from the soil, and also contains many oil components that are relatively low in molecular weight and easily soluble in water among petroleum hydrocarbons that are pollutants in the soil. . In addition, these low molecular weight oil components are generally relatively easy to use for microorganisms.

The leachate collected in the pit 3 is supplied to the first water storage tank 4 by the water supply pump 5a. First water tank 4
Then, a nutrient composition such as a nitrogen source necessary for microbial growth is added to the leachate from the input port 4a, and the mixture is stirred by a stirring means such as a stirrer 4b so that the nutrient composition and oxygen are distributed. It is preferable to install a sensor 4c in the first water tank 4 to monitor the dissolved oxygen concentration and pH of the leachate, and adjust them as necessary. As the stirring means, aeration may be used or used in addition to the stirrer 4b.

If the leachate in the first reservoir 4 is not provided with a sufficient carbon source for indigenous microorganisms to grow,
A limited amount of any hydrocarbon component can be artificially added to the first reservoir 4 to aid in its growth. In this case, it seems that the degree of contamination is temporarily increased. However, since the capacity of the first water storage tank 4 is usually as small as 1000 liters or less, the liquid volume of the entire water storage tank including the second water storage tank 6 described later is reduced. In addition, the amount of the added hydrocarbon component is extremely small, and the added hydrocarbon component is further decomposed in the second storage tank 6 at the subsequent stage, so that when the water is sent to the soil pile 1, it is almost completely decomposed. There is no effect.

It is preferable to sample the microorganism species that grows in the first water tank 4 and check the properties thereof successively. At the stage when the microorganism species capable of decomposing the oil component in the soil pile 1 has multiplied to a predetermined concentration or more in the first water tank 4, the leachate in the first water tank 4 is transferred to the second water tank 6 by the water pump 5b. send. The concentration of microorganisms at the time of transferring leachate from the first water tank 4 to the second water tank 6 can be arbitrarily determined according to the capacity of the first and second water tanks 4, 6 and other conditions. 10 7 in total aerobic heterotrophic bacteria count
It is desirable that the number is multiplied / ml or more.

Next, in the second water storage tank 6, the inlet 6
Water or oil-containing water is added from a, and stirring is further continued by the stirrer 6b. Here, the oil-containing water means not only leachate from the soil pile 1, but also pumping water when excavating oil-contaminated soil, washing water for washing excavated oil-contaminated soil, or the like. It may be added water. In addition, as a stirring method, aeration by the aeration pump 6c can be used or used in addition to the ordinary stirrer 6b.

In the second water storage tank 6, the oil concentration at the initial stage of the supply gradually decreases due to the oil decomposition action of the vigorous microorganisms that occur subsequently. After a period of about two days, when the concentration of the oil-decomposing microorganisms in the second water tank 6 reaches a maximum and the oil concentration falls below a predetermined value, the water in the second water tank 6 is supplied to the water pump 5c. Then, water is sent to the soil pile 1 through the water pipe 7, and the oil-degrading microorganisms grown in the second water tank 6 are returned to the soil pile 1 and transplanted. The second water tank 6 at this time
The microbial concentration in the inside is preferably 10 7 / ml or more in terms of the total number of aerobic heterotrophic bacteria in order to efficiently start the activity of the oil-decomposing microorganisms in the soil pile 1. However, if the number of bacteria is too large, there is a concern that the permeability may decrease near the water injection point into the soil pile, so that 10 9 / ml
It is desirable that:

Further, in the water in the second reservoir 6, a biological surfactant (biosurfactant) secreted during the process of indigenous microorganisms growing in the second reservoir 6 is also stored at a high concentration. The surfactant will be fed into the soil pile 1 together with the grown oil-degrading microorganisms.
Therefore, by the action of the biosurfactant, the contact efficiency between the microorganisms and the oil component in the soil pile 1 is improved from an early stage after the start of the restoration treatment. As a result, according to the present invention, not only is it possible to initially add a large amount of oil-decomposing microorganisms, but also it is possible to obtain an early improvement in the contact efficiency between oil and microorganisms. Action can be expected.

The frequency of water supply from the first water storage tank 4 to the second water storage tank 6 and the frequency and amount of water supply from the second water storage tank 6 to the soil pile 1 are determined by oil-decomposing microorganisms in each of the water storage tanks 4 and 6. Can be set arbitrarily according to the proliferation situation of First water tank 4
When water is supplied to the second water storage tank 6 from the first water storage tank 4, the entire amount in the first water storage tank 4 is not transferred at once, but a part of the oil is stored in the first water storage tank 4. It is easy to maintain the species composition and momentum of the degrading microorganism. However, the entire amount of water in the tank may be injected from the second water storage tank 6 to the soil pile 1.

When water is poured into the soil pile 1 from the second water storage tank 6, water may be combined with the second water storage tank 6 so that the concentration of the oil-decomposing microorganisms is not excessively diluted. In addition, since the volume of the second water storage tank 6 to be used is small and the rate of water evaporation from the soil pile 1 is high, the soil pile 1
If it is difficult to obtain a sufficient amount of water at a time to prevent drying of the soil pile, water can be simultaneously supplied to the soil pile 1 from another water supply facility.

In the second water tank 6, since proteins and the like derived from the proliferating microorganisms precipitate and accumulate at the bottom of the tank, it is preferable to periodically remove the protein from the bottom outlet 6d. Further, in a low-temperature environment such as a cold region, a facility such as a heater can be provided in the first water storage tank 4 and the second water storage tank 6 so as to maintain a constant water temperature so as to maintain a constant growth rate of microorganisms. . It is necessary to pay attention so that the water injection into the soil pile 1 is not partially biased. However, in the case of soil containing a large amount of clay, water injection pipes should be used so that microorganisms in the water to be injected do not block the water. It is desirable to increase the number of water outlets as much as possible.

Also in the present invention, it is preferable to supply air into the soil pile 1 in order to assist the activity of microorganisms, as in the ordinary soil pile method. For example, it is preferable to use a blower 8 to blow air through a blower pipe 8a inserted into the lower part of the soil pile 1 and collect the air from an exhaust pipe 8b inserted into the upper part of the soil pile 1. In addition, it is desirable to provide a cover 9 on the surface of the soil pile 1 to prevent drying and keep heat from outside air.

In the present invention, by repeating the above-described operations, the oil-degrading microorganisms in the growing phase, which are indigenous species, are repeatedly injected into the soil pile 1, and the initial kinetics of oil degradation in the soil are performed. Can be improved. As a result, oil contaminated soil can be repaired in a much shorter time than the conventional soil pile method.

At the time of the implementation, a relatively hardly decomposable oil component may remain after the easily decomposable oil component, for example, the n-alkane component in the soil pile 1 is almost completely decomposed. . In such a case, to grow microorganisms that can decompose even the hardly decomposable oil component from the beginning,
First, a small amount of an optimal hydrocarbon component is adjusted and added together with the nutrient composition to be added to the first water tank 4. Alternatively, after the easily decomposed oil component is decomposed, a nutrient composition corresponding to a microorganism that decomposes the hardly decomposable oil component may be adjusted and added to the first water storage tank 4. In this way, from the relatively early stage of restoration, by adjusting the type of nutrient composition and carbon source to be added to the first water tank 4, the resolution of various persistent oil components among indigenous microorganisms can be improved. The growth of microbial species
It is possible to prioritize artificially.

When excavating oil-contaminated soil from a contaminated site to produce the soil pile 1, when excavating near an aquifer, it is necessary to pump groundwater to the ground at the same time as excavation. Since this pumping water contains oil, it is usually treated with an oil-water separator, but the water after oil separation also contains relatively low-molecular hydrocarbon components, so it is discharged as it is. I can't. In the present invention, pumping water contaminated with such hydrocarbons is supplied to the first water storage tank 4 or the second water storage tank 6 in the same manner as the leachate from the soil pile 1, and the oil content is fed to microorganisms. Can be disassembled.

When the oil content of the oil-contaminated soil is generally 10% by weight or more, which exceeds the microbial treatment capacity of the soil pile, the soil is washed in advance with water containing a surfactant or the like to reduce the oil content. For example, it is usual to perform restoration by the soil pile method after reducing the content to about 5% by weight or less. In this case, the washing water that has washed the oil-contaminated soil is not discharged as it is because it contains oil, and is introduced into the first water tank 4 or the second water tank 6 as leachate or oil-containing water in the present invention.
In both these reservoirs 4, 6 and the soil pile 1,
Decomposition treatment of the contained oil can be performed.

The nonionic surfactant added during the water washing treatment of the contaminated soil is partially free in water after the oil component is decomposed in the second water storage tank 6.
It is again soil pile 1 by water injection from the second water tank 6.
To increase the chance of contact between microorganisms and oil,
It plays a role in assisting oil decomposition.

Although the present invention utilizes indigenous microorganisms, it is also possible to combine the use of microbial preparations with the present invention if the compatibility between the available microbial preparation and the soil to be repaired is good. In that case, by proliferating the microorganisms derived from the microbial preparation in the first water tank or the second water tank, the amount of the microbial preparation to be consumed can be greatly reduced, which is a great advantage in terms of cost.

In the remediation of oil-contaminated soil according to the present invention, the contaminants to be repaired are not particularly limited. Examples of oil contaminants to be repaired include petroleum hydrocarbons such as gasoline, light oil, kerosene, heavy oil, crude oil, machine oil, lubricating oil, and preservative oil.These components include benzene, toluene, and ethylbenzene. , Xylene,
There are ketones, but in addition, chlorinated hydrocarbons,
For example, pentachlorophenol is also included.

[0037]

EXAMPLE An oil-contaminated soil containing an average of 20,000 mg / kg of light oil was dug out and piled up to a height of about 100 cm on the ground covered with a vinyl sheet to form a soil pile weighing 2 tons. On one of the two soil piles thus formed, an experimental device according to the restoration method of the present invention shown in FIG. 1 was installed. On the other soil pile, an experimental device provided with only a reflux water pipe was installed in order to perform a comparative experiment according to the conventional soil pile method. The restoration operation was performed on each oil-contaminated soil as described below. In both experiments, a fixed amount of air was continuously supplied to each soil pile by a blower during the restoration period.

In the restoration method of the present invention, first, water was sprinkled on the soil pile 1, and leachate from the lower part of the soil pile 1 was collected in the pit 3. 200 liters of the supernatant liquid of the leachate collected in the pit 3 is put in the first storage tank 4 having a capacity of 300 liters, and the microorganism medium containing the nitrogen source and the oil of the kind most previously contained in the contamination source are fractionated by a fractionation operation or the like. Approximately 200 saturated hydrocarbon components extracted with a molecular weight of approximately 200 or more
g, and about 100 aromatic components, including those with relatively poor water solubility, also extracted with a molecular weight of about 200 or more.
g was added to adjust the pH to 7.2. Thereafter, the stirring was continued by the stirrer 4b installed in the first water storage tank 4, and the temperature of the leachate in the first water storage tank 4 was kept at 20 ° C., the same as the temperature inside the soil pile 1, during the stirring.

After a lapse of 24 hours, the concentration of microorganisms in the leachate of the first water tank 4 containing oil-degrading microorganisms increased to 10 7 / ml or more in terms of the total number of aerobic heterotrophic bacteria.
At this time, 90% of the leachate in the first water tank 4 is stored in a capacity of 200
It was transferred to the 0 liter second water tank 6. In the second water tank 6, 1000 liters of pumping water and 320 liters of new water containing oil recovered when the oil-contaminated soil is excavated are added, and the amount of water in the second water tank 6 is increased by a total of 150 liters.
0 liter.

Thereafter, leachate from the soil pile 1 was added to the first water storage tank 4, and the same medium and oil were added again to continue stirring. On the other hand, in the second water storage tank 6, while the temperature of the leachate was kept at 20 ° C., stirring by the stirrer 6b was continued with aeration. After 2 days, the second water tank 6
And the microbial concentration is 10 7 cells / m 2 in terms of the total number of aerobic heterotrophic bacteria.
1 or more, the whole amount of water in the second water storage tank 6 was sent to the soil pile 1.

Thereafter, the same operation was repeated at an average cycle of about two days, and water injection into the soil pile 1 and continuous air injection were continued. It should be noted that soil was collected at several locations in the center of the soil pile 1 every few days, and the microbial concentration therein was measured.
As a result, the average concentration of microorganisms in the soil (the number of aerobic heterotrophic bacteria) was on the order of 10 5 CFU / g at the start of the repair operation, but already 10 days after 3 cycles from the start of the operation. It exceeded 7th power CFU / g. For this reason, to the leachate after that point, add new water in an amount equivalent to the volatile matter, and then add only the medium component containing the nitrogen source without newly adding a carbon source such as hydrocarbons. Then, 1500 liters, which is equivalent to one cycle amount in the capacity of the second water storage tank 6, was poured into the soil pile 1 within the same period of about two days. The oil content in the soil pile was measured 80 days after the start of the operation. As a result, the average oil content was 5%.
It had dropped to 00 mg / kg.

On the other hand, in a comparative experiment according to the conventional soil pile method, the water was adjusted to the same amount of the nitrogen source-containing medium composition as that of the present invention according to the water injection timing employed in the above-mentioned repair method of the present invention. Was injected. The water leached from the soil pile after the injection is recovered, and after adding new water in an amount corresponding to the volatile matter, the medium composition is adjusted in the same manner, and the water is again returned to the soil pile at the injection timing in the present invention example. I let it.

As described above, the oil content in the soil pile was measured again after 80 days. As a result, the average oil content in the soil pile in the comparative experiment was 2000 mg / kg. The remaining amount was extremely large in comparison. According to the result of the microbial analysis, the average microbial concentration (the number of aerobic heterotrophic bacteria) in the soil pile was 10 7 CF
It exceeded U / g on the 40th day after 20 cycles, which was 30 days later than the above-mentioned inventive examples.

[0044]

According to the present invention, indigenous microorganisms living in the oil-contaminated soil to be treated are collected together with the leachate of the soil pile, and the microorganisms having an oil-decomposing effect are short-term stored in the two-stage water tank. By injecting into the original soil pile after growing in a while, the activity of oil-degrading microorganisms in the soil pile can be started up more efficiently than ever, and the restoration period of oil-contaminated soil is Can be dramatically reduced as compared with.

In addition, biological surfactants (biosurfactants) generated by the microbial activity in the water tank can be introduced into the soil pile together with the oil-decomposing microorganisms. The contact efficiency with oil is improved, the oil decomposition rate is further increased, and the repair period can be further shortened. Furthermore, even when the hardly decomposable oil component is present in the contaminant, the microorganisms that decompose the hardly decomposable oil component are grown in the storage tank by adjusting the nutrient composition to be used. Can be promoted from the early stages of repair.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an apparatus for carrying out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Soil pile 2 Waterproof sheet 3 Pit 4 First water tank 4a Input port 4b Stirrer 4c Sensor 5a, 5b, 5c Water pump 6 Second water tank 6a Inlet 6b Stirrer 6c Aeration pump 7 Water pipe 8 Blower 9 Cover

Claims (3)

[Claims] 1. A method of recovering leachate containing oil and indigenous microorganisms from a soil pile, storing the leachate in a first water tank, and adding a nutrient composition for microorganisms to the leachate in the first water tank and stirring the leachate. After growing the oil-decomposing microorganisms, then transfer the leachate in the first water tank to the second water tank, and further grow the oil-degrading microorganisms by adding water or oil-containing water and stirring,
A method for repairing oil-contaminated soil, characterized by injecting water in a second water tank into the soil pile and repeating the above operation to decompose contaminated oil in the soil pile with microorganisms. 2. The concentration of microorganisms in the leachate in the second reservoir containing oil-degrading microorganisms is 10 7 in total aerobic heterotrophic bacteria.
The method for repairing oil-contaminated soil according to claim 1, wherein the water is injected into the soil pile after increasing the number within the range from the number of multiplied pieces / ml to the number of 10 <9> pieces / ml or less. 3. A leachate recovery facility for recovering leachate from a soil pile, and an inlet for a nutrient composition for microorganisms and a stirring means for storing leachate supplied from the leachate recovery facility. A first water tank, a second water tank provided with an inlet for water or oil-containing water and stirring means for storing leachate supplied from the first water tank, and And a water injection facility for injecting water into the soil pile.