JP2005305282A - Soil cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soil cleaning method capable of preventing the blocking of the flow of ground water in polluted soil by injection to efficiently purify the polluted soil. <P>SOLUTION: This soil cleaning method is constituted so that nutrients are injected into the polluted soil especially polluted with oil, and microorganisms present in the polluted soil are activated to purify the polluted soil. The polluted soil 8 on the upstream side of ground water is excavated vertically from ground surface 2 to form an injection well 12 in a soil cleaning apparatus 10. Further, a nitrate solution tank 14 is installed on the ground surface 2 above the polluted soil 8 and stirred by an attached stirrer 16 in a hermetically closed and degassed state to store a nitrate solution with a predetermined concentration containing no dissolved oxygen. An injection pipe 18 is connected to the injection well 12 and the nitrate solution tank 14, and an attached injection pump 20 is driven to inject the nitrate solution into the polluted soil 8 through the injection well 12. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a soil purification method, and more particularly, to a soil purification method in which nutrient salts are injected into contaminated soil contaminated with oil to activate microorganisms present in the contaminated soil for purification.

  Conventionally, as a method for purifying contaminated soil contaminated with oil, there is a biological purification method for purifying contaminated soil using microorganisms present in the soil. In other words, aerobic heterotrophic bacteria present in the contaminated soil are removed by drilling from the ground surface to the contaminated soil and directly injecting oxygen sources such as air, low-concentration hydrogen peroxide water, and oxygen generation sources into the contaminated soil. When activated, the oil contained in the contaminated soil is decomposed to purify the contaminated soil. Since this biological purification method can prevent the occurrence of environmental pollution due to the purification process and can reduce the labor and cost required for purification, it is often used as a method for purifying contaminated soil.

Patent Documents 1 and 2 disclose a soil purification method in which nutrient salts such as nitrogen and phosphorus compounds, lipophilic and hydrophilic nutrients, and the like are injected into contaminated soil together with the oxygen source described above. As a result, nutrients necessary for activation can be supplemented for aerobic heterotrophic bacteria in the contaminated soil, so that the activation of the aerobic heterotrophic bacteria can be promoted and the purification of the contaminated soil can be shortened. .
Japanese Patent Laid-Open No. 11-104612 Japanese National Patent Publication No. 9-501841

  However, in the conventional biological purification method and the soil purification methods of Patent Documents 1 and 2, it is indispensable to inject an oxygen source in order to activate the aerobic heterotrophic bacteria in the contaminated soil. For this reason, the amount of dissolved oxygen in groundwater flowing in the contaminated soil increases, and divalent iron ions contained in the groundwater are oxidized to be precipitated into groundwater as iron hydroxide. The precipitated iron hydroxide closes the gaps between the particles constituting the contaminated soil and blocks the flow of groundwater in the contaminated soil. For this reason, when soil purification is performed, the flow of groundwater in the contaminated soil is blocked with time, and the amount injected into the contaminated soil is reduced. Therefore, there is a problem that it takes a long time to purify the contaminated soil. It was.

  The present invention has been made in view of such circumstances, and provides a soil purification method capable of efficiently clogging contaminated soil while preventing the flow of groundwater in the contaminated soil from being blocked by injection. With the goal.

  In order to achieve the above object, the invention according to claim 1 provides nutrient salts from the upstream side of the groundwater flowing through the contaminated soil with respect to the contaminated soil in which a part of the aquifer containing the groundwater is contaminated with oil. In the soil purification method for activating and purifying microorganisms in the contaminated soil by injecting, a nitrate solution that does not contain dissolved oxygen is used as the nutrient salt, so that it exists in the contaminated soil It is characterized by activating facultative anaerobic heterotrophic bacteria and decomposing oil in the contaminated soil.

  The aquifer described here is a layer in which rock fractures and pores in the soil are saturated with groundwater, and in the aquifer, a slow flow of saturated groundwater occurs. In addition to the soil itself, the contaminated soil includes groundwater existing in the soil.

  According to the present invention, by injecting a nitrate solution into a contaminated soil contaminated with oil, facultative anaerobic heterotrophic bacteria present in the contaminated soil are activated by the injected nitrate, and the contaminated soil Oil can be efficiently decomposed as a nutrient source. At this time, the injected nitrate is consumed and consumed for the degradation of oil by facultative anaerobic heterotrophic bacteria, so that it can be prevented from remaining in contaminated soil or groundwater and contaminating. Thereby, the contaminated soil can be efficiently purified without polluting the environment, and the time required for the purification can be shortened.

  What should be noted in the present invention is that biological purification is performed on contaminated soil using facultative anaerobic heterotrophic bacteria. The facultative anaerobic heterotrophic bacterium is a bacterium that is activated even under anaerobic conditions, and can therefore be activated without injecting an oxygen source. Thereby, it can prevent that the iron ion in groundwater oxidizes and precipitates by injection | pouring of an oxygen source, and obstruct | occludes the flow of groundwater. Further, since the injected nitrate solution is adjusted so as not to contain dissolved oxygen, it is possible to prevent the flow of groundwater from being blocked by the injection of the nitrate solution. Therefore, it is possible to efficiently inject the nitric acid solution, so that facultative anaerobic heterotrophic bacteria in the contaminated soil are the dominant bacteria, promoting activation, and shortening the time required for purification of the contaminated soil. it can.

  The nitrate solution preferably has a nitrogen concentration of 10 mg / L or less. Thereby, since the nitrogen concentration of groundwater can satisfy | fill the reference value of tap water by injection | pouring of a nitrate solution, while being able to use a groundwater as a drink state, a contaminated soil can be purified efficiently.

  Invention of Claim 3 measures the nitric acid concentration of the groundwater which flows through the contaminated soil of Claim 1 or 2, and controls the injection amount of the nitrate solution based on the measured value. And

  According to claim 3, by measuring the nitric acid concentration in the groundwater of the contaminated soil, the injected nitrate solution remains in the contaminated soil and the groundwater without being consumed by facultative anaerobic heterotrophic bacteria in the contaminated soil. The amount of nitric acid can be accurately grasped. Therefore, by controlling the injection amount of the nitrate solution based on the measurement value of the nitric acid concentration thus measured, it is possible to prevent the contaminated soil and groundwater from being contaminated by the injection of the excessive nitrate solution. In addition, since the contaminated soil can be effectively purified with an appropriate amount of the nitrate solution, the cost required for injecting the nitrate solution can be reduced.

  As described above, according to the soil purification method according to the present invention, by injecting a nitrate solution into the contaminated soil, the facultative anaerobic heterotrophic bacteria present in the contaminated soil are activated to contaminate the soil. The oil can be decomposed. This eliminates the need to inject an oxygen source into the contaminated soil, so that the injection of the oxygen source can prevent the flow of groundwater from being blocked and the injection efficiency from being lowered, so that the contaminated soil can be efficiently purified. And the time required for the purification of contaminated soil can be shortened.

  Hereinafter, preferred embodiments of a soil purification method according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram of a soil purification apparatus 10 that is a first embodiment suitably using the soil purification method of the present invention. The black arrow indicates the direction in which the nitrate solution flows, and the white arrow indicates the direction in which groundwater flows.

  As shown in FIG. 1, an aquifer 6 including groundwater is formed below a submerged layer 4 that forms the ground surface 2, and a part of the aquifer 6 is contaminated soil contaminated with oil. There are eight.

  The soil purification apparatus 10 is installed near the upper part of the contaminated soil 8 and mainly includes an injection well 12, a nitrate solution tank 14, and an injection pipe 18.

  The injection well 12 is provided on the upstream side of the groundwater flow, and is formed by excavating from the ground surface 2 to the contaminated soil 8 in the vertical direction. It is preferable that the shape, number, and size of the injection wells 12 can be efficiently injected into the contaminated soil 8.

  The nitrate solution tank 14 is installed on the surface 2 above the contaminated soil 8 and stores the nitrate solution in a sealed state. As the nitrate solution, for example, a solution formed by adding sodium nitrate to pumped ground water so as to have a predetermined concentration is used, and the solution is stirred by the attached stirrer 16 so that the concentration becomes constant. The nitrate solution preferably has a nitrogen concentration of 10 mg / L or less. At this time, in the nitrate solution tank 14, storage and stirring are performed in a deaerated state so that oxygen in the air is not dissolved in the nitrate solution.

  The injection pipe 18 is connected to the injection well 12 and the nitrate solution tank 14, and the nitrate solution is injected into the contaminated soil 8 through the injection well 12 by driving the attached injection pump 20.

  Next, the operation of the soil purification method of the present invention will be described using the soil purification apparatus 10 configured as described above.

  When purifying contaminated soil contaminated with oil, a biological purification method that activates microorganisms in the contaminated soil and decomposes the oil to purify it can be performed with little impact on the environment. It is often adopted because it can be done.

  In the conventional biological purification method, aerobic heterotrophic bacteria that are present in a large amount in the soil and are easily activated are used as microorganisms to be activated. Since aerobic heterotrophic bacteria are activated only under aerobic conditions, injection of an oxygen source is essential. In addition, aerobic heterotrophic bacteria can promote activation by adding inorganic substances such as nitrogen and phosphorus. Therefore, in the conventional biocleaning method for contaminated soil contaminated with oil, nutrients and nutrients are injected into the contaminated soil simultaneously with the oxygen source to intentionally activate the aerobic heterotrophic bacteria present in the contaminated soil. As a result, the oil in the contaminated soil, which is an organic matter, is actively decomposed to purify the contaminated soil.

  However, when an oxygen source is injected into the contaminated soil, the divalent iron ions contained in the groundwater are oxidized and deposited as iron hydroxide, and the precipitated iron hydroxide clogs the aquifer. End up. For this reason, since the injection quantity to contaminated soil falls, the purification rate of contaminated soil will fall.

  Therefore, the present inventor pays attention to facultative anaerobic heterotrophic bacteria among microorganisms present in the soil, and in the present invention, facultative anaerobic heterotrophic bacteria, particularly denitrifying bacteria, are injected by injecting a nitrate solution into the contaminated soil. It was made to activate as dominant bacteria.

  A facultative anaerobic heterotrophic bacterium can be activated under both aerobic and anaerobic conditions, and is characterized by having approximately the same resolution as an aerobic heterotrophic bacterium. Therefore, it is possible to activate facultative anaerobic heterotrophic bacteria and decompose oil in the contaminated soil without injecting an oxygen source into the contaminated soil. Therefore, since the divalent iron ions in the groundwater are not oxidized and iron hydroxide is not deposited, the flow of groundwater in the contaminated soil can be prevented from being blocked. Thereby, since a nitrate solution can be stably inject | poured with respect to contaminated soil, while being able to purify contaminated soil efficiently, the time required for purification | cleaning can be shortened.

  Although there are anaerobic heterotrophic bacteria in the soil, it is harder to activate than aerobic heterotrophic bacteria and facultative anaerobic heterotrophic bacteria, and the oil cannot be decomposed efficiently, so it is effective in purifying contaminated soil. It is difficult to use.

  The nitrate solution to be injected is set so that the nitrogen concentration is 10 mg / L or less. For this reason, even if the nitrate solution is injected into the contaminated soil 8, the groundwater can satisfy the reference value of the nitrogen concentration of tap water. Thereby, since groundwater can be used as a drink, the environmental pollution by soil purification can be suppressed.

  FIG. 2 is a configuration diagram of a soil purification apparatus 50 according to the second embodiment that suitably uses the soil purification method of the present invention, and is an example of measuring the nitric acid concentration of the contaminated soil 8. In addition, while attaching | subjecting the same code | symbol to the apparatus and member similar to the soil purification apparatus 10 which is 1st Embodiment, the description is abbreviate | omitted.

  The soil purification apparatus 50 is substantially the same as the soil purification apparatus 10 shown in FIG. 1, but a measurement well 22 is provided on the downstream side of the contaminated soil 8.

  The measurement well 22 is provided downstream of the injection well 12 in the flow of groundwater, and is formed by excavating vertically from the surface 2 to the contaminated soil 8. A nitrate ion sensor 24 for measuring the nitrate ion concentration of groundwater is installed at the lower end of the measurement well 22 so as to be immersed in the groundwater. The nitrate ion sensor 24 is connected to the control unit 26 provided on the ground surface 2 and transmits the measured nitric acid concentration. The control unit 26 is connected to the infusion pump 20 and controls the driving of the infusion pump 20 so that the transmitted measurement value does not exceed a preset set value.

  Therefore, in the soil purification apparatus 50, since an appropriate amount of nitrate solution is always injected into the contaminated soil 8, the soil and groundwater can be prevented from being contaminated by excessive injection of the nitrate solution, and the contaminated soil 8 Can be purified efficiently.

  In addition, in the soil purification apparatuses 10 and 50 mentioned above, the number, shape, material, etc. of each member and apparatus used are not specifically limited. When producing a nitrate solution in the nitrate solution tank 14, the water to be used may be obtained by pumping up ground water or may be supplied from another water source.

  In addition, if groundwater is pumped from the downstream side of the contaminated soil 8 and the pumped groundwater is used to generate a nitrate solution, the time required for the purification of the contaminated soil 8 can be greatly shortened and the cost required for the purification is reduced. can do.

  As Example 1, an investigation was made on the purification ability of contaminated soil in the soil purification method of the present invention.

  What contaminated 2.5 kg of soil with 25 g of lubricating oil was used as contaminated soil. A sodium nitrate solution of 190 mg / L (31 mg / L in terms of nitrate nitrogen concentration) was prepared by depositing 2.5 kg of the contaminated soil thus prepared in a 5 L-poly bottle and adjusting the pH to 7 for the contaminated soil. 2L was added and the purification test of the contaminated soil was conducted. In the purification test, an anaerobic condition was formed by allowing the poly bottle to stand. Then, a part of the contaminated soil after 20 and 32 days was collected, and the hexane extractant concentration in the collected contaminated soil was measured.

  The result is shown in FIG. FIG. 3 is a graph showing the content of hexane extractant in the contaminated soil with respect to the number of days for purification in the purification test of Example 1.

  As shown in FIG. 3, even after 20 days of purification, the hexane extractant concentration in the contaminated soil was 6800 mg / kg-dry, the same as at the start of the test, and the degree of oil contamination did not change. On the other hand, after 32 days, it decreased to 4000 mg / kg-dry, and the oil in the contaminated soil could be decomposed to 41%. In addition, when the nitrate nitrogen concentration in the contaminated soil after 32 days was measured, it was reduced to 0.06 mg / L.

  Therefore, it has been found that by adopting the soil purification method of the present invention, the contaminated soil can be purified by decomposing the oil in the contaminated soil by simply injecting the nitrate solution without injecting any oxygen source into the contaminated soil. .

The block diagram of the purification apparatus which is 1st Embodiment which used the soil purification method of this invention suitably The block diagram of the purification apparatus which is 2nd Embodiment which used the soil purification method of this invention suitably The graph which showed the hexane extract substance content in the contaminated soil with respect to the purification days in the purification test of Example 1

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Ground surface, 4 ... Submerged layer, 6 ... Aquifer, 8 ... Contaminated soil, 10, 50 ... Soil purification apparatus, 12 ... Injection well, 14 ... Nitrate solution tank, 16 ... Stirrer, 18 ... Injection pipe, 20 ... infusion pump, 22 ... well for measurement, 24 ... nitrate ion sensor

Claims (3)

By injecting nutrient salt from the upstream side of the groundwater flowing through the contaminated soil to the contaminated soil in which part of the aquifer containing groundwater is contaminated with oil, the microorganisms in the contaminated soil are activated. In the soil purification method for purification
By using a nitrate solution that does not contain dissolved oxygen as the nutrient salt, the facultative anaerobic heterotrophic bacteria present in the contaminated soil are activated and the oil in the contaminated soil is decomposed. Soil purification method.   The soil purification method according to claim 1, wherein the nitrate solution has a nitrogen concentration of 10 mg / L or less. The soil purification method according to claim 1 or 2, wherein the concentration of nitric acid in groundwater flowing through the contaminated soil is measured, and the injection amount of the nitrate solution is controlled based on the measured value.

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