JP3374229B2 - How to restore contaminated groundwater and soil - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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 utilizing biotechnology (also called in-situ bioremediation) 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 strengthens and uses the purification function originally possessed by the soil ecosystem. is there.

FIG. 3 schematically shows an example of a purification method by a conventional bioremediation technique. In this example, two or more wells 3 and 4 are excavated in a saturated layer 2 near an underground contamination point 1 contaminated with a contaminant such as an organic chlorine compound or 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 addition means 6, and methane, phenol, oxygen, nutrient sources, etc., which are growth substrates for the degrading bacteria are added, and this is added. It injects into the injection well 3 excavated on the upstream side and circulates. 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 decomposed and removed efficiently, and the restoration method has high cost performance.

[0004]

However, in this purification method by bioremediation, organic chlorine compounds such as tetrachloroethylene and pollutants such as oil are easily adsorbed on clay and organic matter in soil, and , Gradually these will be released into the groundwater,
There is a drawback that the removal takes a relatively long time. In addition, although it is possible to decompose and remove pollutants in the saturated layer where groundwater in the soil is saturated, it is possible to decompose in an unsaturated layer where the groundwater is unsaturated and there are gaps such as air. However, it has a problem that it is difficult to remove.

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]

The method for remediating contaminated groundwater and soil according to the present invention is a method of excavating a plurality of wells in a saturated layer in which groundwater flows in the vicinity of an underground contaminated site contaminated with pollutants. Two or more electrodes are spaced apart from each other and buried in the vicinity of the contaminated part, and groundwater containing pollutants is pumped from the well on the downstream side of the groundwater flow at the underground contaminated part while applying a voltage between the electrodes. Is introduced into an anaerobic bioreactor in which hydrogen generated by electrolysis of groundwater at the electrode is introduced to decompose pollutants in the pumped water, and the treated water contains oxygen generated by electrolysis of groundwater at the electrode. And injecting into the saturated layer from the well located on the upstream side of the groundwater flow at the underground pollution location. In addition, the treated water of the anaerobic bioreactor is guided to an aerobic bioreactor to decompose the pollutants in the treated water, and the treated water of the aerobic bioreactor is fed to the groundwater flow upstream side of the underground polluted location. The saturation layer may be injected from the injection well located.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of a method for remediating contaminated groundwater and soil according to the present invention. In this embodiment, the saturated layer 17 near the underground contamination point 1 contaminated with pollutants such as organic chlorine compounds and waste oil.
And excavating two or more wells 11 and 12 on the upstream side and the downstream side of the groundwater flow 5 with the underground pollution point 1 interposed therebetween, and on the upstream side and the downstream side of the groundwater flow 5 of these wells 11 and 12, respectively. Electrodes 14 and 15 are buried, and an anaerobic bioreactor 13 for decomposing pollutants is installed on the ground.
Groundwater pumped from the downstream pumping well 11 is introduced into the anaerobic bioreactor 13 to be treated, and the treated water is again passed through the injection well 12 on the upstream side of the groundwater flow 5 to the saturated layer 17 again.
Configured to inject into.

[0008] The stratum at this underground pollution point 1 is composed of a groundwater flow 5
As shown in FIG. 3, the saturated layer 17 in which groundwater flows, the unsaturated layer 18 above the saturated layer 17, and the impermeable layer 19 below the saturated layer 17. A large amount of pollutants is present in the unsaturated layer 18 and the saturated layer 17, and particularly in the boundary portion between the unsaturated layer 18 and the saturated layer 17 and the boundary portion between the unsaturated layer 18 and the impermeable layer 19, These exist in a state where they are difficult to separate from the soil. Contaminants such as organic chlorine compounds such as tetrachlorethylene exist as undiluted solution,
It exists by being adsorbed to clay and organic matter in soil, and therefore, in the saturated layer 17, the pollutants are gradually released into the groundwater, and the groundwater contains the pollutants.

The wells 11 and 12 are deep enough to reach the saturated layer 17 in the vicinity of the underground pollution point 1 and the underground pollution point 1
It is excavated on the upstream side and the downstream side of the groundwater flow 5. A pumping pipe is inserted into the pumping well 11 on the downstream side up to near the bottom, and groundwater is pumped to the ground through these pumping pipes. The upstream injection well 12 is for returning pumped water to the saturated layer 17 again.

The electrodes 14 and 15 may be conductors inserted to a depth enough to reach the saturated layer 17, and the material and shape are not limited. For example, it is possible to use an electrode plate formed of graphite or the like that is driven to a depth sufficient to reach the saturated layer 17. Moreover, you may use the electrode body which attached the metal wire or the metal net to the outer side of the main body which consists of non-conductive materials.

A direct current can be applied between the electrodes 14 and 15 by using the electrode 14 on the upstream side of the groundwater flow 5 as an anode (+) and the electrode 15 on the downstream side as a cathode (-). As a result, the pollutants in the soil can be separated from the clay and organic matter, and can be electroosmotic to promote the movement of the groundwater flow 5 in the downstream direction. The voltage applied to these electrodes 14 and 15 is in a range that can promote the detachment and movement of pollutants and does not cause loss, and is appropriately in the range of several V to several hundred V depending on the conductivity of the ground. You can set it. In addition, the electrodes 14 and 15
The number and the installation position of the above may be appropriately set according to the scale of the underground pollution point 1 and the groundwater flow 5 so that a voltage can be efficiently applied to the surroundings of the underground pollution point 1.

The anaerobic bioreactor 13 brings microorganisms capable of decomposing at least a part of pollutants such as tetrachloroethylene and groundwater pumped from the pumping well 11 into contact with the pollutants contained in the groundwater by the microorganisms. It is for biological decomposition. The anaerobic bioreactor 13 can be used by selecting an appropriate type for the device configuration and the bacteria to be used depending on the type of contaminant. For example, it is possible to use an anaerobic digestion (methane fermentation) treatment device that is usually used for sewage treatment or industrial wastewater treatment, or one that is filled with a porous support that retains microorganisms capable of decomposing pollutants. it can.

The microorganisms used in the present invention differ depending on the type of pollutant to be treated. When the pollutant is an organic chlorine compound such as tetrachloroethylene, it is separated from soil or anaerobic sludge. Anaerobes, such as Fathepure et al. (Fathepure, BZ, Nengu, JP a
nd Boyd, SA: Appl. Environ. Microbiol., 53,2671-26
74 (1987); Fathepure, BZ, and Boyd, SA: Appl. Env
Iron. Microbiol., 54, 2976-2980 (1988) reported anaerobic bacteria (Methanosarcina sp., Methanosarcina meta.
i, Methanosarcina acetivorans, Methanothrix sp., D
echlorinating bacterium DCB-1, Methanosarcina sp.D
CM), Belay et al. (Belay, N. and Daniels, L .: Appl. Enviro
n. Microbiol., 53, 1604-1609 (1987)), a methanogenic bacterium (Methanococcus thermolithotrophicu
s, M. thermodeltae, Methanobacterium thermoautroph
icum), Egli et al. (Egli, CE, Tschan, T., Scholtz, RS,
Cook, AM and Leisinger, T.: Appl. Environ. Microbio
l., 54, 2819-2824 (1988)), such as sulfate-reducing bacteria (Desulfobacterium autotrophicum, Acetobcte
rium woodii, Clostridium thermoaceticum), Galli et al. (Galli, R. and McCaryt, PL: Appl. Environ. Microbio
L., 55, 837-844 (1989)).
(Clostridium sp.TCA2B strain), Yaguchi et al. (Kumiko Yaguchi, Manabu Watanabe, Ichiro Hirata, Takeshi Ito, Akira Hamada: Water Pollution Research, 14,479
-486 (1991)), such as the Gram-negative tetrachloroethylene-degrading bacterium T strain, can be used.

Further, the cathode 15 is provided with a hydrogen gas introducing pipe 22 for introducing hydrogen gas generated by electrolysis of ground water to the anaerobic bioreactor 13 by applying a voltage to the electrode. Further, the anode 14 is provided with an oxygen gas introduction pipe 23 for introducing oxygen gas generated by electrolysis into the anaerobic bioreactor 13 treated water.
Further, a substrate addition means 6 is provided so that methane, phenol, oxygen, nutrient sources, etc., which are growth substrates for pollutant-decomposing bacteria, can be added to the anaerobic bioreactor 13 treated water as required. Has become. As the nutrient source, an inorganic compound such as an ammonium salt or a phosphate is used, and a pollutant degrading bacterium is added if necessary. As a method of adding oxygen, a method of bubbling the treated water with air or pure oxygen to increase the concentration of dissolved oxygen in the treated water or adding hydrogen peroxide can be applied. Moreover, a part of the anaerobic bioreactor 13 treated water can be discharged through the discharge water channel 21.
Further, in order to prevent the strainer from being clogged by the propagation of microorganisms in the injection wells 12 and the like, the injection wells 12 are provided in plural, and the anaerobic bioreactor 13 treated water and the water having an increased dissolved oxygen concentration are separated. You may inject it into the soil.

A method for repairing contaminated groundwater and soil using the wells 11, 12, the electrodes 14, 15 and the anaerobic bioreactor 13 will be described below in order of their procedure. First, ground water containing pollutants such as tetrachloroethylene is pumped from the pumping well 11 by a pump (not shown) while a voltage of several V to several hundred V is applied between the electrodes 14 and 15. By applying the voltage as described above, the pollutants adsorbed to the clay and organic matter in the saturated layer 17 and the unsaturated layer 18 are released into the groundwater, and the groundwater containing the pollutants is pumped from the pumping well 11. .

Subsequently, the pumped water is introduced into the anaerobic bioreactor 13 on the ground. At this time, hydrogen gas generated by electrolysis of ground water at the cathode 15 is guided to the anaerobic bioreactor 13 through the hydrogen gas introduction pipe 22. By introducing the hydrogen gas to the reactor 13, the inside of the reactor 13 becomes an anaerobic atmosphere, and the activity of anaerobic bacteria is kept high. In the anaerobic bioreactor 13, pollutants such as organic chlorine compounds such as tetrachloroethylene in the pumped water are decomposed by anaerobic bacteria in the reactor. At this time, depending on environmental conditions and the concentration of pollutants, some of these pollutants are not completely decomposed, and some of the chlorine in the molecule remains as dechlorinated organic chlorine compounds such as trichlorethylene.

Next, the treated water treated in the anaerobic bioreactor 13 is introduced into the injection well 12. On this occasion,
Oxygen gas generated by electrolysis of groundwater at the anode 14 is added to the treated water through the oxygen gas introduction pipe 23. By introducing this oxygen gas, the concentration of dissolved oxygen in the treated water introduced into the injection well 12 is increased. Also,
If necessary, the substrate adding means 6 may be added to the treated water.
Substrates such as methane and phenol, and nutrients such as nitrogen compounds and phosphorus compounds are added. The treated water to which oxygen or the like is added moves from the injection well 12 into the soil,
It moves to the downstream direction of the groundwater flow 5 again, and a part thereof is pumped from the injection well 12. By repeating the above process, groundwater is circulated, and in this circulation process, pollutants are decomposed by soil microorganisms and finally become carbon dioxide gas, which is rendered harmless. At this time, since oxygen or the like is added to the treated water, oxygen or the like is supplied to the soil to enhance the activity of aerobic bacteria in the soil. This accelerates the decomposition of contaminants such as organic chlorine compounds such as trichlorethylene remaining in the treated water.

In the above-mentioned example, since the electric current is passed to the underground pollution site 1 by the electrodes 14 and 15 and the ground water is circulated by adding oxygen, nutrients, etc., it is adsorbed by the clay and organic matter in the soil. It can release pollutants such as organic chlorine compounds and oils into groundwater and activate pollutant-degrading microorganisms in the soil to accelerate the decomposition of pollutants. Therefore, it becomes possible to quickly treat the contaminants. Moreover, not only the saturated layer 17, the boundary between the unsaturated layer and the saturated layer, and the boundary between the saturated layer and the impermeable layer, but also the pollutants that are adsorbed to the unsaturated layer 18 or exist in the raw liquid state by electroosmosis. It can be released inside and circulated to promote its decomposition.

Further, since the groundwater pumped from the pumping well 11 is guided to the anaerobic bioreactor 13 for treatment, pollutants can be efficiently dechlorinated. At this time, hydrogen gas generated by electrolysis of groundwater at the cathode 15 is introduced into the anaerobic bioreactor 13 to create an anaerobic atmosphere inside the reactor 13 to keep the activity of anaerobic bacteria high and treat the reactor 13. High performance can be maintained. Further, hydrogen gas obtained by electrolysis can be effectively used. Further, by adding the oxygen gas generated at the anode 14 to the treated water introduced into the injection well 12, the pollutant-degrading microorganisms in the soil can be further activated, and the oxygen gas obtained by electrolysis can be effectively used. can do.

FIG. 2 shows a second embodiment of the method for repairing contaminated groundwater and soil according to the present invention. In this embodiment, an aerobic bioreactor 20 for decomposing pollutants that leads the anaerobic bioreactor 13 treated water is provided on the ground. This aerobic bioreactor 20
A microorganism for decomposing at least a part of pollutants to be treated, such as trichlorethylene, and anaerobic bioreactor 13 treated water are brought into contact with each other to biologically decompose the pollutants contained in the treated water by the microorganisms. It is a thing. An appropriate type of the aerobic bioreactor 20 can be selected and used depending on the type of contaminants and the bacteria used. Basically, it is preferable to use an aerobic closed reactor as a device configuration so that the reactor can be decomposed in the reactor without releasing pollutants such as trichlorethylene into the atmosphere.

Further, the aerobic bioreactor 20 includes
An oxygen gas introducing pipe 24 for introducing oxygen gas generated at the anode 14 to the aerobic bioreactor 20 is provided, and the oxygen gas can be introduced into the reactor 20 through the oxygen gas introducing pipe 24. There is. Also,
The aerobic bioreactor 20 includes an oxygen gas introduction pipe 24.
Separately from this, an aerobic bioreactor 20 is provided with an oxygen supply means (not shown) for introducing pure oxygen or air, hydrogen peroxide, etc. as necessary, so that the dissolved oxygen concentration in the reactor can be controlled. It has become.

The microorganisms used in the aerobic bioreactor 20 include aerobic bacteria isolated from soil or aerobic sludge, such as Fox et al. (Fox, BG et al .: Bioc).
hemistry, 26, 6419-6427 (1990)) reported various microorganisms (Pseudomonas mendocina, P. putida F1, Nitr
osomonas europaea, Mycobacterium sp., etc.) can be used.

In the method of this embodiment, the treated water in the anaerobic bioreactor 13 is supplied to the aerobic bioreactor 2.
0 aerobic bioreactor 20
The treated water is introduced into the injection well 12. At this time, the anode 14
It is desirable to introduce oxygen gas generated by electrolysis of groundwater into the aerobic bioreactor 20 and efficiently perform decomposition treatment under high dissolved oxygen conditions.

In the second embodiment, the treated water of the anaerobic bioreactor 13 is treated in the aerobic bioreactor 20, so that even when an organic chlorine compound such as trichlorethylene remains in the treated water of the anaerobic bioreactor 13, These can be decomposed efficiently. Further, since the oxygen gas generated at the anode 14 is introduced into the aerobic bioreactor 20, the oxygen gas obtained by electrolysis can be effectively used, and the aerobic bioreactor 2 can be used.
The operating cost of 0 can be reduced. In the method of this embodiment, part or all of the oxygen gas generated at the anode 14 may be introduced into the injection well 12 in addition to the treated water of the aerobic bioreactor 20. In each of the above embodiments, the organic chlorine compound is used as the pollutant, but the pollutant is not limited to this, and the same effect can be obtained as long as it is an organic halogen compound.

[0025]

In the method for remediating contaminated groundwater and soil according to the present invention, an electric current is passed to the underground contaminated site by the electrode, and the groundwater is circulated by adding oxygen, a nutrient source, etc. It is possible to release pollutants such as organic chlorine compounds and oils adsorbed by organic matter into groundwater, activate the pollutant-degrading microorganisms in soil, and accelerate the decomposition of pollutants. Therefore, it is possible to quickly dispose of pollutants. In particular, since the contaminants adsorbed on the unsaturated layer can be released and circulated, the unsaturated layer can be purified.

Further, since the groundwater pumped from the pumping well is guided to the anaerobic bioreactor for treatment, pollutants can be efficiently dechlorinated. At this time, hydrogen gas generated by electrolysis of groundwater at the cathode is introduced into the anaerobic bioreactor to create an anaerobic atmosphere inside the reactor, and the processing performance of this reactor can be maintained at a high level. By adding the generated oxygen gas to the reactor treated water introduced into the injection well, the pollutant-degrading microorganisms in the soil can be further activated. Furthermore, by treating the anaerobic bioreactor treated water with the aerobic bioreactor, pollutants can be decomposed more efficiently.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a method for repairing contaminated groundwater and soil according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a method for repairing contaminated groundwater and soil according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a conventional method for repairing contaminated groundwater and soil.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Underground pollution place, 11 ... Pumping well, 12 ... Injection well, 13 ... Anaerobic bioreactor, 14 ... Anode, 1
5 ... Cathode, 17 ... Saturation layer, 20 ... Aerobic bioreactor

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C02F 3/00-3/34 B09C 1/00-1/10

Claims (2)

(57) [Claims] 1. A plurality of wells are drilled in a saturated layer in which groundwater flows near a contaminated underground contaminated site, and two or more electrodes are buried in the vicinity of the underground contaminated site in a spaced manner. While applying a voltage between the electrodes, groundwater containing pollutants was pumped from the well on the groundwater flow downstream side of the ground polluted site, and the pumped water was introduced with hydrogen generated by electrolysis of groundwater at the electrodes. The pollutants in the pumped water are decomposed by being guided to an anaerobic bioreactor, oxygen generated by electrolysis of groundwater at the electrodes is added to the treated water, and the groundwater flow upstream side of the underground polluted site is added. A method for repairing contaminated groundwater and soil, which comprises injecting into the saturated layer from a well. 2. The treated water of the anaerobic bioreactor is introduced into an aerobic bioreactor to decompose pollutants in the treated water, and the treated water of the aerobic bioreactor is used as a groundwater flow at the underground polluted site. The method for restoring contaminated groundwater and soil according to claim 1, wherein the saturated layer is injected from an injection well located on the upstream side.