JP2010046623A - Method of purifying contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of purifying efficiently and economically contaminated soil. <P>SOLUTION: In a bioremediation treatment utilizing a decomposition activity of aerobic microbes to the contaminated soil, the contaminated soil is purified by adding a metal peroxide of a Group II metal as an oxygen release agent, and an organic acid or a mixture of an organic acid and its salt as a neutralizer while satisfying and keeping both of the aerobic property and neutral pH. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for purifying contaminated soil using the decomposition activity by microorganisms. More particularly, the present invention relates to a method for purifying contaminated soil, which maintains aerobic soil and neutral pH and activates and purifies aerobic microorganisms.

  As a result of the enforcement of the Soil Contamination Countermeasures Law (hereinafter referred to as the “Soil-to-Section Law”) in 2003, the number of cases of soil contamination purification is increasing, and as a purification method, bioremediation technology that utilizes microbial degradation activity Development is ongoing.

  In bioremediation, in order to achieve cleanup using aerobic microorganisms such as cyanide compounds and oils in a short time and efficiently, an aerobic environment or neutral region that enhances the degradation activity of microorganisms It is an important key to create and maintain the pH environment.

  As a method for purifying soil contaminated with microorganisms under aerobic conditions, the soil is made into a slurry state with an activated sludge solution, and the slurry is purified by maintaining the aerobic state by supplying oxygen and stirring in a reaction tank. It is known (see Japanese Patent No. 3820180; Patent Document 1). In addition, as a method of maintaining an aerobic state that does not require an oxygen supply device, a method of spraying oxygen-releasing agents such as hydrogen peroxide, calcium peroxide, and magnesium peroxide together with aliphatic salt chlorine compound-degrading bacteria to the soil is proposed. (See JP-A-6-226230; see Patent Document 2). Further, as a treatment for maintaining aerobic properties without installing an apparatus or facility for supplying oxygen, a method of adding an oxygen releasing agent such as peroxide to contaminated soil is known (Japanese Patent No. 3916193). ; See Patent Document 3).

However, the purification in Patent Document 1 requires a dehydration step after the treatment, which is burdened with equipment and treatment.
Patent Document 2 does not mention long-term persistence of oxygen release from hydrogen peroxide, which is a liquid agent, and also measures against pH increase associated with oxygen release from peroxides such as calcium peroxide and magnesium peroxide. Not mentioned.
Patent Document 3 describes countermeasures for increasing the pH associated with oxygen release of peroxide, but it takes a method of loading peroxide into the lower layer of the soil to be treated, and only prevents degradation of the target soil. Thus, no countermeasure is taken against the pH increase in the lower layer loaded, and alkali remains.
From the above, it has been desired to establish an efficient aerobic soil remediation method that makes it possible to maintain and maintain both aerobic and neutral pH in the oxygen release agent addition technique. .

Japanese Patent No. 3820180 JP-A-6-226230 Japanese Patent No. 3961193

  It is an object of the present invention to provide an efficient soil purification method using aerobic bacteria that makes it possible to achieve and maintain both aerobic and neutral pH in the oxygen release agent addition technique.

  As a result of intensive studies to solve the above problems, the present inventors have added an alkaline earth metal peroxide as an oxygen release agent, a biodegradable acid and its salt as a neutralizer, The inventors have found that aerobic and neutral pH can be maintained at the same time and have completed the present invention.

That is, the contaminated soil purification method of the present invention includes the following embodiments 1 to 12.
[1] In a method for purifying contaminated soil using a bioremediation process utilizing biodegradation activity by microorganisms, contaminated soil with a Group 2 metal peroxide as an oxygen release agent and an acid or a mixture of an acid and its salt as a neutralizer A method for purifying contaminated soil, characterized by being added to the soil.
[2] The method for purifying contaminated soil as described in 1 above, wherein the Group 2 metal peroxide used as the oxygen release agent is calcium peroxide and / or magnesium peroxide.
[3] The method for purifying contaminated soil according to 1 or 2, wherein the neutralizing agent is an organic acid or a mixture of an organic acid and a salt thereof.
[4] The organic acid or a mixture of organic acids and salts thereof is selected from succinic acid, citric acid, pyruvic acid, maleic acid, fumaric acid, lactic acid, acetic acid, formic acid, oxalic acid, malic acid, gluconic acid, and tartaric acid. 4. The method for purifying contaminated soil according to any one of 1 to 3, which is at least one organic acid or a mixture of an organic acid and a salt thereof.
[5] The method for purifying contaminated soil according to any one of 1 to 5, wherein the pH is maintained at 5 to 9 and the dissolved oxygen is greater than 0 ppm by the addition of the oxygen releasing agent and the neutralizing agent.
[6] The above-mentioned 1 in which an oxygen release agent and a neutralizing agent are additionally added so that the pH of the treated soil becomes 5 to 9 during the period from the start of the bioremediation treatment until the dissolved oxygen decreases to 0 ppm. The purification | cleaning method of the contaminated soil in any one of thru | or 5.
[7] The method for purifying contaminated soil according to any one of 1 to 6, wherein after the bioremediation treatment starts, a neutralizing agent is additionally added so that the pH of the treated soil becomes 5 to 9.
[8] The method for purifying contaminated soil according to any one of 1 to 7 above, wherein yeast extract and / or peptone is used as a nutrient source for microorganisms.
[9] The method for purifying contaminated soil according to any one of 1 to 8, wherein the target pollutant to be purified is a cyanide compound, oils, and / or a volatile organic compound.
[10] The method for purifying contaminated soil according to any one of 1 to 9, further comprising adding a microorganism having an activity of decomposing the target pollutant to be purified.
[11] The method for purifying contaminated soil as described in 10 above, wherein the target pollutant to be purified is a cyanide compound, and the added microorganism having a cyanide decomposition activity is a microorganism belonging to the genus Arthrobacter.
[12] The method for purifying contaminated soil as described in 11 above, wherein the microorganism belonging to the genus Arthrobacter is Arthrobacter sp. No. 5 strain (FERM P-21400).

  If the soil purification method of this invention is used, the soil purification process by the bioremediation using an aerobic microorganism can be performed efficiently and economically.

Hereinafter, the present invention will be described in more detail.
In the present invention, soil purification treatment with aerobic microorganisms is performed by adding an oxygen release agent, a neutralizing agent, and the like to the soil. The method for adding oxygen release agent, neutralizing agent and the like to the soil and the implementation scale are not particularly limited, and can be performed by a known method in soil purification.

  The oxygen releasing agent, neutralizing agent and the like to be added may be either an aqueous solution or a powder, but it is preferable to mix them so as to diffuse and permeate the soil in both aqueous solutions and powders. When added as an aqueous solution, the increased water may be extracted.

  The treatment temperature is carried out according to circumstances, but when the purification performance is quantitatively confirmed on a lab scale, the soil sample is put in a thermostatic bath or the like and controlled at a temperature of 5 to 50 ° C., preferably 15 to 35 ° C. be able to.

  The timing of adding the oxygen release agent, neutralizing agent, etc. is not particularly limited as long as both aerobic and neutral pH are compatible. Even if each component is added at a separate timing, all components are added simultaneously. Can be either. Further, the number of additions is not limited. From the viewpoint of achieving both aerobic and neutral pH, it is preferable to add all components simultaneously.

[Oxygen release agent]
When a nutrient source is added to the soil, oxygen in the soil is consumed as the aerobic microorganism metabolizes the nutrient source, resulting in an anaerobic state, and the growth and decomposition activity of the aerobic microorganism are eventually greatly reduced. In order to avoid such deterioration in purification performance and maintain an aerobic state, it is effective to add oxygen with equipment installed and repeat soil mixing with heavy machinery, but these are costly Is big.

  Therefore, in the present invention, an oxygen release agent is added as a technique that can reduce the cost burden. The oxygen release agent releases oxygen when dissolved in water, and it is sparingly water-soluble and oxygen release lasts for a long time, so that it is a group 2 metal (Be, Mg, Ca, Sr, Ba, Ra) of the periodic table. The peroxide is used. As the Group 2 metal peroxide, for example, calcium peroxide, magnesium peroxide, or a mixture thereof is preferably used from the viewpoints of economy and oxygen release properties. Moreover, the addition density | concentration can be used normally with 0.001-2.0 w / w% with respect to soil, Desirably about 0.01-0.5 w / w%.

[Neutralizer]
When the oxygen release agent described above is added to the soil, the alkaline earth metal peroxide dissolves in the water, releasing oxygen and simultaneously producing a hydroxide. In order to avoid the increase in pH due to the hydroxide and the decrease in the growth / decomposition activity of microorganisms, the present invention uses an acid or a mixture of an acid and its salt as a neutralizing agent.
Examples of such acids include at least one organic acid selected from succinic acid, citric acid, pyruvic acid, maleic acid, fumaric acid, lactic acid, acetic acid, formic acid, oxalic acid, malic acid, gluconic acid, tartaric acid, and the like. It is preferable to use a mixture of an organic acid and its salt. Biodegradable organic acids and organic acid salts also serve as nutrient sources for microorganisms, and can enhance the degradation activity. Further, when these organic acids are decomposed into microorganisms, the alkaline earth metal hydroxide is carbonated by carbon dioxide generated as a result, so that the effect of neutralization is not impaired.

  Since the neutralizing agent generally exhibits the growth and activation behavior best in the neutral region, it is preferable to add the neutralizing agent so that the pH is 5-9. Further, the neutralizing agent can be added as a buffer solution in which a weak acid and a salt thereof are mixed.

[Nutrition source]
As an additive other than the oxygen release agent and the neutralizing agent, a nutrient source of microorganisms such as a carbon source and a nitrogen source can be added to the contaminated soil in the same manner as a normal bioremediation treatment. The nutrient source to be added is not particularly limited as long as the number of microorganisms and the decomposition activity can be maintained.

  As the carbon source, for example, saccharides such as glucose, sucrose, fructose, and molasses, alone or in combination, are usually 0.001 to 2.0 w / w% with respect to soil, preferably 0.01. It can be used at a concentration of about 0.05% w / w.

  As the nitrogen source, for example, peptone, yeast extract, meat extract, ammonia, ammonium sulfate, ammonium chloride, ammonium phosphate, ammonium nitrate, sodium nitrate, potassium nitrate, urea, etc. alone or in combination can be added to the normal soil. It can be used at a concentration of about 001 to 2.0 w / w%, desirably about 0.01 to 0.05 w / w%.

  Furthermore, if necessary, supply of phosphates such as potassium monohydrogen phosphate and potassium dihydrogen phosphate, metal salts such as magnesium sulfate, ferrous sulfate, calcium acetate and manganese chloride, vitamins, amino acids and nucleic acids Source biotin, thiamine and the like can also be added.

  Among these nutrient sources, it is more preferable to use a yeast extract and / or peptone which are natural products having a large effect on increasing the number of bacteria.

[Addition of bacteria]
In the present invention, in addition to the oxygen release agent, the neutralizing agent, and the nutrient, a microorganism having the activity of degrading the purification target can be added.
The concentration of the microorganism to be added is not limited as long as the decomposition activity can be expressed. However, when considering the diffusion into soil, the penetration and the decomposition activity, 10 ⁶ to 10 ⁹ / g is preferable, and particularly 10 ⁷ to 10 ⁸ / g is more preferable.

Types of microorganisms that can be added to decompose cyanides, oils, and volatile organic compounds include the genus Achromobacter, Acinetobacter, Aeromonas, Arthribacter, Bacillus, Corynebacteriumu, Pseudomonas, Beneckea, Brevibacterium Flavobacterium genus, Fusarium genus, Methylobacter genus, Methylobacteriumu genus, Methylococcus genus, Micromonospra genus, Nocadia genus, Pseudomonas genus, Scytalidium genus, Vibrio genus and the like can be used. Especially for cyan decomposition Arthrobacter.sp. No.5 (FERM No. P-21400) is preferably used, it is preferable to use microorganisms of Pseudomonas genus decomposition of oils, the decomposition of the volatile organic compound Acinetobacter It is preferable to use microorganisms of the genus.
Among these strains, Arthrobacter sp. No. 5 strain preferably used for cyanide degradation was received on October 18, 2007 at the National Institute of Advanced Industrial Science and Technology Patent Biological Deposit Center, receipt number: FERM P Deposited as -21400.

[Addition]
An oxygen release agent and a neutralizing agent can be appropriately added so that the pH of the treated soil becomes 5 to 9 after the start of the bioremediation treatment until the dissolved oxygen starts to decrease to 0 ppm.

[Substance to be purified]
Substances to be purified in the present invention are cyanide compounds, oils, and volatile organic compounds.

  Examples of the cyanide compound include inorganic cyanides such as iron cyano complex, copper cyano complex, metal cyanide complex, nickel cyano complex, potassium cyanide and sodium cyanide, and organic cyanide compounds containing a nitrile group.

  Examples of the oils include alkane hydrocarbons that are chain saturated hydrocarbons, alkene hydrocarbons that are chain unsaturated hydrocarbons such as hexane, octane, undecane, and octadecane, cycloalkanes that are alicyclic hydrocarbons, Examples thereof include aromatic hydrocarbons such as benzene, toluene, naphthalene, and cresol, such as cyclopentane and cyclohexane.

  Furthermore, examples of the volatile organic compound include benzene, toluene, xylene, n-hexane, cyclohexane, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, 1 1,2,2-trichloroethane, trichloroethylene, tetrachloroethylene, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, methylamine, dimethylamine, trimethylamine and the like.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention does not receive any limitation by these description.

Example: Comparison of dissolved oxygen, pH, number of bacteria, and total elution CN by adding each component to soil in a closed system 100 g of a soil sample (specific gravity 1.7 kg / L, moisture content 25%) is put in a 100 L glass container. In accordance with the addition conditions 1 to 7 shown in Table 1, each component was added as an aqueous solution so that the moisture content of the soil sample was 30%, mixed, and then dissolved oxygen (= Dissolved Oxygen = DO) sensor (electrode) Model name: OE-8270, Principle: Diaphragm type galvanic cell method, manufacturer: Toa DKK Corporation, pH sensor (Body type: D-55, Principle: Glass electrode method, manufacturer: Horiba, Ltd.) and exhaust gas recovery line The glass container was covered with a silicon stopper into which (a tube having an inner diameter of 2 mmsus) was inserted. The end of the exhaust gas recovery line was set at the end of the graduated cylinder so that the exhaust gas could be collected in a 50 mL graduated cylinder set upside down in the water charged in the transparent container. . In a process of stationary storage at 30 ° C. for 20 days, DO, pH, and amount of exhaust gas were measured over time, and the number of viable bacteria in the soil sample was measured on the 0th and 20th days on a plate of Nutrient Broth Agar Medium manufactured by DIFCO. A diluted solution obtained by suspending soil with sterile water was applied to the cells and cultured at 35 ° C. for 2 days for measurement. Moreover, the total elution CN of the soil sample was measured on the 0th day and the 20th day. Note that the total CN eluted is the total cyanide concentration in the soil contamination countermeasure method, and was measured according to the Ministry of the Environment Notification No. 18 “Measurement Method for Soil Elution Survey” in FY2003. The unit is mg / L and the soil pollution control law designation standard <0.1.
The measurement results under each addition condition are shown in Table 1.

  Condition 1 was a blank with no added components, but there was almost no change in pH and the number of bacteria, and DO gradually dropped from the initial 2 ppm, and decreased to 1.0 ppm on the 20th day. The total CN eluted was not reduced at all.

Under condition 2 in which only the nutrient was added to the blank, the number of bacteria increased by an order of magnitude from 2 × 10 ⁵ cells / g due to the initial nutrient source and DO, there was almost no pH fluctuation, and DO became 0 ppm. The total CN eluted was slightly reduced with the growth of the fungus.

  Under condition 3 in which only the oxygen release agent calcium peroxide was added, the pH gradually increased from the initial release, and the DO gradually decreased. Under the influence of the increased pH, the number of bacteria died and decreased by an order of magnitude. The total CN eluted was not reduced at all.

  In condition 4 in which calcium peroxide and citric acid were added under the condition that the molar equivalent ratio of citric acid as a neutralizing agent to calcium peroxide in the oxygen release agent was about 0.4, the pH was controlled to 7 units throughout. . Moreover, although DO was also decreasing, it was 4 ppm even on the 20th day, and kept aerobic throughout. As a result, the number of bacteria increased by an order of magnitude using citric acid as a nutrient source. Eluted total CN was reduced to 1.0 mg / L due to bacterial growth, aerobic and neutral pH retention.

  In condition 5 in which yeast extract as a nutrient was further added to condition 4, the growth of the cells was remarkable and increased by two digits. Due to the oxygen consumption of the fungus, the range of decrease in DO was greater than in condition 4. Degradation further progressed from condition 4 due to the effect of adding nutrients, and the total eluted CN was reduced to 0.5 mg / L.

In Condition 6, in which Arthrobacter No. 5 of cyanogen-degrading bacteria was further added to Condition 5, DO disappeared on the 20th day due to the metabolism of the added bacteria and became anaerobic. Due to this effect, the number of bacteria decreased slightly. Eluted total CN was reduced to <0.1 mg / L due to the effect of adding cyanide-degrading bacteria.

  Condition 7 in which succinic acid was added in place of citric acid under the condition that the molar equivalent ratio of oxygen release agent to the oxygen releasing agent was about 0.5 was the same as condition 5 in condition 5.

  In this example, conditions 4, 5, and 7 were able to maintain aerobic (dissolved oxygen is not 0 ppm) and neutral pH in the treatment period of 20 days. In actual processing, the end point of purification is determined by the concentration of the substance to be purified, so a method of adding additional components to cope with the treatment period and the concentration of the substance to be purified is maintained by maintaining the aerobic and neutral pH. be able to.

Claims (12)

  In a method for remediating contaminated soil using bioremediation treatment utilizing biodegradation activity by microorganisms, a Group 2 metal peroxide is added to the contaminated soil as an oxygen release agent and an acid or a mixture of an acid and a salt thereof as a neutralizer. A method for purifying contaminated soil, characterized in that   The method for purifying contaminated soil according to claim 1, wherein the Group 2 metal peroxide used as the oxygen release agent is calcium peroxide and / or magnesium peroxide.   The method for purifying contaminated soil according to claim 1 or 2, wherein the neutralizing agent is an organic acid or a mixture of an organic acid and a salt thereof.   The organic acid or a mixture of an organic acid and a salt thereof is at least one selected from succinic acid, citric acid, pyruvic acid, maleic acid, fumaric acid, lactic acid, acetic acid, formic acid, oxalic acid, malic acid, gluconic acid, and tartaric acid. The method for purifying contaminated soil according to any one of claims 1 to 3, which is an organic acid or a mixture of an organic acid and a salt thereof.   The method for purifying contaminated soil according to any one of claims 1 to 5, wherein the pH is maintained at 5 to 9 and the dissolved oxygen is greater than 0 ppm by the addition of the oxygen releasing agent and the neutralizing agent.   The oxygen release agent and the neutralizing agent are additionally added so that the pH of the treated soil becomes 5 to 9 after the start of the bioremediation treatment until the dissolved oxygen decreases to 0 ppm. The purification method of the contaminated soil in any one of.   The method for purifying contaminated soil according to any one of claims 1 to 6, wherein after the bioremediation treatment is started, a neutralizing agent is additionally added so that the pH of the treated soil becomes 5 to 9.   The method for purifying contaminated soil according to any one of claims 1 to 7, wherein yeast extract and / or peptone is used as a nutrient source of microorganisms.   The method for purifying contaminated soil according to any one of claims 1 to 8, wherein the target pollutant to be purified is a cyanide compound, oils, and / or volatile organic compounds.   The method for purifying contaminated soil according to any one of claims 1 to 9, further comprising adding a microorganism having an activity of decomposing a target pollutant to be purified.   The method for purifying contaminated soil according to claim 10, wherein the target pollutant to be purified is a cyanide compound, and the added microorganism having a cyanide decomposition activity is a microorganism belonging to the genus Arthrobacter.   The method for purifying contaminated soil according to claim 11, wherein the microorganism belonging to the genus Arthrobacter is Arthrobacter sp. No. 5 strain (FERM P-21400).