JP5148365B2 - Method for purifying contaminated soil and groundwater - Google Patents

Description

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

  In recent years, environmental pollution due to organic chlorine compounds such as trichlorethylene, tetrachloroethylene, and tetrachloroethane, which are contained in industrial wastewater, has become a major problem. Many of these contaminants penetrate into the soil and enter the groundwater without being decomposed, expanding the contaminated area through this groundwater. It is strongly desired to establish a technique for preventing the spread of environmental pollution and purifying and repairing an already polluted environment.

  In recent years, a method using biological treatment with microorganisms (bioremediation method) has been proposed as a method for purifying contaminated soil and groundwater. The bioremediation method is a method in which a pollutant is decomposed into a harmless substance by microorganisms living in the contaminated area or introduced from the outside into the contaminated area. In this method, for example, the fungi existing in the contaminated soil are activated by aeration in situ (Patent Document 1), or heating is provided in the well formed in the contaminated area. Thus, it has been proposed to promote the degradation of contaminants by microorganisms (Patent Document 2). In addition, it has been proposed to introduce an activator containing a substrate (carbon source), inorganic nutrient salts such as nitrogen and phosphorus, and a hydrogen donor into the contaminated area to improve the degradation action of the pollutants by microorganisms. .

The activator is usually introduced by a method in which a solid nutrient source is arranged as it is in a hole mined by boring or the like, a method in which a liquid nutrient source is injected through an injection tube inserted in the hole, and the like ( (See Patent Documents 1 and 2). In addition, as shown in FIG. 3, the well tube 101 is formed on the wall surface of the hole, and the solid nutrient source 14 is disposed therein. However, bioremediation has a problem that it takes a long time for purification, and improvement in purification efficiency is required.
JP-A-2005-279415 JP 2007-105594 A

  Therefore, the present invention provides a purification method capable of improving the purification efficiency of contaminated soil and / or groundwater.

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 a nutrient source supply well in which an inner cylinder is disposed in a well casing, and the inner cylinder A heating means using an electric heater is arranged on the bottom of the tube , and then a solid nutrient source is filled , and heating is performed continuously or intermittently so as to maintain the water temperature in the inner cylinder by the heating means. The inner cylinder is arranged with a space apart from the bottom surface of the well and the side surface of the well casing, and has a plurality of water inlets through which groundwater can flow in and out on the side surface and the bottom surface.

  According to the purification method of the present invention, the purification efficiency of contaminated soil and groundwater can be improved.

The present invention is based on the knowledge that the purification efficiency of pollutants can be improved by providing a double structure nutrient source supply well in which an inner cylinder is arranged in a well casing, and heating and supplying the nutrient source through the inner cylinder. Based. In the purification method of the present invention, the details of the mechanism by which the purification of pollutants is promoted are not clear, but the crushing / dissolution of solid nutrients is promoted by the hydropower of groundwater flowing from the side and bottom of the inner cylinder. This is presumed to be because the nutrient source can be diffused in a shorter period of time than the direct arrangement on the bottom of the well. Further, by heating by the heating means disposed within the inner cylinder, since it promotes circulation of groundwater (convection), crushed and dissolved nutrients by a water force is presumed to be because that will be promoted. Furthermore, it is estimated that the activity of microorganisms can be improved by heating with a heating means. However, these assumptions do not limit the present invention.

That is, in the purification method of the present invention, a nutrient source supply well in which an inner cylinder is arranged in a well casing is formed, a heating means using an electric heater is arranged on the bottom surface of the inner cylinder , and then a solid nutrient source filling the, and comprises heating continuously or intermittently to maintain the water temperature in the inner tube by the heating means, the inner cylinder, is arranged with a side surface and spaced space of the bottom surface and the well casing of the well And has a plurality of water inlets through which groundwater can flow in and out on the side and bottom. According to the purification method of the present invention, a solid nutrient source can be diffused in a short time, so that microorganisms can be activated quickly and the purification rate of contaminants can be improved.

[Nutrition source supply well]
In the present invention, the “nutrient source supply well” refers to a well for supplying a solid nutrient source to contaminated soil and / or groundwater and having an inner cylinder disposed in a well casing.

[Inner cylinder]
In the present invention, the “inner cylinder” has a plurality of water inlets (holes) on the side surface and bottom surface, allows groundwater to flow in and out from the side surface and bottom surface, and has heating means and a solid nutrient source disposed inside. Say what you can. The inner cylinder is preferably one in which the nutrient source in the inner cylinder is dissolved by the groundwater flowing through the water-permeable port, and the dissolved nutrient source can be diffused to the outside of the inner cylinder through the water-permeable port. The water permeability port may be formed on the entire inner cylinder, or may be formed only on the side surface and the bottom surface that are in contact with the groundwater. The magnitude | size of a water-permeable opening can be suitably determined according to the magnitude | size of the solid nutrient source arrange | positioned, for example. Examples of the shape of the water-permeable port include a circle, a corner, a hexagon, a vertically long circle, a vertically long angle, a horizontally long circle, and a horizontally long angle. Among these, a horizontally long circle and a horizontally long angle are preferable. The inner cylinder can be formed of, for example, a resin or a steel material having a plurality of holes.

  The inner cylinder is arranged with a space apart from the bottom surface of the nutrient source supply well and the side surface of the well casing in the well. In the present invention, “arranged with a separation space” means that they are arranged in a state of being separated at a certain distance. Therefore, in the well, spaces are formed between the bottom surface of the inner cylinder and the bottom surface of the well, and between the side surface of the inner cylinder and the side surface of the well casing. The distance between the bottom surface of the inner cylinder and the bottom surface of the well is preferably 30 to 50 mm from the viewpoint of promoting convection (circulation) of groundwater. Moreover, it is preferable that the distance of the outer peripheral surface of an inner cylinder and the inner peripheral surface of a well casing is 20-40 mm from the point which promotes the convection (circulation) of groundwater. It is preferable that the inner cylinder is arranged substantially concentrically with the well casing from the viewpoint of uniformly diffusing nutrient sources.

  As the well casing, known well casings used for ordinary pumping wells, nutrient source supply wells, and the like can be used. The well casing is only required to be able to flow into and out of the groundwater, and includes, for example, a screen formed of a water-permeable material, a resin having a plurality of holes, a steel material, or the like. From the viewpoint of suppressing the inflow of soil into the well, a well casing in which a screen is formed at least in a portion disposed in the permeable layer is preferable.

[Nutrition source]
The nutrient source may be solid, and a solid nutrient that is difficult to dissolve in groundwater is preferable. As the solid nutrient source, fatty acids having 10 or more carbon atoms are preferable because they are excellent in sustained release to groundwater and easily become microorganisms. Among them, those containing a saturated fatty acid having 10 or more carbon atoms as a main component are preferable, more preferably higher fatty acids having 12 to 18 carbon atoms, and more preferably, since the melting point is high and it is easy to maintain a solid state in groundwater. Contains higher fatty acids having 14 to 18 carbon atoms. Examples of the fatty acid include capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid and lignoceric acid, and among these, they are easily available. Myristic acid, palmitic acid and stearic acid are preferred. Further, the solid nutrient source may further contain other components such as a surfactant such as calcium carbonate, potassium dihydrogen phosphate, polysorbate, ammonium sulfate, nitrogen-based nutrient salt, phosphorus-based nutrient salt, and the like. . As the nutrient source, a known solid nutrient source may be used.

  Examples of the shape of the solid nutrient source include pellets, lumps and granules. The average particle size of the solid nutrient source is, for example, 0.1 to 10 mm, and preferably 1 to 5 mm.

A commercially available product may be used as the solid nutrient source. As a commercially available product, Amteclean P (trade name, which has a higher fatty acid (general formula C _n H _2n O ₂ (n is an average number of carbon atoms)) as a main component because of its excellent sustained release and high hydrogen-donating ability. A solid product manufactured by Matsushita Electric Industrial Co., Ltd. is preferable. Among them, Amteclean P-SL18 (average carbon number of higher fatty acids: 17.1, melting point: 60 ° C., granules having a diameter of 1 mm), Amteclean P-SL18-661 (main components: stearic acid, average carbon number of higher fatty acids: 15) .3, melting point: 58 ° C., 5 mm diameter pellet), Amteclean P-SL16 (average carbon number of higher fatty acid: 116.7, melting point: 54 ° C., granule of 1 mm diameter), Amteclean P-SL14 (average of higher fatty acid) More preferably, the number of carbon atoms is 13.9, the melting point is 53 ° C., and the diameter is 1 mm.

[Heating means]
As the heating means, for example, an electric heater that can be used in water such as a sheathed heater can be used. According to the purification method of the present invention, since the heating means is arranged so as to be separated from the bottom and side surfaces of the well, for example, the nutrient source and the groundwater can be efficiently heated without taking heat away from the soil on the bottom surface of the well. can do. The amount of heat of the heating means can be appropriately determined according to the diameter of the inner cylinder, the flow of groundwater, and the like. For example, when the diameter of the inner cylinder is 80 mm, it can be set to 30 to 100 W.

[Contaminated soil and / or groundwater]
In the present invention, “contaminated soil and / or groundwater” refers to soil and groundwater containing pollutants. Examples of pollutants include volatile organic compounds (VOC), heavy metals, oils, nitrate nitrogen, nitrite nitrogen, and the like. Examples of volatile organic compounds include organic chlorine compounds, benzene, formaldehyde, toluene, xylene, and the like. Among these, the purification method of the present invention is suitable for the purification of contaminated soil and / or groundwater containing a volatile organic compound, more preferably an organic chlorine compound. Examples of the organic chlorine compound include carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, 1,3-dichloropropene, dichloromethane, tetrachloroethylene, 1,1,1-trichloroethane. 1,1,2-trichloroethane, trichlorethylene and the like. Among these, the purification method of the present invention is particularly suitable for purification of soil and / or groundwater contaminated with tetrachloroethylene, trichloroethylene, cis-1,2-dichloroethylene, 1,1-dichloroethylene, vinyl chloride, and the like.

[Purification method]
In the purification method of the present invention, first, a nutrient source supply well is formed. The nutrient source supply well can be formed, for example, by forming a well casing on the wall surface of a hole mined by boring or the like, and disposing an inner cylinder therein. It is preferable that the nutrient source supply well reaches at least the lower part of the permeable layer from the viewpoint of improving the diffusion of the nutrient source and efficiently activating the microorganisms, and reaches the impermeable layer located below the permeable layer. More preferably. In the present invention, the “permeable layer” refers to a layer in which groundwater exists, and includes an aquifer layer, a saturated layer, and an aquifer layer.

  The diameter of the nutrient supply well can be determined as appropriate depending on the size of the contaminated area, the concentration and type of the contaminant, and is preferably 100 to 300 mm, for example. The diameter of the inner cylinder can be appropriately determined depending on the diameter of the nutrient source supply well, the size of the contaminated area, the concentration and type of the contaminant, and is preferably 60 to 200 mm, for example. When the diameter of the well is 150 to 200 mm, the diameter of the inner cylinder is 90 to 100 mm, the distance between the side surface of the inner cylinder and the side surface of the well (well casing) is 30 to 50 mm, and the bottom surface of the inner cylinder and the bottom surface of the well The distance is preferably 30 to 50 mm.

  It is preferable to form the nutrient source supply well in the contaminated area and / or around the contaminated area from the viewpoint of efficient purification. Further, the number of nutrient source supply wells in one contaminated area may be one or plural, and can be appropriately determined according to, for example, the size of the contaminated area, the concentration of the contaminant, and the like. .

  Next, a heating means and a solid nutrient source are arranged in the inner cylinder. The order in which the heating means and the solid nutrient source are arranged is not particularly limited, but from the viewpoint of heating efficiency, it is preferable to first arrange the heating means on the bottom surface of the inner cylinder and then fill the solid nutrient source. The filling amount of the solid nutrient source is not particularly limited. However, since the frequency of additional filling of the nutrient source can be reduced, it is preferable to fill the entire inner cylinder, that is, the upper end portion of the inner cylinder.

  And it heats with the heating means in an inner cylinder. By heating, diffusion of nutrient sources can be improved, and the activity of microorganisms such as anaerobic microorganisms present in the soil can be improved. The heating by the heating means is preferably performed, for example, to the extent that the water temperature in the inner cylinder becomes 30 ° C. or higher, and 40 to 50 ° C. is more preferable from the viewpoints of microorganism activation and cost. Heating may be performed continuously or intermittently, but is preferably performed continuously from the viewpoint of purification efficiency.

  Next, an example of the purification method of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following examples.

  FIG. 1 is a schematic configuration diagram showing an embodiment of the purification method of the present invention. In a basic underground region composed of a surface layer 1, a water-impermeable layer 2, a water-permeable layer 3 and a water-impermeable layer 4, a contamination region 16 is provided. This is an example in which a nutrient source supply well 10 is provided and purified.

  The nutrient source supply well 10 is mined in a substantially vertical direction from the ground surface to a depth extending from the bottom of the permeable layer 3 to the inside of the impermeable layer 4. A well casing 11 is provided on the wall surface of the nutrient source supply well 10, and an inner cylinder 12 is disposed therein. The well casing 11 includes a screen (strainer) 11a through which groundwater can pass. The screen 11 a is formed from the bottom surface of the water permeable layer 3 nutrient source supply well 10 to the vicinity of the upper part of the water permeable layer 3. The inner cylinder 12 is arranged in the well 10 while maintaining a space apart from the bottom of the well and the well casing 11. The inner cylinder 12 has a heating means 13 and a solid nutrient source 14 disposed therein. Since the inner cylinder 12 has a plurality of water permeable ports on the side surface and the bottom surface, the inflow and outflow of groundwater is possible as indicated by arrows in the figure.

  By supplying the solid nutrient source 14 and heating by the heating means 13, for example, anaerobic microorganisms present in the contaminated soil can be activated, thereby promoting degradation and purification of the contaminants by the anaerobic microorganisms. Moreover, the flow of groundwater can be accelerated | stimulated by heating by the heating means 13, and melt | dissolution of the solid nutrient source 14 and the spreading | diffusion to groundwater and / or soil can be accelerated | stimulated. Thereby, the activity of anaerobic microorganisms can further be improved. Moreover, since a solid nutrient source is used as a nutrient source, for example, microorganisms can be activated continuously.

Soil and groundwater were purified using the nutrient source supply well 10 having the configuration shown in FIG. The diameter of the nutrient source supply well 10 was 150 mm, the diameter of the inner cylinder 12 was 90 mm, the length of the inner cylinder 12 was 10 m, and the upper end of the inner cylinder 12 was filled with a solid nutrient source. Nutrient sources are trade name Amteclean P SL18-661 (Matsushita Electric Industrial Co., Ltd., 5 mm pellet, components: C ₁₈ H ₃₆ O ₂ , polysorbate, calcium carbonate, ammonium sulfate, sodium dihydrogen phosphate, melting point: 58 ° C., Solubility: 0.03 g / 100 g water) was used to fill the entire inner cylinder 12. As the heater, a throwing sheathed heater (100 V-200 W, with 42 ° C. temperature adjustment) was used, and the water temperature in the inner cylinder was heated to 42 ° C. The heating was performed continuously or intermittently so as to maintain the water temperature during the purification period.

  A monitoring well (not shown) was provided downstream of the nutrient source supply well 10. The groundwater is pumped up from the monitoring well every 10 days from the start of supply of nutrients, and pollutants contained in this (tetrachlorethylene (PCE, standard value: 0.03 mg / L), trichlorethylene (TCE, standard value: 0.01 mg / L) , Concentration of dichloroethylene (cis-1,2-DCE, standard value: 0.04 mg / L; 1,1-DCE, standard value: 0.02 mg / L), vinyl chloride (VC)) (mg / L) It was measured. The result is shown in the graph of FIG. 2A.

  Comparative Example 1 was carried out in the same manner as in the above example except that it was not heated with a heater. The result is shown in the graph of FIG. 2B. Further, as Comparative Example 2, the same procedure as in the above Example was performed except that a well having no inner cylinder as shown in FIG. 3 was used and a nutrient source and a heater were directly arranged in the well. The result is shown in the graph of FIG. 2C.

  As shown in FIG. 2A, according to the present example, the PCE concentration became equal to or less than the reference value (0.03 mg / L) 30 days after the start of purification. Further, on the 50th day after the start of purification, the concentration of all pollutants becomes 0.1 mg / L or less, which is below the reference value, and on the 70th day after the start of purification, the concentration of all substances becomes 0.001 mg / L or less. became. On the other hand, as shown in FIG. 2B, in Comparative Example 1 in which heating was not performed with the heater, the cis-1,2-DCE concentration was high even after 60 days from the start of purification, and the concentration of all contaminants was 0. It took 80 days from the start of purification to be 0.001 mg / L or less. Further, in Comparative Example 2 in which the nutrient source and the heater are directly arranged in the well, as shown in FIG. 2C, the purification rate after 30 days from the start of purification, particularly the purification rate of PCE after 30 days from the start of purification is performed. It was slower than the example. In Example, the PCE concentration became substantially 0 before 60 days from the start of purification, but in Comparative Example 2, 70 days or more were required from the start of purification.

  From these results, the solid nutrient source and the heating means were arranged in the inner cylinder, and according to the heated example, the decomposition of the pollutants was faster than in the comparative examples 1 and 2, which were not heated, and the soil and / or The purification efficiency of groundwater was improved. In particular, the decomposition reaction from cis-1,2-DCE to VC could be promoted by using both solid nutrient supply and heating. This is because the temperature difference between the ground water between the inner cylinder and the well casing (outer cylinder) and the ground water in the permeable layer is generated by heating by the heating means arranged in the inner cylinder, and the convection of the ground water is caused by the temperature difference. This is presumably because the (circulation) could be carried out actively. In addition, the space between the inner cylinder and the well casing (outer cylinder) was able to efficiently generate groundwater convection (circulation) because it is easier to move the groundwater than in the permeable layer. it is conceivable that. On the other hand, in Comparative Example 2 that does not use the inner cylinder, only convection of groundwater occurs along the wall surface of the well from the upper part of the well. ) May not have been sufficiently conducted.

  The present invention is useful for purification of contaminated soil and groundwater, and in particular, is useful for purification of soil and groundwater contaminated with organochlorine compounds such as PCE and TCE.

FIG. 1 is a schematic configuration diagram showing an example of the purification method of the present invention. FIG. 2A is a graph showing changes in the concentration of pollutants in groundwater in Examples, and FIGS. 2B and 2C are graphs showing changes in the concentration of contaminants in groundwater in Comparative Examples. FIG. 3 is a schematic configuration diagram illustrating an example of a conventional nutrient source supply well.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface layer 2 ... Impervious layer 3 ... Impervious layer 4 ... Impervious layer 10 ... Nutrient source supply well 11 ... Well casing 11a ... Screen 12 ...・ Inner cylinder 13 ... heating means 14 ... nutrition source 15 ... power source 16 ... contaminated area 101 ... well pipe

Claims (5)

Forming a nutrient supply well in which an inner cylinder is arranged in a well casing;
Arranging a heating means using an electric heater on the bottom surface of the inner cylinder , and then filling a solid nutrient source; and
Heating continuously or intermittently so as to maintain the water temperature in the inner cylinder by the heating means,
The inner cylinder is disposed with a space apart from the bottom surface of the well and the side surface of the well casing, and has a plurality of water-permeable ports through which groundwater can flow in and out on the side surface and the bottom surface. . The method for purifying contaminated soil and / or groundwater according to claim 1, wherein the nutrient source supply well reaches at least the lower part of the permeable layer. The method for purifying contaminated soil and / or groundwater according to claim 1 or 2, wherein the nutrient source contains a fatty acid having 10 or more carbon atoms. The method for purifying contaminated soil and / or groundwater according to any one of claims 1 to 3, wherein the pollutant contains a volatile organic compound. Forming a nutrient supply well in which an inner cylinder is arranged in a well casing;
Arranging a heating means using an electric heater on the bottom surface of the inner cylinder, and then filling a solid nutrient source; and
Heating continuously or intermittently so as to maintain the water temperature in the inner cylinder by the heating means,
The nutrient supply well reaches at least the bottom of the permeable layer,
The nutrient source includes a fatty acid having 10 or more carbon atoms,
Pollutants include volatile organic compounds,
The inner cylinder is disposed with a space apart from the bottom surface of the well and the side surface of the well casing, and has a plurality of water inlets through which groundwater can flow into and out of the side surface and the bottom surface. .

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