JP6344000B2 - Purification method of soil contaminated with organic pollutants - Google Patents

Description

  The present invention relates to a purification method for purifying contaminated ground contaminated by organic pollutants such as volatile organic chlorine compounds.

  As techniques for purifying contaminated ground contaminated with organic pollutants, for example, techniques using microorganisms that decompose organic pollutants, techniques using reduction reactions, and techniques using oxidation reactions are known. Among these techniques, the technique using an oxidation reaction is used when it is desired to purify contaminated ground in which a microorganism that decomposes organic pollutants does not live or contaminated ground in a short period of time. As a technique using an oxidation reaction, a Fenton method using a hydrogen peroxide solution and an iron salt and a method using a persulfate such as sodium persulfate are known.

  For example, Patent Document 1 divides an area containing soil or groundwater contaminated with a volatile organic chlorine compound (hereinafter referred to as VOC), and a sulfate or persulfate such as potassium sulfate or sodium persulfate is included in the compartment. A technique for directly adding is described.

JP 2002-136916 A

  In the Fenton method described above, the reaction ends early. For example, the reaction ends in one day. Thus, since the chemical | medical agent lifetime in the ground is short, there existed a problem that the penetration | infiltration range of a chemical | medical agent was narrow and it was necessary to increase the number of injection wells installed in the purification | cleaning object range. On the other hand, in the method of directly adding persulfate or the like, the reaction of persulfate or the like proceeds more slowly than the hydrogen peroxide solution, so that long-term sustainability of decomposition can be expected. On the other hand, this method has a problem that the decomposition efficiency in the initial stage of injection is low.

  This invention is made | formed in view of such a situation, The objective is to improve the decomposition | disassembly efficiency in the injection | pouring initial stage, ensuring the long-term sustainability of decomposition | disassembly.

  In order to achieve the above object, the present invention provides a purification method for purifying contaminated ground contaminated with organic pollutants, wherein a mixed solution of persulfate and hydrogen persulfate is injected into the contaminated ground. Features. In the present invention, the persulfate is preferably sodium peroxodisulfate, and the hydrogen persulfate is preferably a double salt of potassium hydrogen persulfate. Furthermore, it is more preferable to mix the sodium peroxodisulfate and the double salt of potassium hydrogen persulfate within a range of 1: 1 to 4: 1 by weight.

  According to these inventions, hydrogen persulfate reacts faster than persulfate, improving the decomposition efficiency of organic pollutants at the initial injection stage. And the pH of the ground is lowered with the reaction of hydrogen persulfate, and the decomposition efficiency of organic pollutants by persulfate is improved. This is presumably because iron contained in the ground eluted as the pH of the ground decreased, and functioned as a catalyst for persulfate. Thereby, the oxidizing power by persulfate improves and the decomposition efficiency with respect to the substance which is hard to be oxidatively decomposed can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, when purifying the contaminated ground contaminated with the organic pollutant, the decomposition | disassembly efficiency in the injection | pouring initial stage can be improved, ensuring the long-term sustainability of decomposition | disassembly.

It is a figure explaining the material used for the VOC decomposition | disassembly test and the comparison test. It is a figure explaining the mixing | blending of a VOC decomposition | disassembly test. It is a figure explaining the cis-DCE density | concentration in oxidizing agent density | concentration 0.3%. It is a figure explaining the decomposition rate constant in oxidant concentration 0.3%. It is a figure explaining pH in oxidizing agent concentration 0.3%. It is a figure explaining the cis-DCE density | concentration in oxidizing agent density | concentration 0.25%. It is a figure explaining the decomposition rate constant in oxidizing agent concentration 0.25%. It is a figure explaining pH in oxidizing agent concentration 0.25%. It is a figure explaining the mixing | blending in a comparative test. It is a figure explaining the cis-DCE density | concentration of each test section. Is a diagram illustrating the cis-DCE concentration in oxone blending area and H ₂ O ₂ mixed Ward. It is a figure explaining pH of each test section. It is a flowchart of a purification method.

  The inventors of the present invention have focused on the oxidative decomposition of organic pollutants by persulfate, and have focused on the fact that the decomposition efficiency at the initial stage of injection is low, and mixing hydrogen persulfate to increase the decomposition efficiency at the initial stage of injection. That is, the inventors have conceived that a mixed solution of persulfate and hydrogen persulfate is used as an oxidizing agent for oxidatively decomposing organic pollutants.

  In this embodiment, in order to confirm the decomposition effect of the organic pollutant by the oxidizing agent, a VOC that is a typical organic pollutant was used, and an indoor VOC decomposition test was performed. In order to confirm the superiority of this oxidizing agent, a comparative test was conducted indoors using a mixed solution of hydrogen persulfate and hydrogen peroxide as a comparative oxidizing agent.

  Prior to the description of these tests, the materials used in each test will be described with reference to FIG. As shown in FIG. 1 (a), persulfate, hydrogen persulfate, hydrogen peroxide, VOC, mountain sand, clay, and water (tap water) were used in each test. Hereinafter, each substance will be described.

Persulfate is equivalent to an oxidizing agent for oxidatively decomposing VOC. In this embodiment, a 10% aqueous solution of sodium peroxodisulfate (hereinafter referred to as SPS), which is a kind of peroxodisulfate, was used. SPS is a kind of sulfur oxo acid and is represented by the chemical formula Na ₂ S ₂ O ₈ and has a structure shown in FIG. SPS dissociates persulfate ions when dissolved in water, and VOC is oxidatively decomposed by the persulfate ions. SPS is activated in the presence of divalent iron and promotes the decomposition of VOC. Thus, divalent iron functions as a catalyst for persulfate.

Hydrogen persulfate is also equivalent to an oxidizing agent for oxidatively decomposing VOC. In this test, a 10% aqueous solution of DuPont's trade name “Oxone” (registered trademark) was used as the hydrogen persulfate. Oxone is an oxidizing agent containing potassium hydrogen persulfate as a main component as shown in FIG. Specifically, it is a double salt composed of potassium ion, hydrogen persulfate ion, sulfate ion, and hydrogen sulfate ion, and is represented by the chemical formula 2KHSO ₅ · KHSO ₄ · K ₂ SO ₄ as shown in the figure. .

Hydrogen peroxide also corresponds to an oxidant for oxidatively decomposing VOC and is represented by the chemical formula H ₂ O ₂ . In this test, a hydrogen peroxide solution having a concentration of 35% was used.

  As the VOC material, cis-1.2-dichloroethylene (cis-DCE) was used. A 1000 mg / L aqueous solution of cis-DCE was used in the VOC decomposition test, and a 100 mg / L aqueous solution of cis-DCE was used in the comparative test.

Mountain sand and clay were used to simulate the earth and sand. In this test, soil in which mountain sand and clay were mixed so that the weight ratio was 19: 1 was used. Here, the trade name “Tochikure” of Kanto Kasei Co., Ltd. was used as the clay. This torch clay contains about 70% silicon dioxide (SiO ₂ ), about 14% aluminum oxide (Al ₂ O ₃ ), and about 6% ferric oxide (Fe ₂ O ₃ ).

  The VOC decomposition test will be described. In this VOC decomposition test, an oxidizing agent (oxone, SPS) and VOC (cis-DCE) were added to a glass container charged with a predetermined amount of mixed soil and water, and changes in DCE concentration and pH over time were measured. In addition, since DCE density | concentration falls by decomposition | disassembly with progress of a test, DCE solution was added additionally suitably.

  FIG. 2 is a diagram for explaining the composition of each test section in the VOC decomposition test. In this VOC decomposition test, 13 types of test sections were prepared by changing the concentration of the oxidizing agent and the mixing ratio of oxone and SPS. Hereinafter, each test section will be described. In each test section, a glass container having a volume of 130 mL was used. The mixed soil of mountain sand and clay was 70 g in all cases.

  The test group of No1 is a control group. In this control group, 95 mL of tap water was added to the mixed soil, and 2 mL of DCE solution (concentration 1000 mg / L, the same in the VOC decomposition test) was added.

  The No. 2-7 test plots are test plots with an oxidant concentration of 0.3%. That is, it is a test plot adjusted so that the total weight of oxone and SPS added as an oxidant is 0.3% with respect to the total weight of soil and tap water. In these test sections, 90 mL of tap water was added to the mixed soil, and 2 mL of DCE solution was added.

  The No. 2 test plot is the SPS single plot. That is, in this test group, 5.0 mL of 10% SPS solution was added. Further, the test group No. 3 is an oxone single group. That is, in this test group, 5.0 mL of a 10% oxone solution was added.

  The No. 4-7 test section is a mixed section of SPS and oxone. That is, in the test group No. 4, 2.5 mL of 10% SPS solution and 2.5 mL of 10% oxone solution were added so that the weight ratio of SPS and oxone was 1: 1. In the test group No. 5, 3.3 mL of 10% SPS solution and 1.7 mL of 10% oxone solution were added so that the weight ratio of SPS and oxone was 2: 1. Similarly, 4.0 mL of 10% SPS solution and 1.0 mL of 10% oxone solution were added so that the weight ratio of SPS and oxone was 4: 1 in the No. 6 test plot, and SPS and No. 7 test plot were added. 4.4 mL of 10% SPS solution and 0.6 mL of 10% oxone solution were added so that the weight ratio of oxone was 8: 1.

  The No. 8-13 test plots are test plots with an oxidant concentration of 0.25%. That is, it is a test plot adjusted so that the total weight of oxone and SPS added as an oxidizing agent is 0.25% with respect to the total weight of soil and tap water. In these test sections, 90 mL of tap water was added to the mixed soil, and 2 mL of DCE solution was added.

  The test group of No8 was an SPS single group, and 4.0 mL of 10% SPS solution was added. In addition, the test group of No9 was an oxone alone group, and 4.0 mL of a 10% oxone solution was added.

  The No. 10-13 test section is a mixed section of SPS and oxone. That is, in the test group No. 10, 2.0 mL each of 10% SPS solution and 10% oxone solution was added so that the weight ratio of SPS and oxone was 1: 1. In the test group No. 11, 2.7 mL of 10% SPS solution and 1.3 mL of 10% oxone solution were added so that the weight ratio of SPS and oxone was 2: 1. Similarly, 3.2 mL of 10% SPS solution and 0.8 mL of 10% oxon solution were added so that the weight ratio of SPS and oxone was 4: 1 in the No. 12 test zone, and SPS and 3.4 mL of 10% SPS solution and 0.6 mL of 10% oxone solution were added so that the weight ratio of oxone was 6: 1.

  For convenience, in the following description, the No. 4 and No. 10 test plots are also referred to as 1: 1 test plots, and the No. 5 and No. 11 test plots are also referred to as 2: 1 test plots. Similarly, the No. 6 and No. 12 test plots are also referred to as the 4: 1 test plot, the No. 7 test plot as the 8: 1 test plot, and the No. 13 test plot as the 6: 1 test plot.

  Next, test results will be described. Here, FIGS. 3 to 5 are diagrams for explaining the test results when the oxidant concentration is 0.3%. That is, FIG. 3 is a diagram for explaining the cis-DCE concentration, FIG. 4 is a diagram for explaining the decomposition rate constant, and FIG. 5 is a diagram for explaining the pH. Similarly, FIGS. 6 to 8 are diagrams for explaining the test results when the oxidant concentration is 0.25%. That is, FIG. 6 is a diagram for explaining the cis-DCE concentration, FIG. 7 is a diagram for explaining the decomposition rate constant, and FIG. 8 is a diagram for explaining the pH.

  The decomposition rate constants shown in FIGS. 4 and 7 were calculated based on the measurement results of the VOC concentration (cis-DCE concentration). That is, assuming that the decomposition of VOC proceeds in a primary reaction, the VOC concentration at the time when a certain time k has elapsed is expressed by the following formula (1). And -k in the following formula (1) was calculated as a decomposition rate constant.

VOC concentration = (initial value of VOC concentration) × exp ^−k (1)

  Further, in the test section where the oxidant concentration was 0.3%, after the measurement was made at the time of 1 day from the start of the test, the cis-DCE solution was applied to the No. 3 oxone alone section and the No. 4 1: 1 test section. 2 mL was added, and measurement was performed after 4 days. Then, 2 mL of the cis-DCE solution was added to the No. 3 oxone single section. Further, after 12 days, 15 days, 20 days, and 26 days were measured, 2 mL each of cis-DCE solution was added to each of No. 1 to No. 7 test sections.

  Similarly, in the test group in which the oxidant concentration was 0.25%, after measuring after the first day from the start of the test, and after measuring after eight days, On the other hand, 2 mL of cis-DCE solution was additionally added. In addition, after measuring after 4 days, 2 mL of cis-DCE solution was additionally added to the 1: 1 test section of No10. Furthermore, after measuring after 12 days, 15 days, 20 days, and 26 days, 2 mL of cis-DCE solution was additionally added to each of Nos. 8-13.

  In the control group of No1, as shown in FIG. 3, the cis-DCE concentration was 24.83 mg / L after 1 day, 22.91 mg / L after 4 days, and 22.55 mg / L after 8 days. It was 21.1 mg / L after 12 days. Thereafter, it was 33.3 mg / L after 15 days, 63.08 mg / L after 20 days, 69.07 mg / L after 26 days, and 80.2 mg / L after 34 days. As shown in FIG. 4, with respect to the decomposition rate constant, 0.22 is obtained when 1 day has elapsed, -0.03 when 4 days have elapsed, 0.00 when 8 days have elapsed, and -0.02 after 12 days. Met. Thereafter, it was -0.08 at the lapse of 15 days, 0.02 at the lapse of 20 days, -0.02 at the lapse of 26 days, and -0.03 at the lapse of 34 days. As shown in FIG. 5, the pH was neutral from 7.0 to 7.6 from the first day to the 34th day.

  Hereinafter, the test results at an oxidant concentration of 0.3% will be described.

  In the SPS alone section of No. 2, as shown in FIG. 3, the cis-DCE concentration was 17.00 mg / L after 1 day, 4.73 mg / L after 4 days, and 0.40 mg / L after 8 days. L, 0.03 mg / L at the lapse of 12 days. Thereafter, it was 6.69 mg / L at the lapse of 15 days, 15.89 mg / L at the lapse of 20 days, 13.84 mg / L at the lapse of 26 days, and 1.59 mg / L at the lapse of 34 days. As shown in FIG. 4, with respect to the decomposition rate constant, -0.16 after 1 day, -0.43 after 4 days, -0.62 after 8 days, -0 after 12 days .68. Thereafter, it was -0.44 at the lapse of 15 days, -0.14 at the lapse of 20 days, -0.18 at the lapse of 26 days, and -0.56 at the lapse of 34 days.

  From these results, it was confirmed that in the SPS single section, although the initial decomposition rate is low, the decomposition effect lasts for a long time. Further, as shown in FIG. 5, regarding the pH, the period from the start to the 26th day transitioned between pH 5.2 to 6.7 and neutral to slightly acidic, and on the 34th day, the pH was 4.7 and weak. It showed acidity.

  As shown in FIG. 3, the cis-DCE concentration in No. 3 oxone alone was 0.01 mg / L after 1 day, 0.01 mg / L after 4 days, and 10.47 mg / L after 8 days. L, 5.53 mg / L at the elapse of 12 days. Then, it was 18.90 mg / L at the lapse of 15 days, 41.25 mg / L at the lapse of 20 days, 50.16 mg / L at the lapse of 26 days, and 58.9 mg / L at the lapse of 34 days. As shown in FIG. 4, with respect to the degradation rate constant, -7.6 (not shown) after 1 day, -3.0 (not shown) after 4 days, -0.18 after 8 days. -0.16 at the elapse of 12 days. Thereafter, it was -0.11 at the lapse of 15 days, 0.01 at the lapse of 20 days, 0.04 at the lapse of 26 days, and -0.03 at the lapse of 34 days.

  From these results, it was confirmed that in the oxone alone group, although the initial decomposition rate was extremely high, the decomposition effect was completed in a short period of about one week. Moreover, regarding pH, as shown in FIG. 5, pH2.1 and acidity were shown on the 1st day, and the period from the 4th day to the 20th day showed weak acidity to pH3.0-3.4. After that, the pH gradually increased.

  In the 1: 1 test plot of No4, as shown in FIG. 3, the cis-DCE concentration was 0.01 mg / L after 1 day, 5.11 mg / L after 4 days, and 0.1 after 8 days. 03 mg / L, 0.01 mg / L after 12 days. Thereafter, it was 0.43 mg / L after 15 days, 1.15 mg / L after 20 days, 1.32 mg / L after 26 days, and 1.27 mg / L after 34 days. As shown in FIG. 4, the degradation rate constant was −7.6 (not shown) after 1 day, −0.55 after 4 days, and −1.30 after 8 days. Thereafter, it was -1.54 after 15 days, -0.61 after 20 days, -0.55 after 26 days, and -0.51 after 34 days.

  From these results, it was confirmed that in the 1: 1 test section, the initial decomposition rate was high and the decomposition effect continued for a long time. Moreover, regarding pH, as shown in FIG. 5, it showed acidity with pH2.7 on the 1st day, and it showed weak acidity with pH3.6-4.3 from the 4th to the 15th. From the 20th day onward, the pH gradually increased as in the oxone alone group.

  In the 2: 1 test group of No5, as shown in FIG. 3, the cis-DCE concentration was 16.31 mg / L after 1 day, 2.10 mg / L after 4 days, and 0.2 after 8 days. 03 mg / L, 0.01 mg / L after 12 days. Thereafter, it was 4.42 mg / L after 15 days, 0.89 mg / L after 20 days, 0.84 mg / L after 26 days, and 0.64 mg / L after 34 days. As shown in FIG. 4, the degradation rate constant was −0.20 after 1 day, −0.68 after 4 days, and −1.05 after 8 days. Then, it was -0.60 at the time of 15 days, -0.75 at the time of 20 days, -0.60 at the time of 26 days, and -0.62 at the time of 34 days.

  From these results, in the 2: 1 test zone, the degradation rate on the first day is not so different from that of the SPS single zone, but the degradation rate after the fourth day is higher than that of the SPS single zone, and the degradation effect is also long-term. It was confirmed that it continued for a long time. Moreover, regarding pH, as shown in FIG. 5, pH 3.2-5.2 and weak acidity were shown from the 1st day to the 34th day. In addition, after the 20th, like the oxone single section, etc., the pH gradually increased.

  In the No. 6 4: 1 test section, as shown in FIG. 3, the cis-DCE concentration was 13.27 mg / L after 1 day, 2.93 mg / L after 4 days, and 0.2 after 8 days. It was 0.01 mg / L at the time of 26 mg / L and 12-day progress. Thereafter, it was 6.81 mg / L at the lapse of 15 days, 7.62 mg / L at the lapse of 20 days, 0.87 mg / L at the lapse of 26 days, and 0.21 mg / L at the lapse of 34 days. As shown in FIG. 4, with respect to the degradation rate constant, -0.41 after 1 day, -0.50 after 4 days, -0.60 after 8 days, and -0 after 12 days. .82. Thereafter, it was -0.43 after 15 days, -0.30 after 20 days, -0.69 after 26 days, and -0.83 after 34 days.

  From these results, in the 4: 1 test zone, the degradation rate from the first day to the 12th day is slightly higher than that of the SPS single zone, and the degradation rate after the 20th day is also slightly higher than that of the SPS single zone. It was confirmed that Moreover, regarding pH, as shown in FIG. 5, pH 3.5-6.0 was generally weakly acidic from the 1st day to the 34th day. In particular, after the 20th day, the tendency for pH to be lower than SPS single section was confirmed.

  In the 8: 1 test section of No7, as shown in FIG. 3, the cis-DCE concentration was 16.95 mg / L after 1 day, 5.17 mg / L after 4 days, and 0.2 after 8 days. It was 49 mg / L and 0.03 mg / L at the time of 12 days. Then, it was 6.48 mg / L at the lapse of 15 days, 16.27 mg / L at the lapse of 20 days, 11.03 mg / L at the lapse of 26 days, and 0.62 mg / L at the lapse of 34 days. As shown in FIG. 4, with respect to the degradation rate constant, -0.17 after 1 day, -0.40 after 4 days, -0.59 after 8 days, and -0 after 12 days. .68. Thereafter, it was -0.45 at the lapse of 15 days, -0.14 at the lapse of 20 days, -0.25 at the lapse of 26 days, and -0.71 at the lapse of 34 days.

  From these results, in the 8: 1 test zone, the degradation rate from the first day to the 20th day is almost the same as that of the SPS single zone, and the degradation rate after the 26th day is slightly higher than that of the SPS single zone. It was confirmed that Moreover, regarding pH, as shown in FIG. 5, it changed between pH 3.9-6.2 and weak acidity and neutrality from the 1st day to the 34th day. And generally, the tendency for pH to be slightly lower than SPS single section was confirmed.

  Next, the test results at an oxidant concentration of 0.25% will be described.

  In the SPS single section of No8, as shown in FIG. 6, the cis-DCE concentration was 18.68 mg / L after 1 day, 6.90 mg / L after 4 days, and 1.01 mg / L after 8 days. L, 0.14 mg / L after 12 days. Thereafter, it was 7.18 mg / L after 15 days, 14.36 mg / L after 20 days, 17.94 mg / L after 26 days, and 10.91 mg / L after 34 days. As shown in FIG. 7, with regard to the decomposition rate constant, -0.07 at the lapse of 1 day, -0.33 at the lapse of 4 days, -0.48 at the lapse of 8 days, and -0 at the lapse of 12 days. .50. Thereafter, it was -0.41 at the lapse of 15 days, -0.17 at the lapse of 20 days, -0.16 at the lapse of 26 days, and -0.22 at the lapse of 34 days.

  From these results, the same tendency as the test results at the oxidant concentration of 0.3% was confirmed. That is, in the SPS single section, although the initial decomposition rate was low, it was confirmed that the decomposition effect lasted for a long time. Moreover, regarding pH, as shown in FIG. 8, it changed in pH 5.8-6.6 in the period from the start to the 34th day in the narrow range of neutrality to weak acidity.

  As shown in FIG. 6, the cis-DCE concentration in No. 9 oxone alone was 0.01 mg / L after 1 day, 0.13 mg / L after 4 days, and 0.01 mg / L after 8 days. L, 19.12 mg / L at the elapse of 12 days. Thereafter, it was 29.36 mg / L after 15 days, 43.73 mg / L after 20 days, 54.29 mg / L after 26 days, and 61.26 mg / L after 34 days. As shown in FIG. 7, with respect to the degradation rate constant, -7.6 (not shown) after 1 day, -2.0 (not shown) after 4 days, -0.6 after 8 days. -0.01 at the lapse of 12 days. Thereafter, it was 0.15 at the lapse of 15 days, -0.04 at the lapse of 20 days, -0.06 at the lapse of 26 days, and -0.03 at the lapse of 34 days.

  From these results, it was confirmed that in the oxone alone group, although the initial decomposition rate was extremely high, the decomposition effect was completed in a short period of less than one week. Moreover, regarding pH, as shown in FIG. 8, pH 2.3 and acidity were shown on the 1st day, and pH 3.1-4.2 was weakly acidic in the period from the 4th day to the 34th day. Further, after the 20th day, the pH gradually increased.

  In the 1: 1 test plot of No10, as shown in FIG. 6, the cis-DCE concentration was 0.49 mg / L after 1 day, 0.01 mg / L after 4 days, and 12. It was 0.47 mg / L at the time of 15 mg / L and 12-day progress. Thereafter, it was 0.99 mg / L after 15 days, 1.51 mg / L after 20 days, 1.64 mg / L after 26 days, and 1.88 mg / L after 34 days. As shown in FIG. 7, with regard to the degradation rate constant, -3.7 (not shown) after 1 day has elapsed, -1.3 after 4 days, -0.14 after 8 days, and 12 days have elapsed. It was -0.81 at the time. Thereafter, it was −1.20 at the lapse of 15 days, −0.62 at the lapse of 20 days, −0.51 at the lapse of 26 days, and −0.42 at the lapse of 34 days.

  From these results, it was confirmed that in the 1: 1 test section, the initial decomposition rate was high and the decomposition effect continued for a long time. Moreover, regarding pH, as shown in FIG. 8, pH 2.8 and acidity were shown on the 1st day, and pH 3.5-4.5 and weak acidity were shown from the 4th to the 20th. From the 20th day onward, the pH gradually increased as in the oxone alone group.

  In the 2: 1 test group of No11, as shown in FIG. 6, the cis-DCE concentration was 12.06 mg / L after 1 day, 2.51 mg / L after 4 days, and 0.2 after 8 days. It was 0.05 mg / L at the time of 43 mg / L and 12-day progress. Then, it was 8.71 mg / L at the lapse of 15 days, 16.09 mg / L at the lapse of 20 days, 1.47 mg / L at the lapse of 26 days, and 0.72 mg / L at the lapse of 34 days. As shown in FIG. 7, with respect to the degradation rate constant, -0.51 after 1 day, -0.52 after 4 days, -0.44 after 8 days, and -0 after 12 days. .57. Thereafter, it was -0.33 at the lapse of 15 days, -0.16 at the lapse of 20 days, -0.59 at the lapse of 26 days, and -0.61 at the lapse of 34 days.

  From these results, in the 2: 1 test section, the degradation rate from the 12th day is slightly higher than that of the SPS alone group, the degradation rate from the 12th day to the 20th day is equivalent to the SPS alone group, and The degradation rate after the 20th day was higher than that of the SPS alone group. Moreover, regarding pH, as shown in FIG. 8, pH 3.2-5.8 and weak acidity were shown from the 1st day to the 34th day. In particular, from the fourth day and after the 20th day, it was confirmed that the pH was lower than that of the SPS single section.

  In the No. 12 4: 1 test plot, as shown in FIG. 6, the cis-DCE concentration was 14.75 mg / L after 1 day, 5.28 mg / L after 4 days, and 0.2 after 8 days. It was 88 mg / L and 0.12 mg / L when 12 days passed. Thereafter, it was 7.64 mg / L after 15 days, 14.55 mg / L after 20 days, 9.98 mg / L after 26 days, and 0.98 mg / L after 34 days. As shown in FIG. 7, with respect to the degradation rate constant, -0.30 after 1 day, -0.34 after 4 days, -0.45 after 8 days, and -0 after 12 days. .50. Thereafter, it was -0.39 at the lapse of 15 days, -0.17 at the lapse of 20 days, -0.25 at the lapse of 26 days, and -0.61 at the lapse of 34 days.

  From these results, it was confirmed that in the 4: 1 test section, the degradation rates on the first day and the 34th day were slightly higher than in the SPS single section. Moreover, regarding pH, as shown in FIG. 8, it was generally weak acidity with pH 3.7-6.1 from the 1st day to the 34th day. In particular, for the first day and the 20th day and after, a tendency that the pH was lower than that of the SPS single section was confirmed.

  In the No. 13 6: 1 test section, as shown in FIG. 6, the cis-DCE concentration was 15.75 mg / L after 1 day, 6.11 mg / L after 4 days, and 0.2 after 8 days. It was 0.11 mg / L at the time of 86 mg / L and 12-day progress. Thereafter, it was 6.79 mg / L after 15 days, 14.62 mg / L after 20 days, 16.98 mg / L after 26 days, and 1.45 mg / L after 34 days. As shown in FIG. 7, with respect to the degradation rate constant, -0.24 after 1 day, -0.32 after 4 days, -0.49 after 8 days, and -0 after 12 days. .51. Thereafter, it was -0.43 at the lapse of 15 days, -0.17 at the lapse of 20 days, -0.15 at the lapse of 26 days, and -0.56 at the lapse of 34 days.

  From these results, it was confirmed that the degradation rate from the 1st day to the 34th day was almost the same as that of the 4: 1 test group in the 6: 1 test group. Moreover, regarding pH, as shown in FIG. 8, it showed weak acidity with pH 3.8 about the 1st day, and was lower than SPS single section. However, about the 4th day and after, it changed between pH 5.8-6.5, and the tendency equivalent to SPS single section was confirmed.

  The above results are summarized. When SPS and oxone were mixed and used as the oxidizing agent, it was confirmed that the decomposition efficiency of cis-DCE was increased at the beginning of the reaction from the start to the 12th day, compared with the case of using SPS alone. In particular, when SPS and oxone were used at a weight ratio of 1: 1, it was confirmed that high decomposition efficiency was obtained. On the other hand, even in the test section (2: 2-4: 1) where the mixing ratio of oxone was lowered, it was confirmed that the decomposition efficiency of cis-DCE after the 20th day was increased. This is presumably because iron in the soil (ferric oxide) was in a dissolved state and the iron catalytic effect was generated because the pH of the test section was weakly acidic with 4-5.

  Next, a comparative test will be described. Also in this comparative test, an oxidizing agent (oxone, hydrogen peroxide solution, SPS) and VOC (cis-DCE) were added to a glass container charged with a predetermined amount of mixed soil and water, and the remaining DCE concentration and pH over time. Changes were measured. In addition, since the VOC density | concentration fell by decomposition | disassembly with progress of a test, it added suitably.

  FIG. 9 is a diagram for explaining the composition of each test section in the comparative test. In this comparative test, six types of test sections were prepared by changing the type of oxidizing agent. Hereinafter, each test section will be described. In each test section, a glass container having a volume of 100 mL was used. The mixed soil of mountain sand and clay was 70 g in all cases. In addition, the oxidant concentration was 0.25%.

  The No. 14 test plot is a control plot. In this control group, 95 mL of tap water was added to the mixed soil, and 2 mL of DCE solution (concentration 100 mg / L, the same in the comparative test) was added.

The No. 15 test plot is the SPS single plot. That is, in this test group, 4.0 mL of 10% SPS solution was added. Moreover, the test group of No16 is an oxone single section. That is, in this test group, 4.0 mL of a 10% oxone solution was added. Furthermore, the No. 17 test section is a H ₂ O ₂ single section. That is, in this test group, 1.2 mL of a 35% H ₂ O ₂ solution was added.

The No. 18 test section is a mixed section of SPS and oxone. That is, in the No18 test zone, 2.0 mL of 10% SPS solution and 2.0 mL of 10% oxone solution were added so that the weight ratio of SPS and oxone was 1: 1. The No. 19 test section is a mixed section of SPS and H ₂ O ₂ . That is, in the No19 test plot, 2.0 mL of 10% SPS solution and 0.6 mL of 35% H ₂ O ₂ solution were added so that the weight ratio of SPS and H ₂ O ₂ was 1: 1. For convenience, in the following description, the No. 18 test zone is also referred to as an oxon mixed zone, and the No. 19 test zone is also referred to as an H ₂ O ₂ mixed zone.

  In this comparative test, after measuring at the time of 1 day from the start of the test, after measuring at the time of 7 days, and after measuring at the time of 17 days, each test section of No 14-19 The cis-DCE solution was added to each 2 mL. And cis-DCE density | concentration and pH were measured at the time of a test start, the time of 1 day progress, the time of 7 days progress, the time of 17 days progress, and the time of 26 days progress, respectively.

  In the control group of No14, as shown in FIG. 10, the cis-DCE concentration was 2.26 mg / L after 1 day, 2.92 mg / L after 7 days, and 2.68 mg / L after 17 days. It was 2.55 mg / L after 26 days. As shown in FIG. 12, the pH was neutral from pH 6.6 to 7.3 from the first day to the 26th day.

  In the SPS single section of No15, as shown in FIG. 10, the cis-DCE concentration was 1.85 mg / L after 1 day, 0.10 mg / L after 7 days, and 0.01 mg / L after 17 days. L, 0.01 mg / L after 26 days. Regarding pH, as shown in FIG. 12, it was almost neutral from pH 5.9 to 6.7 from the first day to the 26th day. From these results, it was confirmed that in the SPS single section, although the initial decomposition rate was low, the decomposition effect increased thereafter. This is the same result as the VOC decomposition test described above.

  As shown in FIG. 10, the cis-DCE concentration in No. 16 oxone alone was 0.01 mg / L after 1 day, 0.01 mg / L after 7 days, and 0.01 mg / L after 17 days. L, 0.02 mg / L after 26 days. Regarding pH, as shown in FIG. 12, it showed acidity or weak acidity from pH 2.6 to 3.8 from the first day to the 26th day. From these results, it was confirmed that oxone alone can obtain a high decomposition effect from the beginning.

In the No. 17 H ₂ O ₂ single section, as shown in FIG. 10, the cis-DCE concentration was 1.29 mg / L after 1 day, 2.10 mg / L after 7 days, and 1 after 17 days. It was 1.52 mg / L after 26 days. As shown in FIG. 12, the pH was neutral from pH 6.8 to 7.2 from the first day to the 26th day. From these results, it was confirmed that the H ₂ O ₂ single section had a lower decomposition effect than the other single sections.

  In the oxon mixed section of No18, as shown in FIG. 10, the cis-DCE concentration was 0.01 mg / L at the time of 1 day, 7 days, 17 days, and 26 days. there were. About pH, as shown in FIG. 12, it showed weak acidity with pH 3.1-4.4 from the 1st day to the 26th day. From these results, it was confirmed that a high decomposition effect can be obtained from the beginning in the oxone mixed section.

In the No 19 H ₂ O ₂ mixed section, as shown in FIG. 10, the cis-DCE concentration was 0.01 mg / L after 1 day, 0.01 mg / L after 7 days, and 0 after 17 days. It was 0.96 mg / L after 26 days. Regarding pH, as shown in FIG. 12, it showed acidity of pH 2.2 on the first day. After that, pH 4.1-4.4 and weak acidity were shown. From these results, it was confirmed that in the H ₂ O ₂ mixed section, although the initial decomposition rate was extremely high, the decomposition effect was completed in a short period of about one week.

As shown in FIG. 11, when the oxone mixed group and the H ₂ O ₂ mixed group are compared, it can be seen that there is a large difference in the decomposition effect after the seventh day. That is, after the seventh day, it can be seen that the oxone mixed section has a higher decomposition effect than the H ₂ O ₂ mixed section. This difference is presumed to be due to the fact that SPS and H ₂ O ₂ reacted vigorously in the early stage and the oxidizing power was lost in a short period of time.

  In addition, regarding the oxone alone group and the oxon mixed group, it was confirmed that both of the test groups had a high decomposition effect from the initial stage. When comparing the two test groups, it was considered that the oxone mixed group had a higher decomposition effect than the oxone alone group. For example, with respect to the DCE concentration after 26 days in FIG. 10, the oxone mixed section has a slightly lower result. As described in the VOC decomposition test described above, this is presumed to be because iron in the soil was dissolved and the iron catalytic effect was produced.

  FIG. 13 is a flowchart of the purification method based on the results of the VOC decomposition test and the comparison test described above. Hereinafter, an outline of the purification method will be described with reference to this flowchart.

  First, a sample of the ground to be purified is collected (S1). Here, a ground sample is collected, for example, by excavating the ground to be purified. Once the sample is taken, the organic contaminants (such as VOC) contained in the sample are analyzed. For example, pollutants are extracted into a solvent and analyzed according to JIS K0125. That is, the type and concentration of organic contaminants are measured.

  If the organic pollutant is analyzed, the composition (for example, the concentration and mixing ratio of SPS and oxone) of the purification material composed of a mixed solution of persulfate and hydrogen persulfate, the injection amount, and the injection position are determined (S3). If the mixing | blending etc. of a purification material are determined, a purification material will be inject | poured into a target ground (S4). That is, the purification material is injected through the injection well formed in the target ground. Thereafter, the state of purification of organic pollutants in the target ground is monitored as needed to determine whether additional injection is necessary (S5), and it is determined whether purification of the target ground has been completed (S6).

  Since this purification method uses a mixed solution of persulfate and hydrogen persulfate as a purification material, based on the above test results, a high decomposition effect of organic pollutants can be obtained from the initial stage of injection. It can be said that it will continue for a long time.

  The above description of the embodiment is for facilitating the understanding of the present invention, and does not limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes equivalents thereof. For example, you may comprise as follows.

  Regarding the persulfate, in the above-described embodiment, sodium peroxodisulfate is exemplified, but the present invention is not limited thereto. It may be potassium peroxodisulfate or ammonium peroxodisulfate. In other words, it may be peroxodisulfate.

  Regarding the hydrogen persulfate, in the above-described embodiment, the double salt of potassium hydrogen persulfate is exemplified, but the present invention is not limited thereto. Potassium hydrogen persulfate may be used alone. Moreover, since it is understood that even sodium hydrogen persulfate has the same oxidizing power, this may be used.

  Moreover, although the VOC (cis-DCE) was illustrated regarding the organic pollutant of purification object, it is not limited to this. For example, the present invention can be applied to any organic pollutant that can be decomposed by an oxidizing agent such as oil such as benzene, 1,4-dioxane, and free cyanide.

Claims (1)

A purification method for purifying contaminated ground contaminated with organic pollutants,
A mixed solution obtained by mixing sodium peroxodisulfate as a persulfate and a double salt of potassium hydrogen persulfate as a hydrogen persulfate within a range of 1: 1 to 4: 1 by weight is used as the contaminated ground. A method for purifying contaminated ground, characterized by being injected into the soil.

Images