JP2019000762A - Soil cleaning method - Google Patents

Abstract

To provide a soil cleaning method capable of preventing actions of microorganisms decomposing a volatile organic compound from being inhibited by an inhibitor supplied to a contaminated material supplied to a contamination area via ground water in a surrounding area.SOLUTION: There is provided a soil cleaning method for cleaning soil of a contamination area 3 contaminated by a volatile organic compound by activating actions of microorganisms decomposing the volatile organic compound, including: a process for arranging an injection well 2 for injecting an agent activating the actions of the microorganisms to the soil in the contaminated area 3; a process for arranging an observation well 1 for observing concentration of an inhibitor inhibiting the actions of the microorganisms contained in ground water in a ground water upstream in the contaminated area 3; and an injection process for injecting the agent to the soil from the injection well 2 when concentration of the inhibitor in the observation well 1 at prescribed frequency and a measurement result is over threshold.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a soil purification method.

  As a method for purifying soil contaminated with volatile organic compounds (VOC), there is a technique called bioremediation (bioremediation) using microorganisms or plants (for example, Patent Document 1). And Patent Document 2).

JP 2011-31187 A JP2011-218251A

When purifying contaminated soil using bioremediation, the purification effect decreases if the activity of microorganisms that decompose the pollutants is inhibited. Microorganisms that decompose volatile organic compounds are active under anaerobic conditions with an oxidation-reduction potential (ORP) of about -200 mV.
If inhibitors such as sulfuric acid, nitric acid, iron and manganese are present in the contaminated soil and / or groundwater contaminated with volatile organic compounds, the redox potential (ORP) of the contaminated soil will be low. It becomes difficult. As a result, the activity of microorganisms that decompose volatile organic compounds is inhibited. In particular, since sulfuric acid and nitric acid are substances that exist in a relatively wide range in soil and groundwater, they tend to inhibit the activity of microorganisms that decompose volatile organic compounds.

  In general, when soil contaminated with volatile organic compounds is purified using bioremediation, the microbial activity is activated by supplying the soil with a chemical that activates the activity of microorganisms that decompose volatile organic compounds. To do. When an inhibitory substance is present in the contaminated soil to be purified, an agent that activates the activity of microorganisms may be added in excess according to the content of the inhibitory substance. This can prevent microbial activity from being inhibited by the inhibitory substance. This preventive function is because the inhibitor is highly soluble in groundwater, and most of the inhibitor migrates with the groundwater without adsorbing to the soil, and the agent that activates the activity of microorganisms is easily adsorbed to the soil. The drug that activates the activity of microorganisms is obtained by diffusing after the groundwater flow.

However, in the above method, when an inhibitor is supplied to the contaminated area through the groundwater in the surrounding area, the activity of microorganisms that decompose volatile organic compounds is sufficiently prevented from being inhibited by the inhibitor. Can not.
As a method of solving this problem, a method of injecting a drug into the soil in the surrounding area of the contaminated area contaminated with the volatile organic compound can be considered. However, it is not preferable to inject a drug into the surrounding soil that is not contaminated with volatile organic compounds and does not need to be purified. In addition, it takes time and money to inject a drug into the soil in the surrounding area. Moreover, even if a drug is injected into the soil in the surrounding area, only a temporary effect is obtained, and the activity of microorganisms may be inhibited again after the injection of the drug.

As another method for solving the above problem, a method of preventing the inflow of groundwater from the surrounding area to the contaminated area by installing a steel sheet pile at the boundary of the contaminated area contaminated with the volatile organic compound can be considered. . However, installing a steel sheet pile at the boundary of the contaminated area is very laborious and expensive.
Therefore, it is possible to provide a method that can easily and effectively prevent the activity of microorganisms that decompose volatile organic compounds from being inhibited by an inhibitor that is supplied to a contaminated area through groundwater in the surrounding area. It was requested.

  The present invention has been made in view of the above circumstances, and can prevent the activity of microorganisms that decompose volatile organic compounds from being inhibited by an inhibitor that is supplied to a contaminated area through groundwater in the surrounding area. It is an object to provide a soil purification method.

This inventor repeated earnest research in order to solve the said subject.
As a result, an injection well for injecting chemicals that activate the activities of microorganisms that decompose volatile organic compounds into soil in the contaminated area and an observation well for observing the concentration of inhibitors in the upstream area of groundwater in the contaminated area are provided. The present inventors have conceived the present invention by measuring the concentration of an inhibitory substance in an observation well at a predetermined frequency and injecting a drug from the injection well into the soil when the measurement result exceeds a threshold value.
That is, the present invention relates to the following matters.

[1] A soil purification method that activates the activity of microorganisms that decompose volatile organic compounds to purify soil in a contaminated area that is contaminated with the volatile organic compounds,
Providing an injection well in the contaminated area for injecting an agent that activates the activity of the microorganism into the soil;
Providing an observation well for observing the concentration of an inhibitory substance that inhibits the activity of the microorganisms contained in groundwater in an upstream area of groundwater in the contaminated area;
Soil having a predetermined frequency, measuring the concentration of the inhibitor in the observation well, and injecting the drug from the injection well into the soil when the measurement result exceeds a threshold value Purification method.

[2] The soil purification method according to [1], wherein the threshold value is one or both of 500 mg / L sulfuric acid and 50 mg / L nitric acid.

  In the soil purification method of the present invention, an injection well for injecting a chemical that activates the activity of microorganisms into the soil is provided in the contaminated area, and the activity of microorganisms contained in the groundwater is inhibited in the upstream area of the groundwater in the contaminated area. An observation well for observing the concentration of the inhibitory substance is provided, and the concentration of the inhibitory substance is measured in the observation well at a predetermined frequency. When the measurement result exceeds the threshold value, the drug is injected from the injection well into the soil. Therefore, even if an inhibitory substance is supplied to the contaminated area through the groundwater in the surrounding area, the activity of microorganisms that decompose volatile organic compounds is prevented by the drug injected into the soil from the injection well. it can. Therefore, according to the soil purification method of the present invention, the volatile organic compound in the soil can be efficiently decomposed into microorganisms, and the soil contaminated with the volatile organic compound can be efficiently purified.

It is a top view for demonstrating arrangement | positioning of the injection well installed in the soil purification method of an Example, and an observation well. It is the graph which showed the relationship between the sulfuric acid density | concentration and tetrachlorethylene (PCE) density | concentration in an Example, and elapsed time (the number of days after performing the first injection | pouring process).

Hereinafter, the soil purification method of the present invention will be described in detail. In addition, this invention is not limited only to embodiment shown below.
The soil purification method of this embodiment is a soil purification method that activates the activity of microorganisms that decompose volatile organic compounds and purifies soil in a contaminated area that is contaminated with volatile organic compounds.
Examples of the volatile organic compound include tetrachloroethylene (PCE), trichlorethylene, cis-1,2-dichloroethylene, and the like.

  In the soil purification method of the present embodiment, the step of providing an injection well in the contaminated area, the step of providing an observation well in the upstream area of groundwater in the contaminated area, and measuring the concentration of the inhibitory substance in the observation well at a predetermined frequency, When the measurement result exceeds the threshold, an injection step of injecting the drug from the injection well into the soil is performed.

"Process for providing injection well"
The injection well is used to inject contaminated soil with agents that activate the activities of microorganisms that degrade volatile organic compounds. One or more injection wells may be provided in the contaminated region. The number, shape, size, arrangement, etc. of the injection wells can be appropriately determined according to the shape of the contaminated area, the concentration of volatile organic compounds in the contaminated area, the inflow of groundwater into the contaminated area, and the like.

  A well-known well can be provided as the injection well, and is not particularly limited. For example, as an injection well, a drilling hole formed by drilling soil in a contaminated area, a perforated pipe installed in the drilling hole, a nonporous pipe connected to the upper end of the perforated pipe and extending to the ground, A perforated pipe and / or a filter layer formed by filling a filter medium between a non-porous pipe and a drilling hole, and a supply pipe connected to one end of the non-porous pipe on the ground side for supplying a chemical from a chemical tank Can be used. As the filter agent, dredged sand, mortar, bentonite, gravel and the like can be used.

  Examples of microorganisms that decompose volatile organic compounds include microorganisms that originally live in contaminated areas. In general, microorganisms that decompose volatile organic compounds are active under anaerobic conditions. Specifically, a microorganism that decomposes volatile organic compounds grows at an oxidation-reduction potential (ORP) of −150 mV or less and is more active at about −200 mV. The function of decomposing volatile organic compounds by microorganisms may be a function obtained by only one type of microorganism or a function obtained by combining a plurality of types of microorganisms having different characteristics.

  The drug activates the activity of microorganisms that decompose volatile organic compounds, and conventionally known drugs can be used. Specifically, it is preferable to use a drug mainly composed of a food additive-derived carbohydrate and an amino acid. NS Bioacty (manufactured by Nippon Steel & Sumikin Engineering Co., Ltd.) is a drug mainly composed of carbohydrates and amino acids derived from food additives.

“Process of providing observation well”
The observation well is used to observe the concentration in the groundwater of inhibitors that inhibit the activity of microorganisms that degrade volatile organic compounds. One or more observation wells may be provided in the groundwater upstream area in the contaminated area. The number, shape, size, arrangement, etc. of observation wells can be appropriately determined according to the shape of the contaminated area, the inflow of groundwater into the contaminated area, and the like. For example, a plurality of observation wells may be installed side by side along the boundary of the contaminated area on the upstream side of the groundwater. The observation well may also serve as an injection well.

  As the observation well, for example, a hole formed by drilling the soil in the upstream area of the groundwater in the contaminated area until it reaches the aquifer, a perforated pipe installed in the aquifer in the drilling hole, It is preferable to use a non-porous pipe connected to the upper end of the pipe and extending to the ground, and a perforated pipe and / or a filter layer formed by filling the non-porous pipe and the hole with a filter agent. it can. As the filter agent, dredged sand, mortar, bentonite, gravel and the like can be used.

A conventionally known method can be used as a method for observing the concentration of the inhibitor contained in the groundwater, and is not particularly limited. For example, the groundwater collected in the observation well can be observed by a method of measuring the inhibitor concentration by a method corresponding to the inhibitor.
A water sampler such as a submersible pump or baler can be used for collecting groundwater in the observation well. It is preferable that the water sampler is connected to a supply pipe that supplies groundwater pumped from the aquifer to a measuring device that measures the concentration of the inhibitory substance. The depth of the groundwater to be collected is preferably at an intermediate depth in the perforated section of the perforated pipe forming the observation well.
When the inhibitor is sulfuric acid, the concentration of sulfuric acid contained in the groundwater can be measured by an ion chromatograph method defined in 41.3 of JIS K0102. When the inhibitor is nitric acid, the concentration of nitric acid contained in the groundwater can be measured by absorptiometry according to the method defined in JIS K0102 43.2.1, 43.2.3, 43.2.5 or 43.2.6.

  Inhibitors observed in the observation wells inhibit the activity of microorganisms that decompose volatile organic compounds. Specifically, examples of the inhibitor include sulfuric acid, nitric acid, iron, and manganese. Among these inhibitory substances, sulfuric acid and nitric acid are substances that exist in a relatively wide range in soil and groundwater, and therefore tend to inhibit the activity of microorganisms that decompose volatile organic compounds. If the soil and / or groundwater contains 500 mg / L or more of sulfuric acid and / or 50 mg / L or more of nitric acid, the oxidation-reduction potential (ORP) of the soil is difficult to decrease. As a result, the activity of microorganisms that decompose volatile organic compounds that are actively active at an oxidation-reduction potential (ORP) of about -200 mV is inhibited.

  In the present embodiment, not only the concentration of the inhibitor contained in the groundwater pumped up in the observation well, but also the concentration of the volatile organic compound contained in the groundwater pumped up in the observation well may be observed. As a method for measuring the concentration of the volatile organic compound, a known method can be used. For example, when the volatile organic compound is tetrachloroethylene (PCE), it can be measured by the method defined in JIS K0125 5.1, 5.2, 5.3.1, 5.4.1 or 5.5.

"Injection process"
The injection step is a step of measuring the concentration of the inhibitory substance in the observation well at a predetermined frequency and injecting the drug from the injection well into the soil when the measurement result exceeds the threshold value.
The injection process is performed at a predetermined frequency. The frequency of the injection process can be determined according to the type, concentration, groundwater flow rate, etc. of the inhibitor, and is not particularly limited. For example, the period between the injection process and the next injection process can be 1 to 100 days, preferably 20 to 60 days. The period between the injection step and the next injection step may be different each time, the same case may be included, or may be the same every time. The higher the frequency of the injection process, the more effectively it can be prevented that the activity of microorganisms that decompose volatile organic compounds is inhibited, and the volatile organic compounds in the soil can be efficiently decomposed into microorganisms.

  In the injection step, for example, when measuring the concentration of sulfuric acid as the inhibitor concentration, the threshold is preferably 500 mg / L sulfuric acid, more preferably 100 mg / L sulfuric acid, and 80 mg / L sulfuric acid. More preferably, it is sulfuric acid. By setting the threshold value to 500 mg / L sulfuric acid, it is possible to effectively prevent the activity of microorganisms that decompose volatile organic compounds from being inhibited by sulfuric acid contained in groundwater flowing from the surrounding area.

  In the injection step, for example, when the concentration of nitric acid is measured as the concentration of the inhibitor, the threshold is preferably 50 mg / L nitric acid, and more preferably 10 mg / L nitric acid. By setting the threshold value to 50 mg / L of nitric acid, it is possible to effectively prevent the activity of microorganisms that decompose volatile organic compounds from being inhibited by nitric acid contained in groundwater flowing from the surrounding area.

When the measurement result exceeds the threshold, the concentration and amount of the drug to be injected can be appropriately determined according to the type and concentration of the inhibitor, the frequency of the injection process, and the like.
In addition, when a plurality of injection wells are provided, the drug may be injected from all the injection wells every time the injection process is performed, or there may be an injection well with a low frequency of drug injection. For example, the frequency of injecting the drug from the injection well arranged at the peripheral edge in the contaminated area may be higher than the frequency of injecting the drug from the injection well arranged in the central part of the contaminated area.

  In the soil purification method of the present embodiment, the concentration of an inhibitor that inhibits the activity of microorganisms contained in the groundwater is measured at a predetermined frequency in the observation well, and when the measurement result exceeds a threshold value, the soil is transferred from the injection well to the soil. , Having an injection step of injecting an agent that activates the activity of microorganisms that decompose volatile organic compounds. Therefore, even if an inhibitory substance is supplied to the contaminated area through the groundwater in the surrounding area, the activity of microorganisms that decompose volatile organic compounds is prevented by the drug injected into the soil from the injection well. it can. Therefore, according to the soil purification method of the present embodiment, the volatile organic compound in the soil can be efficiently decomposed into microorganisms, and the soil contaminated with the volatile organic compound can be efficiently purified.

  Moreover, in the soil purification method of this embodiment, it is not necessary to inject | pour a chemical | medical agent into the soil of the surrounding area which is not polluted with a volatile organic compound and does not need to purify. Furthermore, according to the soil purification method of the present invention, for example, a steel sheet pile is installed at the boundary of the contaminated area to prevent the activity of microorganisms from being inhibited by the inhibitory substance supplied to the contaminated area through the groundwater in the surrounding area. This can be easily prevented compared to the case.

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited only to a following example.
Drawing 1 is a top view for explaining arrangement of an injection well and an observation well installed in a soil purification method of an example. In FIG. 1, reference numeral 2 indicates an injection well, reference numeral 1 indicates an observation well, and reference numeral 3 indicates a contaminated region. The contaminated area 3 shown in FIG. 1 is an approximately square area with a side of 10 m where the soil is contaminated with a volatile organic compound containing tetrachlorethylene (PCE). As indicated by arrows in FIG. 1, groundwater flows into the contaminated area 3 from the upper right direction of FIG.
The contaminated area 3 was purified by the following method.

  As shown in FIG. 1, the inflow wells 2 were respectively installed at the centers of the regions divided into nine so that the contaminated region 3 has substantially the same area. As each inflow well 2, a drilling hole formed by drilling the soil in the contaminated area 3, a perforated pipe installed in the drilled hole, a non-porous pipe connected to the upper end of the perforated pipe and extending to the ground A filter layer formed by filling a perforated pipe and / or a non-porous pipe and a drilling hole with a filter agent, and a supply connected to one end on the ground side of the non-porous pipe to supply a chemical from a chemical tank A thing having piping was installed. No. 3 cinnabar was used as a filter agent.

Moreover, as shown in FIG. 1, the observation well 1 was installed in the right corner of the contaminated area 3 in FIG. As the observation well 1, a hole formed by drilling the soil in the upstream area of the groundwater in the contaminated area 3 until it reaches the aquifer, a perforated pipe installed in the aquifer within the borehole, and a perforated pipe A non-porous tube connected to the upper end of the tube and extending to the ground, and a perforated pipe and / or a filter layer formed by filling the non-porous tube and the hole with a filter agent were installed. No. 3 cinnabar was used as a filter agent.
A submersible pump was used as a water sampler to collect groundwater at the observation well. A supply pipe for supplying groundwater pumped from the aquifer was connected to an apparatus (ion chromatograph) for measuring the concentration of sulfuric acid, which is an inhibitor, to the water sampler. The depth of groundwater to be collected in the observation well was set at the intermediate depth in the perforated section of the perforated pipe forming the observation well.

And the sulfuric acid concentration of the groundwater pumped up in the observation well 1 was measured as an initial sulfuric acid concentration. As a result, the initial sulfuric acid concentration was 180 mg / L. The initial concentration of tetrachlorethylene (PCE) contained in the groundwater pumped up from the observation well 1 was measured. As a result, it was 0.3 mg / L.
Next, NS bioacty (manufactured by Nippon Steel & Sumikin Engineering Co., Ltd.) was injected into the soil from all the inflow wells 2 as an agent (first injection step). The injection amount of the drug in the first injection step was set such that the total injection amount from all the inflow wells 2 was 0.6 kg / rice for the entire amount of soil to be purified in the contaminated area 3.

  Thereafter, after 60 days, 90 days, 120 days, 150 days, 170 days, and 190 days after the first injection step, the nitric acid concentration and the PCE concentration pumped up in the observation well 1 were measured. And when nitric acid concentration is more than 80 mg / L (above threshold value) (after 90 days and after 150 days), the injection process of injecting the same drug as the first time into the soil from all the inflow wells 2 at the same injection volume as the first time Went.

FIG. 2 is a graph showing the relationship between sulfuric acid concentration and tetrachlorethylene (PCE) concentration and elapsed time (number of days since the first injection step) in the examples.
As shown in FIG. 2, the sulfuric acid concentration (95 mg / L) 90 days after the first injection step is higher than that after 60 days (50 mg / L). The sulfuric acid concentration after 150 days (81 mg / L) is higher than that after 120 days (64 mg / L). This is presumably because sulfuric acid is supplied to the contaminated area 3 through the groundwater in the surrounding area.

  As described above, in the soil purification method of the embodiment, sulfuric acid is supplied to the contaminated area through the groundwater in the surrounding area, but the sulfuric acid concentration is prevented from being increased by the chemical injected into the soil from the injection well. ing. As a result, the activity of microorganisms that decompose volatile organic compounds is prevented from being inhibited. As shown in FIG. 2, it is estimated that the volatile organic compounds in the soil are decomposed by microorganisms and the soil is purified. Is done.

1 ... observation well, 2 ... injection well, 3 ... contaminated area.

Claims (2)

A soil purification method that activates the activity of microorganisms that decompose volatile organic compounds to purify soil in a contaminated area that is contaminated with the volatile organic compounds,
Providing an injection well in the contaminated area for injecting an agent that activates the activity of the microorganism into the soil;
Providing an observation well for observing the concentration of an inhibitory substance that inhibits the activity of the microorganisms contained in groundwater in an upstream area of groundwater in the contaminated area;
Soil having a predetermined frequency, measuring the concentration of the inhibitor in the observation well, and injecting the drug from the injection well into the soil when the measurement result exceeds a threshold value Purification method.   2. The soil purification method according to claim 1, wherein the threshold value is one or both of 500 mg / L sulfuric acid and 50 mg / L nitric acid.

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