JP3645651B2 - Purification method for contaminated soil - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying soil contaminated with volatile organic compounds, and more particularly, to a method for purifying soil contaminated soil using a decomposition action of microorganisms.
[0002]
[Prior art]
Sudden expansion of industrial activities places various forms of load on the environment, such as contamination by the amount of substances in the soil that exceeds the natural purification capacity of the soil, or contamination by substances that do not have purification capacity in the soil itself In many cases, pollution is widespread and urged to clean up.
[0003]
Among these, contamination with liquid and volatile organic compounds represented by petroleum and its derivatives is in a serious situation, and there is a strong demand for establishment of purification technology. The method of remediation of contaminated soil with volatile organic compounds is largely comprised of a remediation method that includes a shielding wall to surround the contaminated soil area, etc., and a contaminant that is physically, chemically, or biologically contained. It is classified into two methods of decomposing and removing itself. Among these, the method of decomposing and removing the pollutant itself is considered preferable as a fundamental purification method.
[0004]
The decontamination and purification method involves forcibly generating an air flow in the contaminated soil area and using the volatility of the pollutant to discharge the pollutant along with the air flow and then guiding it to a gas processing device such as a UV treatment device or activated carbon treatment device. A so-called vacuum extraction method that decomposes and removes, and a method that purifies contaminated soil excavated by excavation by a method such as heating, UV irradiation, oxidation treatment, etc. on a plant on the ground have been put into practical use. However, these methods have problems such as extremely low purification efficiency when the concentration of pollutants is reduced, inability to be applied depending on the location conditions of the contaminated soil, and large equipment.
[0005]
In recent years, so-called bioremediation (hereinafter abbreviated as BR) that decomposes and removes pollutants using the decomposition action of microorganisms can purify low-contaminated soil, and the energy cost required for purification is low. It attracts attention.
[0006]
In this BR, there is an indigenous microorganism activation method that artificially improves the decomposition ability of microorganisms that have the ability to decompose pollutants in the contaminated soil by supplying nutrients, adjusting oxygen concentration, etc. There is a method of adding decomposing microorganisms, which reserves microorganisms having the ability to decompose pollutants in advance and propagates them into the contaminated soil area.
[0007]
The method of adding degrading microorganisms has the ability to efficiently decontaminate by degrading microorganisms inhabiting in the contaminated soil to be purified and having the degrading ability and putting them in the contaminated soil area, and has the ability to decompose pollutants. Even if the microorganisms are not present in the contaminated soil, that is, even if the indigenous microorganism activation method cannot be applied, it is possible to purify by introducing the decomposed microorganisms grown separately into the contaminated soil area. In particular, in recent years, examples of soil contamination due to compounds that are difficult to decompose and purify in natural environments such as trichlorethylene and tetrachloroethylene have increased, and microorganisms that have the ability to decompose difficult-to-decompose compounds such as trichlorethylene Available due to advances in screening technology or genetic engineering technology For reasons such as Rukoto, the degrading microorganism addition method has attracted attention as an effective purification method.
[0008]
[Problems to be solved by the invention]
However, there are several problems with this method of adding degraded microorganisms. The resolution of decomposing microorganisms is only demonstrated when the decomposing microorganisms come into contact with pollutants, but most of the decomposing microorganisms and volatile substances are transferred and spread in the soil by adding the decomposing microorganisms to a part of the contaminated soil area. It does not advance to a degree sufficient to obtain a practical decomposition rate. In this regard, attempts have been made to inject a necessary amount of decomposing microorganisms into the contaminated soil area, and to appropriately supply nutrients and adjust oxygen concentration in order to support the decomposing activity of the decomposing microorganisms.
[0009]
For example, Savery W. et al. Provide an injection device and extraction device with an injection hole or extraction hole that can be arbitrarily repositioned in contaminated soil, and supplies an arbitrary amount of decomposing microorganisms, nutrients, oxygen, etc. to the intended location. A purification method has been proposed (USP 5111883). Although this technique has greatly improved the technology for supplying decomposing microorganisms and the like to the contaminated soil area, the amount of decomposing microorganisms injected into the contaminated soil area has become enormous and has become a major obstacle in practical use.
[0010]
In addition, Weber O. et al. Added a vacuum extraction method using a borehole provided in the contaminated soil layer, added decomposed microorganisms, nutrients, oxygen, etc. to the pumped contaminated groundwater, treated it in a purification plant as needed, and then contaminated soil surface layer A purification method suitable for unsaturated aquifer soil contaminated with hydrocarbons has been proposed (DE 3839093 C2) by combining methods of circulating to contaminated soil through a return pipe provided nearby.
[0011]
This method improves the degradation activity of decomposing microorganisms in unsaturated aquifer soil and enables faster purification, but requires a large amount of decomposing microorganisms, and vacuum extracted contaminants are conventional technology As in the case of the above, some kind of secondary processing is necessary, so it is inevitable that the equipment will become large. Furthermore, since a large amount of decomposing microorganisms and nutrients are repeatedly supplied during the purification period, there is a high risk that these injected substances including decomposing microorganisms will flow out into the environment.
[0012]
Duane AG and others also installed injection pipes and discharge pipes in the contaminated soil area, supplied gaseous nutrients from the supply pipe to the contaminated soil area, and circulated them through the discharge pipe to secure and decompose nutrient channels in the contaminated soil area. A method for achieving high-speed purification by promoting the resolution of microorganisms has been proposed (USP 5178491).
[0013]
By this method, the nutrient supply to the decomposing microorganisms in the contaminated soil is greatly improved, and the resolution of the decomposing microorganisms is improved. However, from the viewpoint of contact between decomposing microorganisms and contaminants, improvement is hardly expected and is insufficient.
[0014]
[Means for Solving the Problems]
As a result of studying the above problems, the present inventors have found that it is important to accelerate the contact between the decomposing microorganism and the pollutant in order to increase the decomposition rate. It was found that it was effective and simple to forcibly move the pollutants in the contaminated soil and contact them with decomposing microorganisms instead of adding them. In addition, in order to decompose pollutants using the action of decomposing microorganisms, instead of conventional ground bioreactors, a contaminated soil area is provided with a purified soil area in which decomposing microorganisms are injected, and gas containing the pollutant is induced in that area. By doing so, it becomes easy to maintain under the conditions suitable for degrading microorganisms such as temperature and humidity conditions for a long period of time, and furthermore, a volatile organic compound adsorbing material coexists in the vicinity of the decomposing microorganisms. As a result, it was found that extremely efficient decomposition was possible.
[0015]
That is, the present invention is a purification method that utilizes the microbial decomposition action of soil contaminated with volatile organic compounds, and a process for forming a purified soil region containing degraded microbial material and volatile organic compound adsorbing material in the contaminated soil region And a method for purifying contaminated soil, comprising a step of extracting a gas containing a contaminant from the contaminated soil region and circulating the extracted gas to the contaminated soil region via the purified soil region.
[0016]
The present invention will be described in more detail below.
[0017]
In remediation of contaminated soil, it is generally necessary to first grasp the state of contamination accurately and determine the contaminated soil area. It is possible to grasp the contamination state by general means and methods. For example, a method for measuring pollutants by taking a sample of soil or ground water by setting up a borehole or observation well, a borehole and for observation Sensors are inserted into the wells of the soil to monitor the pollutants in the soil layer and groundwater layer, sampling holes are inserted through the borehole and observation well or directly into the soil layer and groundwater layer, and gas or groundwater is sucked there. It is possible by measuring the pollutants contained in
[0018]
From these data, a contaminated soil area is determined, and a purified soil area is formed in the contaminated soil area. The purified soil area is formed by supplying a decomposing microbial material including degrading microorganisms capable of decomposing pollutants and a volatile compound adsorbing material to the contaminated soil area.
[0019]
In addition to degrading microorganisms, the degrading microorganism materials include growth functional materials necessary for the growth of degrading microorganisms, activity maintaining functional materials that allow the degrading microorganisms to exert their degrading activity, and reproductive functional materials that allow the degrading microorganisms to live stably in the soil. It is preferable to include a material appropriately selected from the above in order to promote suitable decomposition.
[0020]
First, examples of degrading microorganisms that decompose pollutants include, for example, Saccharomyces, Hansenula, Candida, Micrococcus, Staphylococcus, Streptococcus, Leuconostoc, Lactobacillus, Corynebacterium, Arthrobacter, Clostridium, Bacillus, Neisseria, Escherichia, Enteric, Microorganisms such as Serratia, Achromobacter, Alcaligenes, Flavobacterium, Acetobacter, Nitrosomonas, Nitrobacter, Thiobacillus, Gluconobacter, Pseudomonas, Xanthomonas, Vibrio Moraxella, one or more of these mutants and gene recombinants of these microorganisms A mixture of There are suitable combinations of decomposing microorganisms depending on the type of pollutant, and they are appropriately selected according to the type of pollutant. In addition to these decomposing microorganisms, decomposing enzymes themselves can be used as decomposing microorganisms.
[0021]
The growth functional material is a nutrient for degrading microorganisms, and for example, bouillon medium, M9 medium, L medium, Malt Extract, MY medium, nitrifying medium, and the like are useful.
[0022]
When degrading enzymes produced from degrading microorganisms are constitutively expressed, no active maintenance functional material is required, but when active enzymes are expressed by a specific inducer (inducer), the inducer is active. It is necessary as a maintenance function material. Examples of inducers include methane-utilizing bacteria, aromatic-assimilating bacteria such as toluene, phenol and cresol, and nitrifying bacteria such as ammonium salts. When directly degrading enzymes are used as decomposing microbial materials, energy sources and minerals for maintaining the expression of enzyme activity are required as activity maintaining functional materials.
[0023]
Reproductive functional materials have the purpose of providing decomposing microorganisms with a comfortable habitat in the purified soil area, thereby preventing the predation of other microorganisms and protozoa, or preventing the diffusion of decomposing microorganisms outside the purified soil area. doing.
[0024]
As the survival functional material, many microbial carriers used in bioreactors such as the pharmaceutical industry, the food industry, and wastewater treatment systems can be used. For example, porous glass, ceramics, metal oxides, activated carbon, kaolinite, bentonite, zeolite, silica gel, alumina, anthracite and other spherical carriers, starch, agar, chitin, chitosan, polyvinyl alcohol, alginic acid, polyacrylamide, carrageenan, agarose Gelatin carriers such as gelatin, cellulose, glutaraldehyde, polyacrylic acid and polyurethane, polymer resins and ion exchange resins. Further, for example, paper made of cotton, hemp, pulp material, etc. mainly composed of cellulose, and cloth made of a modified polymer such as polyester, polyurethane, or polyacetate are also effective. In addition, compost material is useful as a material that has both a growth function and a survival function. Examples thereof include cereals such as wheat straw, sawdust, rice bran, okara, sugar cane, crab and shrimp shells.
[0025]
The volatile organic compound adsorbent material is intended to adsorb and trap gaseous volatile organic compounds (pollutants) extracted from the contaminated soil area, and the adsorbed pollutants are gradually decomposed by decomposing microorganisms. It helps. The volatile organic compound adsorbing material is appropriately selected depending on the type of contaminant, and a nonpolar material is preferable, and a polymer compound that does not have a crystal structure is particularly preferable. For example, a vinyl copolymer containing styrene, (meth) acrylic acid alkyl ester and derivatives thereof as main components is preferable.
[0026]
Volatile organic compound adsorbing materials are dispersed or dissolved in organic solvents because they themselves cause pollution, there is a risk of fire in handling, and there are concerns about damage to decomposing microorganisms. It is preferable that the medium is not water. Among these, a water-dispersible polymer compound is particularly preferable because the liquid viscosity is suppressed during injection for forming a purification region.
[0027]
The fine polymer particles are preferably negatively charged on the surface. As a result, the fine polymer particles are freely dispersed in water at the initial stage of the purification region formation, but the dispersibility decreases as the purification region is formed. That is, the polymer fine particles diffuse freely in the liquid injection range at the time of injection, but are fixed in the purification region after the injection, and it is possible to avoid washing away by rain water, ground water, etc. or subsequent liquid injection. .
[0028]
The decrease in dispersibility during the purification zone formation is due to neutralization of the charge on the surface of the fine particles by polyvalent metal ions such as magnesium ions and calcium ions in the soil. Compared to the metal ion concentration in the vicinity of the inlet, as the injection solution diffuses into the soil and expands the purification region, the relative concentration rapidly increases and the dispersion stability is considered to decrease.
[0029]
The particle diameter of the polymer fine particles is preferably from 0.01 μm to 5 μm.
[0030]
If it is less than 0.01 μm, the viscosity of the dispersion increases and the injection efficiency decreases. On the other hand, if it exceeds 5 μm, it becomes difficult for the polymer fine particles to enter the gap between the soil particles.
[0031]
In order to form a purified soil region containing the above-described microbial material, volatile organic compound adsorbing material, etc., for example, an injection pipe 42 having an inlet 43 is inserted into the contaminated soil region as shown in FIG. A method of injecting an injection liquid containing an organic compound adsorbing material or the like into a contaminated soil region by a liquid injection unit 41 comprising a liquid feed pump, etc., a stirring blade 53 used in the ground improvement method as shown in FIG. A method for supplying an injection solution containing a microbial material, a volatile organic compound adsorbing material, etc. into the excavated soil while excavating the contaminated soil area using a construction machine having a supply system 51, as shown in FIG. It is possible to use any method such as a method in which the excavation hole 61 is provided in the region and the soil containing the decomposed microbial material, the volatile organic compound adsorbing material, etc. is backfilled therein.
[0032]
In particular, the inlet should be removed from the viewpoint of preventing volatilization of pollutants into the atmosphere and the ease of forming the purified soil area and the ease of circulating the extracted gas containing the pollutants to the purified soil area. A method is preferred in which an injection pipe is inserted into the contaminated soil region, and an injection solution containing microbial material, volatile organic compound adsorbing material and the like is injected into the contaminated soil region with a liquid feed pump.
[0033]
In order to extract gas containing pollutants from the contaminated soil area, there is a vacuum extraction method in which an extraction well is provided in the contaminated soil area to forcibly generate an air flow in the contaminated soil area and discharge volatile pollutants along with the air flow. Preferably used.
[0034]
The extracted gas containing the pollutant is circulated to the contaminated soil area through an injection well provided in the purified soil area. The extracted gas is preferably circulated to the contaminated soil area after appropriately measuring the oxygen concentration, carbon dioxide gas concentration, pollutants, and degradation products of the pollutants, and adjusting the components. Of these, the oxygen concentration has a great effect on the resolution of degrading microorganisms, so it is particularly preferable to measure the oxygen concentration in the extracted gas and adjust it to the optimum oxygen concentration according to the results, and then circulate to the contaminated soil area. .
[0035]
An example of a system suitable for carrying out the present invention is shown in FIG. 1, and a purification flow of contaminated soil using the system will be described.
[0036]
Purified soil area by injecting an injection solution containing decomposing microorganism material, volatile organic compound adsorbing material and the like into a contaminated soil area 17 measured and set in advance via an injection pipe 13 having an inlet 14 by a liquid injection unit 11 18 is provided. Contaminants in the contaminated soil region via an extraction pipe 15 embedded in or near the contaminated soil region 17 and having a suction port 16 connected to the gas circulation unit 12 (including a suction element, component measurement element, and gas injection element) The gas containing is extracted. The extracted gas is appropriately measured for the gas component composition by the component measuring element, adjusted for the gas component by the component adjusting element as necessary, and then circulated again to the purified soil region 18 via the injection pipe 13.
[0037]
The series of operations from gas extraction to re-injection / circulation can be either continuous or intermittent. However, it is preferable to take a continuous operation in order to efficiently promote the purification effect.
[0038]
Alternatively, the gas containing the pollutant in the contaminated soil region may be sucked and extracted from the inlet 14 and circulated to the purified soil region through the gas circulation unit 12 and the suction port 16.
Hereinafter, the present invention will be described in detail by way of examples.
[0039]
【Example】
[0040]
[Example 1]
(Create test soil tank)
2 and 3, an injection pipe 25 having an injection port 26 at a depth of 300 mm in the center, four extraction pipes 27 (each having five suction ports with strainers) and a soil layer 21 in the vicinity of the wall surface A gravel layer 22 (40 mm) is placed in the lower layer of a 200-liter drum equipped with a stainless steel tube (not shown) for sampling the gas, and a fine soil and silt test soil layer 21 (750 mm) containing 12 ppm of trichlorethylene is placed thereon. Further, a gravel layer 23 (40 mm) and a sealing layer 24 (40 mm) made of polyurethane were provided as an upper layer to make a test soil tank.
[0041]
(Synthesis of volatile organic compound adsorption materials)
In a 300 ml polymerization vessel equipped with a reflux condenser, a stirrer and a thermometer, 160 ml of water and 2 grams of an anionic surfactant (sodium dodecylbenzenesulfonate) were added and heated to 72 ° C. Next, 2.5 grams of potassium persulfate was added and dissolved, and then 50 grams of a monomer mixture consisting of styrene, butyl acrylate, methyl methacrylate, acrylic acid, acrylamide (40: 30: 24: 4: 2 by weight) and dodecylbenzene. 3 g of sodium sulfonate was mixed and continuously injected in 2 hours, and after completion of addition, the mixture was polymerized at 72 ° C. for 3 hours to obtain an aqueous dispersion of anionic polymer particles having a particle size of about 0.2 μm (resin solids). Min. 25%).
[0042]
(Formation of purified soil area)
A colony of Corynebacterium sp. J1 (Accession No .: FERM BP-5102) on M9 agar medium containing 0.5% sodium malate contains 1.0% sodium malate in the Sakaguchi flask 3 L of M9 medium was inoculated and cultured with shaking at 25 ° C. for 24 hours. 2 times the concentration of M9 medium containing 3% sodium malate and 0.3g / L phenol for J1 inducement, 3L of the above culture solution and 160g of an anionic polymer particle aqueous dispersion obtained by the above method. The mixture was mixed to prepare an injection solution. A spherical purified soil region 29 having an injection radius of about 200 mm was formed by an injection pump (not shown) through the injection pipe 25 of the test soil tank.
[0043]
(Gas extraction, circulation purification)
Immediately after the formation of the purified soil region, the gas in the test soil tank 21 is sucked (5 L / min.) By the air pump 27 through the extraction pipe 27, and at the same time, the sucked gas is injected and circulated into the purified soil region 28 through the injection pipe 25. It was. Every hour after the start of circulation, the gas in the soil tank is sampled from a stainless steel tube (not shown) inserted in the upper part of the test soil tank 21, the vicinity of the inlet and the lower part of the test soil tank, and the concentration of trichlorethylene contained in the gas is determined. Measurement was performed by gas chromatography (FID detector). The time course of the average concentration is shown in FIG.
[0044]
[Comparative Example 1]
A test soil tank similar to the example was prepared, and the same purified soil region as that of the example was formed except that the anionic polymer particle aqueous dispersion was not included in the injected solution. After the formation of the purified soil area, gas extraction and circulation are performed in the same manner as in the example, and the gas in the soil tank is sampled from the stainless steel tube every hour, and the concentration of trichlorethylene contained in the gas is measured by gas chromatography (FID detector). It was measured. The time course of the average concentration is shown in FIG.
[0045]
[Comparative Example 2]
A test soil tank similar to the example was prepared, and the same purified soil region was formed as in the example except that the J1 strain was not included in the injection solution. After the formation of the purified soil area, gas extraction and circulation are performed in the same manner as in the example, and the gas in the soil tank is sampled from the stainless steel tube every hour, and the concentration of trichlorethylene contained in the gas is measured by gas chromatography (FID detector). It was measured. The time course of the average concentration is shown in FIG.
[0046]
[Comparative Example 3]
A test soil tank similar to that of the example was prepared, and the same purified soil region as that of the example was formed except that the anionic polymer particle aqueous dispersion and J1 were not contained in the injection solution. After the formation of the purified soil area, gas extraction and circulation are performed in the same manner as in the example, and the gas in the soil tank is sampled from the stainless steel tube every hour, and the concentration of trichlorethylene contained in the gas is measured by gas chromatography (FID detector). It was measured. The time course of the average concentration is shown in FIG.
[0047]
[Example 2]
The same test soil tank as in Example 1 was prepared. In Example 1, the infusate did not contain phenol for inducing, and instead of J1, Inducerless JM1 (Life Technologies Research Institute accession number: FERM BP -5352) was used to form the same purified soil area except that the colony was used. After the formation of the purified soil area, gas extraction and circulation were performed as in Example 1, and the gas in the soil tank was sampled from the stainless tube every hour, and the concentration of trichlorethylene contained in the gas was gas chromatographed (FID detector). Measured with The time course of the average concentration is shown in FIG.
[0048]
【The invention's effect】
The purification method of the present invention has enabled efficient purification by a simple construction method and operation.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an example of a system that can implement the method of the present invention. FIG. 2 is a schematic diagram of a cross section of a test soil tank used in Examples and Comparative Example 2. FIG. Schematic view from the top of the test soil tank [Fig. 4] Graph showing the change in the concentration of trochlorethylene contained in the test soil obtained in Examples and Comparative Examples 1 and 2 [Fig. 5] Purification using an injection pipe Schematic diagram showing a method for forming a soil area [Fig. 6] Schematic diagram showing a method for forming a purified soil area using a construction machine used for ground improvement [Fig. 7] Using a construction machine used for ground improvement FIG. 8 is a conceptual diagram showing a method for forming a purified soil area by forming excavation holes. FIG. 9 is a diagram showing a method for forming a purified soil area by providing excavation holes. Conceptual diagram [Simple explanation of symbols]
11 Liquid injection unit 12 Gas circulation unit 13 Injection pipe 14 Injection port 15 Extraction pipe 16 Suction port 17 Contaminated soil region 18 Purified soil region 21 Test soil layer 22 Lower gravel layer 23 Upper gravel layer 24 Seal layer 25 Injection pipe 26 Note Inlet 27 Extraction pipe 28 Purified soil area 29 Air pump 41 Liquid injection unit 42 Injection pipe 43 Inlet 44 Contaminated soil area 45 Purified soil area 51 Injection chemical supply system 52 Stirring power 53 Stirring blade 54 Contaminated soil area 55 Purified soil area 61 Excavation Hole 62 Purified soil area 63 Contaminated soil area

Claims (6)

This is a purification method that utilizes the decomposition action of microorganisms in soil contaminated with volatile organic compounds, and has a property of adsorbing the decomposed microbial materials and the volatile organic compounds to the contaminated soil region (hereinafter referred to as volatile organic compound adsorption). Including a step of forming a purified soil region containing a material) and a step of extracting a gas containing a pollutant from the contaminated soil region and circulating the extracted gas to the contaminated soil region through the purified soil region Soil purification method. The method according to claim 1, wherein the volatile organic compound adsorbing material comprises water-dispersible polymer compound fine particles. The method according to claim 2, wherein the surface charge of the polymer fine particles is negative. 4. The method according to claim 2, wherein the polymer fine particles have a particle diameter of 0.01 to 5 [mu] m. The method according to claim 1, wherein the volatile organic compound is a volatile organochlorine compound. 6. The method according to claim 5, wherein the volatile organochlorine compound is trichlorethylene.

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