JP2002011455A - Method and device for cleaning contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for cleaning of contaminated soil in its original position by a degradation effect of microorganisms. SOLUTION: A cleaning area 15 of the contaminated soil 12 is enclosed by cut-off walls 6 up to a prescribed ground surface height (h) from an underground hardly water permeable layer 4 and a well 7 arriving at the peak surface of the hardly water permeable layer 4 from the apex height of the cut-off walls 6 is disposed in the cleaning area 15. Cleaning water 16 in which the nutrient materials of the contaminant degradation bacterial is contained is injected into the contaminated soil 12 in the cleaning area 15 by the well 7 and is sprung from the contaminated soil 12 to the ground surface 1 to form a spring water layer 14. Contaminated oil 5 is floated on the water surface of the spring water layer 14 and is separated as floating oil 10. The cleaning water 16 of the cleaning area 15 is lifted by the well 7 after this separation and simultaneously the air is inhaled into the contaminated soil 12. The contaminants are degraded by the degradation bacteria in the presence of the inhaled air and the injected nutrient materials. The contaminated soil 12 in the cleaning area 15 is cleaned by iterating the process from the injection to the recovery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for purifying contaminated soil, and more particularly to a method and an apparatus for purifying soil contaminated with a substance such as oil decomposable by aerobic microorganisms while remaining in situ. .

[0002]

[Prior art] In the United States and Europe, a technology for biologically treating soil contaminated with oil or the like with aerobic microorganisms has been developed since the 1980s.
It has been implemented. This technology decomposes pollutants by adding nutrients such as nitrogen and phosphorus sources necessary for microbial activation while maintaining appropriate moisture in the contaminated soil and supplying air as an oxygen source. is there.

[0003] In the conventional technology using microorganisms for decomposing pollutants, it is common to excavate contaminated soil and purify it on the ground. One example is as follows. (1) Contaminated soil is excavated and piled up on the ground in a layer with a height of 1 to 2 m. (2) The supply of nutrients is performed by mixing a nitrogen source, a phosphorus source, and other nutrients with a heavy machine such as a backhoe, or by dispersing the nutrients into an aqueous solution and spraying the spread contaminated soil. (3) Supply the air by periodically cutting the soil with heavy equipment,
Alternatively, a ventilation pipe is installed at the bottom. (4) Moisture is maintained by regular watering.

[0004]

However, such a conventional technique has the following problems.

(A) Excavation and backfilling of contaminated soil requires a great deal of expense.

(B) In order to carry out the above-mentioned purification work by stacking excavated contaminated soil in a layer having a height of about 1 to 2 m on the ground, a large site is required. If there is no available open space nearby, the soil must be transported to another suitable location, which is even more expensive. In addition, when the site is small, the purification operation must be performed in several steps, and the period required for the purification becomes longer.

(C) In a method of mixing chemicals such as a nitrogen source and a phosphorus source into the piled soil with a heavy machine such as a backhoe,
It is difficult to achieve a uniform distribution, and contaminants that cannot be purified tend to remain. Further, even if the medicine is made into an aqueous solution and sprinkled, it is difficult to form a water path and to spread the medicine uniformly.

(D) In the method of periodically turning the soil with a heavy machine and supplying air, the height of the pile of soil is limited due to the function unique to the heavy machine, and a large site is required.
It is also unavoidable that there is a part where the air supply is insufficient. Attempts have been made to install a ventilation pipe at the bottom. However, in this case, a place where air can easily pass (short path) is created, and a portion that cannot be purified remains.

(E) When water is regularly sprayed to maintain moisture, water flows out from the bottom, and nitrogen sources and phosphorus sources to be added are washed away, or oil-containing water flows out of the surroundings. May spread contamination.

In order to solve these problems, it has been proposed to treat contaminated soil with microorganisms in situ, but at present, no practical method has been realized yet. Accordingly, an object of the present invention is to provide a method and an apparatus for performing in situ purification of contaminated soil by repeating the decomposition of microbial contaminants.

[0011]

As shown in FIG. 1, in general, a ground 13 has an unsaturated layer 2, an aquifer 3, and a poorly permeable layer 4, and most of the contaminated soil 12 has an unsaturated layer. 2 and contaminants 5 such as oil mixed into the aquifer 3.

In order to achieve the above object, the present inventor encloses the purification area 15 of the contaminated soil 12 in FIG. 1 with a water blocking wall 6 extending from an underground poorly permeable layer 4 to a predetermined height h above the ground, and storing water on the ground. We paid attention to providing space. In this case, a large amount of the washing water 16 is injected into the contaminated soil 12 to cause it to spring out, and the washing water 16 spouted from the contaminated soil 12 is poured into a portion surrounded by the water blocking wall 6 above the ground surface 1. Water can be stored to form the spring layer 14. An example of the water stop wall 6 is a sheet pile. With this water storage, the contaminated soil 12 is washed in
16 can be passed. As a result of repeated experiments and studies on purification of the contaminated soil 12 from this viewpoint,
It has been completed.

Referring to FIG. 1, in the method for purifying contaminated soil according to the present invention, the purification area 15 of the ground 13 in which the contaminated soil 12 is located is formed from the poorly permeable underground layer 4 to a predetermined height h on the ground surface 1. A well 7 which is surrounded by a water stop wall 6 and reaches the impervious layer 4 from the surface height h is provided in the purification area 15, and washing water 16 containing nutrients of pollutant-decomposing bacteria is provided in the purification area 15 by the well 7. Into the contaminated soil 12 and the washing water 16 is discharged from the contaminated soil 12 in the purification area 15 to the ground surface 1 to form a spring layer 14, and the contaminants such as oil 10 having a specific gravity smaller than that of the washing water. Separated from the surface of the layer 14, after the separation of the contaminants, the washing water 16 in the purification area 15 was pumped through the well 7 and air was sucked into the contaminated soil 12 in the purification area 15 and injected with the sucked air. Decompose contaminants by decomposing bacteria in the presence of nutrients, and according to the reduction of inhaled air or injected nutrients, By repeating the process from injection to pumping, the contaminated soil 12 in the purification area 15 is purified.

Preferably, the tank 9 of the washing water 16 is
15 and the washing water 16 is supplied from the tank 9 to the contaminated soil 12.
And the washing water 16 is pumped from the contaminated soil 12 to the tank 9
To be collected.

The apparatus for purifying contaminated soil according to the present invention provides a water stoppage from an underground poorly permeable layer 4 provided around a predetermined purification area 15 of the ground 13 where the contaminated soil 12 is present to a predetermined height h on the ground surface 1. The wall 6, a well 7 provided in the purification area 15 and reaching the low-permeable layer 4 from a predetermined height h above the ground surface, and washing water 16 containing nutrients of pollutant-decomposing bacteria are selectively contaminated by the well 7. 12
It is provided with a pump 8 for injecting or pumping water from contaminated soil 12. When the washing water 16 is injected, the washing water 16 springs out to the surface 1 through the contaminated soil 12 to form the surface spring layer 14 and separates the pollutants 5 having a specific gravity smaller than the washing water from the surface of the spring layer 14. Contaminated soil 12 during pumping of wash water 16
Air is sucked into the inside, and the pollutants are decomposed by decomposing bacteria in the presence of the air and the injected nutrients.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring again to the embodiment of FIG.
The method according to the invention encloses the purification zone 15 of the contaminated soil 12 with a poorly permeable layer 4 at the bottom and a surrounding water barrier 6 to a predetermined height h above the ground surface 1. This is for storing water on the ground surface 1. Then, the washing water 16 is supplied to the well 7 by a pumping means such as a pump 8.
The washing water 16 is injected into the contaminated soil 12 above the poorly permeable layer 4 through the turbidity layer, thereby saturating the washing water 16 with the aquifer 3 and the unsaturated layer 2 in the purification zone 15 and further discharging it upward. Raise to the level 17b at the top of the high spring layer 14. Contaminants having a specific gravity lower than that of water, such as the contaminated oil 5, float away from the contaminated soil 12 in the water and move upward, and become the floating oil 10 on the level 17b, for example, a recovery tank via the overflow channel 18.
Flow into 11. Thus, light contaminants such as the contaminated oil 5 are separated and recovered.

After that, when the washing water 16 is drawn or extracted from the contaminated soil 12 by the well 7 and the pump 8, the water level becomes higher.
17 falls, for example, to the level 17a at the bottom of the contaminated soil 12, where air enters the contaminated soil 12. The decomposing bacteria in the soil are activated by the oxygen in the air thus entered and the nutrients carried by the purifying liquid 16, and start decomposing the contaminants remaining in the contaminated soil 12.

Detecting a decrease in the concentration of oxygen or nutrients in the contaminated soil 12 to a predetermined value or less as the decomposition proceeds,
The water injection process and the pumping process are started according to the detection.

By repeating such a water injection process and a water pumping process, pollutants in the contaminated soil 12 can be decomposed by decomposing bacteria to reduce the concentration thereof. The present invention
For example, petroleum hydrocarbon compounds such as aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, and polycyclic aromatic hydrocarbons,
It is widely applicable to the purification treatment of contaminated soil 12 contaminated with halogenated hydrocarbon compounds and other aerobic biodegradable pollutants. Specifically, the present invention can be applied to the purification of contaminated soil 12 contaminated with crude oil, heavy oil, light oil, kerosene, gasoline, machine oil, chemical products derived from petroleum such as benzene, toluene, xylene, vegetable oil, and the like.

Thus, the object of the present invention, that is, the provision of "a method and an apparatus for purifying contaminated soil by using microorganisms in the present position" can be achieved.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A water blocking wall 6 made of, for example, a sheet pile forms a surrounding wall free of water leakage around a purification area 15 in the ground 13 and is tightly connected to the water-impermeable layer 4 of the ground through a well 7. The washing water 16 to be injected is directed only to the ground surface 1.

The wash water 16 for the contaminated soil 12 is prepared in a tank 9 above ground by adding nutrients to water, preferably groundwater, to a predetermined concentration. An example of the wash water is a water in which a nitrogen source chemical and a phosphorus source chemical are added to water so that the weight ratio of nitrogen to phosphorus and phosphorus to carbon 100 in the pollutant is 100. The nutritional substance can be, for example, one or more substances selected from the group consisting of ammonium salts, nitrates, nitrites, urea, phosphates, polyphosphates, potassium compounds, calcium compounds, magnesium compounds, and iron compounds. The pump 8 supplies the washing water 16 in the tank 9 to the well 7
And into the purification zone 15 via. The well 7 is provided with uniform washing water 16 to the unsaturated layer 2 and the aquifer 3 above the poorly permeable layer 4.
In this way, both the supply of nutrients to microorganisms and decomposing bacteria in the soil and the outflow of the contaminated oil 5 in the soil to the washing water 16 are uniformly generated. Well 7
Has a function of pumping the washing water 16 in the soil to the tank 9 by the pump 8 and also sucking air into the soil.

Preferably, the side wall of the well 7 is
The structure is such that the washing water 16 can be injected and pumped to different depth portions. More preferably, an opening (not shown) is formed in a portion of the side wall of the well 7 that is deeper than a predetermined depth, and the washing water 16 is selectively injected into or withdrawn from the contaminated soil 12 through the opening.

The recovery tank 11 is connected by an overflow channel 18 to the expected surface level 17b of the spring layer 14 on the ground surface 1,
The floating oil 10 on the surface of the spring layer 14 may overflow to the recovery tank 11 and be recovered.

FIG. 1 shows an example in which only one purification region 15 is provided, but two or more purification regions 16 arranged in a horizontal direction can be provided. In this case, the contaminated soil 12 is divided into a plurality of water-blocking walls 6 or equivalent water-blocking structures to the underground water-impermeable layer 4 to form two or more purification zones 15, and washing is performed by pumping water in one purification zone 15. Water 16 is injected into another cleaning zone 15, and the water level 17 in one purification zone 15 decreases and the water level 17 in another
May be simultaneously generated.

FIG. 2 shows that the existing tank 20 is for storing crude oil and a water-blocking structure 21 is provided around the bottom of the tank in order to prevent oil leakage in the underground part. Indicates the presence of In this case, the amount of water required is small, and the present invention can be used most effectively. That is, after the existing tank 20 is removed or floated by jack-up, a small portion of the ground surface is surrounded by the water stop wall 6, and the formation and recovery process of the floating oil 10 by injecting the washing water 16; The contaminated soil 12 can be purified by repeating the process of supplying air and oxygen to the contaminated soil 12 by pumping the washing water 16.

[0027]

As described above, according to the method and apparatus for purifying contaminated soil of the present invention, water is injected into a purification area surrounded by a water stop wall reaching a poorly permeable layer with washing water, and oxygen is supplied to the purification area. Since pumping is repeated, the following remarkable effects are achieved.

(A) Since the water is submerged in washing water containing a nitrogen source and a phosphorus source, these nutrient sources can be uniformly distributed in the soil. (B) Since the contaminated oil is separated and removed as floating oil, it is possible to reduce the amount of oil to be subjected to biological treatment. (C) In general, the determination of the end of the oil-contaminated soil purification process is based on the presence or absence of an oil film when the oil-contaminated soil is poured into water. In the past, there was a case in which an opportunity for water injection was missed, resulting in excessive purification. However, in the submerged purification according to the present invention, there is no risk of missing such an opportunity, and the progress of purification is constantly monitored and an accurate judgment can be made. (D) Uniform oxygen supply to contaminated soil can be performed using oxygen supply by pumping.

(E) Inject water in the purification area blocked by the water stop wall.
Since water is purified by pumping, contaminated soil can be purified without splashing water or chemicals to the surroundings. (F) Since the amount of water circulated during the water injection / pumping process is small,
The surrounding groundwater can be used. (G) Recycling of water and nutrients for decomposing bacteria, and purification at low cost by using groundwater are possible. (H) It is possible to reduce the load of decomposing bacteria by removing the overflow of the floating oil, and to shorten the purification period by continuously monitoring the generation of an oil film corresponding to the end of the purification in the above item (c). (I) A water-blocking / sealing structure with water-blocking walls is indispensable, and there is no danger of pollution diffusion. (Iii) Uniform soil purification by uniform supply of nitrogen source, phosphorus source, oxygen, etc. can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of one embodiment of the present invention.

FIG. 2 is a schematic sectional view of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ground surface 2 ... Unsaturated layer 3 ... Aquifer 4 ... Impervious layer 5 ... Contaminated oil 6 ... Water blocking wall 7 ... Well 8 ... Pump 9 ... Tank 10 ... Floating oil 11 ... Recovery tank 12 ... Contaminated soil 13 … Soil 14… Spring layer 15… Purification area 16… Wash water 17… Water level 18… Overflow channel 20… Existing oil tank 21… Impermeable structure

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2D040 AA00 AB01 AC00 BA00 CA10 CB03 DB01 4D004 AA41 AB02 AB05 AC07 CA19 CA40 CC07 DA01 DA10

Claims (7)

[Claims] 1. A purification area of the ground where the contaminated soil is located is surrounded by a water blocking wall from an underground impervious layer to a predetermined height on the ground, and a well reaching the impervious layer from the ground level is provided in the purification area. Wash water containing nutrients of pollutant-decomposing bacteria is injected into the contaminated soil through the wells, and the wash water is allowed to spring out of the contaminated soil to the surface to form a spring layer, and to remove pollutants having a specific gravity smaller than the wash water. After being separated from the surface of the spring water layer, and after the separation of the pollutants, the washing water in the purification area is pumped through the wells, and air is sucked into the contaminated soil, and the bacteria are decomposed in the presence of the sucked air and the injected nutrients. A method for purifying contaminated soil by decomposing contaminants by repeating the process from injection to pumping according to a decrease in inhaled air or injected nutrients. 2. The cleaning method according to claim 1, wherein the cleaning water tank is provided outside the purification area, the cleaning water is injected into the contaminated soil from the tank, and the cleaning water is pumped from the contaminated soil to the tank. How to clean contaminated soil. 3. The method for purifying contaminated soil according to claim 1 or 2, wherein washing water is injected into and pumped from different depths of the contaminated soil through side walls of the well. 4. The method for purifying contaminated soil according to claim 3, wherein the cleaning water is injected into the contaminated soil through an opening formed in a portion of the side wall of the well deeper than a predetermined depth, or is pumped from the contaminated soil. Method. 5. The method for purifying contaminated soil according to claim 1, wherein the contaminant having a specific gravity smaller than that of the washing water is guided to a collection tank provided outside the purification area by an overflow channel. 6. An apparatus for purifying contaminated soil, wherein a water stop wall from a subterranean poorly permeable layer provided around a predetermined purification area on the ground where the contaminated soil is located to a predetermined height above the ground surface is provided in the purification area. A well which reaches a poorly permeable layer from a predetermined height above the ground surface, and a pump for selectively injecting or pumping up washing water containing nutrients of pollutant-decomposing bacteria into the contaminated soil by the wells, When water is injected into the contaminated soil, contaminants with a specific gravity smaller than that of the wash water are separated from the surface of the spring water layer by discharging the wash water to the surface of the contaminated soil through the contaminated soil. An apparatus for purifying contaminated soil by decomposing contaminants by decomposing bacteria in the presence of inhaled air and injected nutrients. 7. The purifying apparatus according to claim 6, wherein said nutrient substance of said contaminant-decomposing bacteria is ammonium salt, nitrate, nitrite, urea, phosphate, polyphosphate, potassium compound,
An apparatus for purifying contaminated soil as one or more substances selected from the group consisting of calcium compounds, magnesium compounds, and iron compounds.