JP2018034086A - Process for clarifying contaminated soil and groundwater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for clarifying contaminated soil and groundwater, which solves the conventional problem, in which the process can be adopted even in places where pumping is difficult and, on top of that, does not require the addition of catalyst.SOLUTION: "Process for clarifying contaminated soil and groundwater" of the present invention is a clarification process for clarifying a soil and groundwater contaminated with 1,4-dioxane, and is a process comprising a soil warming step and an injection step. In the soil warming step, by applying voltage to three or more electrode wells built in the soil and passing an electric current through the soil, the soil and groundwater is warmed. In addition, in the injection step, persulfate dissolved in room temperature water is injected into the soil or groundwater in a warmed state and, by this persulfate salt being warmed, sulfate radicals are generated, and, by this sulfate radicals, 1,4-dioxane is decomposed.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a technique for purifying contaminated soil and groundwater, and more specifically, to a method for purifying soil and groundwater contaminated by 1,4-dioxane using sulfate radicals. .

  Soil contamination is a condition in which soil is contaminated with substances that are harmful to human health, and is caused by the infiltration of harmful substances from the surface due to careless handling in operational activities, or the presence of harmful substances contained in smoke. It occurs when it falls to the ground surface and accumulates or infiltrates, and it sometimes occurs when contaminated soil is brought in when embankment or embedding is performed. This hazardous substance is specified by the Soil Contamination Countermeasures Law, and a total of 25 substances such as volatile organic compounds, heavy metals, and agricultural chemicals are currently designated as hazardous substances.

  In addition to the specific hazardous substances specified by the Soil Contamination Countermeasures Law, there are also known substances that damage human health, such as dioxins and PAH (polycyclic aromatic hydrocarbons). Suspected 1,4-dioxane has also attracted attention in recent years. 1,4-Dioxane is added to an organic solvent as a reactant or stabilizer, and may be by-produced in the production process of a surfactant or a PET (Polyethylene terephthalate) resin. In addition, 1,4-dioxane may be mixed as an impurity in raw materials and products, or may be unintentionally contained in wastewater from the manufacturing process, so it is not used directly. It is not uncommon for 1,4-dioxane to be discharged. In Japan, with the increase of 1,4-dioxane detection cases in rivers and groundwater, it was added to the target substances of water quality standards and groundwater environment standards in November 2009, and in May 2012, the Water Pollution Control Law Emission regulations into the environment have been made due to wastewater standards and underground penetration regulations.

  1,4-Dioxane is a hardly decomposable synthetic chemical substance that is easily dissolved in water and hardly volatilizes, and is different in nature from volatile organic compounds (VOCs). In addition, 1,4-dioxane has a feature of low adsorptivity to soil particles, and is different in properties from heavy metals and agricultural chemicals that are likely to remain in the shallow layer portion. Therefore, the behavior of 1,4-dioxane in the underground environment (permeability, how the groundwater contamination spreads, etc.) is different from VOC, heavy metals, and agricultural chemicals, and therefore a purification method adopted for VOC, heavy metals, etc. Then, 1,4-dioxane may not be purified properly.

  Since 1,4-dioxane is easily dissolved in water, it may be present in high concentration in the aquifer (layer with groundwater). Therefore, groundwater pumping treatment is effective as a purification method. Bioremediation (soil pollution purification using microorganisms) used for VOCs and oils is also considered as a purification method. However, although the presence of microorganisms capable of decomposing 1,4-dioxane has already been confirmed, The current situation is that purification at the position has not been put to practical use.

  In addition to groundwater pumping treatment, in-situ purification by underground injection of oxidant may be performed. Although 1,4-dioxane is difficult to decompose, it has been confirmed that it is decomposed by a radical reaction, and 1,4-dioxane can be decomposed by promoting radical generation from the drug. Patent Document 1 also proposes a technique for purifying soil and groundwater by adding persulfate together with a catalyst such as bisulfite. The radical reaction of persulfate is promoted by adjusting the molar ratio of the catalyst to be added to the persulfate, and 1,4-dioxane is decomposed by this radical reaction.

JP 2011-173089 A

  Groundwater pumping treatment as a purification method for 1,4-dioxane is effective not only as a direct purification measure but also in terms of preventing diffusion, but with appropriate well design (number, arrangement, pumping amount, etc.) Otherwise, there is a difficulty that the expected purification effect cannot be obtained. In addition, if the groundwater concentration greatly exceeds the drainage standard, advanced water treatment facilities are required, and it is difficult to pump a sufficient amount of groundwater (such as low-fluidity groundwater or pore water in difficult-to-permeate water layers). In some cases it cannot be adopted.

  In-situ purification by underground injection of one oxidizer can be applied to groundwater with low fluidity, but the conventional method requires the addition of a catalyst such as iron salt, and in order to obtain a purification effect Had to add an iron catalyst in an appropriate ratio to the oxidant, which required considerable labor and cost. Further, precipitation of the added iron salt has caused problems such as well blocking.

  An object of the present invention is to provide a method for purifying contaminated soil and groundwater that can be used even in places where pumping is difficult, and that does not require the addition of a catalyst.

  The invention of the present application focuses on the point of generating sulfate radicals in a thermally activated state by persulfating the heated soil and groundwater, thereby decomposing 1,4-dioxane. It was an invention made based on an idea that did not exist.

  The “contaminated soil and groundwater purification method” of the present invention is a purification method for purifying soil and groundwater contaminated with 1,4-dioxane, and includes a soil heating step and an injection step. In the soil warming step, the soil and groundwater are warmed by Joule heat by applying (applying voltage) to three or more electrode wells constructed in the soil and passing an electric current through the soil. Moreover, in an injection | pouring process, the persulfate melt | dissolved in normal temperature water is inject | poured into the soil or groundwater of a warmed state, A sulfuric acid radical is generated by heating this persulfate. Then, 1,4-dioxane is decomposed by this sulfuric acid radical.

  The “contaminated soil and groundwater purification method” of the present invention may be a method of heating soil or groundwater to 40 to 50 ° C. in the soil heating step.

  The “contaminated soil and groundwater purification method” of the present invention can be a method of injecting a drug (persulfate dissolved in room temperature water) toward the aquifer in the injection step.

The “contaminated soil and groundwater purification method” of the present invention has the following effects.
(1) Since it is not accompanied by pumping, it can be widely used even in places where pumping treatment is difficult, and since it does not require the addition of an iron catalyst, labor and cost can be reduced as compared with conventional oxidant injection methods.
(2) Since the electric heating method (method of heating the soil itself with Joule heat) is used, the soil etc. can be continuously heated, and even if a normal temperature chemical is injected, 40 to 50 ° C.) state can be maintained.
(3) Since it can be dissolved at room temperature, that is, there is no need to warm the drug itself, the loss of persulfate can be reduced.
(4) Since the target temperature of soil or the like may be about medium to high temperature (for example, 40 to 50 ° C.), energy consumption can be suppressed as compared with other heating methods (for example, steam or heater).
(5) Heating is possible even after the injection of persulfate (especially because the persulfate is ionized, which facilitates electricity flow), so the characteristics of persulfate have a longer duration of effect than other oxidants. You can save it.
(6) Since the reactivity is increased by heating, the amount of the drug can be reduced as compared with the case of carrying out at normal temperature.

The flowchart which shows the flow of the main processes of "the purification method of contaminated soil and groundwater" of this invention. Sectional drawing which shows several electrode wells. The top view which shows the electrode well arrange | positioned planarly so that a triangle may be formed. Sectional drawing which shows the condition where a chemical | medical agent is inject | poured toward an aquifer.

  An example of the embodiment of the “contaminated soil and groundwater purification method” of the present invention will be described with reference to the flowchart shown in FIG. One feature of the present invention is that the soil and groundwater are heated in advance, and the persulfate is injected into the heated soil and groundwater. Therefore, it is divided into two steps, that is, a step of heating the soil and groundwater and a step of injecting persulfate.

1. Heating by the electric heating method In the case of the present invention, as a method of heating the soil and groundwater, the equipment scale required for heating can be reduced, the temperature can be easily adjusted, the heat itself is heated, and the heat capacity is high and the temperature is lowered. The electric heating method is suitable because it is difficult to do. Hereinafter, heating by the electric heating method will be described.

  Three or more electrode wells are installed in the soil to be purified (Step 10). FIG. 2 is a cross-sectional view showing a plurality (three in this figure) of electrode wells 10. This electrode well 10 is formed of a steel casing. Therefore, as shown in FIG. 2, by connecting the casing of each electrode well 10 to the power supply device 20, a current flows between the electrode wells 10 and the soil on the way. Joule heat can be generated. Therefore, each electrode well 10 is preferably arranged so as to surround the target soil, and for example, can be arranged so as to form a triangle as shown in FIG. Note that each of the four triangles shown in FIG. 3 is a regular triangle having a side of about 3.5 m, but of course, the electrode well 10 can be arranged to have various shapes.

  When the electrode well 10 can be installed, it is applied to the electrode well 10 using the power supply device 20 as described above (Step 20). A current flows between the applied electrode wells 10, Joule heat is generated in the soil between the electrode wells 10, and the temperature of the soil and groundwater rises accordingly. At this time, the magnitude of the applied voltage may be adjusted so that the soil and groundwater have a preset temperature.

  By the way, as a result of searching for a method for generating sulfate radicals from persulfate without the use of a catalyst such as iron salt, the inventors of the present invention have found that sulfate radicals are generated by heating. Specifically, it has been confirmed that when dissolved persulfate is injected under conditions where soil and groundwater are heated to an appropriate temperature, the persulfate is thermally activated to generate sulfate radicals. That is, the generation of sulfuric acid radicals is promoted by heating instead of the iron catalyst. Furthermore, the inventor of the present invention promotes the generation of sulfate radicals in a situation where the temperature of the soil and groundwater is medium and high. In particular, when persulfate is injected into the soil or groundwater at 40 to 50 ° C., It has been confirmed that it is likely to occur.

  In other words, the purpose of raising the temperature of soil and groundwater is to create an environment where sulfuric acid radicals can be generated. Therefore, after adjusting a voltage so that the temperature of soil and groundwater may become medium high temperature (especially 40-50 degreeC), it is good to apply to each electrode well 10. FIG. It should be noted that the actual temperature of the heated soil or groundwater is considered to be different from the predicted (or analyzed) temperature, so that it is applied to the electrode well 10 while observing the actual temperature (Step 30). You can also do it. In this case, as shown in FIG. 3, a temperature observation well 30 may be constructed between the electrode wells 10, and the temperature and soil temperature may be observed using the temperature observation well 30.

2. Injection of chemical | medical agent While applying to the electrode well 10, the chemical | medical agent inject | poured into soil or groundwater is adjusted (Step40). A chemical | medical agent melt | dissolves a persulfate in normal temperature (15-25 degreeC) water, and sodium persulfate, potassium persulfate, ammonium persulfate etc. can be illustrated as a persulfate used here. The reason why the water for dissolving persulfate is room temperature is that persulfate is not thermally activated at room temperature, so it dissolves in room temperature water to prevent the generation of sulfate radicals before reaching the soil or groundwater. This is because it can be sent to soil or groundwater in the state of persulfate by dissolving in room temperature water.

  After confirming that the soil and groundwater have reached the target temperature (medium / high temperature) (Step 30), the drug is adjusted (Step 40), and the drug is injected into the soil and groundwater (Step 50). At this time, as shown in FIG. 3, the injection well 40 constructed in the target soil can be used. Specifically, the drug is pumped from the storage tank using a pumping means such as a pump, and the drug is injected into the soil and groundwater from the injection well 40. Alternatively, the drug may be injected using the electrode well 10 instead of the injection well 40.

  Since 1,4-dioxane has the property of being easily dissolved in water, it can be considered that a large amount exists in groundwater. Therefore, it is recommended to inject the drug by selecting a soil layer containing groundwater. FIG. 4 is a cross-sectional view showing a situation in which a medicine is injected toward the aquifer. Since the aquifer has a high water permeability, it contains a lot of groundwater, that is, since a large amount of 1,4-dioxane is present, it is effective to select this aquifer and inject a drug. Of course, the drug may be injected as a whole without selecting a soil layer.

  Since the medium and high temperatures are maintained in the soil and groundwater, the chemical that has reached the soil and groundwater gradually increases in temperature to a medium and high temperature. As a result, the persulfate is thermally activated to generate sulfate radicals (Step 60). ). Then, 1,4-dioxane is decomposed by this sulfuric acid radical (Step 70). After the injection of the drug is continued for a preset time, the drug injection is stopped, and the application to the electrode well 10 is also stopped (Step 80).

  The “contaminated soil and groundwater purification method” of the present invention can be used in an operation area (or an operation site) where 1,4-dioxane is used, discharged, or by-produced. Considering that the present invention is extremely useful for improving the environment in Japan, it can be said that the invention can be used not only industrially but also can make a great social contribution.

10 Electrode well 20 Power supply 30 Temperature observation well 40 Injection well

Claims (3)

In a purification method for purifying soil and groundwater contaminated with 1,4-dioxane,
A soil heating step of heating the soil and groundwater by applying current to the soil by applying to three or more electrode wells constructed in the soil;
Injecting persulfate dissolved in room temperature water into warm soil or groundwater, and injecting sulfuric acid radicals by heating the persulfate,
A method for purifying contaminated soil and groundwater, wherein 1,4-dioxane is decomposed by the sulfate radical.   The method for purifying contaminated soil and groundwater according to claim 1, wherein in the soil heating step, the soil or groundwater is heated to 40 to 50 ° C.   The method for purifying contaminated soil and groundwater according to claim 1 or 2, wherein in the injection step, persulfate dissolved in room temperature water is injected toward the aquifer.

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