JP2006102716A - Cleaning condition evaluation method for contaminated soil and contaminated soil cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning condition evaluation method for contaminated soil and a contaminated soil cleaning method capable of accurately and safely cleaning the contaminated soil by evaluating safety in a cleaning technology having the possibility of generating a combustible gas, especially safety in a cleaning method using iron and using the result of evaluation. <P>SOLUTION: The cleaning condition evaluation method for contaminated soil comprises the steps of subjecting the contaminated soil to be cleaned to a plurality of conditions to prepare a plurality of samples of contaminated soil, sealing the samples in sealed systems, measuring the quantity of a combustible gas produced in the sealed systems, measuring the cleaning efficiency of objects to be cleaned in the samples and evaluating the conditions from the measured results of the generation quantity of the combustible gas and the cleaning efficiency. The contaminated soil cleaning method on the basis of the evaluation result is also disclosed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for evaluating purification treatment conditions for contaminated soil and soil contaminated with soil, sediment, sludge, and even groundwater contaminated with chemical substances, particularly organochlorine compounds, which can be safely and efficiently purified. It relates to a purification method.

  Organochlorine compounds such as trichlorethylene and tetrachlorethylene are widely used in various factories and cleaning shops as cleaning agents for degreasing. In recent years, contamination of groundwater and soil by these chlorinated organic compounds, which are suspected of carcinogenic substances, has become a major social problem.

The purification measures that have been taken so far include mainly the containment process, excavation and containment process of contaminated soil, and the pump-and-treat method using a combination of pumping aeration, vacuum extraction and activated carbon adsorption. In recent years, in particular, it has been studied and put into practical use by injecting iron powder into groundwater and soil contaminated with organochlorine compounds and bringing them into contact for reduction treatment. Conventionally, since purification efficiency is prioritized, a purification agent having a larger hydrogen gas generation amount has been researched and put into practical use (for example, Patent Document 1). However, it is assumed that hydrogen gas is generated over a long period of time, particularly when iron is used as a permeation wall or a barrier wall for soil or groundwater purification with high water content.
JP 2004-113976 A

Among conventional technologies, purification technologies that may generate flammable gases, such as purification methods that add metals such as iron and aluminum compounds to contaminated soil, have been widely adopted in recent years because they can be purified easily at low temperatures. Has been. However, in the purification method using, for example, iron, hydrogen gas is generated as shown in the following formula (1) or (2), so that the generated hydrogen gas accumulates and becomes an explosion range (4 to 75%). Care must be taken to avoid this.
3Fe + 4H ₂ O → Fe ₃ O ₄ + 4H ₂ (1)
^{_{Fe + 2H 2 O → Fe 2+}} + 2OH - + H (2)

  Therefore, an object of the present invention is to accurately evaluate the safety against hydrogen gas in a purification technique that may generate flammable gas, in particular, a purification method using iron, and based on the evaluation result, the contaminated soil can be safely It is another object of the present invention to provide a method for evaluating the treatment conditions of contaminated soil and a method for purifying contaminated soil, which can be reliably purified.

  The present inventors examined a method for purifying soil and groundwater contaminated with organochlorine compounds such as trichlorethylene (TCE) and cis-1,2-dichloroethylene (c-DCE) using iron, in particular, using a vial test. As a result, it was found that the hydrogen gas concentration in the gas may exceed 4% in some cases in a closed system when soil, water, and iron powder exist. Furthermore, when the inventors added iron to various soil species and measured the hydrogen gas concentration in a closed system, the amount of hydrogen generated when iron was added to the soil was confirmed to vary greatly depending on the soil. It has also been found that it is difficult to predict the hydrogen gas generated simply from the amount of added iron by calculation, and that the amount of hydrogen generated depends on the amount of iron powder and pH. For this reason, when performing a purification treatment in which iron is added to the soil to be purified, a contaminated soil sample that has been subjected to the purification treatment to be carried out in advance is sealed in a closed system for each soil to be purified. Under the circumstances, it was found that measuring the amount of hydrogen gas generated is effective for examining the treatment conditions of contaminated soil, and the present invention has been completed. Based on the test results, the generation period of hydrogen can be predicted, and appropriate treatment conditions for suppressing hydrogen generation can be examined by changing the iron addition amount, pH, etc. Based on this, we provide a purification method that purifies safely by examining the required amount of generated gas, dilution method with inert gas (nitrogen, etc.), and air diffusion method by blowing air on the ground surface. be able to.

  That is, the method for evaluating the purification treatment conditions for contaminated soil according to the present invention creates a contaminated soil sample that has been subjected to purification treatment under a predetermined condition for the contaminated soil to be purified, and encloses the sample in a closed system, The method comprises measuring the amount of combustible gas generated in a closed system and evaluating the predetermined condition based on the measurement result.

  In this contaminated soil purification treatment condition evaluation method, in particular, the purification treatment is preferably a treatment of adding any one or more of iron compounds such as metallic iron, iron salts, and iron chelates.

  The present invention also provides a method capable of comparing and evaluating a plurality of conditions. That is, according to the method for evaluating purification treatment conditions for contaminated soil according to the present invention, a plurality of contaminated soil samples are prepared by subjecting the contaminated soil to be purified to purification treatment under a plurality of conditions, and each sample is enclosed in a sealed system. In addition to measuring the amount of combustible gas generated in a closed system, measure the purification efficiency of the purification target substance in each sample, change the measurement result of the combustible gas generation amount and change or decomposition of the elution concentration of the purification target substance. The method comprises evaluating the plurality of conditions from a measurement result of purification efficiency such as efficiency.

  In this contaminated soil purification treatment condition evaluation method, a suitable condition or an optimum condition can be selected from among the plurality of conditions as the condition of the purification treatment actually performed on the contaminated soil to be purified. Alternatively, it is determined based on the evaluation results of the plurality of conditions. For example, when it is clearly estimated that a suitable or optimal condition exists between the two conditions, it is actually performed based on those conditions. It is also possible to determine the conditions for the purification treatment.

  Also in this contaminated soil purification treatment condition evaluation method, it is particularly preferable that the purification treatment is a treatment of adding any one or more of iron compounds such as metallic iron, iron salts, and iron chelates.

  Evaluation of a plurality of conditions can be performed as follows, for example. Evaluate multiple conditions by changing the amount of additive for purification treatment, or evaluate multiple conditions by changing the soil pH in the purification treatment, or combine these to meet multiple conditions The method of evaluating is mentioned.

  The contaminated soil purification method according to the present invention comprises a method characterized in that the contaminated soil is purified based on the evaluation result by the above-described contaminated soil purification treatment condition evaluation method.

  In this contaminated soil purification method, it is particularly desirable to purify the contaminated soil while taking safety measures against flammable gases such as hydrogen gas.

  As the safety measure, for example, purification is performed while blowing air to the surface of the purification area, purification is performed while gas is diffused from at least one well, purification is performed while sucking gas from at least one gas suction well, at least one Purify while injecting gas from one gas injection well, inject gas from at least one gas injection well, and purify while sucking gas from at least one gas suction well, monitor the gas concentration near the purification area Measures such as purifying can be adopted. Among these, the method of purifying while monitoring the gas concentration in the vicinity of the purification area can be implemented in combination with other safety measures or with a predetermined purification process.

  As described above, since the generation amount and concentration of hydrogen gas may be a problem during the purification treatment, it is desirable to discharge the gas so that the hydrogen concentration in the gas in the purification area is below the explosion range.

  According to the method for evaluating purification treatment conditions for contaminated soil according to the present invention, purification treatment conditions that generate flammable gas, particularly regarding the generation of hydrogen gas in a purification method using iron, purification treatment conditions, particularly regarding safety. Can be evaluated accurately. And in the contaminated soil purification method which concerns on this invention, since an actual purification process is performed based on this evaluation result, a contaminated soil can be purified safely and reliably and efficiently.

Hereinafter, the present invention will be described in detail together with preferred embodiments and examples.
The present invention can be applied to any purification treatment that theoretically generates flammable gas, but is particularly suitably applied to hydrogen gas in purification treatment using iron. For example, in the case of purification using iron powder, it can also be applied to purification of groundwater, sediment, etc. in addition to soil purification. In addition, the type of contaminants to be purified is not particularly limited as long as it is a purification process using iron powder. Organochlorine compounds (TCE, PCE, dioxins, PCBs, etc.), purification of oil contaminants, iron It can also be applied to insolubilization treatment of other heavy metal materials and the like.

  When applying a purification treatment method for adding iron to contaminated soil, the present invention evaluates and sets an appropriate treatment condition in advance, and a contaminated soil purification method for purifying the contaminated soil safely and reliably based thereon. provide.

  The term “appropriate treatment conditions” as used herein refers to treatment conditions in which the concentration of hydrogen discharged to the outside of the system is within a safe range while the contaminated soil can be purified in the soil purification process. It also includes processing conditions in which the hydrogen concentration is within a safe range after taking safety measures such as a method of dilution with gas (nitrogen, etc.), a method of air diffusion by blowing air on the ground surface.

  In setting appropriate treatment conditions, first, for example, the amount of hydrogen generation as a flammable gas in each system is measured by changing the treatment conditions such as the amount of iron powder added to the contaminated soil and the pH condition. At the same time, the concentration of the pollutant to be purified in each system is measured. Next, a comparative evaluation of the purification efficiency and hydrogen generation amount in each system is performed. From this, appropriate processing conditions are set such that the hydrogen gas concentration discharged outside the system to be purified is within the safe range, or at least the hydrogen gas concentration discharged outside the system after taking safety measures is within the safe range. Can be set. Embodiments of the present invention will be described below.

  To measure the amount of hydrogen generated, first, a certain amount of contaminated soil to be purified is collected and iron powder is added to a predetermined concentration. The soil is placed in a fixed-volume sealed bottle having a butyl rubber stopper and sealed with an aluminum seal. At this time, it is desirable that the head pace portion in the sealed bottle is filled with nitrogen in order to reproduce the air or reduced state in consideration of the state at the actual site. It is desirable to shield the light. The bottle is left standing, and the gas in the head space is collected with a gas tight syringe while keeping a sealed state through a butyl rubber stopper every predetermined time, and injected into a gas chromatograph analyzer for quantitative analysis of hydrogen gas. Do. At this time, the concentration can be measured with a gas detection tube or the like. The rate of hydrogen generation can be calculated from the rate of increase in the hydrogen gas concentration in the headspace, and the amount of soil gas suction, dilution rate with inert gas (nitrogen, etc.), Therefore, it is possible to study the amount of blast for the purpose. Further, by measuring the change in the hydrogen gas concentration over time, it is possible to predict the period until the hydrogen generation rate at the actual site decreases. The above operation is performed in the same manner by creating an experimental system in which processing conditions such as the amount of iron powder added and pH are changed. On the other hand, the purification efficiency of contaminated soil is also evaluated separately for each treatment condition created.

  Compare the predicted values of hydrogen generation rate and period obtained in a series of operations and the purification efficiency under the treatment conditions, and the best purification efficiency, hydrogen gas generation is within the safe range, or at least the soil as mentioned above Sufficiently safe conditions are set as appropriate processing conditions when safety measures are taken, such as a gas suction amount, a dilution method with an inert gas (nitrogen, etc.), and an air diffusing method by blowing air on the ground surface.

Examples are shown below, but the following examples do not limit the scope of the present invention.
Example 1
Various soils (5 g) were placed in a 60 mL vial, and after adding 10 mL of water and 0.2 g of iron powder, the vial was sealed with a rubber stopper and an aluminum seal, and the experiment was started. Table 1 shows the results of measuring the hydrogen gas concentration in the vial after 100 hours for different soils A, B, and C by gas chromatography. As is clear from Table 1, it can be seen that the amount of hydrogen generated when iron powder, water, and soil are present varies greatly depending on the soil species.

Example 2
Soil A used in Example 1 is simulated by PCE, and kneaded by adding 15 mL of water and iron powder in the amounts shown in Table 2 to 50 g of contaminated soil, and predetermined with sulfuric acid or sodium hydroxide. After adjusting the pH of the solution, it was put into a 700 mL vial and sealed with a rubber stopper and an aluminum seal to start the experiment. Table 2 shows the results obtained by measuring the decomposition rate of the hydrogen gas concentration in the vial bottle head space and the initial concentration of PCE by gas chromatography after 800 hours.

  From Table 2, it can be seen that when the amount of iron powder and soil pH are different, the hydrogen generation behavior and the PCE decomposition rate are different. Here, by comparing conditions (1) and (2), if the amount of iron powder is reduced from 2.5 wt% to 1.0 wt%, the hydrogen gas generation rate will not change much, but the PCE decomposition rate will decrease. Then, it was planned to carry out purification work while adopting condition (2) and taking safety measures. The hydrogen gas concentration here is the condition under the vial test, and does not indicate the actual concentration in the field, but is presumed to exhibit relatively the same behavior. In setting appropriate processing conditions, it is preferable to perform analysis under various conditions as described above and set conditions suitable for the purpose.

Claims (14)

  Create a contaminated soil sample that has been purified under the specified conditions for the contaminated soil to be purified, enclose the sample in a closed system, and measure the amount of combustible gas generated under the closed system. A method for evaluating the condition for purification of contaminated soil, characterized in that the predetermined condition is evaluated based on a measurement result.   2. The method for evaluating purification treatment conditions for contaminated soil according to claim 1, wherein the purification treatment is a treatment of adding any one or more of iron compounds such as metallic iron, iron salts, and iron chelates.   Create multiple contaminated soil samples that have been purified under multiple conditions for contaminated soil to be purified, enclose each sample in a closed system, and measure the amount of combustible gas generated in the closed system And measuring the purification efficiency of the substance to be purified in each sample, and evaluating the plurality of conditions from the measurement result of the amount of combustible gas generation and the measurement result of the purification efficiency. Evaluation methods.   The conditions for the purification treatment for the contaminated soil to be purified are selected from the plurality of conditions or determined based on the evaluation results of the plurality of conditions. Evaluation methods.   The method for evaluating purification treatment conditions for contaminated soil according to claim 3 or 4, wherein the purification treatment is a treatment for adding any one or more of iron compounds such as metallic iron, iron salts, and iron chelates.   The contaminated soil purification treatment condition evaluation method according to any one of claims 3 to 5, wherein a plurality of conditions are evaluated by changing an amount of an additive for the purification treatment.   The polluted soil purification treatment condition evaluation method according to any one of claims 3 to 6, wherein a plurality of conditions are evaluated by changing a soil pH in the purification treatment.   The contaminated soil purification method characterized by purifying contaminated soil based on the evaluation result by the purification treatment condition evaluation method of the contaminated soil in any one of Claims 1-7.   The method for purifying contaminated soil according to claim 8, wherein the contaminated soil is purified while taking safety measures against combustible gas.   The contaminated soil purification method according to claim 9, wherein the safety measure purifies the ground surface of the purification area while blowing air.   The contaminated soil purification method according to claim 9, wherein the safety measure purifies the gas while dissipating gas from at least one well.   The method for purifying contaminated soil according to claim 9, wherein the safety measure purifies while monitoring the gas concentration in the vicinity of the purification area.   The contaminated soil purification method according to any one of claims 8 to 11, wherein purification is performed while monitoring a gas concentration in the vicinity of the purification area.   The contaminated soil purification method according to any one of claims 8 to 13, wherein the gas is discharged so that a hydrogen concentration in the gas in the purification area is equal to or less than an explosion range.