KR101290546B1 - Method of purifying soil and/or groundwater - Google Patents

Abstract

In purifying soil and / or groundwater contaminated with hardly decomposable organic compounds, it is an object to provide an effective purification method with a low environmental load, and to purify the dicarboxymethylamine-based biodegradable chelating agent of the formula After addition at a molar ratio of 0.5 to 4.0 times the iron ions present in the soil and / or ground water of interest to produce a complex of the biodegradable chelating agent and the iron ions, the clarification subject is preferably pH 5 to 5 using a pH buffer. The purification is carried out by the addition of an oxidizing agent while keeping it at 10.

Formula 1

Hardly degradable organic compounds, soil, groundwater, purification, dicarboxymethylamine biodegradable chelating agents, pH buffers, oxidants

Description

Method of purifying soil and / or groundwater

The present invention provides a method for purifying soil and / or groundwater using conventional hydrogen peroxide as an oxidizing agent, which is capable of contaminating the purification without lowering the pH of the purification target, shortening the purification treatment period, and The present invention also relates to a method of purifying soil and / or groundwater that can be purified.

It has been found that the pollution of organic matter in soil and / or groundwater greatly affects the environment, and various regulations have been maintained, and at the same time, it is necessary to purify the pollution accumulated and left unattended. The organic substance herein refers to a hardly decomposable organic substance which is difficult to be decomposed by living organisms. Examples of the organic substance include pesticides, preservatives, petroleum and aromatic compounds contained in oils thereof, and chlorinated organic compounds.

For the organic contamination, various physical, chemical and biological purification methods have been attempted. In the physical purification method, it is possible to purify a contaminated site, but there is a drawback that a secondary treatment of the removed pollutant is required. Biological purification is a method that has little effect on the surrounding environment, but has a drawback that it is difficult to apply to high concentrations of pollution. On the other hand, the chemical purification method does not require secondary treatment in order to decompose the pollutants of interest, and is applicable to high concentrations of pollution.

By adding an oxidizing agent such as hydrogen peroxide and a compound capable of supplying iron ions as a catalyst (e.g. ferrous sulfate, hexahydrate, etc.), hydroxy radicals are generated, and the radicals and organics are reacted to oxidize and decompose organic matters. Fenton method is known. Among chemical purification methods, the Fenton method is applied to purify soil contaminated with hardly decomposable organic compounds (Japanese Patent Laid-Open No. 7-75772 (Patent Document 1)).

In normal Fenton method, the optimum pH range is said to be 3-4. In the case where the pH range is more than neutral, the reaction rarely proceeds because the iron ions of the catalyst become hydroxide and precipitate out. However, when it is assumed that the soil purification is performed in such an optimum pH range of pH 3 to 4, there is a possibility of occurrence and expansion of secondary pollution by the elution of heavy metal components in the soil. It is proposed to purify to a constant pH near neutral using a buffer. In JP-A-2004-202357 (Patent Document 2) and JP-A-2004-305959 (Patent Document 3), addition of an oxidizing agent and a buffer in order to prevent a drop in pH due to decomposition of contaminated organic matter. Has been devised, but means for preventing precipitation in the high pH range of metal ions, such as iron, are not specified, and metal components contained in groundwater, such as iron, depending on the type of oxidant and the environment of the purification site. Blockage of the flow path and piping due to precipitation of water may cause problems in the purification operation.

In addition, addition of an oxidizing agent and a chelating agent has been devised to prevent precipitation of metal ions serving as a catalyst such as iron. In Japanese Unexamined Patent Publication No. 2002-159959 (Patent Document 4), a chelating agent is added mainly for the purpose of preventing precipitation of iron. However, since the use pH range is acidic, the range of the prescribed molar ratio is specified. Is a small amount of about 1/3 of iron, and considering the pH range of the liquid, there remains a risk of causing secondary contamination such as elution of heavy metals. Moreover, although Unexamined-Japanese-Patent No. 2000-301172 (patent document 5) uses the chelating agent and the oxidizing agent together, the addition of the chelating agent is only for the purpose of preventing precipitation of metal ions, such as iron, There is no means for preventing the pH drop, and considering the pH range of the liquid, there is a high possibility of causing secondary contamination such as elution of heavy metals.

Addition of chelating agents in neutral vicinity has also been devised. In Japanese Laid-Open Patent Publication No. 2003-503197 (Patent Document 6), it is proposed to add a chelating agent mainly on EDTA. However, EDTA is biodegradable, and when used in actual soil purification, especially in situ purification, there is a possibility that it will greatly affect the surrounding environment, such as ecosystem, it is expected to be a big problem in use. Further, as described in Patent Literature 5, the lack of the addition amount of the chelating agent causes precipitation of metal ions, and the excessive addition decreases the purification effect, and therefore, there is a high possibility that the purification cannot be effectively performed in any case.

Problems to be solved by the invention

The present invention has been proposed in view of the above-mentioned problems of the prior art, and is a simple method of purifying soil and groundwater contaminated with hardly decomposable organic compounds in situ without affecting the surrounding environment, ecosystem and others. It is an object of the present invention to provide a method for purifying soil and / or groundwater that can be applied, furthermore, can be safely and effectively purified in a short period of time, and also capable of purifying high concentration pollution.

Means for solving the problem

MEANS TO SOLVE THE PROBLEM The present inventors earnestly researched in order to solve the above-mentioned problem, and, as a result, the biodegradable chelating agent is added to the purification object to form iron ions, followed by the addition of an oxidizing agent, and preferably, further purification by adding a pH buffer. By the treatment, it is found that there is no possibility of secondary contamination by the elution of heavy metals, and it is possible to purify the metal ions such as iron, which are catalysts for the decomposition reaction of the contaminants, and to purify efficiently. The present invention has been reached.

That is, this invention relates to the purification method as described in following (1)-(7).

(1) A method for purifying soil and / or groundwater, wherein the dicarboxymethylamine-based biodegradable chelating agent of the following formula (1) is added to the purification target in a molar ratio of 0.5 to 4.0 times the iron ions present in the purification target, and the biodegradation is performed. A biodegradable chelating agent addition step of generating a complex of the chelating agent and iron ions, and an oxidizing agent addition step of maintaining the purification target at pH 5 to 10 and adding an oxidizing agent after the formation of the complex, .

In the above formula (1)

R is an organic group containing no nitrogen atom

X is H or an alkali metal.

(2) In the above item (1), R in the formula (1) is -CH (CH ₃ ) COOX, -CH (COOX) C ₂ H ₄ COOX, -CH (COOX) CH ₂ COOX or -C ₂ H ₄ SO ₃ X, wherein X is H or an alkali metal.

(3) The purification method according to item (1) or (2), wherein in the oxidizing agent addition step, the purification target is maintained at pH 7 to 9 and oxidizing agent is added.

(4) At least 1 according to any one of items (1) to (3), wherein at least one selected from the group consisting of sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate in the oxidizing agent addition step Purification method characterized by adding the pH buffer of the species.

(5) The purification method according to any one of items (1) to (4), wherein the oxidant is hydrogen peroxide.

(6) The method according to any one of items (1) to (5), wherein before the step of adding the biodegradable chelating agent, the pH of the purification target is lowered from 6 or more to 5 or less and 6, and the iron ions in the soil are eluted in the groundwater. A purification method comprising a pretreatment step.

(7) The purification method according to any one of items (1) to (6), which includes a pretreatment step of adding iron ions to the purification target before the biodegradable chelating agent addition step.

Effects of the Invention

The purification method of the present invention has the following effects.

(1) In the high pH range in which heavy metals do not elute, contaminating organic compounds can be decomposed at a remarkable and rapid decomposition rate without inhibiting the reaction of the decomposition agent (iron chelating complex as oxidant and catalyst).

(2) Since the formation and precipitation of hydroxides in the high pH range of metal ions such as iron as catalysts can be effectively prevented, purification is possible without causing blockage of the soil and / or groundwater flow paths or piping by the precipitate. Work can be done.

(3) The agent used is a biodegradable chelating agent, and a very low environmental load such as hydrogen peroxide as an oxidant and carbonate as a pH buffer can be used.

(4) Purification can be performed even for high concentration pollution.

Therefore, according to the present invention, it is possible to safely clean the soil and / or groundwater contaminated with the organic compound in a short time. In addition, it is possible to clean in situ without significantly affecting the surrounding environment such as ecosystem.

In the present invention, the soil and / or ground water to be purified is contaminated with hardly decomposable organic matter. Examples of the organic substance include agrochemicals, preservatives, petroleum and aromatic compounds contained in oils thereof, organochlorine compounds and the like. Toluene, benzene, etc. are mentioned as an aromatic compound contained in petroleum and its fraction. Trichloroethylene (TCE), tetrachloroethylene (PCE), etc. are mentioned as an organochlorine compound.

Hydroxy radicals produced by the reaction of hydrogen peroxide and iron ions of the present invention have strong oxidizing power and are adaptable to soil contamination of not only organic chlorine compounds but also toluene, benzene and oil-based soils.

The purification method of the present invention is a biodegradable chelate in which a biodegradable chelating agent is added to the purification target at a molar ratio of 0.5 to 4.0 times the iron ion present in the purification target to generate a complex of the biodegradable chelating agent and iron ions. And an oxidant addition step of maintaining the purification target at a pH of 5 to 10 and adding an oxidant after the complex formation.

(1) Biodegradable Chelating Agent Addition Process

Iron ions present in the purification target generate hydroxy radicals by reaction with an oxidizing agent to oxidatively decompose the organic pollutants in the purification target. Therefore, it is good if iron ion is contained in the purification object in the density | concentration so that it can oxidatively decompose efficiently. Although the iron ion concentration in a preferable purification object depends also on a contamination level, it is about 15-100 mg / L, for example.

If the iron ions originally exist in the groundwater and / or soil in an appropriate amount, it is not necessary to add them separately. However, depending on the conditions such as the purification period, it is also possible to improve the effect and shorten the purification treatment period by adding iron ions to the purification target as a pretreatment in advance. When adding iron ions, the compound which can supply iron ions to a purification object can be added. Examples of the compound capable of supplying iron ions include iron salts such as ferrous sulfate and ferrous chloride. There is no restriction | limiting in particular in the usage-amount of iron salt, It selects suitably according to the level of pollution required. In general, the amount of iron salt added is 0 to 0.1% by weight based on the total amount of the purification target in terms of ferrous sulfate. As a method for supplying iron salt, a method of supplying iron salt in an aqueous solution to the soil and / or ground water by means of a facility such as a well installed in the soil may be mentioned. As a density | concentration of aqueous solution of iron salts, O-10 weight% is preferable.

In order to suppress elution of heavy metals, it is preferable to perform the biodegradable chelating agent addition process in this invention, without lowering the pH of a purification object (maintaining pH 5 or more). However, when the pH of the purification target is 6 or more, it may be adjusted to 5 or more and less than 6, and pretreatment may be performed to elute iron ions in the soil into groundwater. The pretreatment is a method of eluting iron in the groundwater to lower the pH to 5 or less by adding acidic components such as inorganic acids such as hydrochloric acid and sulfuric acid or organic acids such as acetic acid to the soil and / or ground water. The biodegradable chelating agent is then added. In this way, when the pH of the purification target is 6 or more, it is possible to supply the required amount of iron ions to the groundwater by adjusting it to 5 or more and less than 6 in advance. In other words, when the iron ions in the groundwater are insufficient, the pH of the purification target is slightly acidic, so that the iron ions in the ground are dissolved in the groundwater and the required iron ion concentration can be ensured without adding iron salts from the outside.

As a method of supplying an acid component for pretreatment, the method of supplying the acid component made into aqueous solution to the soil and / or groundwater by installation, such as a well installed in the soil, is mentioned. As concentration of an acid component aqueous solution, 0-10 weight% is preferable.

Although the biodegradable chelating agent to be added is recognized as biodegradable in the biodegradability test and the intrinsic biodegradability test shown in the OECD guidelines, among these, the dicarboxymethylamine chelating agent of the following formula (1) is used.

Formula 1

In the above formula (1)

R is an organic group containing no nitrogen atom

X is H or an alkali metal.

Examples of the alkali metal of X include sodium (Na) and potassium (K).

Preferably, R represents an organic group having 1 to 10 carbon atoms, more preferably 1 to 4 carbon atoms, which does not contain a nitrogen atom. More preferably, R represents an organic group containing no nitrogen atom, and contains at least one selected from the group consisting of -COOX and -SO ₃ X. More preferably, R represents an organic group having 1 to 4 carbon atoms that does not contain nitrogen atoms, and includes at least one selected from the group consisting of -COOX and -SO ₃ X.

Particularly preferred among the dicarboxymethylamine-based biodegradable chelating agents of Chemical Formula 1, R in Chemical Formula 1 is -CH (CH ₃ ) COOX, -CH (COOX) C ₂ H ₄ COOX, -CH (COOX) CH ₂ COOX or —C ₂ H ₄ SO ₃ X where X is H or an alkali metal.

Examples of such dicarboxymethylamine biodegradable chelating agents include methylglycine diacetic acid, glutamic acid diacetic acid, aspartic acid diacetic acid, 2-aminoethanesulfonic acid diacetic acid, and sodium salts thereof. By addition of the chelating agent, a complex of iron ions present in the object of purification can be produced, and formation and precipitation of iron hydroxide can be prevented.

If the addition of the chelating agent is insufficient, precipitation of iron hydroxide is caused, and if the addition of the chelating agent is excessive, the purification is inhibited. Therefore, the chelating agent is preferably used at a molar ratio of 0.5 to 4.0 times the amount of the chelating agent. In particular, the molar ratio of the chelating agent 1.0 to 2.0 times with respect to 1 mol of iron ions is preferable because of the high effect of the addition of the chelating agent. As a supply method of a chelating agent, the method of supplying the chelating agent which became aqueous solution to the soil or groundwater by facilities, such as a well installed in the soil, is mentioned. The supply can be carried out continuously or intermittently. As concentration of the chelating agent aqueous solution, 50-5000 mg / L is preferable.

(2) oxidizer addition process

In the purification method of the present invention, after the formation of the complex, the purification target is maintained at pH 5 to 10 and an oxidant is added (oxidant addition step). After the formation of the complex of the biodegradable chelating agent and iron ions, the purification target is maintained at a high pH range and the contaminated organic matter is decomposed, so that elution of heavy metals can be suppressed, and formation and precipitation of iron hydroxide can be suppressed.

Examples of the oxidizing agent include hydrogen peroxide, percarbonate, percarbonate, perborate, perboric acid, peracetic acid, peracetate, and the like, but hydrogen peroxide is most preferable in terms of influence on the surrounding environment, operability, price, and versatility. The hydrogen peroxide injection concentration varies depending on the degree of contamination, the amount of water injected into the soil, and the amount of pumped water, but 0.5 to 5% by weight is preferable with respect to the amount of water injected. In general, there is no restriction on the amount of hydrogen peroxide used, and it is appropriately selected according to the pollution situation, the surrounding environment, and the purification period. As a supply method of an oxidizing agent, the method of supplying the oxidizing agent made into aqueous solution to the soil and / or groundwater by facilities, such as a well installed in the soil, is mentioned. The supply can be carried out continuously or intermittently. As concentration of the oxidizing agent aqueous solution, 0-35 weight% is preferable.

In the said oxidizing agent addition process, since it is preferable to add an oxidizing agent in the pH range in which the effect of a chelating agent is exhibited, it is necessary to maintain the purification object at pH 5-10, Preferably it is pH 7-9. However, when an oxidizing agent is added, decomposition of the contaminated organics in the purification target may proceed, and the pH of the purification target may decrease. For this reason, it is preferable to add the pH buffer which can give the said pH range.

Although the pH buffer can be suitably selected and used, such as a carbonate type, a phosphate type, an acetic acid type, A carbonic acid type buffer is preferable considering the point which can control to pH 7-9 which is the most effective, and environmental load. As the carbonic acid-based buffer, sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate and the like can be used. Examples of the phosphate buffer include disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and the like. Acetic acid, sodium acetate, etc. can be used as an acetic acid type buffer.

Among them, from the viewpoint of cost, solubility, and pH, it is preferable to use sodium hydrogencarbonate alone or to use sodium hydrogencarbonate and sodium carbonate together. Moreover, it is also preferable to use acetic acid and sodium acetate together.

If the pH of the purification target is in the range of 5 to 10, even if the pH decreases, it is not necessary to add a pH buffer, but in order to shorten the purification period, it is preferable to control the pH to 7 to 9 by adding a pH buffer. As a buffer supply method, the method of supplying the aqueous solution which made into the target pH to soil or groundwater by facilities, such as a well installed in the soil, is mentioned.

Although the purification method of this invention assumes the use in the purification process of the soil and / or groundwater in the original position first, it is not limited to this, It is applicable also to the secondary process which is not the original position.

Example

The embodiment implemented using this invention is shown below. The examples do not limit the scope of the invention.

<Examples 1-6, Comparative Examples 1-9>

In a 134 ml vial bottle, 15 mg-Fe / L of FeSO ₄ · 7H ₂ O and an chelating agent are equimolarly added to iron ions to form an iron chelate complex. Thereafter, simulated contaminated water in which tetrachloroethylene (PCE) was dissolved at a concentration of 19 to 28 mg / L as a volatile organic compound, 680 mg / L (for pH range 5 to 6), or 63 mg / L (pH range) to hydrogen peroxide Conditions at 7 to 8), or 660 mg / L (conditions at pH range 9 to 10), and a buffer with a combination of sodium bicarbonate / sodium carbonate or acetic acid / sodium acetate to maintain a constant pH in the reaction solution After the addition, it was sealed and the purification test was done. After a certain time (1 h) from the start of the reaction, the concentration of PCE in the liquid was measured to confirm the progress of the purification. Methylglycine diacetic acid (sodium salt; trade name "Trilon (trilon) M" (registered trademark), BASF Japan Corporation), L-glutamic acid diacetic acid (sodium salt; Tokyo Kasei reagent) When the chelating agent is not added as a comparison to Examples 1 to 6 in Table 1, the results of using gluconic acid and ethylenediamine disuccinic acid which are biodegradable but outside the claims of the present application are shown in Comparative Example 1 in Table 1. To 9 are shown.

In the case of using the chelating agent within the claims of the present application shown in Examples 1-6, the decomposition of PCE was 45% or more, and the effect of promoting the PCE decomposition reaction by the addition of the chelating agent was shown at pH 5-10. However, in the case where the chelating agents shown in Comparative Examples 1, 4 and 7 were not added and the chelating agents outside the claims shown in Comparative Examples 2, 5 and 8 were added, the progress of the PCE decomposition reaction was hardly observed. In addition, when the chelating agent other than the claims shown in Comparative Examples 3, 6, and 9 were added, PCE decomposition proceeded, but the amount of PCE decomposition was about half or less of the chelate in the claims of the present application under the same pH conditions. From the above result, it was shown that addition of the specific biodegradable chelating agent prescribed | regulated by this invention is very effective at the decomposition | disassembly of organochlorine compound in pH 5-10.

<Examples 7 to 14, Comparative Examples 10 to 16>

In a 134 ml vial bottle, 15 mg-Fe / L and a chelating agent are previously added to FeSO ₄ .7H ₂ O to form an iron chelate complex. The chelating agent changed the addition amount by the molar ratio with respect to the added iron ion. Thereafter, simulated contaminated water in which tetrachloroethylene (PCE) was dissolved at a concentration of 26 to 52 mg / L as a volatile organic compound, and a combination of sodium bicarbonate / sodium carbonate to maintain a constant pH of 7 to 9 in the reaction solution. 65 mg / L of a buffer and hydrogen peroxide were added, and it sealed and performed the purification test. After a lapse of 1 hour from the start of the reaction, the concentration of PCE in the liquid was measured to confirm the progress of the purification. The results of using methylglycine diacetic acid and glutamic acid diacetic acid as chelating agents are shown in Examples 7 to 11 and 12 to 14 in Table 2, and the results at addition molar ratios other than the claims of the present patent are shown in Comparative Examples 10 to 12 in Table 2. In Comparative Examples 13 to 16 in Table 2, results of using ethylenediamine tetraacetic acid, which is biodegradable and outside the scope of the present patent, are shown.

In Examples 7 to 11 using methylglycine diacetic acid, the added molar ratio of the chelating agent was 0.5 to 4.0 times with respect to the iron ions, and the residual PCE concentration was low at the added molar ratio in this range, and the decomposition of PCE was sufficiently progressed. However, in Comparative Examples 10 to 11, the addition molar ratio of the chelating agent was in the range other than 0.5 to 4.0 times with respect to the iron ions. In this case, the residual PCE concentration was high and the PCE decomposition reaction did not proceed significantly. In addition, although precipitation of iron hydroxide was not seen in Examples 7-11 and Comparative Example 11, it was confirmed clearly in Comparative Example 10.

In Examples 12 to 14 using glutamic acid diacetic acid, the residual PCE concentration was low at the addition molar ratio within the claims of the present application, and the decomposition of PCE was sufficiently proceeded as in the case of using methylglycine diacetic acid. In particular, when the added molar ratio of the chelating agent was 2 or more with respect to the iron ions, the decomposition rate was higher than 55%. However, in the addition amount of the chelating agent outside the claims of the present application, a decrease in the PCE decomposition rate was confirmed (Comparative Example 12).

In Comparative Examples 13 to 16 using ethylenediamine tetraacetic acid, precipitation of iron hydroxide was not observed. However, when the addition molar ratio of the chelating agent shown in Comparative Examples 14 to 16 was 2 or more with respect to iron ions, the progress of the PCE decomposition reaction was almost It was not seen, and it was shown that addition of excess chelating agent inhibited the decomposition reaction.

From the above results, it was found that the chelating agent having the structure and performance specified in the present invention has an addition molar ratio of 0.5 to 4.0 times to the iron ions within the scope of the present application, and is very effective in the decomposition of the organochlorine compound.

According to the present invention, since after forming a complex of a biodegradable chelating agent and iron ions having a very low environmental load, the purification target is maintained at a high pH range and an oxidizing agent is added, thereby preventing secondary contamination by the elution of heavy metals. It is possible to effectively prevent clogging the flow path or the pipe due to the generation and precipitation of iron hydroxide.

Therefore, the soil and / or groundwater contaminated with the organic compound can be efficiently and safely purified in a short time, and can be purified in situ without particularly affecting the surrounding environment such as an ecosystem. It is also very effective for the purification treatment for high concentration contamination.

Claims (7)

As a method for purifying soil, ground water, or both thereof, a dicarboxymethylamine-based biodegradable chelating agent represented by Chemical Formula 1 is added to the purification target in a molar ratio of 0.5 to 4.0 times the iron ions present in the purification target. Soil, groundwater, characterized in that it comprises a step of adding a biodegradable chelating agent to produce a complex of a chelating agent and iron ions, and an oxidizing agent adding a oxidizing agent after maintaining the pH of the purified object after the formation of the complex Or a purification method of both. Formula 1

In the above formula (1) R is an organic group containing no nitrogen atom, X is H or an alkali metal. The compound of claim 1, wherein R in Formula 1 is -CH (CH ₃ ) COOX, -CH (COOX) C ₂ H ₄ COOX, -CH (COOX) CH ₂ COOX or -C ₂ H ₄ SO ₃ A process for the purification of soil, ground water or both, characterized by representing X, wherein X is H or an alkali metal. The method for purifying soil, groundwater or both according to claim 1 or 2, wherein in the oxidizing agent addition step, the purifying object is maintained at pH 7 to 9 and the oxidizing agent is added. The method according to claim 1 or 2, wherein in the oxidizing agent addition step, at least one pH buffer selected from the group consisting of sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate is added. Purifying soil, groundwater or both. The method of claim 1 or 2, wherein the oxidant is hydrogen peroxide. The soil according to claim 1 or 2, comprising a pretreatment step of eluting iron ions in the soil in groundwater by lowering the pH of the purification target from 6 or more to 5 or less than 6 before adding the biodegradable chelating agent. Methods of Purifying Groundwater or Both The method for purifying soil, ground water or both according to claim 1 or 2, further comprising a pretreatment step of adding iron ions to the purification target before the biodegradable chelating agent addition step.