JP3694294B2 - In-situ purification method for contaminated soil and / or groundwater - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying soil and / or groundwater contaminated with volatile organic chlorine compounds or nitrate nitrogen, and in particular, performs in situ purification of soil and / or groundwater contaminated with volatile organic chlorine compounds or nitrate nitrogen. The present invention relates to a method for injecting and diffusing a cleaning agent.
[0002]
[Prior art]
Conventionally, with respect to groundwater contamination by volatile organic chlorine compounds and nitrate nitrogen, a method of purifying the water by performing water treatment after pumping has been employed (see, for example, Patent Document 1).
Also known is a method of circulating hot water through the aquifer, heating the viscous soil by heat conduction of the ground, promoting the desorption of volatile organochlorine compounds from the soil and purifying them by suction removal (for example, , See Patent Document 2).
[0003]
In addition, a countermeasure method using a permeable purification wall using iron powder or biodegradable polymer (aliphatic polyester resin, starch polymer and protein) is known (for example, see Patent Document 3).
In addition, in a method for decomposing organochlorine compounds in soil and / or groundwater by the action of microorganisms by supplying a hydrogen donor to soil and / or groundwater, the hydrogen donor is selected from the group consisting of acetic acid, formic acid and salts thereof. There is known a method for supplying one or two or more kinds of decomposition inhibitors (for example, see Patent Document 4).
[0004]
In in-situ bioremediation, in which hydrogen donors are supplied to soil and / or groundwater, and organic chlorine compounds in soil and / or groundwater are decomposed by the action of microorganisms, organic chlorine compounds are decomposed, and soil and / or groundwater There is known a method for preventing the secondary contamination by the hydrogen donor and its intermediate product by accelerating the decomposition of the hydrogen donor supplied to (see, for example, Patent Document 5).
[0005]
Further, a method is known in which the temperature of contaminated soil is maintained at a temperature lower than the optimum temperature for the growth and decomposition of decomposing microorganisms, and the magnitude and duration of decomposing activity of the decomposing microorganisms are adjusted (for example, Patent Document 6). reference).
[Patent Document 1]
Japanese Patent Publication No. 6-96143 [Patent Document 2]
Japanese Patent Laid-Open No. 2001-54784 [Patent Document 3]
JP-A-11-156351 [Patent Document 4]
JP 2000-107743 A [Patent Document 5]
JP 2000-259611 A [Patent Document 6]
JP-A-9-267083 [0006]
[Problems to be solved by the invention]
However, Patent Document 1 is intended to move pollutants and is not a technique related to in-situ purification agent injection. In addition, in Patent Document 1, there are many problems such as non-uniformity of the ground and slow movement speed of the substance, and there is a problem that a long period of time is required to purify to an environmental standard value or less.
Further, in Patent Document 2, the purification target area is limited to the vicinity of the suction well, and there is a problem that the purification effect is lost when the suction is stopped.
[0007]
Moreover, in patent document 3, since a purification | cleaning agent is solid, there exists a problem that a purification object area is restricted to the vicinity and downstream.
Moreover, in patent document 4,5,6, since a purification | cleaning agent may spread | diffuse out of the contamination range, and since it does not stay for a long time in a contaminated area, an effect is not maintained and it is necessary to use it in large quantities continuously. There is a problem.
[0008]
In addition, there is a known method of purifying pollutants by injecting potassium permanganate, but there is a risk that it will diffuse out of the contaminated area, and it will not stay in the contaminated area for a long time, so the effect will not continue. is there.
It is also known to purify pollutants by injecting oxidants such as ozone and hydrogen peroxide, but the purifiers themselves are highly toxic and may diffuse out of the contamination range. There is a problem that the duration of the effect itself is very short.
[0009]
In addition, there is a problem that DCE (dichloroethylene) and VC (vinyl chloride) may accumulate in the dechlorination reaction in an anaerobic state with a simple hydrogen donor.
The present invention has been made in order to solve such a conventional problem, and its purpose is to purify the in-situ purification of soil contaminated with volatile organic chlorine compounds or nitrate nitrogen and / or groundwater contamination. It is an object of the present invention to provide an in-situ purification method for contaminated soil and / or groundwater that can reliably inject and diffuse water and maintain the effect of the purification agent.
[0010]
[Means for Solving the Problems]
The invention according to claim 1 is that the purifier having a melting point of 10 to 40 ° C. is heated to a viscosity of 5.0 mpa · s or less, and is contaminated with volatile organic chlorine compounds or nitrate nitrogen in soil or groundwater . Pressurized injection using a chemical solution injection method at a pressure of 1 to 5 kgf / cm ² , diffuses into the contaminated soil and / or groundwater, and is solidified and then decomposed by microorganisms grown under anaerobic conditions to.
[0012]
The present invention is to heat a cleaning agent having a melting point equal to or higher than that in soil and / or ground water, to reduce the viscosity by liquefying, and in a contaminated soil and / or ground water with volatile organic chlorine compounds or nitrate nitrogen In-situ purification of contaminated soil and / or groundwater contamination with volatile organochlorine compounds or nitrate nitrogen, which can be solidified as the temperature drops and control the movement and fixation of the purification agent after being diffused by It is invention regarding the injection | pouring and diffusion method of this.
[0013]
In the present invention, by using in combination with the pumped water recharge method, not only the dechlorination reaction in an anaerobic state but also the movement speed can be controlled and the aerobic decomposition can be promoted.
In the present invention, in order to make the time for the purifier having a melting point of 10 ° C. to 40 ° C. from liquid to solid to be 5 minutes or more in the ground temperature, the injection temperature of the purifier is set to the melting point of the purifier + 20 ° C. or more. . The heating temperature is limited to 70 ° C. in terms of operability and work environment.
[0014]
In addition, the purifier which can be applied to the present invention cannot be used in the present invention if the viscosity does not decrease even when the temperature is raised to the heating limit of 70 ° C. (for example, the viscosity is 1000 mpa · s or more). Moreover, in the state mixed with warm water, since it needs to diffuse after injection | pouring, it needs to be 5.0 mpa * s or less, for example.
The liquefied cleaning agent supplied to soil and / or groundwater contaminated with volatile organochlorine compounds or nitrate nitrogen is solidified in the contaminated soil and / or groundwater, and organic chlorine compounds and nitrate nitrogen in the contaminated soil and / or groundwater. Is decomposed by the action of living organisms. Examples of the organic chlorine compound include TCE (trichloroethylene) and PCE (tetrachloroethylene), DCE (dichloroethylene), carbon tetrachloride, and dichloromethane.
[0015]
When the purification agent liquefied with warm water is supplied to soil contaminated with volatile organic chlorine compounds or nitrate nitrogen and / or groundwater, the liquefied purification agent diffuses widely with warm water.
In that case, the phase change of the purifier is controlled by changing the temperature of the hot water and the injection amount (injection pressure) according to the contamination status. As the temperature decreases, the purification agent can be fixed after being diffused into contaminated soil and / or groundwater.
[0016]
The fixed purification agent can release hydrogen ions around the purification agent for a long period of time, and at the same time, increase the organic carbon concentration of groundwater in the range of 0.1 to 1000 mg / l.
In the present invention, the cleaning agent is a hydrogen donor, which is an organic compound that can be decomposed by microorganisms to generate molecular hydrogen and organic acids or organic substances that can be used by microorganisms.
[0017]
As the hydrogen donor, for example, one consisting of one or more selected from the group consisting of organic acids, organic acid salts, alcohols and proteins / biosurfactants is applicable.
Examples of the organic acid include carboxylic acids such as stearic acid and salts thereof, poly-3-hydroxyalkanoate, poly-3-hydroxybutyric acid, and polyvinyl alcohol.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to embodiments shown in the drawings.
FIG. 1 is a conceptual diagram showing an in-situ purification method for groundwater according to an embodiment of the present invention.
In this embodiment, the example applied to the in-situ purification method in case the contaminant 7 exists in the aquifer 1 is shown.
First, the measurement well 2 is provided in the ground, and the presence of the contaminant 7 in the aquifer 1 is confirmed.
[0020]
Next, a preliminary injection test to be described later is performed to determine the injection pressure of the cleaning agent, the time during which the cleaning agent solidifies, and the heating conditions. Moreover, the pumping well 6 is provided as needed.
Next, pressure is applied through an injection pipe or well 3 installed in the contaminated area, and the heating agent liquefied by heating is injected into the ground and diffused.
Next, since the injected liquefied purification agent 5 is usually in the range of 5 ° C. to 20 ° C., the ground temperature is gradually cooled, and when it becomes below the melting point, it is solidified when dispersed in the target ground. To do.
[0021]
Here, the purification agent 5 is selected to require 10 minutes or more to solidify. At this time, by appropriately setting the water permeability coefficient of the target ground, the temperature characteristics of the purifying agent 5 to be injected (melting point, viscosity change, solubility change), the concentration of the purifying agent 5, the injection amount, the injection pressure, and the heating temperature, 1 It is possible to arbitrarily control the diffusion region of the purifier from the injection pipe or well 3 in the range to a range of 0.5 to 5 m.
[0022]
The heating conditions are determined by the following procedure.
The water permeability of the ground, temperature and groundwater level, viscosity, gap ratio, injection pipe or well 3 etc. are determined by the solidification time of the cleaning agent 5 and the influence range (0.5 to 5 m) by the injection test. Determine heating conditions and injection pressure.
For example, a case where n-hexadecane having 16 carbon atoms (melting point: 18 ° C.) is used as the purifier 5 will be described.
[0023]
The n-hexadecane heated to 30 ° C., 50 ° C., and 70 ° C. to become liquid is mixed with warm water and used. While changing the pressure at an injection pressure of 0.2 kg / cm ² or less per 1 m depth of the target ground, a standard sand injection test and an injection test to the injection target soil are performed at 30 ° C., 50 ° C., and 70 ° C., respectively. For example, as shown in FIG. 2, a graph is created from the result of the injection test on the target soil, and conditions such as the influence range are determined.
[0024]
3 and 4 show the standard sand injection test and the injection test to the soil to be injected at 30 ° C, 50 ° C and 70 ° C.
As an injection method, the liquid purification agent 5 is injected by a pressure pump (infusion pump).
It is also possible to forcibly inject using other compressors suitable for the present invention. After the injection, the influence range can be further expanded by heating the ground.
[0025]
As a heating method, use of hot water, a microwave, or a heater is used.
Confirmation of the completion of the injection of the cleaning agent 5 is generally performed by using a test body excavated by excavation or by a pigment discrimination method (mixing a pigment in the injection material or spraying a reagent in advance) in the same manner as the chemical solution injection method. Confirm with that.
In addition, as an essential measurement item for organic injections, there is a method of measuring the COD concentration in the nearby groundwater and estimating it from the change, but this is auxiliary.
[0026]
PCE and TCE are dechlorinated and decomposed by the action of the released hydrogen ions or hydrogen. The cleaning agent 5 is used as a substrate for decomposing microorganisms such as PCE and TCE.
In addition, microbial activity in groundwater is improved due to the increase in organic carbon concentration, nitrate nitrogen is consumed with the growth of nitrate-reducing bacteria, and organic chlorine compounds such as PCE and TCE are improved due to improved activity of anaerobic microorganisms. Hydrogen substitution dechlorination.
[0027]
Next, FIG. 3 and FIG. 4 show the standard sand injection test and the injection test into the soil to be injected at 30 ° C., 50 ° C., and 70 ° C.
As shown in FIGS. 3 and 4, the injection test apparatus 10 used in this example is manufactured in accordance with a standard sand injection test.
The injection test apparatus 10 is provided with an upper lid 13 provided with a drain pipe 16 provided with a pore (for example, hole diameter φ2 mm) 15 and a cock 17 as in prepact concrete, and an injection pipe 19 provided with a cock 20. A miter box 11 having a bottom plate 18 and fastened by a bolt 21, a pressure / heating tank 25 provided with an inlet 26 for the purifying agent 5, and the pressure / heating tank 25 communicated with each other via a conduit 28. , A pressure line 30 connecting the pressure and heating tank 25 and the injection pipe 19, a pressure gauge 30 provided in the pipe line 29, a drain line 31 provided in the pipe line 29, pressure and heating An exhaust line 32 communicating with the tank 25 and the line 29 is provided.
[0028]
In this injection test apparatus 10, the miter box 11 is filled with standard sand 12 in a loose state (gap ratio around 0.85) and a dense state (gap ratio around 0.65).
Here, when the cleaning agent 5 is injected, a coarse wire mesh 23 is placed on the top of the pebbles 22 under the sand layer so that water does not flow, and the upper lid 13 is covered with a cloth 24 to prevent the sand from flowing out. To do.
[0029]
Next, the liquid cleaning agent 5 is supplied from the pressure and heating tank 25 to the standard sand 12 which is divided into three or five layers in the miter box 11 and tamped while water-tightening, and from the injection pipe 19 at the lower end. Inject and infiltrate into standard sand 12.
Next, when the overflow water from the upper part of the miter box 11 changes to the color of the purifier 5, the injection is stopped, the time required until that time is set as the injection time, and the injection pressure is also changed.
[0030]
As the temperature of the cleaning agent 5 decreases, the viscosity of the cleaning agent 5 increases and the permeability decreases. Moreover, it is necessary to measure the temperature change of the miter box 11 itself.
Next, an injection test for the target soil will be described.
A test according to the standard sand injection test described above is performed on the soil collected from the site. At this time, it is desirable to use a sample that is not disturbed as much as possible. Depending on the soil, there are things that are difficult to collect in an undisturbed state, but in such a case, it is divided into 3 layers or 5 layers and then created.
[0031]
The influence range is calculated using the injection time and injection pressure measured at each heating temperature from the standard sand injection test and the influence range of the mold.
For the calculation, the Karol equation and the Pirson equation are known, but it is necessary to judge together with the result of the on-site test construction (using n-hexadecane in silty soil).
[0032]
In this invention, promotion of the purification effect by ground heating combined use can be aimed at.
As described above, a sufficient purifying effect can be obtained by injecting the purifying agent 5 and leaving it thereafter, but the purifying effect can be further promoted by using ground heating together.
For example, by injecting hot water almost continuously from the injection pipe or well 3 in FIG. 1 and controlling the ground temperature in the area to be purified within a range of 25 ° C. to 40 ° C. Can be expected.
[0033]
The mobility of volatile organic substances (VOC) such as PCE and TCE in groundwater and soil is increased, the number of contact with the purifier is increased, and the purification rate is improved.
By heating the ground, microorganisms in the ground are activated, the ground becomes an anaerobic atmosphere, and the VOC decomposition rate is accelerated.
Denitrifying bacteria are activated by heating the ground in the range of 25 ° C. to 35 ° C., and the denitrification rate of nitrate nitrogen is improved.
[0034]
Heating the ground increases the mobility and solubility of the hydrogen donor, making it easier to contact microorganisms. As a result, the purification effect of both nitrate nitrogen and VOC is enhanced.
In the present invention, for example, as shown in FIGS. 5 and 6, recharging from the pumping well 6 can be performed.
FIG. 5 shows the penetration state when the viscosity of the cleaning agent 5 is small, and FIG. 6 shows the penetration state when the viscosity of the cleaning agent 5 is high (split injection).
[0035]
The following effects can be expected by recharging the hot water from the injection pipe or the well 3 and circulating the pumped water.
The flow rate of groundwater is improved, the removal rate from the ground is improved, and the contact efficiency between the pollutant 7 and the purifier 5 is improved.
Here, as the construction method, the following known construction methods can be considered.
[0036]
Injection of hot water or steam from the injection pipe or well 3 and pumping of hot water from the pumping well 6 are performed.
An electric heater is installed in the injection pipe or well 3, and the ground, and the area to be purified is directly heated.
A microwave is irradiated in the horizontal direction from the inside of the injection pipe or the well 3 or the measurement well 2 to directly heat the groundwater.
[0037]
In the above embodiment, the case where the present invention is applied to the in-situ purification method for groundwater has been described. However, the present invention is not limited thereto, and the in-situ purification method for contaminated soil or the in-situ purification of contaminated soil and groundwater is described. You may apply to a construction method.
[0038]
【Example】
(Example 1)
O Ground conditions VOC contamination in the sand layer, injected at low to medium pressure, and sufficiently diffused (diffusion range 40 to 100 cm).
○ Experimental method Experimental conditions: No pumping recharge Injection pressure: 1 to 2.5 kg / cm ²
Injection volume: 5% solution 2m ³
Cleaner: Biodegradable polymer (decomposes at 10 carbon atoms and releases acetic acid)
Nutrients: Nitrogen, phosphorus, etc. Ground temperature: 15 ° C
Injection temperature: 55 ° C
○ Result It was possible to fix the contaminated groundwater after diffusion of the cleaning agent.
[0039]
As shown in FIG. 7, VOC could be purified by the action of the cleaning agent and nutrients.
As shown in FIG. 7, cis-DCE became below the reference value after 50 days.
As shown in FIG. 8, the TOC (total organic matter) concentration temporarily increased after the injection of the cleaning agent, but it changed to a low concentration after 20 days.
[0040]
(Example 2)
○ Ground conditions Mainly sandy silt, partly lenticular sand layer. The purifier was heated with warm water and fluidized, and then injected with a high-pressure pump, and diffused unevenly in the ground (diffusion range 10 cm to 150 cm).
[0041]
After injection, purification was promoted by ground heating by hot water injection.
○ Experimental method Experimental conditions: Recharge pumping. Recharge with warm water (40 ° C) on the 40th day.
Injection pressure: 3-5 kg / cm ²
Injection amount: 10% solution 1m ³
Cleaner: Biodegradable polymer (decomposes at 10 carbon atoms and releases acetic acid)
Nutrients: Nitrogen, phosphorus, etc. Ground temperature: 15 ° C
Injection temperature: 65 ° C
○ Results Diffusion range of the split injection in the non-uniform ground was narrow. Due to the slow purification rate, hot water was injected after 40 days. Therefore, hydrogen was further released from the diffused purifier, and the decomposition and purification of the organochlorine compound proceeded (see FIGS. 9 and 10).
[0042]
(Example 3)
It was confirmed that the effect of purifying VOC by the solid hydrogen donor was promoted by heating.
○ Experimental method Initial concentration: cis-DCE 9.2 mg / l, TCE 0.45 mg / l, PCE 0.17 mg / l
Cleaner: Biodegradable polymer (C9, decomposes to generate acetic acid)
Nutrient salts: Nitrogen, phosphorus, etc. Culture method: Static culture in sealed glass bottles at 15 ° C, 20 ° C, 30 ° C ○ As a result, TCE and PCE can be decomposed by adding organic substances to groundwater collected at contaminated sites (See FIGS. 11, 12, 13, and 14).
[0043]
As shown in FIG. 12, cis-DCE has a slower decomposition rate than TCE shown in FIG. 11, PCE shown in FIG. 13, and the like, but a clear decrease was observed when the culture temperature was 30 ° C.
As is apparent from FIGS. 11, 12, 13, and 14, the decomposition rate of VOCs could be improved by increasing the culture temperature from 15 ° C. → 20 ° C. → 30 ° C.
[0044]
【The invention's effect】
According to the present invention, by controlling the phase change of a purifier such as a hydrogen donor, and moving and fixing in a groundwater, it is possible to purify a wide range of groundwater pollutants at a low cost and quickly. .
According to the present invention, the contact efficiency between the pollutant and the purifying agent is remarkably deteriorated due to the unevenness of the ground, and the purification period can be shortened in the contaminated area that requires time until the completion of the purification.
[0045]
In addition, according to the present invention, the required number of injection wells can be reduced, and the cost of well installation can be reduced.
Moreover, according to this invention, the effect of a purifier can be maintained and the influence range can be controlled.
Moreover, according to the present invention, not only an anaerobic state can be created, but also purification of DCE (dichloroethylene) and VC (vinyl chloride) can be promoted.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an in-situ purification method for groundwater according to an embodiment of the present invention.
FIG. 2 is a graph showing a relationship between a heating temperature and a moving distance at the time of injecting a purifying agent in the in-situ purification method for groundwater according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram showing a standard sand injection test applied to an in-situ purification method for groundwater according to an embodiment of the present invention.
FIG. 4 is an explanatory view showing a standard sand injection test applied to an in-situ purification method for groundwater according to an embodiment of the present invention.
FIG. 5 is a conceptual diagram showing an in-situ purification method for groundwater according to an embodiment of the present invention.
FIG. 6 is a conceptual diagram showing an in-situ purification method for groundwater according to an embodiment of the present invention.
FIG. 7 is a graph showing changes in VOC concentration in Example 1 of the present invention.
FIG. 8 is a graph showing a change in TOC concentration in Example 1 of the present invention.
FIG. 9 is a graph showing changes in VOC concentration in Example 2 of the present invention.
FIG. 10 is a graph showing a change in TOC concentration in Example 2 of the present invention.
FIG. 11 is a graph showing changes in TCE concentration in Example 3 of the present invention.
FIG. 12 is a graph showing changes in cis-DCE concentration in Example 3 of the present invention.
FIG. 13 is a graph showing changes in PCE concentration in Example 3 of the present invention.
FIG. 14 is a graph showing an ORP (redox potential) change in Example 3 of the present invention.

Claims (1)

A cleaner having a melting point of 10 to 40 ° C. is heated to a viscosity of 5.0 mpa · s or less, and is contaminated with volatile organic chlorine compounds or nitrate nitrogen in soil or groundwater at a pressure of 1 to 5 kgf / cm ² . Contaminated soil and / or groundwater characterized by being injected under pressure using a chemical solution injection method , diffused into the contaminated soil and / or groundwater, solidified and then decomposed by microorganisms grown under anaerobic conditions In-situ purification method.

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