JP6212842B2 - Purification method for contaminated soil - Google Patents

Description

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

  As a purification method for soil and groundwater contaminated with volatile organic chlorine compounds, it is called bioaugmentation, in which microorganisms with high degradability for volatile organic chlorine compounds are cultured and administered to the contaminated site for purification. There is technology (Patent Document 1).

  In the method of Patent Document 1, anaerobic microorganisms and nutrients are diluted with deoxygenated water (tap water, groundwater, industrial water, etc.) and injected into the soil to disperse the microorganisms over a wide area. It is intended to improve the decomposition efficiency of chlorine compounds. According to the method of this patent document 1, it can inject | pour into soil, without reducing the activity of anaerobic microorganisms, and can perform favorable bioaugmentation.

JP2011-194307

  The method of Patent Document 1 requires an aerobic biofilm treatment apparatus for deoxygenating diluted water, and therefore there are a variety of necessary processes such as start-up of this apparatus, installation on the site, removal work, and industrial waste treatment. There was a problem that it was complicated.

  The present invention provides a method for purifying contaminated soil capable of efficiently purifying soil contaminated with an organic chlorine compound such as chlorinated ethylene, and further groundwater in the soil by an in-situ bioaugmentation method. With the goal.

The method for purifying contaminated soil according to the present invention includes a first nutrient solution injection step for injecting a nutrient solution into soil contaminated with an organic chlorine compound to make the soil anaerobic, and then chlorinated ethylene in the soil. a chlorinated ethylene-decomposing bacteria implantation step of implanting degrading bacteria containing water, then have a second nutrient injection step of injecting a nutrient solution into the soil, the first nutrient solution injection step and the The nutrient solution to be injected in the nutrient solution injection step of 2 is citric acid and / or a salt thereof, the chlorinated ethylene-degrading bacterium is a bacterium belonging to the genus Dehalococcides, and soil or After the ORP of the groundwater becomes -100 mV or less, a chlorinated ethylene-decomposing bacteria injection step is performed, and the concentration of the nutrient in the nutrient solution injected in the second nutrient injection step is 100 to 10,000 mg / L as carbon. And PH of the nutrient solution is 6-8, but the injection amount of the nutrient solution is 100 to 10000 times the chlorinated ethylene-decomposing bacteria-containing water injected by the chlorinated ethylene-decomposing bacteria injection process.

  When nutrients are injected into soil contaminated with organochlorine compounds, tetrachloroethylene and trichlorethylene are decomposed by a reductive dechlorination reaction by indigenous general anaerobic microorganisms, and cis-1,2-dichloroethylene (hereinafter cis-). May be referred to as DCE), and the concentration of cis-DCE increases. When chlorinated ethylene-decomposing bacteria are injected into the soil having a high cis-DCE concentration, the growth rate of dehalococcides bacteria having chlorinated ethylene-degrading activity is increased, and efficient purification is performed. Can do.

  When the nutrient is injected again after the injection of the chlorinated ethylene-decomposing bacteria, the soil can be kept anaerobic and the chlorinated ethylene-decomposing bacteria can be grown. Moreover, when the injection of nutrients is started immediately after the injection of chlorinated ethylene-decomposing bacteria, the effect of diffusing the chlorinated ethylene-decomposing bacteria in the soil is also exhibited.

  In using an anaerobic chlorinated ethylene-degrading bacterium, it is necessary to prevent a decrease in the activity of microorganisms due to contact with oxygen. According to the present invention, diluting water can be obtained by injecting nutrients into the soil in advance. Without using an aerobic biofilm treatment device for deoxygenating, it can be injected into the soil and grown in the soil without reducing the activity of anaerobic chlorinated ethylene-degrading bacteria, Good bioaugmentation can be performed.

It is explanatory drawing of embodiment. It is explanatory drawing of the reference example 1. FIG. It is explanatory drawing of the reference example 2. FIG.

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

  In the present invention, the soil or groundwater to be treated 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 are exemplified. In the present invention, tetrachloroethylene and / or trichlorethylene is particularly contained at a high concentration, for example, as a main component, and cis-1,2 -Soil with a low concentration of dichloroethylene, particularly lower than the growth maintenance concentration, and further groundwater in the soil are suitable as treatment targets.

  The microorganism used in the present invention for decomposing chlorinated ethylene is preferably a bacterium belonging to the genus Dehalococcides having chlorinated ethylene decomposing activity, and in particular, the activity of decomposing vinyl chloride (VC) alone into ethylene. Dehalococcides bacteria having the above are preferred.

  In the present invention, by adding a nutrient agent in advance to the soil or groundwater to be purified and keeping it in an anaerobic state, the reductive dechlorination reaction of a general anaerobic microorganism indigenous decomposes tetrachloroethylene and trichlorethylene, cis-DCE is generated and a reducing atmosphere (preferably the ORP of soil or groundwater is −100 mV or less).

  Tetrachloroethylene and trichlorethylene are decomposed by a reductive dechlorination reaction by an indigenous general anaerobic microorganism in an anaerobic state to produce cis-1,2-dichloroethylene (hereinafter sometimes referred to as cis-DCE), and cis. -The concentration of DCE increases. In soil or groundwater in which the concentration of cis-DCE is high and anaerobic, the growth rate of dehalococcides bacteria having chlorinated ethylene decomposition activity is increased, and efficient purification is performed. Can do.

  Any nutrient may be used as long as it has an effect of decomposing tetrachloroethylene or trichloroethylene to produce cis-DCE by a reductive dechlorination reaction by an indigenous general anaerobic microorganism, and its composition and concentration are limited. Various types can be used. Preferred nutrients include at least one selected from citric acid, lactic acid, propionic acid, butyric acid, sucrose, and salts thereof, and have a density of 1.05 g / mL or more, preferably 1.2 to 1.3 mg. The thing adjusted to / mL is mentioned. It is preferable to add such a nutrient to the range of 0.1 to 10 g / L, preferably 0.5 to 5 g / L per soil or groundwater. As a frequency of injecting the nutrient, it is preferable to repeat the addition at intervals of 1 to 6 months, particularly 3 to 4 months.

  Since the growth rate of the genus Dehalococcides is proportional to the cis-DCE concentration, injecting the genus Dehalococcides at a low cis-DCE concentration results in a slow growth of the genus Dehalococcides in the soil. The Dehalococcides bacterium injected into the basin is diluted by being washed downstream by groundwater flowing from the upstream, and the growth rate of the genus Dehalococcides is reduced. Therefore, in order to rapidly inject the injected Dehalococcides bacteria in the area to be purified, the cis-DCE concentration in the soil at the time of the injection of Dehalococcides bacteria is determined by the growth of the Dehalococcides bacteria. It is preferable that the concentration is increased above the maintenance concentration. The growth maintaining concentration of the genus Dehalococcides is a cis-DCE concentration at which the growth amount of the genus Dehalococcides is larger than the diluted effluent amount due to the groundwater flow. It is desirable to determine the conditions for injecting nutrients.

  In this way, after adding nutrients, after confirming that the ORP and substrate (cis-DCE) concentrations in the soil are conditions suitable for the growth of chlorinated ethylene-degrading bacteria such as dehalococcides bacteria, chlorine By injecting a chlorinated ethylene-decomposing bacterium, the chlorinated ethylene-decomposing bacterium rapidly grows and an organic chlorine compound such as chlorinated ethylene is efficiently decomposed.

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 groundwater. It is preferable to inject | pour so that it may become a density | concentration.

  A bacterium belonging to the genus Dehalococcides having chlorinated ethylene decomposing activity contains tetrachloroethylene and trichloroethylene at a high concentration and grows in soil or groundwater having a low concentration of cis-1,2-dichloroethylene, but has a low growth rate. In contrast, dehalococcides bacteria have a high growth rate in soil or groundwater with a high concentration of cis-1,2-dichloroethylene. Since the growth rate of Dehalococcides bacteria is proportional to the concentration of cis-1,2-dichloroethylene, if the Dehalococcides bacteria is injected with a high concentration of cis-1,2-dichloroethylene, the growth rate is increased. Speed increases and purification efficiency improves.

  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 inject water containing chlorinated ethylene-decomposing bacteria (hereinafter sometimes referred to as a culture solution) as described below. That is, if the ORP of the soil is -100 mV or less, the culture solution is injected by inserting an injection pipe (such as a hose) on the outlet side of the culture solution tank below the groundwater surface of the aquifer.

  If the aquifer is a confined aquifer, it may be injected directly into the well pipe without using a hose (the air remaining in the well is very small, and the first nutrient injection process is Is consumed). When the ORP of the soil is -100 mV or higher, it is preferable to inject the culture solution after confirming that the nutrient solution is additionally injected and the ORP is -100 mV or lower.

  After the culture solution injection step, a second nutrient injection step is performed. Thereby, the activity of chlorinated ethylene-decomposing bacteria can be maintained, the soil can be kept anaerobic, and the organic chlorine compounds can be efficiently decomposed.

  In addition, since it is necessary to open the well to the atmosphere when injecting the culture solution, it is desirable to inject additional nutrients as soon as possible in order to reduce the influence of oxygen contamination from the atmosphere. For example, the second nutrient injection step is started immediately after the culture solution injection, for example, within 3 hours, particularly within 1 hour. The volume of the nutrient to be injected in the second nutrient injection step is desirably in the range of 100 to 10,000 times the amount of the culture fluid injected. If the nutrient solution is too small, the microorganisms cannot be dispersed extensively. Moreover, when there is too much capacity | capacitance of a nutrient, microorganisms will spread in donut shape in soil, and nonuniformity will generate | occur | produce in processing efficiency.

  The nutrient solution concentration of the nutrient solution used in the second nutrient solution injection step is preferably in the range of 100 to 10,000 mg / L as carbon. If the nutrient concentration is too low, the hydrogen required for the chlorinated ethylene-decomposing bacteria to decompose chlorinated ethylene is insufficient, and if the nutrient concentration is too high, the activity of the chlorinated ethylene-degrading bacteria is inhibited. Further, the pH of this nutrient solution is preferably in the range of 6 to 8, and the ORP is preferably +200 mV or less, particularly preferably −100 mV or less.

  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 so as to reach the impermeable layer 3 in the vicinity of the most upstream portion in the groundwater flow direction of the contaminated groundwater existing area W, and a nutrient solution or an anaerobic microorganism culture solution is injected into the soil.

  The aqueous nutrient solution solution stored in the tank 10 is supplied to the injection well 6 via the pump 11, and the culture solution is supplied from the tank 12 to the injection well 6 via the metering pump 13.

  Nitrogen gas is introduced into the top of the tank 12 from a nitrogen gas cylinder 14 via a pressure control valve (not shown), and the atmosphere above the tank 12 is changed to a nitrogen atmosphere.

  The reason why nitrogen gas is supplied into the tank 12 from the nitrogen gas cylinder 14 is to prevent air from flowing into the tank 12 from the outside as the culture fluid flows out of the tank 12 and the dispersion level decreases. is there.

Hereinafter, Reference Example 1 and Reference Example 2 will be described. In Reference Example 1, the test apparatus shown in FIG. 2 was used, and in Reference Example 2, the test apparatus shown in FIG. 3 was used. In these test apparatuses, Toyoura standard sand is spread on 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 this container C, 25 m ^{3 of} city water was poured to prepare on-site simulated soil. In addition, a slit is provided in the lower 3 to 5 m of the PVC pipe so that water can be sampled.

  In Reference Example 1 (FIG. 2) corresponding to the embodiment, the nutrient solution and the culture solution are poured into the container C from the tanks A and B. Reference Example 2 (FIG. 3) corresponding to the comparative example has the same configuration as Reference Example 1 (FIG. 2) except that the nutrient solution is passed through the activated carbon column D and then supplied to the container C. ing.

  The conditions of the nutrient solution, anaerobic microorganism, and culture solution used in the test are as follows.

Nutrient solution: trisodium citrate dihydrate (concentration 10 g / L) and nitrogen and anaerobic microorganisms and a phosphorus: cell concentration of de Haro Cocco y des bacterium cultures: 10 ⁹ / L

[Reference Example 1]
1 m ³ of the nutrient solution was injected into the 10 Hr container C from the pipe P at 100 L / Hr. One week later, 100 mL of water was collected from the pipe P and analyzed for ORP. As a result, the groundwater ORP was -180 mV. Therefore, 1 L of an anaerobic microorganism culture solution was injected from the pipe P, and immediately thereafter, 1 m ^{3 of} an aqueous nutrient solution was injected at 100 L / Hr for 10 hours.

  After completion of the injection, 100 mL of groundwater was collected from the pipe P, and 2 mL thereof was injected into 100 mL of simulated groundwater in a 150 mL vial prepared as described below, and then immediately 0.22 mL (6.0 mg / mL) of chloroethylene gas. (Corresponding to L) was injected into the head space. The culture was continued at 30 ° C. for 1 week, the chloroethylene concentration in the head space was measured, and the chloroethylene concentration in the simulated groundwater was calculated.

  As a result, the chloroethylene concentration in the simulated groundwater was 0.01 mg / L, and the chloroethylene decomposition rate was 100%.

<Method for preparing simulated groundwater>
100 mL of 1 wt% sodium citrate hexahydrate, 0.05 wt% ammonium dihydrogen phosphate, and 1 mg / L resazurin dissolved in city water was placed in a 150 mL vial, and the head space was changed to N After substituting with ₂ gas, it is sealed with butyl rubber and left at 30 ° C. for 3 days. Resazurin is colorless and reduced to form simulated groundwater.

[Reference Example 2]
In Reference Example 1, when supplying the nutrient solution to container C, the nutrient solution was continuously passed through an activated carbon column (activated carbon name: Mitsubishi Calgon F400, 3 kg packed) kept at 30 ° C. at a water flow rate of 100 L / Hr. Watered. After confirming that the redox potential of the water collected at the column outlet was −188 mV, it was injected into the container C via the pipe P. All other tests were performed under the same conditions as in Reference Example 1. Then, 2 mL of sampled water is injected into the simulated groundwater under the same conditions as in Reference Example 1, immediately chloroethylene gas is injected into the head space, and culture is continued at 30 ° C. for one week, and the chloroethylene concentration in the head space is measured. The chloroethylene concentration in the simulated groundwater was calculated.

  As a result, the chloroethylene concentration in the simulated groundwater was 0.01 mg / L, and the chloroethylene decomposition rate was 100%.

  From the above, it was found that according to Reference Example 1, it was possible to inject into the soil without reducing the activity of the anaerobic chlorinated ethylene-decomposing bacteria without using an activated carbon column. Moreover, since the injection volume of the nutrient solution is the same in Reference Examples 1 and 2, it is possible to disperse microorganisms in the same range by the method of Reference Example 1, and good bioaugmentation. It was recognized that can be done.

1 Ground 6 Injection well

Claims (1)

A first nutrient solution injection step for injecting a nutrient solution into soil contaminated with an organic chlorine compound to make the soil anaerobic;
Then, a chlorinated ethylene-decomposing bacteria injection step for injecting chlorinated ethylene-decomposing bacteria-containing water into the soil,
Then, we have a second nutrient injection step of injecting a nutrient solution into the soil,
The nutrient to be injected in the first nutrient solution injection step and the second nutrient solution injection step is citric acid and / or a salt thereof,
The chlorinated ethylene-decomposing bacterium is a genus Dehalococcides
After the ORP of soil or groundwater becomes -100 mV or less by the first nutrient injection process, the chlorinated ethylene-decomposing bacteria injection process is performed,
The concentration of the nutrient in the nutrient solution injected in the second nutrient injection step is 100 to 10,000 mg / L as carbon, and the pH of the nutrient solution is 6 to 8, and the nutrient solution is injected. The method for purifying contaminated soil, wherein the amount is 100 to 10,000 times the chlorinated ethylene-decomposing bacteria-containing water injected in the chlorinated ethylene-decomposing bacteria injection step .

Images