JP2009279471A - Method of purifying contaminated soil and ground water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of purifying contaminated soil and/or ground water using silicon sludge and having an improved purification speed. <P>SOLUTION: The method of purifying contaminated soil and/or ground water comprises forming a trench or hole (4) in an contaminated area (6) and/or its surrounding areas and arranging bags (5) of a biodegradable fiber containing silicon sludge in the trench or hole (4). Alternatively, a purification wall is formed with bags of a biodegradable fiber containing silicon sludge in the contaminated area and/or its surrounding areas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for purifying contaminated soil and / or groundwater.

  Methods for purifying soil and groundwater contamination include vacuum extraction, pumping aeration, lime, iron powder, soil excavation and replacement, soil moisture cleaning, insolubilization, gas / liquid mixed well, air The sparging method, bioremediation method and the like are known.

Also, a method of mixing a silicon suspension (silicon sludge) with soil in order to improve anaerobic conditions in the soil and effectively induce or promote the action of decomposing pollutants by microorganisms has been proposed (Patent Document). 1).
Japanese Patent No. 2921491

  However, the conventional purification method in which silicon is simply introduced into the soil to induce or promote the decomposition action by microorganisms has the merit that silicon sludge discharged as waste in the semiconductor industry can be effectively used, but the purification rate is high. There is a problem that it is not enough. Therefore, the present invention provides a purification method using silicon sludge and a method for purifying contaminated soil and / or groundwater with an improved purification rate.

  The present invention is a method for purifying contaminated soil and / or groundwater, wherein a groove or a hole is formed in a contaminated area and / or a peripheral area thereof, and biodegradable containing silicon sludge in the groove or hole. A method for purifying soil and / or groundwater, including disposing fiber bags.

  In another aspect, the present invention provides a method for purifying contaminated soil and / or groundwater, wherein a purification wall is formed using a bag of biodegradable fibers containing silicon sludge in the contaminated area and / or its surrounding area. It is the purification method of the soil and / or groundwater including providing.

  According to the present invention, the purification rate can be improved in the purification of contaminated soil and / or groundwater.

[Silicon sludge]
In the present invention, the silicon sludge may include a slurry, suspension, and sludge containing silicon particles (preferably metal silicon particles). The type and origin of the silicon sludge are not particularly limited, but for example, silicon sludge discharged as waste in the semiconductor industry, that is, silicon sludge discharged from a silicon wafer manufacturer / factory or a semiconductor manufacturer / factory is suitable. Can be used for Specifically, silicon sludge generated from both-end cutting process, ingot rough polishing process, slicing process, double-sided process, etc. in silicon ingot production stage; silicon sludge generated from mirror polishing process, background process, etc. in wafer processing stage; Examples include silicon sludge generated from a damascene process at the semiconductor assembly stage. Such discharged silicon sludge can be obtained as appropriate.

  The present invention is based on the idea of bringing silicon sludge and groundwater into contact with each other in soil and using the hydrogen generated thereby to chemically decompose and decontaminate the pollutants. The present invention promotes the purification of pollutants by filling silicon sludge into a bag of biodegradable fibers and placing the bag in grooves or holes formed in the contaminated area and / or its peripheral area. Based on the knowledge that it can. That is, the method for purifying contaminated soil and / or groundwater of the present invention (hereinafter also referred to as the purification method of the present invention) includes forming grooves or holes in the contaminated area and / or the peripheral area thereof, and A purification method comprising disposing a bag of biodegradable fibers containing silicon sludge in a hole.

  In the purification method of the present invention, the details of the mechanism for promoting the purification of the pollutants are not clear, but the pollutants such as volatile organic compounds are adsorbed on the fibers of the bag body, and hydrogen generated from the pollutants and the silicon sludge. It is estimated that the frequency of contact with water is increased, and as a result, chemical decomposition of pollutants is promoted. In addition, the silicon sludge disposed in the groove or the hole becomes a harmless substance (silicon dioxide) after releasing hydrogen by an oxidation reaction with air or oxygen in groundwater. As will be described later, pollutants such as volatile organic compounds are adsorbed on natural fibers such as hemp and fibers of polylactic acid ester as a main component, and the adsorbed pollutants are in contact with hydrogen generated from silicon sludge. Purified by chemical reaction, the fibers of the bag body are decomposed by anaerobic microorganisms. It is presumed that the purification of pollutants is promoted by the synergistic effect of this chemical action and the action by microorganisms. Furthermore, by forming grooves and holes and arranging silicon sludge in the form of a bag body, a space is formed between the plurality of bag bodies even after covering the grooves and holes after placement, and this space is utilized. Hydrogen diffusion is promoted. As a result, hydrogen is likely to be supplied also to the impermeable layer above the permeable layer, and it is estimated that the purification of contaminants is further promoted. However, the present invention is not limited to these mechanisms, and may include, for example, expansion of the anaerobic condition region by efficient diffusion of hydrogen and the accompanying promotion of purification of contaminants by microorganisms.

  According to the purification method of the present invention, unlike the conventional method using microorganisms, since the chemical decomposition is promoted by adopting the form of the bag body, the purification rate can be accelerated. Moreover, since the purification method of the present invention uses a bag of biodegradable fibers, there is no risk of further contamination due to the present invention, and the environment is excellent. Furthermore, the purification method of the present invention is economically superior because it can reuse silicon sludge discharged from the semiconductor industry that has been simply discarded.

[Bag of biodegradable fiber]
In the present invention, a biodegradable fiber bag refers to a bag manufactured using a fabric containing biodegradable fibers, preferably a fabric mainly composed of biodegradable fibers. The biodegradable fiber of the bag is preferably excellent in adsorption of contaminants from the viewpoint of promoting purification, and from the point of increasing the adsorption amount by increasing the surface area, weaving a bundle of fibers of about 0.5 to 1 mm. A knitted fabric is preferred. In addition, the bag body preferably has strength capable of withstanding the load when silicon sludge is filled from the viewpoint of handling such as transportation. In the present invention, “biodegradable” means that it is decomposed while placed in soil and does not negatively affect the environment. As the biodegradable fiber, polylactic acid, polylactic acid ester, biodegradable plastic fiber such as aromatic-aliphatic polyester, natural fiber such as natural hemp or natural straw, and recycled fiber can be used. Those that can satisfy the requirements are preferable. The size of the biodegradable fiber bag is not particularly limited, and for example, a bag having a width of 30 to 100 cm and a length of 50 to 200 cm can be used. Specific examples of the bag body in the present invention include sandbag bags of biodegradable fibers, and commercially available sandbag bags of biodegradable fibers can be used.

[Combination ingredients]
In addition to silicon sludge, other components may be added to the bag. Examples of the other components include inorganic carbonates, alkali metal salts, alkaline earth metal salts, or a combination thereof from the viewpoint of efficiency of hydrogen generation and purification efficiency associated therewith. Examples of inorganic carbonates include sodium hydrogen carbonate, sodium carbonate, calcium carbonate, ammonium carbonate, and ammonium hydrogen carbonate. The pH of the soil is maintained in a neutral region, and there is no concern of contamination by nitrogen sources. From the viewpoint that generation of hydrogen can be promoted, sodium hydrogen carbonate and calcium carbonate are preferable. Examples of the alkali metal salt include salts of lithium, sodium, potassium and the like. The counter ions include ions that form chlorides, sulfates, and carbonates that have little influence on the contamination of groundwater and soil. Among these, sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, and sodium hydrogen carbonate are preferable because they have little influence on microorganisms and little influence on the environment. Examples of alkaline earth metal salts include magnesium salts and calcium salts. The counter ions include ions that form chlorides, sulfates, and carbonates that have little influence on the contamination of groundwater and soil. Among these, calcium carbonate and magnesium carbonate are preferable because they have little influence on microorganisms and little influence on the environment.

[Pollutants]
The pollutants to be purified by the purification method of the present invention can include volatile organic compounds, nitrate ions, and nitrite ions. Examples of the volatile organic compound include tetrachloromethane, trichloromethane, dichloromethane, hexachloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1-dichloroethane, tetrachloroethylene, trichloroethylene, cis-1, 2-dichloroethylene, trans-1,2-dichloroethylene, 1,1-dichloroethylene, vinyl chloride, 1,2,3-trichloropropane, 1,2-dichloropropane, benzene, toluene, ethylbenzene, hexachlorobutadiene, 1,2- Dibromoethane, Freon 113, N-nitrosodimethylamine and the like can be mentioned.

[Purification method]
In the purification method of the present invention, first, grooves or holes are formed in the contaminated area and / or the peripheral area. The groove or hole can be formed by a known excavation means. It is preferable that the groove or hole reaches at least the lower part of the water permeable layer where the pollutant exists, and reaches the impermeable layer located under the water permeable layer from the viewpoint of suppressing the diffusion of the pollutant and improving the efficiency of the purification. More preferably. In the present invention, the “permeable layer” means a layer in which groundwater exists, and includes an aquifer. In the present invention, the “impermeable layer” refers to a layer in which groundwater is not aerated, and includes a hardly permeable layer and an unsaturated layer.

  The groove or hole is preferably formed in a substantially vertical direction since the contaminant penetrates from the ground to the underground. Further, the position where the groove or hole is formed is preferably the position where the pollutant is present in the soil and / or its periphery from the viewpoint of the efficiency of purification, and the periphery is preferably the downstream side of the groundwater passing through the contaminated area. The position that blocks the groundwater is more preferable. When the hole is formed, the diameter thereof is preferably 20 to 100 cm, more preferably 30 to 60 cm, from the viewpoint of the efficiency of purification and the effect on the environment. One or a plurality of holes may be formed, and the number and size of the holes can be appropriately adjusted depending on the degree of contamination. When the groove is formed, the width is preferably 50 to 3000 cm, and more preferably 30 to 2000 cm, from the viewpoint of purification efficiency and influence on the environment. The length of the groove to be formed can be appropriately determined according to, for example, the contaminated region. The groove may be formed by continuously forming the hole. The groove may be straight or curved and may be formed so as to surround the contaminated area.

  Next, a biodegradable fiber bag containing silicon sludge is placed in the formed groove or hole. The amount of the bag body to be arranged is preferably added to the extent that the height of the bag body reaches the impermeable layer above the water permeable layer beyond the water permeable layer from the viewpoint of purification efficiency. It is preferable that a sufficient amount of the silicon sludge bag body is disposed since excessive contamination of silicon with soil does not normally cause new contamination.

  It is preferable to cover the groove or hole after the placement of the silicon sludge bag body from the viewpoint of environmental conservation. Moreover, by covering the soil, an environment of a reducing atmosphere can be created in the ground, and purification of pollutants can be promoted.

  The silicon sludge bag body arranged in the groove as described above can function as a purification wall. Therefore, the purification method of the present invention is a purification method including providing a purification wall using a bag of biodegradable fibers containing silicon sludge in a contaminated area and / or its peripheral area as another aspect. Moreover, this invention can provide the purification | cleaning wall formed by arrange | positioning the bag body of the biodegradable fiber containing a silicon sludge as another aspect. In these embodiments, the purification wall is not particularly limited except that a biodegradable fiber bag containing silicon sludge is used as the purification material. In addition, the purification wall is preferably provided at a position where the contaminant is present in the soil and / or its periphery from the viewpoint of efficiency of purification, and the periphery is preferably a downstream side of the groundwater passing through the contaminated area. A position that blocks groundwater is more preferable. It is preferable that the lower part of the purification wall reaches at least the lower part of the water permeable layer where the pollutant exists, from the viewpoint of suppressing the diffusion of the pollutant and the efficiency of the purification, and to the impermeable layer located under the water permeable layer. More preferably, it has been reached. It is preferable that the lower part of the purification wall reaches at least the lower part of the water permeable layer where the pollutant exists, from the viewpoint of suppressing the diffusion of the pollutant and the efficiency of the purification, and to the impermeable layer located under the water permeable layer. More preferably, it has been reached. Moreover, it is preferable to introduce the upper part of the purification wall to such an extent that the height of the bag body reaches the impermeable layer above the water permeable layer beyond the water permeable layer from the viewpoint of purification efficiency.

  Next, an embodiment of the purification method of the present invention will be described with reference to FIGS. However, the purification method of the present invention is not limited to this form. FIG. 1 shows a schematic cross-sectional view of the purification method when the contaminated portion 6 reaches the surface layer 3, the upper water-impermeable layer 2 and the water-permeable layer 1. FIG. 2 is a schematic top view of the purification method of the present invention. In FIG. 2, the same components as those in FIG. In order to purify the contaminated portion 6, first, as shown in FIG. 1, a groove 4 that passes through the water permeable layer 1 and reaches the lower impermeable layer 3 is formed by excavation. The groove 4 is formed downstream of the direction of groundwater flow (arrows in FIGS. 1 and 2) passing through the contaminated portion 6, and as shown in FIG. 2, the groove 4 is a direction that blocks the flow from the contaminated portion 6 (substantially orthogonal direction). ). Next, a biodegradable fiber bag 5 filled with silicon sludge is placed. As shown in FIG. 1, the bag body 5 is disposed so as to reach the upper impermeable layer 2. The groove 4 is finally covered with soil (not shown). As a result, as shown in FIG. 2, the purification wall 7 is formed in the direction (substantially orthogonal direction) in which the flow of groundwater passing through the contaminated part 6 is blocked, and the contaminants originating from the contaminated part 6 are efficiently decomposed and purified.

  The purification rate was compared between the purification method of the present invention in which silicon sludge was filled in a biodegradable bag and placed in the soil, and the purification method in which the sludge was directly mixed with the soil without using the bag.

[Contaminated soil]
Using soil mined from soil contaminated with TCE (Trichlorethylene), contaminated experimental soil with a clay layer, gravel layer, topsoil layer structure from the bottom layer in a 3m wide × 5m deep × 3m deep experimental plot Produced. The TCE concentration in the mined contaminated soil was 3000 ppm. As confirmed by the microarray method, anaerobic microorganisms that decompose TCE existed in the contaminated soil. An injection well is formed at one end in the width direction of the experimental section, and groundwater is pumped into the gravel layer of the experimental contaminated soil, adjusted to move about 1 m per day at a water level of 50 cm in height from the upper surface of the clay layer. did. As the groundwater, groundwater flowing under the contaminated soil was used.

[Silicon sludge bag]
Silicon sludge bag body filled with silicon sludge discharged from a semiconductor factory into a sandbag bag (manufactured by Toray Industries, Inc.) mainly composed of biodegradable polylactic acid fibers as a bag body filled with silicon sludge Was made.

[Measurement method of TCE]
The concentration of TCE was measured according to the method specified in 5.1, 5.2, 5.3.1, 5.4.1, or 5.5 of JIS standard K0125.

  As an example, a groove having a width of 0.5 m, a depth of 5 m, and a depth of 2.5 m was excavated in the experimental contaminated soil, and five silicon sludge bags were arranged, and then covered with the excavated soil. The progress of purification of the TCE concentration after burying the silicon sludge bag body was observed according to the above measurement method. On the other hand, as a comparative example, an attempt was made to purify TCE by mixing silicon sludge in an amount equal to the buried silicon sludge bag body with the contaminated soil for experiment. The purification results of Examples and Comparative Examples are shown in graphs A and B in FIG. The vertical axes of graphs A and B indicate the concentration (ppm) of TCE.

  As shown in FIG. 3, in the case of Example (A), the purification rate in the initial stage was fast, and purification was possible in 110 days to 0.03 mg (0.3 ppm) per liter of test solution, which is the Japanese environmental standard. On the other hand, in Comparative Example (B), 140 days or more were required up to 0.3 ppm. Therefore, the example was superior in purification rate than the comparative example. Moreover, this result suggested that the contact efficiency between the hydrogen generated from the silicon sludge and the pollutant in the example using the bag was superior to the comparative example not using the bag.

  The purification method of the present invention is useful, for example, in the fields of environmental conservation and environmental restoration.

FIG. 1 is a schematic cross-sectional view showing an embodiment of the purification method of the present invention. FIG. 2 is a schematic top view showing an embodiment of the purification method of the present invention. FIG. 3 is a graph showing the results of Example (A) and Comparative Example (B) of the purification method of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water-permeable layer 2 Water-impermeable layer 3 Surface layer 4 Groove 5 Silicon sludge bag body 6 Contamination part 7 Purification wall

Claims (5)

A method for the purification of contaminated soil and / or groundwater,
A method for purifying soil and / or groundwater, comprising forming a groove or a hole in a contaminated area and / or a peripheral area thereof, and disposing a bag of biodegradable fiber containing silicon sludge in the groove or hole. . A method for the purification of contaminated soil and / or groundwater,
A method for purifying soil and / or groundwater, comprising providing a purification wall using a bag of biodegradable fibers containing silicon sludge in a contaminated area and / or a peripheral area thereof.   The method for purifying soil and / or groundwater according to claim 1 or 2, wherein the biodegradable fiber bag is a biodegradable sandbag.   The soil and / or groundwater purification method according to any one of claims 1 to 3, wherein the groove, hole, or purification wall is formed on a downstream side of groundwater that passes through a contaminated region.   The method for purifying soil and / or groundwater according to any one of claims 1 to 4, wherein the pollutant contains a volatile organic compound.

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