JP5054246B1 - Method for recovering radioactive cesium from contaminated environmental media using lactic acid bacteria - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover radioactive cesium from soil contaminated with radioactive cesium or sludge environmental medium, and to release the radioactive cesium strongly bound to organic matter in the environmental medium from the environmental medium, such as biological methods. A method for easily adsorbing by the method is provided.
A method for recovering radioactive cesium from soil or sludge environmental medium contaminated with radioactive cesium, wherein the environmental medium is suspended by adding water to the environmental medium. And releasing anaerobic cesium bound to organic substances in the environmental medium by adding lactic acid bacteria to the anaerobic culture.
[Selection] Figure 6

Description

  The present invention relates to a method of releasing and recovering radioactive cesium from soil contaminated with radioactive cesium or sludge environmental medium using lactic acid bacteria. In particular, the present invention relates to a method for facilitating recovery by releasing radioactive cesium into water using lactic acid bacteria from soil or sludge environmental medium that is hard to release while strongly carrying radioactive cesium.

  Recently, purification of radioactive contamination of environmental media such as water and soil caused by leakage of radioactive materials due to accidents and troubles from nuclear power plants has been studied. When radioactive materials are released from the nuclear power plant into the atmosphere, the radioactive materials diffuse around while floating in the atmosphere. Radioactive substances fall to the ground due to rainfall, etc., enter water such as rivers and soil such as fields, and pollute every corner of these environmental media.

  Among the radioactive substances that cause radioactive contamination of environmental media, a particularly problematic substance is radioactive cesium with a long half-life. When radioactive cesium enters the soil, the radioactive cesium binds strongly with clay and organic matter contained in the soil, remains in the soil for a long time, continues to release radioactivity, and causes external exposure. In addition, when human cesium is taken into the body by ingesting crops grown using soil or water contaminated with radioactive cesium, the radioactive cesium is distributed throughout the body and exposed to internal exposure over a long period of time. Bring.

  As a method for removing radioactive cesium, a chemical treatment method such as a physical adsorption method using an inorganic ion exchanger or a selective ion exchange resin or a solvent extraction method using crown ether has been proposed (see Patent Document 1). ). Recently, the physical adsorption method using clay such as zeolite is also known in the press. These physical or chemical methods are effective to some extent for recovering radioactive cesium from high-level radioactive liquid waste, but from water and soil that has been contaminated at low concentrations and extensively due to radioactive leaks from nuclear power plants. In order to recover radioactive cesium, the efficiency is extremely low and the cost is high. In addition, chemical methods are not safe and impractical. Furthermore, the physical method has a huge amount of adsorbent that has adsorbed radioactive cesium, and there is a problem of securing land for intermediate treatment and final disposal.

  On the other hand, as a method for removing radioactive cesium, biological removal methods using microorganisms are also attracting attention, and the inventor of the present application uses a specific strain of Rhodobacter sphaeroides, a kind of photosynthetic bacteria, Has already proposed a method for purifying an environmental medium contaminated with (see Patent Document 2).

  This biological method is more effective for adsorption of radioactive cesium from environmental media than physical or chemical methods. However, when the environmental media is not water but soil or sludge, Since radioactive cesium is in a strongly bound state, no matter what method is used to adsorb it, it is difficult to release radioactive cesium from soil or sludge, and there are cases where radioactive cesium cannot be adsorbed effectively. is there.

JP-A-5-317697 Japanese Patent Application No. 2011-208475

  The present invention was devised in view of the current state of the prior art, and its object is to provide a method for recovering radioactive cesium from soil contaminated by radioactive cesium or sludge environmental medium, and strongly against organic matter in the environmental medium. It is intended to provide a method for releasing bound radiocesium from an environmental medium and easily adsorbing it by a conventionally known method such as a biological method.

  As a result of intensive studies to achieve the above object, the present inventor added water to soil or sludge environmental medium to suspend the environmental medium, and then added and cultured lactic acid bacteria that are safe for the human body. As a result, it was found that the organic matter in the environmental medium liberates radioactive cesium and releases it into water, and can be easily adsorbed by a conventionally known method, thereby completing the present invention.

That is, this invention consists of the following (1)-(4).
(1) A method for recovering radioactive cesium from soil or sludge environmental medium contaminated with radioactive cesium, wherein the environmental medium is suspended by adding water to the environmental medium. A method comprising releasing radioactive cesium bound to an organic substance in an environmental medium into water by adding lactic acid bacteria and anaerobic culture.
(2) The method further comprises adsorbing the radioactive cesium released in water to the cells of Rhodobacter sphaeroides SSI strain (FERM P-21462) and collecting the cells adsorbed with radioactive cesium from the environmental medium. (1) characterized by these.
(3) Described in (1) or (2), wherein the soil is a field soil, a house garden soil, a park soil, a school school ground soil, a satoyama soil, or a forest soil the method of.
(4) The method according to (1) or (2), wherein the sludge is a sludge accumulated at the bottom of a swimming pool, a water treatment plant, a sewage treatment pond, or an agricultural pond. .

  Since the method of the present invention is carried out by adding lactic acid bacteria having the ability to decompose lactic acid by degrading organic matter in contaminated soil or sludge to water-suspended soil or sludge, it strongly supports radioactive cesium. The organic matter to be decomposed immediately can release and release radioactive cesium into water. Therefore, since radioactive cesium is in a state released from the soil or sludge into water, it can be adsorbed very easily by a conventional adsorption method such as a biological method. Moreover, since the method of this invention releases radioactive cesium from soil or sludge by addition of lactic acid bacteria and water, work is easy and it is very safe.

FIG. 1 shows the measurement results of Experiment 1A. FIG. 2 shows the measurement results of Experiment 1B. FIG. 3 shows the measurement results of Experiment 1C. FIG. 4 shows the measurement results of Experiment 2A. FIG. 5 shows the measurement results of Experiment 2B. FIG. 6 shows the measurement results of Experiment 2B. FIG. 7 shows the measurement results of Experiment 2C. FIG. 8 shows the measurement results of Experiment 2C. FIG. 9 shows the measurement results of Experiment 2D. FIG. 10 shows the measurement results of Experiment 2D.

  When the environmental medium contaminated with radioactive cesium is water, the radioactive cesium is liberated in the water, so that it can be adsorbed easily. However, when the environmental medium is soil or sludge, Since radioactive cesium is strongly bound to organic matter, its adsorption is not easy. In the method of the present invention, when the contaminated environmental medium is soil or sludge, the radioactive cesium is to be recovered from the organic matter in the soil or sludge after being released by lactic acid bacteria. Radioactive cesium bound to organic matter in the environmental medium by adding water to the environmental medium of the soil or sludge to make the environmental medium in a suspended state, adding lactic acid bacteria to the environmental medium in this state and performing anaerobic culture Is released into water. By this method, even if the polluted environmental medium is soil or sludge, radioactive cesium can be easily adsorbed by a conventionally known adsorption method.

  The environmental medium contaminated with radioactive cesium to be purified by the method of the present invention is soil or sludge, for example, soil or sludge in the vicinity of a nuclear power plant that has caused radioactive leakage due to an accident or trouble. Specifically, the soil includes soil in a field near a nuclear power plant, soil in a garden in a house, soil in a park, soil in a school yard, soil in a satoyama, and soil in a forest. Examples of sludge include sludge that accumulates at the bottom of swimming pools, water treatment plants, sewage treatment ponds, agricultural ponds, etc. in the vicinity of nuclear power plants.

  In the method of the present invention, first, water is added to the soil or sludge environmental medium to suspend the environmental medium. Specifically, the amount of water added is sufficient if the soil or sludge is in a suspended state. For example, it is preferable to add 20% by volume or more of water to the volume of the environmental medium of the soil or sludge. . The environmental medium is suspended in order to secure a release site for radioactive cesium incorporated in the environmental medium, and to secure a culture area for lactic acid bacteria to be added later. This is also for facilitating the adsorption of radioactive cesium released from the medium.

  Next, in the method of the present invention, lactic acid bacteria are added to suspended soil or sludge environmental medium. Lactic acid bacteria are bacteria having the ability to strongly lactically ferment sugar, and those belonging to the genus Lactobacillus, Streptococcus, Pediococcus, Leuconostoc and the like are preferable. In the present invention, any type can be used as long as it can decompose organic matter in soil or sludge environmental medium to produce lactic acid. Not only homolactic bacteria producing only lactic acid but also heterolactic bacteria producing lactic acid and acetic acid can be used. When using lactic acid bacteria, obtain a small amount of the target environmental medium in advance, add the lactic acid bacteria that are to be used to the suspension, and incubate them to confirm the high organic matter decomposing ability. It is preferable to select them. Thus, when a lactic acid bacterium having a high ability to decompose organic matter is selected in advance, the decomposition of the organic matter in the soil or sludge environmental medium and the release of radioactive cesium into water become more efficient.

  Next, the environmental medium to which lactic acid bacteria are added is anaerobically cultured. Specifically, the environmental medium may be maintained for a certain period without aeration at a temperature suitable for the growth of lactic acid bacteria. The culture temperature varies depending on the type of lactic acid bacterium, but is generally 10 to 40 ° C, preferably 15 to 35 ° C. In addition, although the amount of lactic acid bacteria varies depending on the culture conditions, the culture period is generally about 1 day to about 2 weeks after the addition of lactic acid bacteria. Glucose, peptone, and vitamins (vitamin B1, nicotinic acid, biotin, etc.) may be added to the culture solution before the start of culture or during culture, if necessary, in order to promote the growth of lactic acid bacteria. Further, instead of vitamins, waste containing a large amount of vitamins such as brewer's yeast, fish or animal viscera may be added. By anaerobic culture, lactic acid bacteria decompose organic substances in the soil or sludge environmental medium, and at that time, radioactive cesium bound to the organic substances is released into water.

  The radioactive cesium released into the water from the soil or sludge environmental medium by the lactic acid bacteria can then be adsorbed by conventionally known methods. The adsorption can be performed by a biological, physical, or chemical method, but is preferably performed by a biological method from the viewpoint of safety, efficiency, and cost.

  In the case of using a biological method, for example, radioactive cesium can be adsorbed to cells of a specific microorganism strain called Rhodobacter sphaeroides SSI strain (hereinafter simply referred to as SSI strain). The SSI strain is a natural mutant obtained during subculture of the photosynthetic bacterium Rhodobacter sphaeroides S strain (hereinafter simply referred to as S strain). The SSI strain has been deposited as FERM P-21462 at the Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba City, 1-1-1 Central, Ibaraki Prefecture (deposited on December 7, 2007).

  Conventional photosynthetic bacterial strains, including the parent strain S, do not show any aggregability, but SSI strains produce large amounts of cell surface proteins and RNA during culture. Cells aggregate. Due to the presence of these proteins and RNA, the SSI strain is considered to electrically adsorb radioactive cesium. The mycological properties of the SSI strain are exactly the same as the parent S strain, except that it exhibits agglutination due to the production of large amounts of cell surface proteins and RNA.

  SSI stocks are safe and harmless to the human body and the environment. In fact, the photosynthetic bacteria to which the SSI strain belongs are soil bacteria that play an important role in the purification of the environment in nature, can decompose organic matter in human waste and food wastewater, and are useful for purification of water quality.

  The SSI strain can be grown under any culture conditions as long as the strain can grow effectively. For example, a glutamate-malate medium is used at a temperature of 30 ° C. to 35 ° C. under aerobic dark conditions or standing light. It can be easily performed by culturing under conditions (under irradiation with tungsten light of 5 klux to 10 klux).

  The SSI strain can be used by being administered to an environmental medium in various forms. For example, the SSI strain can be used to produce a granular bacterial cell aggregate, which is smaller than a suspended environmental medium. Prepared by putting the bacterial cell aggregate into a mesh bag with an opening and administering the bag into an environmental medium, or by impregnating the culture medium of the bacterial cell of SSI strain into a carrier made of ceramic etc. and drying it A method of administering the microbial cell-immobilized carrier in an environmental medium is preferable.

  The granular bacterial cell aggregate can be prepared by preparing a liquid suspension of the bacterial cells of the SSI strain, making a mixed solution to which polysaccharides are added, and drying the mixed solution. Polysaccharides have the role of gelling a liquid suspension to bind cells together. For example, alginic acid, starch, carrageenan, pectin and the like are used. The bacterial cell aggregate is preferably formed into a substantially spherical shape by a molding machine, and the particle size thereof is preferably 0.5 cm to 3 cm. As the bag with a mesh, a bag having a mesh size that cannot pass through the bacterial cell aggregate but can pass through the suspended environmental medium can be used. Thereby, contact of an environmental medium and a microbial cell aggregate and prevention of the outflow of the microbial cell aggregate from a bag are achieved.

  As the carrier used for the microbial cell immobilization carrier, those having a surface structure capable of immobilizing microbial cells can be used. For example, a porous carrier is preferable in terms of the specific surface area. The raw material of the porous carrier is not particularly limited, but it is preferable to use waste glass from the viewpoint of cost reduction. It is preferable that the porous carrier contains a magnetic material by means such as applying iron powder to a part of the surface and sintering it, in order to facilitate recovery with a magnet.

  The collection time of the bacterial cells varies depending on the amount of the bacterial cells and the culture conditions, but is generally about 1 day to about 2 weeks after the addition of the bacterial cells. In the case of a bacterial cell aggregate, the collected bacterial cells can be greatly reduced in weight and volume by drying or incineration. Moreover, the bag collect | recovered from the environmental medium can put a new microbial cell aggregate again after a decontamination process, and can be used repeatedly. In the case of a cell-immobilized carrier, the carrier recovered from the environmental medium is washed with hydrochloric acid or nitric acid to separate the radioactive cesium and the bacterial cell from the carrier to prepare an aqueous solution containing the radioactive cesium in a high concentration. be able to. This aqueous solution can be subjected to further incineration, chemical treatment and final disposal.

  When a physical method is used, radioactive cesium is adsorbed by, for example, a physical adsorption method using an inorganic ion exchanger or a selective ion exchange resin, or a physical adsorption method using clay such as zeolite. In addition, when a chemical method is used, radioactive cesium is separated by a chemical treatment method such as a solvent extraction method using crown ether.

  Hereinafter, the present invention will be concretely demonstrated by examples. In addition, description of an Example is given only for an understanding of invention, and this invention is not limited at all by this.

1. Decontamination of radioactive Cs from sediment (sludge) accumulated in swimming pool water
experimental method
Preparation of concentrated sludge Sludge collected at the bottom of a public school pool in Fukushima City was collected. Initially, I was asked to decontaminate the water in the pool, but as of September 2011, the pool water was only detected with a radioactivity of 1.10 μSv / h or less, and the bottom had a slightly higher activity. (1.38 μSv / h) was detected. The sludge was the leaves of the surrounding hedge trees entering the water and corroded by the wind, and the sea urchins that were generated in the summer were corroded and accumulated on the bottom. As of September, the air dose around the pool was 1.18-1.39 μSv / h. A high dose of 20-30 μSv / h was detected from the sludge in the groove around the pool.

  Therefore, 1 ton of muddy water containing sludge at the bottom of this pool was drawn into the tank with a submersible pump, and 1 L of a 0.5% by weight solution of natural coagulating precipitant chitosan (Fuji Clean, Sapporo) was added, pH 6.5 The mixture was allowed to stand at 7.0 for 24 hours to precipitate sludge, and then the supernatant was discharged to collect 30 L of sludge that had settled to the bottom. The sludge showed a radiation dose of 12-15 μSv / h. This sludge was used in the experiment as a concentrated sludge.

The concentrated sludge had a solid content of 6.69 g dry solid / L and COD (Mn) of 32,000 mg / L. The radioactivity is 14.4 μSv / h, ¹³⁴ Cs is 6,912 Bq, ¹³⁷ Cs is 8,567 Bq (15,479 Bq in total as radioactive Cs), and radioactive iodine ¹³¹ I is not detected at 2 Bq or less. (Analysis with germanium semiconductor detector [Canberra, USA] at Fukushima City Environmental Radiation Monitoring Center).

Cultivation of Rhodobacter sphaeroides SSI strain and production of cell assembly Rhodobacter sphaeroides SSI strain is cultured using a normal glutamate malate medium (GM medium) in a 1.5 L roux culture bottle. This was carried out for 2-3 days under stationary light conditions (5 klux). After the culture, the culture solution was centrifuged (10,000 × g, 20 minutes) and concentrated to OD660 = 20. An equal amount of 4% by weight alginic acid (final concentration 2% by weight) was added to this concentrated solution and stirred well to form spherical particles having a diameter of about 2 cm. These spherical particles were immersed in a 2% by weight calcium chloride solution overnight to prepare granular bacterial cell aggregates.

Concentrated sludge decontaminated bacterial cell aggregates by bacterial cell aggregates About 210 pieces (about 10 g dried) in a mesh bag (nylon, 1.0 x 1.0 cm mesh, cylindrical shape with a diameter of 15 cm and a length of 30 cm) (Corresponding to the weight of cells), 9 bags were prepared, put into a concentrated sludge, and left for a predetermined period.

Measurement of radioactivity Radioactivity was measured using Aloka TGS121 (Aloka Hitachi) and Dose RAE2 (PRM-1200, USA). For Aloka TGS121, the sensor portion was wrapped in a waterproof vinyl bag and measured at a water depth of 1-3 cm. About DoseRAE2, since it was small, the whole was covered with the waterproof vinyl bag, and it immersed in water depth 1-3cm and measured. Each was measured three times, the average value was determined, and displayed in μSv / h and cps units. 1 μSv / h was 3.33 cps.

(Experiment 1A) Sludge decontamination (repeated batch processing)
The collected sludge was adjusted to pH 2.0-1.6 with concentrated nitric acid and allowed to stand for 24 hours. The purpose of this treatment was to dissolve Cs adsorbed on sludge with nitric acid. However, as a result, Cs was hardly dissolved as Cs ^{+ in} water. In the experiment of the National Institute of Advanced Industrial Science and Technology, elution of Cs from soil using nitric acid is attempted, but it hardly dissolves at room temperature, and it is considered difficult to elute Cs by decomposition of nitric acid at room temperature. However, this nitric acid-treated sludge was used in the experiment as a lysate-concentrated sludge in the hope that it would elute a little.

Experimental conditions (1) 50 L of dissolved concentrated sludge was placed in a 55 L square plastic container.
(2) 4 g / L of glucose and 0.15 g / L of peptone were added thereto, and the pH was adjusted to 6.5 to 7.0 with 6N-NaOH or 6N nitric acid. Since the temperature was outdoor, it was not controlled (28.2 to 15.9 ° C.).
(3) Aeration was performed at 0.2-0.3 vvm, and the first batch treatment was performed.
(4) Every other day, the bag was taken out of the container, the sludge was thoroughly stirred, and the radioactivity was immediately measured at a depth of 1-3 cm. Radioactive substances in water were measured by repeatedly filtering dissolved sludge with cotton cloth to obtain transparent water, and then measuring the radioactivity at a depth of 1-3 cm.
(5) Three days later, the bag remains intact, the dissolved and concentrated sludge is removed, a new dissolved and concentrated sludge is added, glucose and peptone are added in the same manner, and the pH is adjusted and aerated at 0.2 to 0.3 vvm. The second batch treatment was performed, and the radioactivity was measured in the same manner.
(6) Three days later, the dissolution and concentration sludge was similarly replaced, and the third batch treatment was performed in the same manner. Similarly, the radioactivity was measured.

Experimental Results The experimental results are shown in FIG. The following can be seen from FIG.
(1) In radioactive decontamination of dissolved concentrated sludge, the radioactivity of the first 47.78 cps solution was reduced to 8.66 cps after 2 days, with a removal rate of 82%. The air dose around this pool is 1.2 μSv / h, or 4.0 cps of radioactivity, and if this is subtracted as background, (8.86−4.0) / (47.78−4.0) ) X100 = 11.1%, that is, about 90% of radioactive material was decontaminated. Moreover, the radioactive substance in water was hardly detected and was almost the same as the background value.
(2) The radioactivity was similarly reduced in the second batch treatment. However, the degree of reduction was more gradual than the first time, probably because the temperature decreased. Rhodobacter sphaeroides SSI strain has been shown to be highly active at 25-35 ° C.
(3) The radioactivity was also reduced in the third batch treatment.
(4) From the above results, the Rhodobacter sphaeroides SSI strain cell assembly was transferred to Rhodobacter sphaeroides SSI strain cells by stripping Cs bound to sludge. It was suggested that
In addition, it was confirmed that the radioactivity was reduced even after three repeated treatments, and it was revealed that the bacterial cell aggregate could be used repeatedly.
The reason why the radioactivity can be removed is that Rhodobacter sphaeroides SSI produces an adhesive substance (EPS) on the surface of the fungus, which is negatively charged, similar to the removal of harmful metal Cd ^2+. It is estimated that Cs ⁺ ions are attracted by electrical attraction. In addition, it has been reported that photosynthetic bacteria are actively taking up potassium by a potassium pump, and Cs having similar chemical properties may also be taken into cells by a potassium pump. Therefore, it is estimated that Cs ⁺ adsorbed on the sludge is removed.

(Experiment 1B) non nitrated sludge decontamination experiment 1A, were subjected to nitric acid treatment for the purpose of dissolving the Cs ⁺ as much water Cs, most Cs ⁺ have not dissolved in water. Therefore, in this experiment, it was investigated whether radioactive decontamination of sludge was possible by using concentrated sludge directly without nitric acid treatment.

Experimental conditions Batch treatment was performed under the same conditions as in Experiment 1A, except that concentrated sludge was used instead of nitric acid-treated sludge (dissolved concentrated sludge), and radioactivity measurement was also performed under almost the same conditions.

Experimental Results The experimental results are shown in FIG. The following can be seen from FIG.
(1) Contaminated concentrated sludge could be decontaminated as it was without using dissolved concentrated sludge. On the first day, the radioactivity was reduced from 38.93 cps to 12.45 cps, with a removal rate of 86%. Considering the background, (12.45-4.0) / (38.93-4.0) x100 = 26.48%, that is, 73.5% decontamination was completed. In this experiment, the temperature was low, the activity of Rhodobacter sphaeroides SSI strain was not sufficient, and Cs once adsorbed to Rhodobacter sphaeroides SSI strain was slightly re-eluted. Did not decrease so much.
(2) From the above results, it was suggested that nitric acid treatment is not always necessary, and that concentrated sludge can be decontaminated directly. This is important in terms of reducing cost and complexity of operation.

(Experiment 1C) Radioactive substance decontamination when the amount of bacterial cell aggregates was halved Considering practical costs, decontamination was performed with the amount of bacterial cell aggregates halved.

Experimental conditions (1) Batch treatment was performed under the same conditions as in Experiment 1A except that the amount of bacterial cell aggregates was halved, and radioactivity measurement was also performed under substantially the same conditions.

Experimental Results The experimental results are shown in FIG. The following can be seen from FIG.
(1) There was sufficient radioactivity removal ability even if the amount of the bacterial cell aggregate was halved. Further weight loss of the cell aggregate is also conceivable.
(2) No radioactivity was detected in the sludge moisture fraction, as in Experiment 1A. It was confirmed that most of the radioactive material was present in the sludge precipitation fraction.

(Experiment 1D) Volume reduction by drying and incineration of cell aggregates after radioactive decontamination In the conventional decontamination method of radioactive substances, the amount of intermediate waste after removal becomes enormous, It is a problem. Since the cell aggregate used in the method of the present invention is composed of a photosynthetic bacterial cell and a natural organic substance such as Ca alginate, the volume could be reduced by drying and incineration.

Experimental conditions (1) A part of the bacterial cell aggregate (852 g in wet weight) after being used for radioactive decontamination was placed in a beaker and heat-dried in an oven at 80-900C for 3 days.
(2) Further, carbonized at 500-6000C and incinerated. This is because if Cs is 6400C or higher, it may be vaporized and scattered.
(3) This experiment was conducted in an area with little radioactivity. The background value was 0.12 μSv / h.

Experimental Results (1) The weight of the microbial cell aggregate after drying was 23.8 g, and a weight reduction of 97.2% was possible.
(2) During this drying, the air dose in the oven was 0.12-0.13 μSv / h, which was almost the same as the background value. This indicates that the radioactivity has not leaked into the air.
(3) The weight of the cell aggregate after carbonization and incineration (after about 1 day) was 5.59 g, and a weight reduction of 99.3% was possible. The air dose in the oven was 0.12-0.13 μSv / h, which was almost the same as the background value. This indicates that the radioactivity has not leaked into the air.
(4) The volume of the bacterial cell aggregate could be reduced by 98.3% after carbonization and incineration.
(5) As described above, it was possible to reduce the volume and the volume of the intermediate waste containing the radioactive substance by about 98 to 99% without leakage of radioactivity. This carbonized / incinerated ash requires a final treatment because it contains a large amount of radioactive material, but the volume of intermediate treatment can be greatly reduced and is extremely useful from a practical standpoint.

2. Radioactive decontamination of soil with bacterial cell assembly (Experiment 2A) Decontamination of clay soil with bacterial cell assembly Since sludge was successfully radioactively decontaminated, Rhodobacter sphaeroides SSI strain Attempt was made to decontaminate the soil. As the contaminated soil, clayey contaminated soil widely distributed in Fukushima Minamisoma City was used.

Experimental conditions (1) 5 kg (wet weight) of clayey soil and 10 L of water (radioactive material 0.1 μSv / h or less) were placed in a 20 L square container and well suspended. Four of the same were prepared.
(2) No bacterial cell aggregate was put in one container and used as a control. The remaining three containers were each loaded with one bag, two bags, or three bags with varying amounts of bacterial cell aggregates. As in Experiment 1A, 210 bacterial cell aggregates were placed in one bag. Further, as in Experiment 1A, glucose 4 g / L and peptone 0.15 g / L were added, pH was adjusted to 6.0-7.5, and aeration was performed at 0.2-0.3 vvm. Sampling was performed every other day to measure radioactivity. The temperature was kept at 25 ° C. with a heater.
(3) For sampling, the bag was taken out of the container, the solution was well suspended, and immediately after Experiment 1A, the sensor was immersed in the solution (water depth: 1-3 cm) and the radioactivity was measured.
(4) At the time of sampling, the residual glucose concentration in the container was measured with a test paper, and if it did not remain, glucose and peptone were added in the same manner.
(5) The air dose at the experimental site in Minamisoma was 0.3-0.5 μSv / h during the experimental period.

Experimental Results The experimental results are shown in FIG. The following can be seen from FIG.
(1) Radioactive decontamination of clay soil by the cell assembly of Rhodobacter sphaeroides SSI strain is not as decontamination as sludge, and even in a container filled with 3 bags, the first 24.18 cps after 7 days The radioactivity was 20.15 cps, a reduction of only about 16%. Furthermore, even if a new bacterial cell aggregate was replaced and introduced on the 8th day, it was 16.78 cps after 15 days, a reduction of only about 31%.
(2) From the above results, the adsorption of radioactive Cs to clayey soil was stronger than the adsorption to sludge, and sufficient decontamination was not easy with the Cs suction of Rhodobacter sphaeroides SSI strain.

(Experiment 2B) Decontamination of contaminated soil by anaerobic fermentation and lactic acid fermentation From Experiment 2A, it was estimated that Cs adsorption to clayey soil was quite strong. This was consistent with the fact that it was not easy to elute Cs by treating soil with nitric acid or acid.
On the other hand, the present inventors have been conducting purification experiments on sludge accumulated in rivers and the seabed for a long time, but found that lactic acid producing bacteria that decompose organic matter and produce lactic acid are widely inhabited in sludge. Yes. In addition, it has been found that addition of vitamins (vitamin B1, nicotinic acid, biotin) to these bacteria increases lactic acid production activity, promotes anaerobic fermentation, and promotes organic decomposition of sludge. Therefore, there is a possibility that the organic matter in the contaminated soil is decomposed in anaerobic conditions due to the action of lactic acid producing bacteria and anaerobic digestive bacteria, and Cs strongly adsorbed by the organic matter in the soil may be easily eluted in the aqueous solution. Inspired.
The lactic acid-producing bacteria group was used after being cultured in a lactic acid bacteria culture medium from a commercially available environmental purification material (Ehime AI) used for purification of garbage, sludge, and rivers. This environmental purification material is an environmental purification material consisting of yogurt, natto, and yeast, and is widely used in Ehime Prefecture.

Experimental conditions (1) As soil, humus soil containing a lot of radioactive leaves and other soils was collected from soil in Satoyama, Minamisoma City. Two things were prepared by adding 10 L of water to 5 kg (wet weight) of clay soil containing humus. Each was placed in a 20 L transparent cylindrical container and stirred well to be in a suspended state. When the radioactivity of this suspended clay soil was measured, it had a radioactivity of 24.38 cps immediately before the start of the experiment.
(2) The lactic acid bacteria group was cultured as follows.
Lactic acid bacteria medium (BCP liquid medium: glucose 1.0 g / L, yeast extract 2.5 g / L, peptone 5.0 g / L, Tween 80 1.0 g / L, L-cysteine 0.1 g / L, bromocresol purple 1 g of a commercially available Ehime AI solution was added to 1 L of a medium sterilized at 115 ° C. for 20 minutes and cultured at 35 ° C. for 6 days under static dark conditions. After 6 days, the group of lactic acid bacteria grew to OD660 = 0.7, the culture solution showed an acidic yellow color, and it was confirmed that 0.4 g / L of lactic acid was produced (using Boehringer Mannheim F kit). A species of lactic acid bacteria that inhabit many groups. As a result of isolation of Aspergillus oryzae occupying the majority (about 90% or more) of the seed culture solution of this group of lactic acid bacteria and identifying the gene sequence, 99.4% of the known Lactobacillus casei JCM1134 (Accession No. D16551) was identified. It had the homology of. From this, this seed culture solution was considered to be a culture solution containing Lactobacillus casei as a main lactic acid bacterium.
(3) Glucose 4 g / L, peptone 0.15 g / L, and vitamins (vitamin B1 5 mg / L, nicotinic acid 5 mg / L, biotin 0.05 mg / L) are added to the two containers prepared in (1) It was. As a control, bacteria were not added to one container, and 1 L of a lactic acid bacteria group culture solution was added to the remaining containers and stirred well, and both were subjected to anaerobic fermentation at 35 ° C.
(4) Sampling was performed every 2-3 days. Stir the cylinder well and let it stand for 20 seconds. After the precipitate and the turbid suspension (mud fraction) are clearly separated, the supernatant suspension is separated by decantation. The radioactivity of the sedimented soil fraction was measured (measured by pushing a sensor into the soil). Furthermore, a part of the mud fraction was centrifuged (3,000 rpm, 10,000 × g, 20 minutes), a transparent water fraction was also collected, and the radioactivity at a depth of 1-3 cm was measured in the same manner.
(5) Glucose concentration was measured at the time of sampling, and glucose and peptone were similarly added when not detected.

Experimental Results Experimental conditions are shown in FIGS. The following can be seen from FIGS.
(1) In the control anaerobic fermentation alone, a relatively large amount of radioactivity remained in the soil fractions precipitated after 2 and 6 days, and not much radioactivity was detected in the supernatant mud fraction ( FIG. 5). On the other hand, when the lactic acid bacteria group was added, the radioactivity of the precipitated soil fraction was greatly reduced over 3-14 days (FIG. 6). In contrast, a relatively large amount of radioactivity was detected in the supernatant mud fraction. In clear water, radioactivity was hardly detected in the control experiment.
(2) This is due to the combined action of lactic acid fermentation and anaerobic fermentation, the organic matter adsorbing Cs in the humus is decomposed, and Cs is eluted and suspended in the fine mud of the mud fraction. It suggests. It was considered that this Cs elution was promoted by the activity of the lactic acid bacteria group.
(3) When anaerobic fermentation was performed with the addition of lactic acid bacteria group, the clay soil separated after 14 days had a radioactivity of 17.83 cps at the beginning of 6.49 cps after 14 days, and had a radioactivity of about 64%. It was recognized that it was decontaminated. Furthermore, for the sediment fraction soil, the radioactivity that was 24.38 cps just before the start of the experiment became 8.32 cps after 14 days (FIG. 6), and it was confirmed that about 66% of the radioactivity was decontaminated. It was.
(4) As described above, the present inventors have found a new fact that 64% of soil radioactivity can be decontaminated by a combination of lactic acid bacteria and anaerobic fermentation. Such a report has not been reported so far, and is a very simple method, and is considered to be a useful decontamination method in terms of cost.

(Experiment 2C) Radioactive decontamination using a combination of Rhodobacter sphaeroides SSI strains and lactic acid fermentation and anaerobic fermentation In anaerobic fermentation and lactic acid fermentation, much of the soil radioactivity is divided into fine mud fractions. As a result, it was thought that radioactivity in the mud fraction could be regarded as sludge and decontaminated with the cell assembly of Rhodobacter sphaeroides SSI strain to further decontaminate the entire soil.

Experimental conditions (1) 5 kg each of clay soil containing humus soil and soil rich in sand were collected (Haramachi, Minamisoma City) and suspended in 10 L of water.
(2) Glucose, peptone, and vitamins were added and stirred well as in Experiment 2B. Furthermore, 1 L of lactic acid bacteria group culture solution was added and stirred well. Then, anaerobic fermentation and lactic acid fermentation were performed at 35 ° C. for 3 days.
(3) Three days later, two bacterial cell aggregates of Rhodobacter sphaeroides SSI strain (including 210 bacterial cell aggregates per bag) are added, and the temperature is set to 30 ° C., and glucose, peptone, and vitamins are added. Was added in the same manner, and decontamination was performed while aeration was performed at 0.2-0.3 vvm.
(4) Sampling was carried out by removing the bag as in Experiment 2A, and then stirring well and immediately measuring the radioactivity.
(5) The glucose concentration was measured at the time of sampling, and if consumed, glucose and peptone were added as in Experiment 2A.

Experimental Results Experimental results are shown in FIGS. 7 and 8 show the following.
(1) In the soil containing humus, the radioactivity, which was initially 42.42 cps, decreased to 12.65 cps after 14 days (FIG. 7). The removal rate was 70.2%.
(2) In the soil rich in sand, the radioactivity which was 28.62 cps at first was reduced to 10.48 cps after 14 days (FIG. 8). The removal rate was 63.3%. It seems that the soil containing a lot of sand was more easily eluted into the mud fraction of Cs in anaerobic fermentation and lactic acid fermentation, so that Cs was easily transferred to the cell aggregate.
(3) In this way, 63.3 to 70.2% of the radioactivity in the soil can be decontaminated by a combination of anaerobic fermentation, lactic acid fermentation and cell assembly treatment of Rhodobacter sphaeroides SSI strain. It became clear.

(Experiment 2D) Radioactive decontamination by combination of cell assembly of Rhodobacter sphaeroides SSI strain with lactic acid fermentation and anaerobic fermentation -Part 2
The same experiment as in Experiment 2C was conducted except that soil containing humus soil collected from another satoyama area in Minamisoma City was used. The radiation decontamination effect by the combination was reconfirmed. Furthermore, the radioactivity of each of the soil, mud, and water fractions was measured to confirm the radiation decontamination effect in more detail.

Experimental conditions (1) 5 kg of clay soil containing humus soil (soil of another satoyama several kilometers away from the point collected in Experiment 2C) was collected and suspended in 10 L of water. This was dispensed into three water tanks. Among these, one water tank was used for control experiments. At the start of the experiment, this soil itself had a radioactivity of 35.2 cps before being suspended in water.
(2) Glucose, peptone, and vitamins were added and stirred well as in Experiment 2C. Furthermore, 1 L of lactic acid bacteria group culture solution was added and stirred well. Then, lactic acid fermentation and anaerobic fermentation were performed at 35 ° C. for 4 days.
(3) After 4 days, 2 or 3 bags of Rhodobacter sphaeroides SSI strain cells (including 210 cell assemblies per bag) were placed in two water tanks. The remaining one aquarium was not charged with the bacterial cell aggregate as a control. Glucose, peptone, and vitamins were added in the same manner as in Experiment 2C at a temperature of 30 ° C., and decontamination was performed while aeration was performed at 0.2-0.3 vvm.
(4) After 14 days, two or three fresh cell aggregates of Rhodobacter sphaeroides SSI were replaced, and the addition of nutrients and aeration were continued in the same manner, and the experiment was continued for another 24 days.
(5) Sampling was performed in the same manner as in Experiment 2C, after the bag was removed, the mixture was well stirred and the radioactivity was measured immediately. However, in Experiment 2D, after measuring the radioactivity of the entire soil suspension (FIG. 9), some soil suspensions were allowed to stand as in Experiment 2B (however, the standing time was The soil was changed to 40 seconds instead of 20 seconds for ease of the experimental operation, and the precipitate fraction soil was separated into the upper mud fraction, and the radioactivity was measured (FIG. 10).
(6) The glucose concentration was measured during sampling, and if consumed, glucose, peptone, and vitamins were added as in Experiment 2C.

Experimental Results The experimental results are shown in FIGS. The following can be understood from FIGS.
(1) From FIG. 9, even if the soil was changed to another one, the same results as in Experiment 2C (see FIGS. 7 and 8) were obtained. That is, as shown in FIG. 9, four days after lactic acid fermentation and anaerobic fermentation, three bags of Rhodobacter sphaeroides SSI strains were introduced and aerated, and the radioactivity of the soil suspension was initially Although it was 24.41 cps, it decreased to 11.38 cps after 14 days. This was a 53.4% removal rate. However, when it was replaced with fresh SSI cell aggregates on the 14th day and the experiment was further continued, the radioactivity of the soil suspension decreased to 10.22 cps after 24 days. This was a 58.13% removal rate. An experiment using two bags of Rhodobacter spheroides SSI strains also showed similar results. In Experiment 2C, 63.3% to 70.2% of decontamination was possible, so Experiment 2D had a slightly lower result than Experiment 2C. This is different in organic matter depending on the type of humus and is easy to decompose. This seems to be due to the presence of humus and humus that is difficult to decompose. Thus, similar results were obtained even in soil containing other humus, because the decontamination techniques of Experiment 2C and Experiment 2D This proves the versatility that can be used for decontamination.
(2) In the experiment shown in FIG. 9, the radioactivity of the sediment fraction soil, the upper mud fraction, and the transparent water fraction after centrifugation was measured in detail. FIG. 10 shows the result. Only data for 3 bags of Rhodobacter spheroides SSI strains are shown.
As can be seen from FIG. 10, in the control experiment in which the bacterial cell aggregate was not added, the radioactivity transferred from the soil to the upper mud fraction by lactic acid fermentation and anaerobic fermentation and the radioactivity of the precipitated soil itself gradually increased. When 3 bags of the aggregate were added, the radioactivity of the upper mud fraction and the sedimented fraction soil gradually decreased, indicating that the radioactivity was adsorbed or absorbed by the bacterial cell aggregate. At this time, the radioactivity of the precipitate fraction soil in the experiment of adding 3 bags of bacterial cell aggregates 24 days later was 11.72 cps, and the radioactivity of the first soil was 35.16 cps, so the removal rate was 66 0.7%. The decontamination of the soil by lactic acid fermentation and anaerobic fermentation in Experiment 2B was a removal rate of 65.9%, and almost the same decontamination effect was obtained.
(3) There was almost no radioactivity in the clear water fraction, similar to sludge decontamination.
(4) Furthermore, when the bacterial cell aggregate was added, as shown in FIG. 10, the radioactivity removal of the upper mud fraction decreased from the initial 24.41 cps to 8.39 cps after 24 days, and 65 Since 6% decontamination can be performed, the decontamination effect is higher than lactic acid fermentation alone. In other words, by combining decontamination with Rhodobacter spheroides SSI strains with lactic acid fermentation rather than decontamination using only lactic acid fermentation, approximately 70% of the total radioactivity can be decontaminated in the soil and upper mud fraction. , Can greatly increase the decontamination effect.

  2. From the result of radioactive decontamination of soil, the method of the present invention is very effective in releasing radioactive cesium bound to organic matter in water by adding lactic acid bacteria to suspended soil and culturing anaerobically. It became clear that. This result suggests that the method of the present invention can also be applied to sludge having a lower radioactive cesium adsorption capacity than soil, and the radioactive cesium releasing effect is extremely high even when sludge is targeted.

  As described above, the method of the present invention can efficiently release radioactive cesium into the water from soil contaminated with radioactive cesium or sludge environmental medium. Moreover, since the method of this invention releases radioactive cesium from soil or sludge by addition of lactic acid bacteria or water, it is extremely safe.

  In particular, lactic acid bacteria and photosynthetic bacteria (Rodobacter spheroides SSI strain) used in the method of the present invention have been used as fertilizers, soil conditioners, and growth promoters in the agricultural field for many years, and safety has also been established. Physical radiation decontamination (zeolite treatment, etc.) and chemical radioactivity decontamination (crown ether, nitric acid, oxalic acid, ferrocyanide treatment, etc.) have not been established for safety and are affected by crops and the human body. Although it is unknown and is not acceptable for decontamination of agricultural soil and other soils, lactic acid bacteria and photosynthetic bacteria are familiar to farmers, and the method of the present invention is easy to accept.

  Furthermore, about 30% of the radioactivity (radioactive cesium) remains in the soil decontaminated with about 70% of the radioactivity by the treatment with the lactic acid bacteria and photosynthetic bacteria of the present invention, which is in the crystal structure of the soil. It is radioactivity derived from cesium that has been strongly bound, and cannot easily migrate into water. Even chemical treatment such as acid treatment cannot be eluted in water at room temperature and pressure. Therefore, even if the soil decontaminated by the method of the present invention is used for agricultural production or horticultural production, there is no possibility that the radioactive cesium that can be transferred already exists, and the radioactive cesium is not transferred to the plant body or crop. That is, the soil decontaminated by the method of the present invention is a radioactive cesium-insoluble soil, and if the residual radioactivity is low, the possibility of using it directly for agricultural production or horticultural production is also opened. Therefore, the method of the present invention is extremely useful industrially.

Claims (4)

  A method of recovering radioactive cesium from soil or sludge environmental medium contaminated with radioactive cesium, adding water to the environmental medium to suspend the environmental medium, and adding lactic acid bacteria to the environmental medium in this state And then releasing the radioactive cesium bound to the organic matter in the environmental medium into the water by anaerobic culture.   The method further comprises adsorbing radioactive cesium released in water to the cells of Rhodobacter sphaeroides SSI strain (FERM P-21462) and recovering the cells adsorbed with radioactive cesium from an environmental medium. The method of claim 1.   3. The method according to claim 1, wherein the soil is a field soil, a residential garden soil, a park soil, a school school ground soil, a satoyama soil, or a forest soil.   3. A method according to claim 1 or 2, wherein the sludge is a sludge deposited at the bottom of a swimming pool, a water purification plant, a sewage treatment pond, or an agricultural pond.

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