JPH09234489A - Restoration method for polluted ground water and soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable rapid decomposition and removal and to enable the decomposition and removal of the contaminants of unsatd. strata as well at the time of executing purification and restoration by bioremediation. SOLUTION: Plural wells 21, 22 are excavated to the saturation strata 12 near the underground polluted point 1 polluted with the contaminants and >=2 horizontal electrodes 24, 25, 26, 27 parted from each other in a vertical direction, are embedded near the underground polluted point 1. Drains 28, 29 are installed between the underground polluted point 1 and the horizontal electrodes 24, 27. While voltage is impressed among the respective horizontal electrodes 24, 25, 26, 27, the ground water is pumped up from the well 22 existing on the downstream side of the underground water stream 5. At least one kind among oxygen, nutrient sources for the bacteria for decomposing the contaminants in the soil and substrate are added to at least a part of the ground water and, thereafter, the saturation strata 12 are impregnated with the water from the well 21 existing on the upstream side of the ground water stream 5 of the underground polluted point 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for repairing and purifying soil and groundwater contaminated with organic chlorine compounds such as trichloroethylene and tetrachloroethylene and pollutants such as waste oil.

[0002]

2. Description of the Related Art Recently, bioremediation (also called in-situ bioremediation) utilizing biotechnology has been attracting attention as a purification method for removing pollutants from such contaminated soil and groundwater. Bioremediation is a technology that decomposes and detoxifies pollutants by utilizing the function of microorganisms that live in the soil, and artificially enhances and uses the purification function originally possessed by the soil ecosystem. .

FIG. 3 schematically shows an example of a purification method by a conventional bioremediation technique.
Reference numeral 2 in the figure is a saturated layer in which groundwater flows. In this method, two or more wells 3 and 4 are excavated in the saturated layer 2 in the vicinity of the underground contaminated site 1 contaminated with pollutants such as organic chlorine compounds and oil. At least a part of the groundwater pumped from the pumping well 4 drilled on the downstream side of the groundwater flow 5 is guided to the substrate adding means 6 to supply methane, phenol, air (oxygen), and nutrient sources which are growth substrates for the degrading bacteria. In addition, this is injected into the injection well 3 drilled on the upstream side and circulated. As a result, the activity of the pollutant-degrading bacteria present in the saturated layer 2 and the like can be enhanced, and the pollutant can be efficiently decomposed and removed, and the restoration method has high cost performance.

[0004]

However, in this purification method by bioremediation, pollutants of organic chlorine compounds such as trichlorethylene are present in a liquid state or are adsorbed by clay and organic matter in soil. Many of them are removed, and these are gradually released into the groundwater, which has the disadvantage that it takes a relatively long time to remove them. In addition, although it is possible to decompose and remove pollutants in the saturated layer where groundwater is saturated, it is difficult to decompose and remove in the unsaturated layer where the groundwater is unsaturated and there is a gap where air etc. exist. There is such a problem.

An object of the present invention is to provide a method capable of decomposing and removing in a short time when purifying and repairing by bioremediation and also capable of decomposing and removing contaminants in an unsaturated layer.

[0006]

In order to solve the above-mentioned problems, the invention according to claim 1 excavates a plurality of wells in a saturated layer in the vicinity of an underground polluted site contaminated with pollutants, and the underground pollution. By embedding two or more horizontal electrodes in the vicinity of the place while vertically separating them, and applying a voltage between each horizontal electrode,
Groundwater is pumped from a well located on the downstream side of the groundwater flow, and after adding at least one of oxygen, a nutrient source of pollutant-decomposing bacteria in soil, and a substrate to at least a part of the groundwater, Contaminated groundwater, characterized by injecting into the saturated layer from a well located upstream of the groundwater flow,
It is a soil restoration method. The invention according to claim 2 is the method for repairing contaminated groundwater and soil according to claim 1, characterized in that a drain is provided between the underground pollution location and the horizontal electrode. In the invention according to claim 3, horizontal electrodes are buried in the upper part and the lower part of the boundary between the saturated layer and the unsaturated layer in the soil, respectively, and the drain is provided in the unsaturated layer between the underground pollution point and the horizontal electrode. The method for repairing contaminated groundwater and soil according to claim 2. In the invention according to claim 4, horizontal electrodes are buried in the upper part and the lower part of the boundary between the saturated layer and the impermeable layer in the soil, respectively, and the drain is provided in the impermeable layer between the underground pollution point and the horizontal electrode. The method for repairing contaminated groundwater and soil according to claim 2.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
FIG. 1 shows an example of a method for repairing contaminated groundwater and soil according to the present invention. In this example, a plurality of wells 21 and 22 are drilled in the saturated layer 12 near the underground pollution point 1 contaminated with pollutants such as organic chlorine compounds and waste oil, and four horizontal electrodes 24 are provided near the underground pollution point 1. , 25, 26, 27
Are buried in layers separated from each other, and the drain 28 is provided between the underground pollution point 1 in the unsaturated layer 11 and the horizontal electrode 24 and between the underground pollution point 1 in the impermeable layer 13 and the horizontal electrode 27, respectively. , 29 are provided and groundwater pumped from the well 22 on the downstream side of the groundwater flow 5 at the underground pollution point 1 is introduced into the substrate adding means 23, and then the well 21 on the upstream side of the groundwater flow 5 at the underground pollution point 1 to the saturated layer 12 It is roughly configured to inject water into and circulate it.

[0008] The stratum at this underground pollution point 1 is composed of a groundwater flow 5
The saturated layer 12 in which groundwater flows, the unsaturated layer 11 above it, and the impermeable layer 1 below the saturated layer 12
It consists of three. A large amount of pollutants is present in the unsaturated layer 11 and the saturated layer 12, especially in the boundary portion of each stratum, and is present in a state where it is difficult to separate. Contaminants of organochlorine compounds such as trichlorethylene are accumulated in the liquid state at the boundary of the stratum, or are adsorbed by clay and organic matter in the soil. Therefore, in the saturated layer 12, the pollutants are gradually added to groundwater. The groundwater contained pollutants.

The wells 21 and 22 are excavated to a depth enough to reach the saturated layer 12 near the underground pollution site 1.
Two or more wells 21 and 22 are provided, and are provided at least on the upstream side of the groundwater flow 5 and on the downstream side of the groundwater flow 5 in the underground pollution site 1. A pumping pipe is inserted into the well 22 provided on the downstream side of the groundwater flow 5 at the underground pollution point 1 up to near the bottom so that the pump can pump the groundwater. Further, the well 21 provided upstream of the groundwater flow 5 in the underground pollution place 1 is configured so that water can be poured into the saturated layer 12 from here, and a water-permeable pipe is inserted, for example. The wells 21 and 22 may be provided with at least one well 21 for water injection on the upstream side of the groundwater flow 5 with respect to the underground pollution point 1 and a well 22 for pumping water on the downstream side. The number of wells and the installation positions can be changed as appropriate.

The horizontal electrodes 24, 25, 26 and 27 are
A conductor is embedded so as to extend in the horizontal direction.
The material and shape are not particularly limited. For example, as shown in FIG. 2, a horizontal groove-like hole having a width of 30 cm and a length of 2 to 5 m is dug in the ground, and an electrode plate 31 made of graphite or the like may be inserted into the hole. Further, charcoal, carbon particles 32, etc. may be filled in the gap around the electrode plate 31. Alternatively, an electrode body in which a metal wire or a metal net is attached to the outside of the body made of a non-conductor may be used. Horizontal electrodes 24, 25, 26,
Two or more 27 are provided, and these are provided in layers in the vertical direction with a space therebetween. In particular, since pollutants are likely to accumulate near the boundary between the unsaturated layer 11 and the saturated layer 12, it is preferable to provide horizontal electrodes 24 and 25 at the upper part and the lower part near the boundary, respectively. Further, since pollutants easily accumulate near the boundary between the saturated layer 12 and the impermeable layer 13, it is preferable to provide the horizontal electrodes 26 and 27 at the upper and lower parts of the boundary, respectively.

These horizontal electrodes 24, 25, 26, 27
A direct current is applied to, but it is preferable that the anodes (+) and the cathodes (−) are alternately arranged. In this example, the upper horizontal electrode 24 near the boundary between the unsaturated layer 11 and the saturated layer 12 is the anode (+), the lower horizontal electrode 25 is the cathode (−), and the boundary between the saturated layer 12 and the impermeable layer 13 is the same. An electric current is applied so that the upper horizontal electrode 26 in the vicinity and the lower horizontal electrode 27 become the anode (+) and the cathode (−), respectively. The voltage applied between the two horizontal electrodes 24, 25 (26, 27) sandwiching the boundary of each layer is within the range where the desorption and movement of the pollutants can be promoted and the loss does not occur. Depending on the situation, it may be appropriately changed within the range of several V to several hundred V. Further, the number and the installation positions of the horizontal electrodes 24, 25, 26, 27 are configured so that the pollutants can be efficiently separated and moved into the saturated layer 12 on the downstream side of the groundwater flow 5 with respect to the water injection well 21. It is preferable that the underground pollution state and groundwater flow 5
It may be appropriately set according to The horizontal electrodes 24, 25,
The positive and negative of 26 and 27 may be switched at any time.

The drains 28 and 29 are made of an adsorbent capable of adsorbing contaminants. It is preferable that the drains 28 and 29 are arranged so as to efficiently adsorb pollutants that have desorbed from the underground pollution point 1 to a portion other than the saturated layer 12. In this example, the underground pollution point 1 and the horizontal electrode in the unsaturated layer 11 are arranged. 24, and between the underground contamination point 1 in the impermeable layer 13 and the horizontal electrode 27. The adsorbent having adsorbed the contaminants can be appropriately taken out, treated, and preferably reused. Drains 28, 29
Is not limited to the adsorbent and may be configured to pump the pollutants to the ground together with water, for example, by using a well for pumping water, as long as it is configured to collect and treat the separated pollutants. Good. The number and installation position of the drains can be changed as appropriate, and the drains may be provided in the saturated layer.

The substrate adding means 23 is a well 2 for pumping water.
Before the groundwater pumped from 2 is poured into the saturated layer 12 from the well 21 for water injection, it is a growth substrate for pollutant-degrading bacteria inhabiting the soil for at least a part of this groundwater. At least one of methane, phenol, etc., air (oxygen), and nutrient sources (nitrogen source, inorganic salts such as phosphates, etc.) is added, and it is provided on the ground. The substance added to the groundwater here is used to enhance the activity of the pollutant-degrading bacteria that can decompose this pollutant, depending on the type of pollutant to be treated and the type of pollutant-degrading bacteria present in the soil. A suitable substance is selected.

For example, organochlorine compounds such as tetrachloroethylene and trichlorethylene are anaerobic bacteria that inhabit soil or anaerobic sludge, for example, Fathep.
ure et al (Fathepure, BZ, Nengu, JP and Boyd, SA: Ap
Pl. Environ. Microbiol., 53,2671-2674 (1987); Fathep
ure, BZ and Boyd, SA: Appl. Environ. Microbiol.,
54,2976-2980 (1988)) reported anaerobic bacteria (Me
thanosarucina sp., Methanosarucina metai, Methanosa
rucina acetivorans, Methanothrix sp., Dechlorinati
ng bacterium DCB-1, Methanosarucina sp.DCM), Bela
y et al. (Belay, N. and Daniels, L.:Appl. Environ. Microbi
ol., 53, 1604-1609 (1987)), a methanogenic bacterium (Methanococcus thermolithotrophics, M. thermo)
deltae, Methanobacterium thermoautotrophicum), Eg
li et al. (Egli, CE, Tschan, T., Scholtz, RS, Cook, AM
and Leisinger, T .: Appl. Environ. Microbiol., 54,28
19-2824 (1988)) and other sulfate-reducing bacteria (D
esulfobacterium autotrophicum, Acetobacterium wood
ii, Clostridium thermoaceticum), Galli et al. (Galli,
R. and McCaryt, PL: Appl. Environ. Microbiol., 55,8
37-844 (1989)) reported anaerobic bacteria (Clostrid
ium sp.TCA2B strain), Yaguchi et al. (Kumiko Yaguchi, Manabu Watanabe, Ichiro Hirata, Takeshi Ito, Akira Hamada: Water Pollution Research, 14,479-486 (199)
It can be degraded by bacteria such as the Gram-negative tetrachloroethylene-degrading bacterium T strain reported in 1)). Therefore, when these anaerobic bacteria inhabit the soil near the underground contamination point 1, the substrate addition means 2
In 3, it is preferable to add a substrate and a nutrient source to groundwater without adding oxygen, which can enhance the activity of anaerobic bacteria and accelerate the decomposition and removal of pollutants.

Trichlorethylene is an aerobic bacterium that lives in soil or aerobic sludge, for example, Fox.
Et al. (Fox, BG et al .: Biochemistry, 26, 6419-6427 (19
90)) reported by various microorganisms (Pseudomonas men
docina, P. putida F1, Nitrosomonas europaea, Mycob
acterium sp. etc.) can be decomposed. Therefore, when these aerobic bacteria inhabit the soil in the vicinity of the underground pollution site 1, it is preferable to add oxygen, a substrate, and a nutrient source to the groundwater in the substrate adding means 23. The activity of aerobic bacteria can be increased to accelerate the decomposition and removal of pollutants. In these various aerobic bacteria, an activity-inducing substrate of an enzyme directly involved in the decomposition of trichlorethylene may be added to the circulating groundwater, which can enhance the ability of each aerobic bacteria in the soil to decompose. Such activity-inducing substrates include methane when the degrading enzyme possessed by the aerobic bacterium is methane monooxygenase, and toluene, phenols and degrading enzymes when the degrading enzyme is toluene monooxygenase or toluene dioxygenase. Ammonia is used in the case of ammonia monooxygenase, and propane is used in the case of the decomposing enzyme being propane monooxygenase.

In addition, pollutant-decomposing bacteria involved in the treatment of pollutants may be added to the circulating groundwater, whereby the number of pollutant-decomposing bacteria existing in the saturated layer 12 increases and the pollutant is decomposed, Removal is further promoted. Furthermore, by adding a small amount of a surfactant to the circulating groundwater as necessary, the contaminants strongly adsorbed to the clay in the ground can be very effectively released into the groundwater.

In order to repair the underground pollution point 1 by bioremediation, that is, to decompose and remove pollutants, by constructing such an equipment structure around the underground pollution point 1, between the horizontal electrodes 24 and 25, and horizontally. Electrodes 26, 27
Groundwater is pumped from the well 22 for pumping while applying a voltage in between, and after introducing this into the substrate adding means 23, water is again poured from the well 21 for water injection into the saturated layer 12 to circulate groundwater.

Then, the substrate adding means 23 adds oxygen, a substrate, a nutrient source, etc. to the groundwater and introduces them into the saturated layer 12 to enhance the activity of the pollutant degrading bacteria inhabiting the soil, Pollutants are efficiently decomposed and removed. In addition, by applying a voltage to the horizontal electrodes 24, 25, 26, 27, desorption and removal of pollutants adsorbed to clay and organic matter in the soil are promoted, so that the pollutants can be decomposed and removed in a short time. It can be carried out. Further, it becomes possible to decompose and remove the contaminants existing in the unsaturated layer 11 and the impermeable layer 13, which were difficult to remove the contaminants.

Further, since pollutants are likely to accumulate near the boundary between the unsaturated layer 11 and the saturated layer 12, horizontal electrodes 24 and 25 are provided at the upper and lower portions of this boundary, respectively.
It is possible to effectively remove the pollutants. Similarly, contaminants are likely to accumulate near the boundary between the saturated layer 12 and the impermeable layer 13. Therefore, by disposing the horizontal electrodes 26 and 27 above and below this boundary, respectively, the contaminants can be effectively removed. You can And these horizontal electrodes 2
The pollutants that have desorbed into the saturated layer 12 and moved to by applying a voltage to 4, 25, 26, and 27 are decomposed and removed by the pollutant-decomposing bacteria. In addition, the contaminants that have desorbed and moved into the unsaturated layer 11 and the impermeable layer 13 are drained.
It is adsorbed by 8, 29 and appropriately processed.

[0020]

As described above, according to the invention of claim 1, a plurality of wells are excavated in the saturated layer in the vicinity of the underground polluted portion contaminated with pollutants, and the wells are located on the downstream side of the groundwater flow. Pumping groundwater from the well, adding oxygen, at least one of a nutrient source for pollutant-degrading bacteria in the soil, and a substrate to at least a part of the groundwater, and then arranging the groundwater upstream of the underground pollution point The groundwater in the saturated layer is circulated by injecting it into the saturated layer from the well, and oxygen and the nutrient source of pollutant degrading bacteria in the soil or the substrate are introduced into the saturated layer by this circulating groundwater. The activity of pollutant degrading bacteria inhabiting
By embedding two or more horizontal electrodes in the vicinity of the underground pollutant in the vertical direction with a space between them, and applying a voltage between each horizontal electrode, it is possible to promote the removal and movement of pollutants. It is possible to purify and restore water in a short time, and it is also possible to remove contaminants in the unsaturated layer.

According to the second aspect of the present invention, the drain is provided between the underground pollutant and the horizontal electrode so that the pollutant desorbed from the underground pollutant by applying a voltage to the horizontal electrode is drained. It can be efficiently collected and processed. According to the invention of claim 3, horizontal electrodes are buried in the upper part and the lower part of the boundary between the saturated layer and the unsaturated layer in the soil, respectively, and the drain is formed in the unsaturated layer between the underground pollution point and the horizontal electrode. By setting up, the pollutants accumulated near the boundary between the saturated layer and the unsaturated layer can be effectively released, and the contaminants that have desorbed and moved from the underground pollution location to the unsaturated layer are also collected at the drain. Therefore, it is possible to effectively purify and restore contaminated groundwater and soil. According to the invention of claim 4,
By burying horizontal electrodes above and below the boundary between the saturated layer and the impermeable layer in the soil, and by providing drains in the impermeable layer between the underground pollution point and the horizontal electrode, the saturated layer and the impermeable layer are formed. The pollutants accumulated near the boundary with the layer can be effectively released, and the pollutants that have separated from the underground pollution location to the impermeable layer and moved can also be collected and treated at the drain. It can effectively purify and repair soil.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a method for repairing contaminated groundwater and soil according to the present invention.

FIG. 2 is a cross-sectional view showing an example of a horizontal electrode.

FIG. 3 is a schematic configuration diagram showing an example of a conventional method for repairing contaminated groundwater and soil.

[Explanation of symbols]

1 ... Underground pollution location, 5 ... Groundwater flow, 11 ... Unsaturated layer, 1
2 ... Saturated layer, 13 ... Impermeable layer, 21, 22 ... Well, 2
4, 25, 26, 27 ... Horizontal electrodes, 28, 29 ... Drains.

Claims (4)

[Claims] 1. A plurality of wells are excavated in a saturated layer in the vicinity of an underground polluted point contaminated with pollutants, and two or more horizontal electrodes are buried vertically apart in the vicinity of the underground polluted point, While applying a voltage between the horizontal electrodes, groundwater is pumped from a well located on the downstream side of the groundwater flow, oxygen is at least a part of the groundwater, a nutrient source for pollutant degrading bacteria in the soil,
And at least one of the substrates are added, and then the method is performed by injecting into a saturated layer from a well located on the upstream side of the groundwater flow at the underground pollution location into the saturated layer. 2. The method for remediating contaminated groundwater and soil according to claim 1, wherein a drain is provided between the underground contamination location and the horizontal electrode. 3. A horizontal electrode is embedded above and below a boundary between a saturated layer and an unsaturated layer in soil, and a drain is provided in the unsaturated layer between the underground pollution point and the horizontal electrode. The method for remediating contaminated groundwater and soil according to claim 2. 4. A horizontal electrode is buried above and below the boundary between the saturated layer and the impermeable layer in soil, and a drain is provided in the impermeable layer between the underground pollution point and the horizontal electrode. The method for remediating contaminated groundwater and soil according to claim 2.