WO2018159741A1

WO2018159741A1 - Method for purifying contaminated groundwater

Info

Publication number: WO2018159741A1
Application number: PCT/JP2018/007709
Authority: WO
Inventors: 雅子伊藤; 陽高畑; 傳喜片山; 成志吉川; 幸樹柴田
Original assignee: 大成建設株式会社; 東洋製罐グループホールディングス株式会社
Priority date: 2017-03-01
Filing date: 2018-03-01
Publication date: 2018-09-07
Also published as: JP2018143918A; JP6906330B2

Abstract

The purpose of the invention is to provide a method for purifying contaminated groundwater that can purify contaminated groundwater and can prevent the groundwater from recontamination by keeping a large area of ground in a low contamination state over a long period of time. Provided is a method for purifying contaminated groundwater using anaerobic microorganisms to purify contaminated groundwater or to prevent the groundwater from recontamination, wherein the method is characterized in that a particulate hydrolyzable resin and a water-soluble organic compound are used together as the hydrogen donor, and in that a mixed solution is formed by adding the hydrolyzable resin to the water-soluble organic compound, stirring same, and then adding water, and the mixed solution is then injected into the ground.

Description

Purification method of contaminated groundwater

The present invention relates to a contaminated groundwater purification method for purifying contaminated groundwater or preventing recontamination of groundwater.

地下 Groundwater contamination by chemical substances may be regulated by environmental standards, etc., and many countermeasures have been studied and implemented. Among such countermeasures, a method of purifying the groundwater without causing a significant change in the location where groundwater contamination occurs is particularly useful.

One of the effective methods for purifying groundwater contamination is a method (bioremediation) of decomposing harmful substances using microorganisms. Various attempts have already been made to purify harmful chemical substances in groundwater by effectively utilizing microorganisms present in the soil in situ. Among hazardous chemical substances, volatile organochlorine compounds such as tetrachlorethylene and trichlorethylene (hereinafter sometimes referred to as “VOCs”) have established groundwater environmental standards, and technologies for their purification are highly demanded. Is. In addition, nitrate water and nitrite nitrogen (hereinafter sometimes referred to as “nitrate / nitrite nitrogen”) have established groundwater environmental standards, and technologies for their purification are required. .

Purification technology using anaerobic microorganisms is known as a purification technology for groundwater contamination by VOCs and nitrate / nitrite nitrogen. It purifies VOCs and nitrate / nitrite nitrogen by making the groundwater environment anaerobic and providing a hydrogen donor as an energy source for anaerobic microorganisms that degrade VOCs and nitrate / nitrite nitrogen Technology.

For example, when a water-soluble organic compound is injected into the ground as an energy source for anaerobic microorganisms, oxygen is consumed by the aerobic microorganisms and an anaerobic environment is formed. As a result, anaerobic microorganisms are activated, and purification of VOCs and nitrate / nitrite nitrogen proceeds. Here, the water-soluble organic compound is a substance that becomes a nutrient source or a hydrogen donor for activating the aerobic microorganism and the anaerobic microorganism.

Since water-soluble organic compounds dissolve in water and easily flow out in the ground where the groundwater flow rate is high, additional injection of water-soluble organic compounds is required before purification is completed, which requires time, labor and cost. there were. Furthermore, even if the concentration of VOCs decreases, the VOCs contained in the surrounding soil may elute and cause contamination again. At this time, if water-soluble organic compounds have disappeared, sufficient anaerobic environment necessary for purification cannot be maintained, and it becomes difficult for anaerobic microorganisms to purify VOCs. Rebound). Therefore, there has been a demand for means for preventing re-contamination of groundwater in a place where contamination may occur or where purification has been completed.

Various methods have been disclosed as techniques for purifying VOCs and nitrate / nitrite nitrogen using anaerobic microorganisms. Patent Document 1 is characterized in that a purifier is melted by heating, pressurized and injected into contaminated soil or groundwater, diffused, and decomposed by microorganisms grown under anaerobic conditions after solidification. In-situ purification methods for contaminated soil and / or groundwater contamination are disclosed.

Japanese Patent No. 3694294

In the in-situ purification method described in Patent Document 1, since the purification agent is solidified in the soil, it is possible to maintain an anaerobic environment and to prevent recurrence of groundwater contamination. However, when the temperature of the environment to be applied is low, the temperature of the cleaning agent is rapidly lowered and solidified, so that the range in which the cleaning agent reaches from the injection well is narrowed, and the region to be purified in the soil is reduced. It will be limited.

In order to keep the anaerobic environment in the long term in order to cope with the highly permeable ground and to suppress the rebound after purification, inject the organic compound that is a nutrient source of anaerobic microorganisms into the ground in the form of solid powder The method is effective. In particular, a high molecular weight resin is suitable for the purpose of maintaining an anaerobic environment for a long period of time because it does not easily collapse even in the soil and gradually decomposes over time.

The solid powder organic compound to be injected is preferable because the smaller the particle shape, the better it can be injected into a wide range of ground. On the other hand, since the organic compound processed into a fine powder has an increased surface area, it tends to aggregate and it is difficult to uniformly disperse it in water as a medium. In particular, a resin in the form of a solid powder generally has a problem that it does not disperse in water only when added to water, but aggregates and becomes non-uniform, and floats on the water surface, resulting in a significant decrease in handling.

The present invention has been made in view of the above circumstances. That is, an object of the present invention is to provide a method for purifying contaminated groundwater that can maintain a low contamination state in a wide area of soil for a long period of time, purify contaminated groundwater, and prevent recontamination of groundwater. It is to be.

The present inventors follow the procedure of adding a water-soluble organic compound to a particulate hydrolyzable resin and stirring, then adding water to form a mixed solution, and then pouring the mixed solution into the soil. Thus, it has been found that aggregation of the particulate hydrolyzable resin can be suppressed and a hydrogen donor can be provided over a wide area in the soil. In addition, it has been found that the combined use of a water-soluble organic compound and a hydrolyzable resin as a hydrogen donor makes it possible to maintain an anaerobic environment in the soil and suppress recontamination. .

The present invention has been made based on such knowledge. That is, the present invention is a method for purifying contaminated groundwater, which uses anaerobic microorganisms to purify contaminated groundwater or prevents recontamination of groundwater, and as a hydrogen donor, a particulate hydrolyzable resin And the water-soluble organic compound together, the hydrolyzable resin is added to the water-soluble organic compound and stirred, then water is added to form a mixed solution, and then the mixed solution is poured into the soil. This is a purification method for contaminated groundwater.

The pollutant in the contaminated groundwater may be at least one of a volatile organochlorine compound, nitrate nitrogen, and nitrite nitrogen.
The water-soluble organic compound preferably contains at least one of alcohol, alcohol derivative, carboxylic acid and carboxylic acid derivative.
The hydrolyzable resin is preferably an aliphatic polyester.
The hydrolyzable resin preferably contains at least one of polylactic acid and polyoxalate.
The average particle size of the hydrolyzable resin is preferably 1 to 100 μm.
Moreover, a packer can be installed in the upper part of the well for injection | pouring of the said mixed solution in soil, and the said mixed solution can be inject | poured into soil using a pump.

The method for purifying contaminated groundwater of the present invention can maintain a state of low contamination over a wide area in the soil for a long period of time, thereby purifying the contaminated groundwater or preventing recontamination of the groundwater.

It is the figure which showed the particle size distribution by the dynamic light scattering method of the particle | grains of a hydrolysable resin. It is a figure which shows the particle size distribution of the hydrolysable resin in the mixed solution which disperse | distributed hydrolyzable resin only to water. It is a figure which shows the particle size distribution of the hydrolysable resin in the mixed solution which disperse | distributed the hydrolyzable resin which added sodium lactate. It is the figure which showed the peak distribution of the primary particle and secondary particle | grains of the hydrolysable resin in a mixed solution for every kind of water-soluble organic compound to add. It is the figure which showed the average particle diameter of the primary particle | grains of the hydrolysable resin in a mixed solution for every kind of water-soluble organic compound to add. It is the figure which showed the polydispersity index of the primary particle | grains of the hydrolyzable resin in a mixed solution for every kind of water-soluble organic compound to add. It is the figure which showed the reach | attainment distance of the particulate hydrolyzable resin in the soil (in the case of the mixed solution which disperse | distributed hydrolyzable resin only in water). It is the figure which showed the reach | attainment distance of the particulate hydrolyzable resin in soil (in the case of the mixed solution which disperse | distributed the hydrolyzable resin which added sodium lactate). It is the figure which showed an example of the concrete method when inject | pouring a mixed solution in soil.

Embodiments of the present invention will be described in detail below. However, the embodiment described below is an example of the embodiment of the present invention, and the present invention is not limited to these contents, and various modifications can be made within the scope of the gist.

This embodiment is a method for purifying contaminated groundwater by using anaerobic microorganisms to purify contaminated groundwater or preventing recontamination of groundwater. Contaminants of contaminated groundwater are not particularly limited, but among the pollutants, groundwater environmental standards are set for VOCs and nitrate / nitrite nitrogen. The purification method of the present embodiment is suitable for contaminated groundwater containing VOCs or nitrate / nitrite nitrogen. Moreover, the purification method of this embodiment is effective not only for contaminated groundwater but also for the purification of soil recontaminated with VOCs.

(Pollutant)
VOCs have been widely used industrially as solvents and cleaning agents. Specific examples of VOCs include tetrachloroethylene (PCE), trichlorethylene (TCE), cis-1,2-dichloroethylene (cis-1,2-DCE), 1,1-dichloroethylene (1,1-DCE), vinyl chloride ( VC or VCM), 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,2-dichloroethane, ethane tetrachloride, carbon tetrachloride, chloroform, dichloromethane and the like.

In the purification of contaminated groundwater containing VOCs, VOCs are dechlorinated using anaerobic microorganisms in an anaerobic environment to change them into compounds that do not contain chlorine. Anaerobic microorganisms that degrade VOCs are activated by the presence of a hydrogen donor in an anaerobic environment.

Main sources of nitrate and nitrite nitrogen are nitrogen fertilizer, livestock manure and domestic wastewater. Some of these substances are converted into nitrate nitrogen through ammonia nitrogen and nitrite nitrogen by the action of microorganisms in the soil. Nitrate and nitrite nitrogen is easily dissolved in water and is not easily retained in soil, and therefore has a property of being easily dissolved in groundwater.

Purification of VOCs and nitrate / nitrite nitrogen by anaerobic microorganisms is performed by the following process.
(I) Even in the soil where anaerobic microorganisms are present, the aerobic microorganisms are active in an aerobic environment. In order to activate anaerobic microorganisms, it is necessary to remove oxygen in the environment to make an anaerobic environment. To create an anaerobic environment, nutrient sources and hydrogen donors are injected into the soil to activate aerobic microorganisms and consume oxygen in a limited area of the soil.

(Ii) In the anaerobic environment without oxygen, the presence of a hydrogen donor activates anaerobic microorganisms. Nitrate and nitrite nitrogen is finally converted into harmless nitrogen by anaerobic denitrifying bacteria. VOCs are replaced with hydrogen by anaerobic dechlorinating bacteria, and finally converted into harmless substances such as ethylene and ethane that do not contain chlorine.

(Water-soluble organic compounds)
A water-soluble organic compound is an organic compound containing hydrogen, metabolized by microorganisms to become a nutrient source, and also functions as a hydrogen donor when substituting the chlorine atom of VOCs with a hydrogen atom. Examples of water-soluble organic compounds include alcohols, carboxylic acids, amines, esters, and derivatives thereof. Further, the water-soluble organic compound preferably contains at least one of alcohol, alcohol derivative, carboxylic acid and carboxylic acid derivative. In particular, the water-soluble organic compound is preferably either a carboxylic acid or a carboxylic acid derivative, and the carboxylic acid derivative is more preferably a carboxylate. As the water-soluble organic compound, only a specific type may be used, or a plurality of types may be mixed and used. Further, the water-soluble organic compound is preferably an organic compound composed of only carbon atoms and hydrogen atoms, or carbon atoms, hydrogen atoms and oxygen atoms. In addition, the water-soluble organic compound is preferably an organic compound having a low molecular weight that is biodegradable so as not to remain in the soil.

Specific examples of water-soluble organic compounds are as follows. Examples of the alcohol include ethylene glycol, polyethylene glycol, glycerin and the like. Examples of the carboxylic acid include glycolic acid, lactic acid, malic acid, succinic acid, ascorbic acid, acetic acid and the like. Examples of the carboxylate include sodium lactate, sodium ascorbate, and sodium succinate. In addition, biodegradable nutrient sources such as yeast extract, soy milk, corn milk, peptone, beef tallow, coconut oil, and soybean oil may be added to the water-soluble organic compound.

(Hydrolyzable resin)
The hydrolyzable resin is a resin that is hydrolyzed in the presence of water to generate a low molecular weight monomer. The generated monomer is an organic compound that contains carbon and hydrogen atoms, as well as water-soluble organic compounds. It is metabolized by microorganisms to become a nutrient source and replaces the chlorine atoms in VOCs with hydrogen atoms. It also functions as a hydrogen donor.

The hydrolyzable resin is a high molecular weight resin that is insoluble in water, so it is not susceptible to chemical degradation or microbial degradation, and remains on the contaminated ground for a long period of time, releasing the hydrogen donor continuously. It is possible. In addition, since it does not decompose rapidly, it does not increase the total organic carbon concentration (TOC) and has a low environmental impact.

When a water-soluble organic compound and a hydrolyzable resin are used in combination, the water-soluble organic compound functions as a nutrient source or hydrogen donor that acts on microorganisms in the short term, and a nutrient source on which the hydrolyzable resin acts on microorganisms in the long term. Or it functions as a hydrogen donor. When a water-soluble organic compound and a hydrolyzable resin are used in combination, an anaerobic environment can be maintained continuously. Further, by changing the ratio between the water-soluble organic compound and the hydrolyzable resin, the balance between the activation of the short-term and long-term anaerobic microorganisms can be controlled. Further, since the hydrogen donor is also supplied from the hydrolyzable resin, consumption of the water-soluble organic compound can be suppressed, and the injection amount of the water-soluble organic compound used in the entire purification operation can be reduced.

Furthermore, once the target area has been purified, VOCs and nitrate / nitrite nitrogen that have been contained in the surrounding soil will elute, or new VOCs and nitrate / Nitrite nitrogen may flow in or groundwater level may change, causing pollution again. Even in such a case, since the activity of the anaerobic microorganisms is maintained in an anaerobic environment, recontamination can be suppressed.

By changing the weight average molecular weight (Mw) of the hydrolyzable resin, the period during which the hydrolyzable resin remains in the contaminated ground and releases the hydrogen donor can be adjusted. If the weight average molecular weight of the hydrolyzable resin is too small, it will be hydrolyzed within a short period of time, making it difficult to sustain for a long time as a hydrogen donor. Therefore, the weight average molecular weight of the hydrolyzable resin is preferably 12,000 or more. In addition, when the hydrolyzable resin has a weight average molecular weight of 12,000 or more, the hydrolyzable resin can be formed into a pellet shape or a powder shape to maintain the shape. In addition, since the hydrolysis rate varies depending on the type and pH of the hydrolyzable resin, the period during which the hydrolysis rate remains in the contaminated ground and releases the hydrogen donor can be changed by changing the type and pH of the hydrolyzable resin. Can be adjusted.

Specifically, the hydrolyzable resin is a polyester, polyamide, polysaccharide, protein or the like in which monomers are polycondensed by an ester bond, an amide bond, a glycoside bond, a peptide bond, or the like. Specific examples of the monomer constituting the polyester include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, Dicarboxylic acids such as decanedicarboxylic acid and cyclohexanedicarboxylic acid; polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, bisphenol A, polyethylene glycol; Hydroxy carboxylic acids such as glycolic acid, lactic acid, malic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxybenzoic acid; glycolide, caprola Ton, butyrolactone, valerolactone, propiolactone, lactones, such as undecalactone, and the like.

Specific examples of the monomer constituting the polyamide include dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, anthracene dicarboxylic acid; hexa Examples include diamines such as methylenediamine, nonanediamine, methylpentadiamine, and phenylenediamine; and lactams such as caprolactam, undecane lactam, and lauryllactam. Specific examples of the monomers constituting the polysaccharide and protein include monosaccharides such as glucose, fructose and galactose; α-amino acids such as glutamic acid, aspartic acid, glycine and lysine.

Examples of the polysaccharide and protein polycondensed by the glycosidic bond or peptide bond include starch, modified starch, cellulose, chitin, chitosan, gluten, gelatin, soybean protein, collagen, keratin and the like.

Among hydrolyzable resins, aliphatic polyester is preferable from the viewpoint of easy decomposability. Among the aliphatic polyesters, poly (α-hydroxy acid), poly (β-hydroxyalkanoate), poly (ω-hydroxyalkanoate), polyalkylene dicarboxylate and the like are preferable from the viewpoint of biodegradability. Specific examples of preferred hydrolyzable resins include polyglycolic acid, polylactic acid, poly (β-hydroxybutyric acid), poly (β-hydroxyvaleric acid), poly-β-propiolactone, poly-ε-caprolactone, polyethylene Succinate, polybutylene succinate, polyethylene oxalate, polybutylene oxalate and the like can be mentioned. These hydrolyzable resins may be used only in specific types, or a plurality of types may be mixed and used. As the type of the hydrolyzable resin, an appropriate type of hydrolyzable resin can be selected and used according to the soil quality of the ground to be purified.

The hydrolyzable resin preferably contains at least one of polylactic acid and polyoxalate because it has an appropriate hydrolysis rate and is excellent in handleability. Both polylactic acid and polyoxalate are composed of only carbon atoms and hydrogen atoms and are biodegradable. Here, the polyoxalate means a copolymer such as polyethylene oxalate or polybutylene oxalate obtained by copolymerizing oxalic acid and a diol such as ethylene glycol or butylene glycol.

When polylactic acid and polyoxalate are used in combination, a new effect can be expressed as described below.
Polylactic acid generates lactic acid when hydrolyzed. Lactic acid is particularly useful as a microbial nutrient source and hydrogen donor. However, since the hydrolysis rate of polylactic acid in an anaerobic environment is not large, when it is desired to activate the activity of anaerobic microorganisms, the amount of lactic acid generated may be insufficient.
On the other hand, polyoxalate has a higher hydrolysis rate than polylactic acid and generates oxalic acid by hydrolysis. This oxalic acid serves as a catalyst for hydrolysis of polylactic acid.

When polylactic acid and polyoxalate are used in combination, oxalic acid is first generated by hydrolysis of polyoxalate. When the concentration of oxalic acid is increased, hydrolysis of polylactic acid is promoted to generate lactic acid, It works effectively on activation. By changing the amount ratio of polylactic acid and polyoxalate, it is possible to control the elution rate and sustainability of the decomposition product relatively freely. The combined use method of polylactic acid and polyoxalate may be used as a resin that is melt-mixed and combined, or may be used by mixing particles of each resin.

In the ground where the flow rate of groundwater is large, even if water-soluble organic compounds are injected into the soil, the water-soluble organic compounds dissolve in the groundwater and are likely to flow out together with the groundwater, so the state of being purified for a long time is continued. That was difficult.
On the other hand, the hydrolyzable resin of this embodiment is particulate. When the hydrolyzable resin is particulate, the hydrolyzable resin can be retained in the gaps between the soil particles. In addition, when the hydrolyzable resin stays in the gap between the soil particles, the gap between the soil particles is blocked, so that the flow rate of groundwater can be reduced. In other words, when particulate hydrolyzable resin is used, the flow rate of groundwater in the purification target area is reduced, and the hydrolyzable resin stays in the soil even in the ground where the flow rate of groundwater is high, and the original hydrogen donor The function can be demonstrated. In addition, when the hydrolyzable resin is in the form of particles, even if oxygen, nitrate ions, sulfate ions, etc. flow in as components of the inflowing groundwater, these components are not affected by the oxidation action etc. It is hard to be affected by.

The particle size of the hydrolyzable resin can be set to an appropriate particle size according to the soil quality of the ground to be purified. However, when injecting a cleaning agent containing hydrolyzable resin from the injection well in the soil, if the particle size of the hydrolyzable resin is small, the distance that the hydrolyzable resin reaches around the injection well by the injection operation It becomes long and it becomes possible to purify a wide area in the soil. Therefore, the average particle size of the hydrolyzable resin is preferably 1 to 100 μm, and more preferably 1 to 10 μm. The particle size of the hydrolyzable resin can be measured by a dynamic light scattering method or the like. Further, the hydrolyzable resin particles can be formed into an appropriate shape according to the soil quality of the ground to be purified. The average particle size of the hydrolyzable resin is the average particle size of primary particles of the hydrolyzable resin, and is usually measured as a 90% diameter (d90). The 90% diameter is the particle diameter at which the cumulative curve becomes 90% when the cumulative curve is determined with the total volume of the group of particles as 100%.

As described above, in this embodiment, an anaerobic environment can be stably maintained over a long period of time by using a water-soluble organic compound and a particulate hydrolyzable resin in combination as a hydrogen donor. It is. As a result, even if VOCs and nitrate / nitrite nitrogen contained in the surrounding soil elute and cause pollution again, it is possible to suppress recontamination. Furthermore, even when purifying the ground with high water permeability, the particulate hydrolyzable resin functions as a plugging material for the gaps between the soil particles, suppressing the water permeability of the groundwater and reducing the consumption of hydrogen donors. It is possible to suppress and increase the sustainability of purification of groundwater contaminated with anaerobic microorganisms.

The composition ratio between the particulate hydrolyzable resin and the water-soluble organic compound is not particularly limited, and should be appropriately changed according to the characteristics of each component, the type of the target pollutant, the duration of the anaerobic environment, etc. Can do. As a typical composition, for example, the mixing ratio of the hydrolyzable resin and the water-soluble organic compound is 1: 1 to 3 by mass ratio.

Next, the procedure of the contaminated groundwater purification method of this embodiment will be described.
The contaminated groundwater purification method of this embodiment is performed by injecting a purification agent containing a water-soluble organic compound and a hydrolyzable resin into the soil of the contaminated ground.

Here, when the surface of the hydrolyzable resin is hydrophobic, when it is mixed with water, it floats on the water surface or floats in the water as a non-uniform lump. Difficult solution. In addition, when the particle size of the hydrolyzable resin is small, the surface area increases, so that it easily aggregates and forms secondary particles that become lumps and difficult to uniformly disperse in water.

As a method for uniformly dispersing the particulate hydrolyzable resin in water, there is a method of adding a dispersant such as a surfactant. However, many types of dispersants are not applicable from the viewpoint of environmental protection. Also, environmentally safe and highly biodegradable dispersants are expensive.

The inventors of the present invention have studied the method for solving the above problem, and found that the following method is an excellent method. First, as a first step, a step of adding a water-soluble organic compound to a particulate hydrolyzable resin and stirring the mixture is performed, and the surface of the hydrolyzable resin particles is made to conform to the water-soluble organic compound. As a result, the surface of the hydrolyzable resin particles can be easily adapted to water. Next, when a step of adding water is performed as the second step, the particulate hydrolyzable resin is dispersed in water relatively easily. As a result, an aqueous solution in which the hydrolyzable resin particles are relatively uniformly dispersed is formed.

The stirring device used in the first step is not particularly limited, and a known mixer, blender, or the like can be used. Conditions for stirring (stirring speed, stirring time, etc.) can also be set as appropriate.

In the production of the purifier, by performing the above two steps, the aggregation of the particulate hydrolyzable resin is suppressed, the formation of secondary particles is suppressed, and the particulate hydrolyzable resin is uniformly placed in water. It became possible to disperse. The obtained mixed solution is then poured into the soil as a cleaning agent. Since the particulate hydrolyzable resin is uniformly dispersed in the purifying agent, it becomes possible to supply the purifying agent having a uniform component to a wide area in the soil.

In the above procedure, since it is not necessary to add a dispersant or the like as the third component, only the essential component is necessary, which is simple and can reduce the manufacturing cost.

In order to inject the cleaning agent into the soil, a well having a general screen (opening) can be used as a well for injecting into the soil. A water-soluble organic compound is mixed with the hydrolyzable resin and stirred, and the resulting mixture is added to a storage tank storing water and stirred to obtain a mixed solution. Thereafter, an injection pump is provided between the pipes connecting the storage tank and the injection well, and a backflow prevention packer is installed at one upper portion of the injection well. By pumping the mixed solution in the storage tank using a pump, the cleaning agent is injected into the soil through the screen of the well. In this method, since the cleaning agent is preferentially injected into a highly permeable area around the injection well, it is possible to efficiently reduce the flow rate of groundwater. The method for injecting the cleaning agent into the contaminated ground is not particularly limited, and a known method such as a natural injection method from an existing well for injection can be appropriately applied.
In addition, when purifying contaminated groundwater, water quality monitoring for quantifying the oxygen concentration in the groundwater, the contaminant concentration, and the remaining amount of the purifier is appropriately performed as necessary.

Hereinafter, the present invention will be specifically described with reference to test examples.
As a particulate hydrolyzable resin, a polylactic acid resin (weight average molecular weight 15,000) blended with 10% polyoxalate was used. FIG. 1 is a view showing a particle size distribution of the hydrolyzable resin particles by a dynamic light scattering method. The particle size distribution was measured using a Laser Micron Sizer LMS-2000e manufactured by Seishin Enterprise Co., Ltd.

When the cumulative curve is determined with the total volume of the particle population as 100%, the particle size at which the cumulative curve becomes 90% is 90% diameter (μm). The hydrolyzable resin particles had a 90% diameter of 23 μm. Accordingly, the average particle size of the primary particles of this hydrolyzable resin was set to 23 μm, and the following studies were advanced.

The following were used as water-soluble organic compounds.
Lactic acid: manufactured by Kanto Chemical Co., Ltd. Reagents Sodium lactate: manufactured by Wako Pure Chemical Industries, Ltd. Reagents Sodium ascorbate: manufactured by Kanto Chemical Co., Ltd. Reagents Sodium succinate: manufactured by Kanto Chemical Co., Reagents

2.0 g of the above water-soluble organic compound was added to 1.0 g of the particulate hydrolyzable resin and stirred using a mortar.

Next, 10 ml of water was added and further stirred, and the hydrolyzable resin and the water-soluble organic compound were dispersed in water while stirring with a magnetic stirrer to obtain a mixed solution.

The particle size distribution of the particles dispersed in the obtained mixed solution was measured using the following apparatus.
Measuring device: ELSZ-1000, manufactured by Otsuka Electronics Co., Ltd.

2 and 3 are diagrams showing the particle size distribution of the hydrolyzable resin in the mixed solution. FIG. 2 shows, as a comparison, a mixed solution when dispersed in water without adding a water-soluble organic compound to the particulate hydrolyzable resin (hereinafter referred to as “mixture in which the hydrolyzable resin is dispersed only in water”). The particle size distribution in the “solution”). FIG. 3 shows a mixed solution in which sodium lactate is added to a particulate hydrolyzable resin and stirred, and then water is added and dispersed (hereinafter, the hydrolyzable resin to which sodium lactate has been added is dispersed. The particle size distribution in the “mixed solution”).

As shown in FIG. 2, in the case of a mixed solution in which a hydrolyzable resin is dispersed only in water, the ratio of secondary particles having a particle size larger than 23 μm (23,000 nm) is large, whereas in FIG. As shown, in the case of a mixed solution in which a hydrolyzable resin added with sodium lactate is dispersed, the ratio of primary particles having a particle size smaller than 23 μm is large. That is, it can be seen that aggregation of primary particles is suppressed. Note that not all particles having a particle size smaller than 23 μm are primary particles, and statistically, secondary particles are also partially mixed.

FIG. 4 is a diagram showing the peak distribution (relative ratio) of the primary particles and secondary particles of the hydrolyzable resin in the mixed solution for each type of water-soluble organic compound to be added. For comparison, the leftmost side of the figure shows a mixed solution in which a hydrolyzable resin is dispersed only in water. It was found that by adding the water-soluble organic compound, the ratio of secondary particles decreased and the ratio of primary particles (first peak) increased. That is, it was found that aggregation of primary particles was suppressed by preliminarily incorporating a water-soluble organic compound into the hydrolyzable resin.

FIG. 5 is a diagram showing the average particle diameter of primary particles of the hydrolyzable resin in the mixed solution for each type of water-soluble organic compound to be added. For comparison, the leftmost side of the figure shows a mixed solution in which a hydrolyzable resin is dispersed only in water. It was found that by adding a water-soluble organic compound, aggregation of primary particles was suppressed and the average particle size of primary particles in a region of 23 μm or less was reduced.

FIG. 6 is a diagram showing the polydispersity index of primary particles of the hydrolyzable resin in the mixed solution for each type of water-soluble organic compound to be added. For comparison, the leftmost side of the figure shows a mixed solution in which a hydrolyzable resin is dispersed only in water. It was found that by adding the water-soluble organic compound, the aggregation of the primary particles was suppressed and the polydispersity index of the primary particles in the region of 23 μm or less was reduced. Here, the polydispersity index is a measure of the polydispersity of the particle size distribution, that is, the spread of the particle size distribution.

FIG. 7 and FIG. 8 are diagrams showing the reach distance of the particulate hydrolyzable resin in the soil. This figure shows the results of a model experiment on the permeability of the particulate hydrolyzable resin in the soil. The mixed solution in which the hydrolyzable resin was dispersed only in water and the mixed solution in which the hydrolyzable resin to which sodium lactate was added were prepared. A certain amount of each mixed solution was naturally permeated from the top of the glass column filled with silica sand. The distribution of the reachable distance (cm) from the top of the hydrolyzable resin that has moved through the glass column and the amount of resin moved (mg / g) is shown in the figure. FIG. 7 shows the case of a mixed solution in which the hydrolyzable resin is dispersed only in water, and FIG. 8 shows the case of the mixed solution in which the hydrolyzable resin added with sodium lactate is dispersed. It has been found that the reach of the particulate hydrolyzable resin is increased by adding the water-soluble organic compound.

FIG. 9 is a diagram showing an example of a specific method for injecting the mixed solution into the soil. The underground soil structure consists of a pavement 20 on the surface, a buried layer 21 of about 2.5 m below it, an aquifer 22 of about 6.5 m below it, and a silt layer 23 below it. It has become. The aquifer 22 is a layer mainly made of sand, includes groundwater, and has a permeability coefficient k of 10 ⁻⁶ to 10 ⁻⁵ m / s. The silt layer 23 is a layer made of fine-grained soil mainly composed of cohesive soil, and the hydraulic conductivity k was 10 ⁻⁹ to 10 ⁻⁸ m / s. The injection well 10 is installed to a depth that reaches the silt layer 23, and a screen (opening) 11 is formed over the thickness of the aquifer 22 so that the purifier can be injected into the aquifer 22. Have.

The in-vehicle injection device 1 mounted on the truck bed was used as an injection device for the cleaning agent into the soil. In the vehicle-mounted injection device 1, the water-soluble organic compound is mixed with the hydrolyzable resin and stirred, and the resulting mixture is added to the storage tanks 2 </ b> A and 2 </ b> B storing water and stirred, so that a mixed solution for injection Was prepared. The composition of the mixed solution was about 1 kg: about 2 kg: 1 kl of hydrolyzable resin: water-soluble organic compound: water. An injection pump 3, a flow meter 4, and a pressure gauge 5 are installed in a pipe 6 that connects the storage tanks 2 </ b> A and 2 </ b> B and the injection well 10. In addition, a packer 12 for preventing backflow is installed at one upper portion of the injection well 10.

9 ml of the mixed solution was injected into the soil at about 40 l / min using the injection pump 3, and the injection pressure at the tube head during that time was measured. As a result, the particulate hydrolyzable resin was supplied into the soil from the injection well 10 without remaining in the

storage tanks

2A and 2B in a dull form. Throughout the injection period, the injection pressure was 0.0 MPa, and no increase in the injection pressure was observed, and it was confirmed that the purifier could be easily injected around the injection well 10.

Claims

A method for purifying contaminated groundwater that uses anaerobic microorganisms to purify contaminated groundwater or prevent recontamination of groundwater,
As a hydrogen donor, a particulate hydrolyzable resin and a water-soluble organic compound are used in combination,
A method for purifying contaminated groundwater, comprising adding the hydrolyzable resin to the water-soluble organic compound and stirring, then adding water to form a mixed solution, and then pouring the mixed solution into the soil.
The method for purifying contaminated groundwater according to claim 1, wherein the contaminant of the contaminated groundwater is at least one of a volatile organic chlorine compound, nitrate nitrogen and nitrite nitrogen.
The method for purifying contaminated groundwater according to claim 1 or 2, wherein the water-soluble organic compound contains at least one of alcohol, an alcohol derivative, a carboxylic acid, and a carboxylic acid derivative.
The method for purifying contaminated groundwater according to any one of claims 1 to 3, wherein the hydrolyzable resin is an aliphatic polyester.
The method for purifying contaminated groundwater according to any one of claims 1 to 4, wherein the hydrolyzable resin contains at least one of polylactic acid and polyoxalate.
6. The method for purifying contaminated groundwater according to claim 1, wherein the hydrolyzable resin has an average particle size of 1 to 100 μm.
The packer is installed above the well for injecting the mixed solution into the soil, and the mixed solution is injected into the soil using a pump. How to purify contaminated groundwater.