JP6152631B2 - Purification method for contaminated soil - Google Patents

Description

  The present invention relates to a method for purifying soil contaminated with an organic chlorine compound such as chlorinated ethylene by an in-situ bioaugmentation method, and in particular, purifies by injecting anaerobic chlorinated ethylene-degrading bacteria into the soil. Regarding the method.

  As a method for remediating soil contaminated with volatile organic chlorine compounds, etc., if there are indigenous microorganisms that decompose volatile organic chlorine compounds at the contaminated site, add nutrient sources for the microorganisms to the target areas for contamination purification. Biostimulation methods that promote the degradation of pollutants by activating these microorganisms have been put into practical use. In addition, a bioaugmentation method in which microorganisms having a high decomposing ability for volatile organic chlorine compounds are cultured and administered to a contaminated site or the like for purification is also performed.

  Methods for dechlorination of volatile organochlorine compounds by microorganisms include dechlorination methods by aerobic microorganisms and dechlorination methods by anaerobic microorganisms.

  In dechlorination by an aerobic microorganism, co-metabolism can be caused by supplying toluene, phenol, methane as an electron donor and oxygen as an electron acceptor to the ground. Dechlorination by aerobic microorganisms has a high rate of dechlorination, but because microbial growth and dechlorination are independent, it acquires extra energy to grow microorganisms apart from dechlorination A carbon source is needed.

  In the case of dechlorination by anaerobic microorganisms, energy is acquired in conjunction with dechlorination by halogen respiration, so there is no need for a carbon source to acquire extra energy for growth like co-metabolism, Efficiency is good.

Since anaerobic microorganisms have their survival or growth inhibited by oxygen, it is necessary to remove free oxygen for the survival or growth of anaerobic microorganisms. Aerobic bacteria are the catalase and superoxide needed to break down the toxic substances of free oxygen.
It has enzymes such as dismutase, but anaerobic bacteria do not have these enzymes, and active oxygen acts lethally. Therefore, prior to bioaugmentation, sugars and organic acids are added to the ground, and tetrachloroethylene and trichlorethylene are decomposed by the reductive dechlorination reaction of indigenous anaerobic microorganisms existing in the ground. Has been made (Patent Document 1).

JP2012-86191

  In the method of Patent Document 1, the soil reduction treatment period is affected by the type and concentration of organic matter in the soil, the type and concentration of indigenous microorganisms, and even if it is desired to shorten the reduction treatment period, it is effective for that purpose. There was no means.

  An object of the present invention is to provide a method for purifying contaminated soil that can efficiently purify soil contaminated with an organic chlorine compound such as chlorinated ethylene in a short period of time by an in-situ bioaugmentation method.

The method for purifying contaminated soil according to the present invention comprises a nutrient injection step for injecting a nutrient solution into soil contaminated with an organic chlorine compound to make the soil anaerobic, and then water containing chlorinated ethylene-decomposing bacteria into the soil. In a method for purifying contaminated soil having a chlorinated ethylene-decomposing bacteria injection step for injecting 10 ⁶ to 10 ^9, facultative anaerobic microorganisms capable of decomposing the nutrient before, after or simultaneously with the nutrient injection step. the water containing facultative anaerobic microorganisms comprising at cell / mL concentration, and is characterized in carrying out the facultative anaerobic microorganisms containing water injection step of injecting into the soil.

The passing anaerobic microorganisms, particularly Trichoderma genus bacteria is preferred.

  It is preferable to perform the chlorinated ethylene-decomposing bacteria injection step after the ORP of soil or groundwater becomes −100 mV or less by the nutrient injection step and the nutrient-degrading microorganism injection step.

  The concentration of the nutrient in the nutrient solution injected in the nutrient injection step is 100 to 10,000 mg / L as carbon, and the pH of the nutrient solution is preferably 6 to 8.

  When a nutrient and a nutrient-degrading microorganism are injected into soil contaminated with an organochlorine compound, the microorganism decomposes the nutrient, and oxygen in the soil is consumed at this time, and the soil becomes anaerobic. In particular, when facultative anaerobic microorganisms such as Trichococcus bacteria are used as microorganisms, the soil becomes anaerobic in a short period of time. When the chlorinated ethylene-decomposing bacteria are injected after the soil becomes anaerobic in this way, the growth rate of the chlorinated ethylene-decomposing bacteria increases and efficient purification can be performed.

It is explanatory drawing of embodiment. It is explanatory drawing of an Example and a comparative example.

  Hereinafter, the present invention will be described in more detail.

  In the present invention, the soil to be treated (may be groundwater in the soil) is soil or groundwater contaminated with an organic chlorine compound such as chlorinated ethylene. Examples of chlorinated ethylene include tetrachloroethylene (PCE), trichlorethylene (TCE), cis-1,2-dichloroethylene (cis-DCE), trans-1,2-dichloroethylene (trans-DCE), 1,1-dichloroethylene (1, 1-DCE), vinyl chloride (VC), and their dechlorinated intermediates.

  In the present invention, nutrients and nutrient-degrading microorganisms are added to the soil to be purified in advance and kept in an anaerobic state, thereby making the soil a reducing atmosphere (preferably the ORP of the soil or groundwater is −100 mV or less).

As the nutrient-degrading microorganism, anaerobic microorganisms, particularly facultative anaerobic microorganisms are preferable, and Trichococcus bacteria are particularly preferable. The nutrient-degrading microorganism is desirably injected into the soil as microorganism-containing water having a concentration of 10 ⁶ cells / mL or more, for example, 10 ⁶ to 10 ⁹ cells / mL.

  The nutrient-degrading microorganisms may be injected either before, during or after the nutrient injection. In the case of anaerobic microorganisms other than facultative anaerobic microorganisms, it is preferable to be at the time of or after the injection of the nutrient.

  Suitable nutrients include sugars such as glucose, starch, acetic acid, citric acid or salts thereof, methanol, ethanol, peptone, yeast extract, biodegradable polymers such as polylactic acid, triglycerides, fatty acids, etc. Particularly preferred is acetic acid, citric acid or a salt thereof.

  The volume of the nutrient solution to be injected in the nutrient injection step is preferably in the range of 0.1 to 10 times the amount of the nutrient-containing microorganism-containing water injection amount. If the volume of the nutrient solution is too small, the nutrient-degrading microorganisms cannot be dispersed widely. In addition, when the volume of the nutrient solution is excessively large, nutrient-degrading microorganisms spread in a donut shape in the soil, resulting in uneven processing efficiency.

  The nutrient solution concentration of the nutrient solution used in the nutrient solution injection step is preferably in the range of 100 to 10,000 mg / L, particularly 1000 to 3000 mg / L as carbon. When the nutrient concentration is too low, the hydrogen required for the nutrient-degrading microorganisms to degrade the nutrient is insufficient, and when the nutrient concentration is too high, the activity of the nutrient-degrading bacteria is inhibited. The pH of this nutrient solution is preferably in the range of 6-8.

  Thus, after injection of nutrients and nutrient-degrading microorganisms, it was confirmed that the ORP in the soil was suitable for the growth of chlorinated ethylene-degrading bacteria, preferably the ORP was -100 mV or less, for example, -100 to -200 mV. In addition, by injecting chlorinated ethylene-decomposing bacteria, the chlorinated ethylene-degrading bacteria grow rapidly, and organic chlorine compounds such as chlorinated ethylene are efficiently decomposed.

  As a chlorinated ethylene-degrading bacterium, a Dehalococcides bacterium having a chlorinated ethylene-degrading activity is suitable.

When injecting chlorinated ethylene-decomposing bacteria into soil, dehalococcides bacteria may be injected alone, or a culture solution obtained by culturing dehalococcides bacteria with other bacteria may be injected. The concentration of the bacterium belonging to the genus Dehalococcides in the culture solution to be injected into the soil is preferably about 10 ⁹ to 10 ¹² cells / L. Such a culture solution is about 10 ⁷ to 10 ⁹ cells / L in the soil. It is preferable to inject so that it may become a density | concentration.

  In injecting chlorinated ethylene-decomposing bacteria into the soil, it is preferable to prevent a decrease in the activity of microorganisms due to contact with oxygen. In order to prevent a decrease in the activity of microorganisms due to contact with oxygen, it is preferable to make the inside of a tank storing chlorinated ethylene-decomposing bacteria-containing water (hereinafter sometimes referred to as a culture solution) a nitrogen gas atmosphere.

  Hereinafter, an example of a soil purification method according to the method of the present invention will be described with reference to FIG.

  An impermeable layer 3 or a hardly permeable layer exists at a predetermined depth from the ground surface 1, and an aquifer 2 exists above the impermeable layer 3. 4 is the groundwater level. An injection well 6 is provided to reach the impermeable layer 3 near the most upstream part of the groundwater flow direction in the contaminated groundwater existing area W, and nutrient solution, facultative anaerobic microorganisms, and chlorinated ethylene-decomposing bacteria culture medium are placed in the soil. Inject.

Hereinafter, Example 1, Reference Example 1, and Comparative Example 1 will be described. In Example 1, Reference Example 1, and Comparative Example 1, the test apparatus shown in FIG. 2 was used. In this test apparatus, a natural soil is filled in a container C having a width of 5 m, a depth of 5 m, and a height of 5 m, and a vinyl chloride pipe P having a diameter of 25 mm is installed vertically (vertically) in the center. In this container C, 25 m ^{3 of} city water was poured to prepare on-site simulated soil. A slit is provided in the lower 3 to 5 m of the PVC pipe so that water (simulated groundwater) can be sampled. The water temperature can be adjusted to 20 ° C.

  The conditions of the aqueous nutrient solution solution, facultative anaerobic microorganism, and chlorinated ethylene-degrading bacterium used in the test are as follows.

Aqueous nutrient solution: trisodium citrate dihydrate (concentration 1 wt%) and ammonium dihydrogen phosphate (concentration 0.05%) facultative anaerobic microorganisms: Trichococcus bacteria Chlorinated ethylene-decomposing bacteria: Halococcoides bacteria

[Example 1]
When 100 mL of groundwater was collected from the pipe and ORP was measured, it was +80 mV. Next, 1 m ^{3 of} an aqueous nutrient solution was injected at 100 L / h from the central pipe, and subsequently 1 L of a facultative anaerobic microorganism culture solution (bacterial concentration of 10 ⁶ cells / L) was injected from the pipe.

Two hours later, 100 mL of simulated groundwater was collected from the pipe and analyzed for ORP. As a result, it was -100 mV. In addition, 100 mL of groundwater was collected from the pipe, 1 mL of the above nutrient solution was added, 1 mg / L resazurin was dropped, taken into a 150 mL vial, the headspace was replaced with N ₂ gas, and then sealed with butyl rubber. . Next, 1 mL of a culture solution containing 10 ¹¹ cells / mL of dehalococcides was inoculated, and 0.22 mL of chloroethylene gas (corresponding to 6.0 mg / L) was immediately injected into the headspace.

  The culture was continued at 30 ° C. for 1 week, the chloroethylene concentration in the headspace was measured, and the chloroethylene concentration in the water in the vial and the chloroethylene decomposition rate were calculated. The results are shown in Table 1.

[Reference Example 1]
The test was conducted in the same manner as in Example 1 except that a facultative anaerobic microorganism culture solution to be injected was used having a bacterial concentration of 10 ⁴ cells / L.

  Similar to Example 1, the ORP of the simulated groundwater measured after 2 hours was +20 mV.

  Table 1 shows the chloroethylene concentration in the water in the vial and the calculated value of the chloroethylene decomposition rate based on the measurement result of the chloroethylene concentration in the headspace measured after one week in the same manner as in Example 1.

[Comparative Example 1]
The test was conducted in the same manner as in Example 1 except that no facultative anaerobic microorganism culture solution was injected.

  Similar to Example 1, the ORP of the simulated groundwater measured after 2 hours was +80 mV.

  Table 1 shows the chloroethylene concentration in the water in the vial and the calculated value of the chloroethylene decomposition rate based on the measurement result of the chloroethylene concentration in the headspace measured after one week in the same manner as in Example 1.

As shown in Table 1, according to an example in which a culture solution containing 10 ⁶ cells / mL or more of facultative anaerobic microorganisms is injected together with a nutrient before injecting a culture solution containing chlorinated ethylene-decomposing bacteria, It can be anaerobic, can prevent a decrease in the activity of chlorinated ethylene-decomposing bacteria due to contact with oxygen, and can perform in-situ bioaugmentation well.

1 Ground 6 Injection well

Claims (2)

A nutrient injection process for injecting a nutrient solution into soil contaminated with organochlorine compounds to make the soil anaerobic,
Then, in the purification method of contaminated soil having a chlorinated ethylene-decomposing bacteria injection step of injecting chlorinated ethylene-decomposing bacteria-containing water into the soil,
Previous the nutrients implantation step, after or simultaneously, the water containing facultative anaerobic microorganisms containing the nutrient degradable facultative anaerobic microorganisms at ¹⁰ 6 ~10 9 cell / ^mL concentration, injected into the soil A method for purifying contaminated soil, comprising performing a step of injecting water containing facultative anaerobic microorganisms.   The method for purifying contaminated soil according to claim 1, wherein the facultative anaerobic microorganism is a genus Trichococcus.

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