JP6058255B2 - In-situ purification method - Google Patents

Description

  The present invention relates to an in-situ purification method for purifying a ground containing an organic chlorine compound without excavation (in-situ).

In recent years, soil contamination and associated groundwater contamination has become a social problem due to the outflow of pollutants from factories, waste disposal sites, illegal dumping places, and the like.
Among such pollutants, it has been confirmed that volatile organochlorine compounds such as tetrachloroethylene and trichlorethylene, which are frequently contaminated, are dechlorinated and rendered harmless by anaerobic microorganisms.

  Conventionally, an in-situ purification method that purifies by injecting an organic material that can form an anaerobic environment and supply hydrogen necessary for dechlorination to the ground contaminated with volatile organic chlorine compounds, etc. It has been developed and put to practical use.

  For example, as shown in Non-Patent Document 1, by injecting a liquid containing an organic material from a purification well installed in the ground contaminated with an organic chlorine compound, the volatile organic chlorine compound is removed by dechlorination. It has been confirmed that it will be purified.

“Chemistry and Biology”, Agricultural Chemical Society of Japan, 2011, Vol. 49, no. 4, p. 256-260

However, in the conventional purification method, when the ground is polluted with other pollutants together with organic chlorine compounds, there are cases where pollutants that cannot be purified by dechlorination remain in the ground.
In addition, by supplying an organic material to the ground, gas may be generated as a secondary matter, or the organic material may remain even after purification is completed.

  From such a viewpoint, an object of the present invention is to provide an in-situ purification method that can purify the ground contaminated with a plurality of contaminants.

In order to solve the above-mentioned problem, the in-situ purification method of the present invention provides a first stage for producing an anaerobic environment state by supplying a liquid containing an organic material from a purification well into a ground containing an organic chlorine compound, A second stage for producing an aerobic environment state by supplying a high oxygen concentration gas containing oxygen equal to or higher than air from the purification well into the ground which has become an anaerobic environment state in the first stage. In the first stage, a low oxygen concentration gas having a lower oxygen content than air is supplied from the purification well simultaneously with the liquid, and in the second stage, water containing an inorganic salt is supplied to the purification well. From the high oxygen concentration gas.
Here, the high oxygen concentration gas may be air, or a gas having the same or higher oxygen concentration than air.

  According to this in-situ purification method, after promoting the dechlorination of organochlorine compounds by promoting the growth of anaerobic microorganisms in the first stage, the aerobic microorganisms are grown as the second stage. It is possible to promote the purification of pollutants that cannot be purified in the first stage, and the removal or decomposition of secondary gas.

In addition, according to the in- situ purification method of the present invention, an anaerobic environment state can be created more quickly, and the ground is less likely to become an aerobic environment, so that purification can be performed more effectively. Further, it is possible to prevent the organic material supplied from the purification well from being decomposed before reaching the ground to be purified. As a result, the organic material reaches the ground, and purification can be performed uniformly.

In addition, according to the in- situ purification method of the present invention, aerobic microorganisms are activated over a long period of time and the decomposition ability is promoted, so that purification can be performed more effectively. In addition, air and liquid flow paths are blocked by the growth of aerobic microorganisms, and then the flow of injected air and liquid repeatedly moves to other voids in the soil. It becomes possible to supply uniformly into the ground, and an aerobic environment can be created uniformly.

  According to the in-situ purification method of the present invention, the ground contaminated with a plurality of contaminants can be purified.

It is an outline of an in-situ purification system used by an embodiment of the invention, and is a mimetic diagram showing an operation situation of an in-situ purification system in the first stage. It is a schematic diagram which shows the operation | movement condition of the in-situ purification system in a 2nd step. It is a graph which shows the time-dependent change of the oxidation-reduction potential of the culture solution of the 1st step in an Example. It is a graph which shows a time-dependent change of the total organic carbon concentration of the culture solution of the 1st step in an Example. It is a graph which shows a time-dependent change of the total number of bacteria of the culture solution of the 1st step in an Example. It is a graph which shows the time-dependent change of VOCs of the culture solution of the 1st step in an Example. It is a graph which shows the time-dependent change of VOCs of the culture solution of the 1st step in an Example.

The in-situ purification method according to the embodiment of the present invention includes a first stage in which at least an anaerobic environment is created in the ground G contaminated with an organochlorine compound to promote dechlorination of the organochlorine compound; And a second stage for creating an aerobic environment state in the ground G that has become an anaerobic environment state.
Hereinafter, the area where the pollutant exists in the ground G and the basin where the contaminated groundwater exists are referred to as “polluted area”.

  This embodiment demonstrates the case where the in-situ purification method of this embodiment is employ | adopted with respect to the ground G in which the unsaturated layer G1, the saturated layer G2, and the impermeable layer G3 were laminated | stacked from the ground surface GL side. The contaminated area exists in the saturated layer G2.

  In the first stage, as shown in FIG. 1, the first liquid W <b> 1 and the first gas A <b> 1 are simultaneously injected into the contaminated region using the purification well (sparging well) 10 installed in the ground G.

The first liquid W1 of the present embodiment is composed of water containing an organic material that promotes formation of an anaerobic environment and dechlorination by anaerobic microorganisms.
In addition, you may make the 1st liquid W1 contain an inorganic substance as needed.

  By supplying the first liquid W1 to the contaminated area, anaerobic microorganisms in the contaminated area are activated, and the microbial degradation activity in the contaminated area can be increased.

The first gas A1 is a gas having a lower oxygen content than air (low oxygen concentration gas).
When the first gas A1 is injected, the contaminated area is less likely to become an aerobic environment, and therefore, the contaminated area is likely to become an anaerobic environment, and the first liquid W1 (organic material) supplied from the purification well 10 is to be purified. It is prevented from being decomposed before reaching the position, so that the organic material can reach the contaminated area and can be purified uniformly.

  In the present embodiment, a gas having a nitrogen gas content higher than the atmosphere is used as the first gas A1. The first gas A1 is a gas having a lower oxygen content than air, and is limited as long as the contaminated area can be made an anaerobic environment by being injected into the ground. However, it is effective if it is preferably selected from at least one selected from the group consisting of inert gas containing almost no oxygen, particularly nitrogen, carbon dioxide, argon gas and helium. Moreover, you may use the gas which removed oxygen from air with the oxygen removal apparatus.

The first gas A1 may be injected when the organic chlorine compound is present at a high concentration in the contaminated area, or when the water permeability of the contaminated area is low and the injection speed of the first liquid W1 is slow.
Therefore, for example, when the concentration of the organic chlorine compound is low or the water permeability of the contaminated region is high, the injection of the first gas A1 may be omitted.

  In the second stage, the second liquid W2 and the second gas A2 are simultaneously injected from the purification well 10 into the contaminated area.

The second liquid W2 of the present embodiment is composed of water containing an inorganic salt. Inorganic salts are materials that promote the growth of aerobic microorganisms.
Note that the second liquid W2 may be injected when nutrients necessary for the decomposition of organic substances by the aerobic microorganisms are insufficient in the contaminated area after the first stage, and the injection may be omitted.

The second gas A2 is a high oxygen concentration gas containing oxygen equal to or higher than air, and air is used in the present embodiment. The supply amount of the second gas A2 (air) is appropriately adjusted according to the degradation rate by the aerobic microorganism, the contamination concentration, and the like. In addition, it may replace with air and may employ | adopt the gas whose oxygen concentration is higher than air as 2nd gas A2.
An aerobic environment state is formed by supplying the second gas A2 containing oxygen to the contaminated region that has become an anaerobic environment state in the first stage, and activation of the aerobic microorganisms is promoted.

Hereinafter, the in-situ purification system 1 used in the in-situ purification method of this embodiment will be described.
The in-situ purification system 1 includes a purification well 10, a compressor 20, a first liquid tank 30, a second liquid layer 40, and a suction device 50, as shown in FIG.

  As shown in FIG. 1, the purification well 10 can supply the liquid W (the first liquid W1 and the second liquid W2) and the gas A (the first gas A1 and the second gas A2) to the contaminated area. And has an inner diameter capable of supplying the liquid W and the gas A into the contaminated region (saturated layer G2).

In the present embodiment, the purification well 10 is formed by disposing a steel pipe 11 having an opening near the lower end thereof in the ground G.
In order to prevent intrusion of earth and sand into the purification well 10, a screen 12 that allows ventilation and water flow is disposed in the opening of the steel pipe 11. In addition, the material of the pipe material which comprises the purification well 10 is not limited.

  The purification well 10 is formed so that the opening (screen 11) at the lower end is disposed at a position deeper than the contaminated area. The purification well 10 of the present embodiment is formed so as to penetrate the unsaturated layer G1 and have a lower end located in the vicinity of the boundary surface RL between the saturated layer G2 and the impermeable layer G3. The depth of the purification well 10 is not limited as long as the gas A and the liquid W can be reliably supplied to the contaminated area. Moreover, the opening part (screen 11) should just be arrange | positioned in the saturation layer G2, and does not necessarily need to be the boundary surface RL vicinity.

In this embodiment, although the purification well 10 is formed vertically, the purification well 10 does not necessarily need to be vertical.
Moreover, although this embodiment demonstrates the case where the one purification well 10 is arrange | positioned, multiple purification wells 10 may be formed. The number and arrangement of the purification wells 10 are not limited, and may be appropriately set according to the range of the contaminated area, the concentration of contamination, the influence range of the purification well 10 (the reach range of the gas A and the liquid W), and the like. .

  The compressor 20, the first liquid tank 30, and the second liquid tank 40 are connected to the upper end portion of the purification well 10. In the present embodiment, the first liquid tank 30 and the second liquid tank 40 are provided separately, but the same liquid tank may be used as the first liquid tank 30 and the second liquid tank 40.

The compressor 20 is connected to the purification well 10 via an air supply pipe 21.
The compressor 20 supplies the compressed gas A to the purification well 10 via the air supply pipe 21.

  A valve, a flow meter, a pressure gauge, and the like (not shown) for adjusting the amount of gas A to be supplied are disposed at predetermined positions of the air supply pipe 21 as necessary.

A first gas tank 22 in which the first gas A1 is stored is connected to the compressor 20 of the present embodiment.
The first gas tank 22 is connected to the compressor 20 via a valve 23. The valve 23 is opened in the first stage, while being shielded so that the first gas A1 is not supplied to the compressor 20 in the second stage.

  In the first stage, the compressor 20 compresses the first gas A <b> 1 supplied from the first gas tank 22 and sends it to the purification well 10. In the second stage, the compressor 20 compresses air and sends it to the purification well 10. .

In the first stage, when the injection of the first gas A1 is omitted, the first gas tank 22 of the in-situ purification system 1 may be omitted.
Further, a gas from which oxygen has been removed from the air may be supplied to the purification well 10 by installing an oxygen removing device (not shown) in the compressor 2 instead of the first gas tank 22.

The first liquid tank 30 stores the first liquid W1. The first liquid W1 is generated by mixing water and an organic material in the first liquid tank 30. Note that the first liquid W <b> 1 may be supplied to the first liquid tank 30 previously generated at another location.
The first liquid tank 30 is connected to the purification well 10 via a liquid feed pipe 31 and a water feed pump 32.

  The first liquid W <b> 1 is supplied to the purification well 10 via the liquid supply pipe 31 by the water supply pump 32 in the first stage.

The second liquid tank 40 stores the second liquid W2. The second liquid W2 is generated in the second liquid layer 40 by mixing water and an inorganic salt. Moreover, you may supply to the 2nd liquid layer 40 what was previously produced | generated in another place as the 2nd liquid W2.
The second liquid tank 40 is connected to the purification well 10 via a liquid feed pipe 41 and a water feed pump 42.

  As shown in FIG. 2, the second liquid W2 is supplied from the second liquid tank 40 to the purification well 10 via the liquid supply pipe 41 by the water supply pump 42 in the second stage.

The suction device 50 sucks the gas rising from the contaminated area by injecting the gas A into the ground G, performs a detoxification process, and releases it to the atmosphere.
The suction device 50 of this embodiment includes suction wells 51 and 51, a suction blower 52, and an adsorption tower 53.

The suction well 51 is a well formed in the unsaturated layer G1 above the contaminated region. The suction well 51 is configured to be able to suck the gas (gas rising from the contaminated area) A3 in the saturated layer G2.
The suction well 51 only needs to be formed so that the gas A3 that has risen in the saturated layer G2 can be sucked. Even if the lower end of the suction well 51 faces the upper end of the saturated layer G2. Alternatively, the entire suction well 51 may be disposed in the unsaturated layer G1 (above the groundwater level WL), or the lower end of the suction well 51 may enter the saturated layer G2.

  The suction well 51 is connected to a suction blower 52 provided on the ground via an intake pipe 54 connected to the upper end.

  The suction blower 52 sucks the gas in the saturated layer through the suction well 51 and supplies the sucked gas A3 to the adsorption tower 53.

  The adsorption tower 53 has activated carbon disposed therein, adsorbs the pollutant contained in the gas A3 supplied from the suction blower 52, detoxifies it, and then exhausts it to the atmosphere.

Note that the configuration of the suction device 50 is not limited to the above configuration, and may be appropriately configured. For example, instead of the suction well 51, an exhaust pipe (horizontal well) may be provided horizontally above the contaminated area.
Further, the method of processing the sucked gas by the adsorption tower 53 is not limited.
Further, the suction device 50 may be arranged as necessary and may be omitted.

  Hereinafter, the operation of the in-situ purification method according to the present embodiment will be described.

  First, as a first stage, the compressor 20 and the water pump 32 are operated, and the first gas A1 and the first liquid W1 are simultaneously injected from the purification well 10 into the ground G (contamination region) as shown in FIG. To do.

  By supplying the first gas A1 and the first liquid W1 to the contaminated region (saturated layer G2), the inside of the contaminated region (saturated layer G2) quickly becomes an anaerobic environment and is supplied from the purification well 10 together with the first gas A1. The first liquid W1 thus made reaches the entire desired contaminated area without being decomposed so much.

  In addition, when the first liquid W1 that is nutrient water of anaerobic microorganisms is supplied to the contaminated region (saturated layer G2), the anaerobic microorganisms are activated by the first liquid W1 that passes through the gaps between the soil particles, and the organic chlorine compound is Dechlorination of pollutants proceeds because anaerobic decomposition generates hydrogen.

  The first gas A1 discharged from the lower end of the purification well 10 rises upward while being diffused in the outer peripheral direction of the upper and lower wells 10 due to the pressure of the compressor 20 and the buoyancy in the saturated layer G2, and is thus supplied to the entire contaminated region.

  By supplying the first gas A1 to the entire contaminated area, the contaminated area becomes an anaerobic environment, and the anaerobic microorganisms are activated.

  Here, as pollutants (organochlorine compounds) that can be purified in the first stage, for example, tetrachloroethylene, trichloroethylene, trans-1,2-dichloroethylene, cis-1,2-dichloroethylene, 1,1-dichloroethylene, vinyl chloride monomer, Examples include 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,2-dichloroethane, carbon tetrachloride, and dichloromethane.

  When the purification of the organic chlorine compound in the first stage is completed, as the second stage, the compressor 20 and the water pump 42 are operated, and the second gas is passed from the purification well 10 to the ground G (contaminated area) as shown in FIG. A2 and the second liquid W2 are injected simultaneously.

By supplying the second gas A2 (air) to the contaminated area (saturated layer G2), the contaminated area becomes an aerobic environment, and aerobic microorganisms are activated.
At this time, since the second liquid W2 is injected together with the second gas A2, since the microorganisms are activated over a long period of time by the inorganic salt contained in the second liquid W2 and the decomposition ability is promoted, it is more effective. It becomes possible to perform purification.

  In addition, the flow path of the second gas A2 and the second liquid W2 is blocked by the growth of aerobic microorganisms, and the flow of the second gas A2 and the second liquid W2 injected thereafter is another void in the soil. Therefore, the second gas A2 can be uniformly supplied to the entire contaminated area, and an aerobic environment can be created uniformly.

By activating the aerobic microorganisms in the contaminated area, it is possible to remove or decompose the gas generated as a secondary during the purification period of the first stage.
Here, examples of the gas to be removed or decomposed in the second stage include methane, ethane, ethylene, and hydrogen sulfide.

Moreover, even if the organic substance supplied in the ground G in the first stage remains in the ground G even after the purification in the first stage is completed, it can be decomposed in the second stage.
Examples of such organic substances include sugars, proteins, amino acids, organic acids, fats and oils, and higher fatty acids.

In addition, contaminants that could not be purified during the first purification period (pollutants that cannot be purified by dechlorination) can be decomposed and purified by aerobic microorganisms.
Such pollutants include trichlorethylene, cis-1,2-dichloroethylene, vinyl chloride monomer, 1,2-dichloroethane, dichloromethane, benzene, toluene, ethylbenzene, m-xylene, p-xylene, o-xylene, oils And cyan compounds.

  In the first stage and the second stage, by operating the suction blower 52, the gas A injected into the ground G and rising in the saturated layer G2 by the buoyancy is sucked in the upper part of the unsaturated layer G1. Aspirate with 51,51.

  The gas A sucked by the suction well 51 is detoxified by the adsorption tower 53 and then released to the atmosphere.

  Thus, according to the in-situ purification method of the present embodiment, even if the ground G is contaminated with a plurality of contaminants, it can be purified.

  In addition, supply of a gas (first gas A1 or second gas A2) that creates an anaerobic environment or an aerobic environment and supply of a liquid W (first liquid W1 or second liquid W2) necessary for microbial decomposition are performed simultaneously. Thus, it is possible to cope with high concentration contamination, and the purification efficiency does not decrease even after the contamination concentration is reduced.

  In addition, by supplying the gas A and the liquid W in the first stage and the second stage using the same purification well 10, the manufacturing cost of the in-situ purification system can be reduced.

  The embodiment according to the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and the above-described components can be appropriately changed without departing from the spirit of the present invention.

  For example, ground conditions (soil quality, layer thickness, etc.) are not limited to the contents shown in the embodiment.

Moreover, you may arrange | position a pumping well as needed and pump groundwater.
In the case where a pumping well is provided, the ground water pumped by the pumping well may be detoxified, and then used as water constituting the first liquid W1 or the second liquid W2.

  Moreover, you may arrange | position the water-impervious wall around a contamination area | region as needed. Thereby, the outflow of the contaminated groundwater from the contaminated area and the outflow of the gas A and the liquid W injected into the soil can be prevented, and the influence on the surrounding area can be prevented.

Hereinafter, the result of the indoor test which confirmed the effect by implementing purification in an aerobic environment state after purification by an anaerobic environment state in the in- situ purification method according to the present invention will be described.

  In this laboratory test, contaminated groundwater was collected from an aquifer contaminated with a plurality of volatile organic compounds (VOCs), and an anaerobic culture test and an aerobic culture test were performed on the groundwater.

(1) Groundwater condition Table 1 shows the organic matter concentration, the number of bacteria, and the VOCs concentration in contaminated groundwater.
As shown in Table 1, five types of VOCs exceeding the environmental standard value were detected from the contaminated groundwater.

(2) Anaerobic culture test A 97-day culture test was conducted on contaminated groundwater in an anaerobic state, and the culture solution (contaminated groundwater) was collected over time to obtain a redox potential (ORP) and total organic carbon concentration (TOC). The total number of bacteria and the VOCs concentration were analyzed.
The culture was collected eight times on days 0, 12, 18, 25, 32, 39, 70 and 97.

  From the start of culture to the 10th day, the total organic carbon concentration (TOC) decreased (see FIG. 4) and the total bacterial count tended to increase (see FIG. 5). TOC) and the increase or decrease in the total number of bacteria was not observed.

  As shown in FIGS. 6 and 7, the dechlorination of the organic chlorine compound is performed by reducing the redox potential (ORP) to about −150 mV for 1,2-dichloroethane, cis-1,2-dichloroethylene, and vinyl chloride monomer. It was confirmed that it was dechlorinated after the 40th day (see FIG. 3).

On the other hand, as shown in FIG. 7, completion of dechlorination could not be confirmed for dichloromethane.
There was no change in benzene.

As a result of the above, dechlorination of 1,2-dichloroethane, cis-1,2-dichloroethylene, and vinyl chloride monomer proceeds if an anaerobic state is formed, but during this period, almost no decrease in organic matter is observed. It was.
On the other hand, for dichloromethane and benzene, the decrease in concentration hardly progressed under anaerobic conditions.

(3) Aerobic culture test Concentrated nutrient salt was added to the culture solution after the completion of the anaerobic culture test, and shake culture (aerobic culture) was performed for 7 days.
The test results are shown in Table 2.

As shown in Table 2, it was confirmed that by supplying air (oxygen) and nutrients to the culture solution, the total number of bacteria increased about 10 times, and benzene and dichloromethane were decomposed to below the detection limit. .
Moreover, the total organic carbon concentration (TOC) was also reduced to 20 mg / L, and it was confirmed that 85% or more of the organic substances were removed.

  As a result of the above, it was proved that it is possible to purify the ground contaminated with a plurality of pollutants by performing the purification in the aerobic environment state after the purification in the anaerobic environment state.

1 In-situ purification system 10 Purification well G Ground A1 First gas (low oxygen concentration gas)
A2 Second gas (high oxygen concentration gas)
W1 first liquid (liquid containing organic material)
W2 Second liquid (water)

Claims (1)

A first stage in which an anaerobic environment is created by supplying a liquid containing an organic material from a purification well into a ground containing an organic chlorine compound;
A second stage for producing an aerobic environment state by supplying a high oxygen concentration gas containing oxygen equal to or higher than air from the purification well into the ground that has become an anaerobic environment state in the first stage. A position purification method,
In the first stage, a low oxygen concentration gas having a lower oxygen content than air is supplied simultaneously with the liquid from the purification well ,
In the second step, the in-situ purification method is characterized in that water containing an inorganic salt is supplied simultaneously from the purification well with the high oxygen concentration gas.

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