Method and device for removing strontium using spore-forming bacteria

Abstract

The objective of the present invention is to develop a contaminated water treatment system that can shorten the time spent working in radiation controlled areas and minimize the risk of exposure during work. [Solution] We developed a method to remove strontium by inducing spore formation outside a radiation controlled area, producing and storing bacteria in the spore forming process, transporting them into a radiation controlled area, and introducing the spore forming bacteria into a tank in which contaminated water is adjusted to an environment in which the spore forming bacteria can survive, thereby forming spores. Compared to conventional methods, the time spent working in a radiation controlled area is shorter, so not only is it possible to minimize the risk of exposure to radiation during work, but it is also easier to control the state of the spore forming bacteria, and it is possible to stably supply bacteria with spore forming ability, thereby maintaining high efficiency in contamination treatment.

Description

[Technical field]

[0001] The present invention relates to a safe method and treatment apparatus for treating contaminated water containing radioactive materials, particularly strontium, using spore-forming bacteria. [Background technology]

[0002] More than 12 years have passed since the Great East Japan Earthquake, but efforts to decommission the Fukushima Daiichi Nuclear Power Plant are still ongoing. Contaminated water has been an issue since the beginning of the accident, and although the release of treated water from the Advanced Liquid Processing System (ALPS) into the ocean will begin in 2023, treatment of the contaminated water is not complete. According to Tokyo Electric Power Company, the inflow of groundwater and rainwater into the reactor buildings has been reduced by approximately 540m from before countermeasures due to pumping of groundwater and construction of frozen soil walls. 3 / day (May 2014), but is still around 140m 3 / day (average for 2020), the amount of contaminated water generated is still a major issue.

[0003] Not only is the amount of contaminated water large, but it also contains 63 types of radioactive material, including strontium and cesium, making it difficult to treat. There are two main methods for treating contaminated water: using chemicals or adsorbents, and using microorganisms. The method currently being used for treating contaminated water at the Fukushima Daiichi Nuclear Power Plant uses chemicals and adsorbents, and 62 types of radioactive material, excluding tritium, have been removed. The main problems with this method include a low removal rate, low adsorption performance, the existence of nuclides that are difficult to remove, a large number of columns, a short service life for the absorbent, high operating costs due to the high cost of the absorbent, and the generation of a large amount of absorbent material adsorbing high-level radioactive materials as waste, which requires treatment and storage.

[0004] As a method for treating contaminated water, in addition to a method using chemicals or adsorbents, a method for removing water-soluble metal ions from contaminated water or wastewater using microorganisms is known (Non-Patent Document 1, Patent Documents 1-5). Non-Patent Document 1 discloses a method for removing strontium contaminated from industrial wastewater into drinking water using thermophilic bacteria (Bacillus genus). Patent Document 1 discloses an apparatus and method for treating radioactive wastewater containing organic matter and radioactive materials generated in nuclear facilities and the like using microorganisms. Patent Document 2 discloses a method for purifying contaminated water by absorbing and adsorbing radioactive materials, mainly cesium, into a biofilm formed by microorganisms. Patent Document 3 discloses a method for removing cesium and strontium from wastewater by adsorbing cesium using denitrifying bacteria and cesium-accumulating bacteria (Rhodococcus genus) and adsorbing strontium to the mycelium of a microorganism belonging to the Hebeloma genus. The present inventor has also disclosed a method for treating contaminated water containing strontium using spore-forming bacteria (Patent Documents 4 and 5). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-064732 A [Patent Document 2] JP 2013-104765 A [Patent Document 3] JP 2007-271306 A [Patent Document 4] Patent No. 6280661 [Patent Document 5] JP 2019-128187 A [Non-patent literature]

[0006] [Non-Patent Document 1] Chaalal, O., et al., 2015, J. Indust. Eng. Chem. Vol.21, p.822-827. [Non-Patent Document 2] Foerster, HF & Foster, JW, 1966, J. Bacteriol. Vol.91, p.1333-1345. Summary of the Invention [Problem to be solved by the invention]

[0007] The method described in Non-Patent Document 1 is a method for removing strontium to a level suitable for drinking water, but it is not considered that it can be applied as it is because the amount and strontium concentration of the assumed contaminated water are different from those of the contaminated water generated in the accident of a nuclear power plant, and various contaminants are contained in the contaminated water. In addition, the invention described in Patent Document 1 is a method for treating washing wastewater generated when washing clothes, etc. to which radioactive materials are attached, in a nuclear facility, etc., and the assumed amount and concentration of the contaminated water are low, so it cannot be applied as it is to the contaminated water generated in the accident of a nuclear power plant. The invention described in Patent Document 2 is an invention for adsorbing and removing cesium to a biofilm formed by microorganisms contained in sludge, and the invention described in Patent Document 3 is an invention for adsorbing and removing cesium using activated sludge containing denitrifying bacteria. It is thought that the treatment capacity changes depending on the microorganisms that make up the biofilm and activated sludge, but there is no mechanism for controlling the amount and type of microorganisms contained in the activated sludge, making it difficult to adjust the treatment capacity. The invention described in Patent Document 4 is a method for removing strontium using spore-forming bacteria, and Patent Document 5 is a method for removing strontium and cesium using bacteria of the genus Bacillus and Rhodococcus.

[0008] However, the methods using microorganisms in Patent Documents 2 to 4 require work in a radiation controlled area for a certain period of time to check the culture conditions of the microorganisms in the treatment device. Work in a controlled area with high radiation levels is desirably done for as short a time as possible because of the risk of exposure. The present invention aims to provide an apparatus and method that shortens the time spent in a high radiation level area as much as possible, while taking safety into consideration, and that can quickly and efficiently treat a large amount of contaminated water and generate little industrial waste after treatment. In particular, the present invention aims to provide a method for efficiently and inexpensively reducing the concentrations of strontium and cesium, which are contained in large amounts in the water to be treated and have a large impact on living organisms. [Means for solving the problem]

[0009] The present invention relates to a method for safely treating contaminated water containing metal ions, particularly water containing radioactive strontium, and a treatment device used therefor. (1) A method for treating contaminated water contaminated by radiation, comprising: an adjustment step of adjusting the contaminated water to an environment in which spore-forming bacteria can survive; an absorption step of introducing bacteria in the spore-forming process, in which spore formation has been induced in advance, into the adjusted contaminated water to absorb strontium; and a solid-liquid separation step of separating the water into strontium-purified water and a solid containing strontium. Bacteria in the spore-forming process, which have been induced to form spores in advance, are added to the contaminated water and allowed to absorb strontium, thereby enabling stable and efficient absorption of strontium.

[0010] (2) The contaminated water treatment method according to (1), wherein the bacteria undergoing spore formation are cultured outside a radiation controlled area to induce spore formation, and then washed, concentrated, and stored in a spore-forming state. Since the process of inducing the spore-forming ability of spore-forming bacteria is carried out outside a radiation-controlled area, it is possible to reduce the time spent working in the controlled area, thereby minimizing the risk of exposure.

[0011] (3) A method for treating contaminated water according to (2), characterized in that the bacteria in the spore-forming process are stored at a temperature of 4°C or lower. It was revealed that bacteria in the spore-forming process can be stored for long periods of time while maintaining their spore-forming ability if stored at temperatures below 4°C.

[0012] (4) A water treatment device using spore-forming bacteria, comprising a contaminated water adjustment tank for adjusting the contaminated water to an environment in which the spore-forming bacteria can survive, an absorption tank into which bacteria in the spore-forming process are introduced to absorb strontium, and a solid-liquid separation tank for separating Sr-purified water from a solid in which Sr is concentrated. Conventionally, a culture tank was required to grow spore-forming bacteria, but in this embodiment, the culture tank is installed outside the radiation controlled area, resulting in a simpler configuration and reducing costs such as construction costs.

[0013] (5) The water treatment device according to (4), wherein the solid-liquid separation tank is provided with a separation membrane for carrying out solid-liquid separation. By carrying out solid-liquid separation using a separation membrane, water treatment can be carried out more efficiently. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a flow diagram showing a water treatment method according to the present embodiment. [Diagram 2] Figure showing the strontium (Sr) absorption ability of spore-forming bacteria. (A) shows the Sr concentration in the supernatant, and (B) shows the percentage of Sr absorbed by the bacterial cells. [Diagram 3] FIG. 1 shows the rate of Sr absorption into the bacterial cells as a function of culture time. [Figure 4] This figure shows the results of culturing spore-forming bacteria stored for different periods and temperatures in a strontium-containing medium and observing spore formation under a microscope. [Diagram 5] FIG. 1 is a schematic diagram illustrating a water treatment device according to an embodiment. [Figure 6] FIG. 1 is a diagram illustrating a conventional water treatment device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The method for treating contaminated water according to the present embodiment uses spore-forming bacteria that incorporate water-soluble metals into spores, forms spores, collects them, and performs water treatment. The spores are composed of a spore coat, a cortex, and a core, and the core contains polymers such as DNA, RNA, and proteins, and contains large amounts of dipicolinic acid and calcium ions as low-molecular weight substances. Dipicolinic acid accounts for 5 to 15% of the dry weight of the spores. It is believed that calcium ions, which are cations, are present in the form of chelates with dipicolinic acid having a carboxylate residue. During spore formation, a large amount of dipicolinic acid is synthesized within the cells, and a large amount of calcium ions are absorbed from outside the cells. Strontium belongs to the same group as calcium on the periodic table and exhibits similar properties to calcium. Therefore, it is known that strontium ions are absorbed during core formation (Non-Patent Document 2). The mechanism of absorption of strontium into spore-forming cells is by incorporation into the core during spore formation. By utilizing this property, strontium can be concentrated and removed from the treated water by forming spores in spore-forming bacteria and collecting the spores together with the sludge. Under conditions suitable for growth, spore-forming bacteria grow by repeated cell division as vegetative cells. However, when placed under conditions unsuitable for growth, they have the property of forming spores within the cells and entering a dormant period. Spores have a strong structure and are extremely resistant to heat, physical pressure, chemicals, etc. As a result, once strontium is taken in, it becomes possible to keep it within the spores. In addition, in the tank where spores are formed, not only spore-forming bacteria but also other microorganisms grow and form a biofilm, so it is possible to remove a certain amount of other radioactive materials by adsorption to the biofilm.

[0016] The conventional water treatment method involved setting up a culture tank in a radiation controlled area to culture spore-forming bacteria in the vegetative cell state, mixing the cultured vegetative cells with contaminated water in a mixing tank, creating conditions for spore formation in a spore formation tank, causing the spores to absorb strontium, and separating and treating treated water from which strontium has been removed and sludge containing large amounts of spores that have absorbed strontium (Figure 6, Patent Document 4).

[0017] Although this method can automatically monitor the temperature, pH, etc. of each tank, it is necessary to take samples and monitor the culture state in some processes, such as inoculating the culture tank with bacteria and checking the state of vegetative cells and spore formation, so work in a radiation controlled area is required for a certain period of time. An increase in the amount of work leads to an increase in the time and dose of radiation exposure of workers. Furthermore, the treated water from which strontium has been removed after solid-liquid separation still contains residual medium components and their metabolites. Since the treated water usually contains other radioactive nuclides, it is sent to the purification process of other nuclides after strontium purification. In that case, substances derived from the medium components may have a negative effect on the next process. In addition, if the strontium removal process is the final process of decontamination, it is necessary to ensure that there are no substances derived from the medium components that exceed the environmental standard concentration.

[0018] Although it is possible to reduce the effects of radiation exposure on the human body by using radiation protection clothing, etc., it is desirable to keep work in the radiation controlled area as short as possible in consideration of the effects on the human body. The present inventor developed a method for preserving spore-forming bacteria while maintaining spore-forming ability by culturing spore-forming bacteria to induce spore-forming ability, stopping the culture during spore formation and preserving at low temperature, and completed the present invention. According to this method, it is possible to preserve spore-forming bacteria for a long period of time outside the radiation controlled area while maintaining spore-forming ability. In addition, it is possible to transport spore-forming bacteria to the radiation controlled area and directly put them into a water treatment device to form spores and remove strontium. As a result, it is possible to complete work in the radiation controlled area in an extremely short time, and the risk of exposure to radiation can be minimized. In addition, preserving bacteria in a state of spore-forming ability allows spore formation to be performed using bacteria with a certain level of ability at all times, making it possible to perform stable processing.

[0019] The present invention will be described below with reference to data. The method described below is one embodiment, and other methods can be applied to the culture method and spore formation method. FIG. 1 shows the water treatment method of the present invention. Outside the radiation controlled area, the spore-forming bacteria are pre-cultured and then cultured in a spore formation medium, and the bacteria are washed and concentrated during the spore formation process, and stored in a state in which they have spore formation ability. As the spore-forming bacteria, in addition to the Bacillus thuringiensis and B.weihenstehanensis used here, any bacteria such as B.megaterium, B.mycoides, and B.pseudomycoides may be used as long as the conditions for good spore formation can be set. In the following experiments, B. thuringiensis NBRC101235, B. thuringiensis NBRC110358, and B. weihenstehanensis NBRC101238 obtained from the NITE Biotechnology Center (NBRC) were used (hereinafter, each bacterium will be referred to by its NBRC number, such as #101235).

[0020] [Example 1] Setting the main culture time to obtain a main culture solution with high Sr absorption capacity For pre-culture of each bacterium, 50 mL of tryptosoya bouillon medium (Nissui Pharmaceutical) was placed in a 300 mL Erlenmeyer flask with a baffle, a colony on tryptosoya agar was inoculated, and rotary shaking culture was performed at 30°C and 110 rpm for 18 hours. For the main culture to induce strontium (Sr) absorption ability and the Sr absorption test, the following operations were performed for each of the three bacterial species. 300 mL of Sr absorption ability expression medium (composition shown in Table 1) was placed in a 1000 mL Erlenmeyer flask, 1 / 100 volume of the pre-culture liquid was inoculated, and rotary shaking culture was performed at 30°C and 110 rpm. The bacterial liquid was sampled at predetermined intervals and the turbidity was measured. Before and after the turbidity reached a plateau (after 15, 18, 21, and 24 hours of culture), the Sr absorption ability was measured by the following method. 30 mL of the main culture bacterial liquid was sampled and centrifuged at 1500 rpm for 10 minutes. The resulting precipitate was suspended in 10 mL of pure water and centrifuged again under the same conditions to obtain bacterial cells in which Sr absorption ability had been induced as a precipitate (operations corresponding to washing and concentration in Figure 1). The bacterial cells collected before and after the turbidity reached a plateau are considered to be in the process of vegetative cells ceasing proliferation and forming spores. Therefore, they are considered to have a high Sr absorption ability. The bacterial cells in which spore formation had been induced are hereafter referred to as Sr absorption ability-induced bacterial cells. An investigation was conducted on Sr absorption ability and the conditions for Sr absorption.

[0021] [Table 1] NaH 2 PO 4 A 100-fold concentrated solution of each of strontium and glucose was prepared and sterilized in an autoclave at 121°C for 20 minutes. After cooling, the required amount was added to the sterilized medium containing the remaining ingredients to prepare a medium for expressing Sr absorption ability.

[0022] [Example 2] Study on induction of Sr absorption ability (1) The amount of Sr absorbed by the collected bacteria was measured by collecting 30 mL of the main culture solution 15, 18, 21, and 24 hours after the start of the main culture, and using the Sr absorption-inducing bacteria prepared from them. Each of the bacteria was suspended in 30 mL of an aqueous Sr solution containing 20 mg / L Sr, and the suspension was transferred to a 300 mL baffled Erlenmeyer flask and cultured at 30°C and 110 rpm for a specified time (24 hours or more). The Sr concentration in the supernatant obtained by centrifugation was measured by known inductively coupled plasma mass spectrometry (ICP-MS) to measure the bacterial absorption ability (Figure 2A).

[0023] As shown in FIG. 2(B), #110358 and #101238 absorbed about 60% of Sr 15 and 18 hours after the start of culture in the Sr aqueous solution. These strains are considered to absorb Sr relatively early after the start of culture under these conditions, and release Sr into the supernatant after a certain time has passed. On the other hand, #101235 took longer to absorb Sr than #110358 and #101238, taking 21 to 24 hours, but under these conditions it maintained Sr without releasing it after a certain time had passed, so analysis was performed using #101235 from here on.

[0024] [Example 3] Examination of Sr absorption capacity When the Sr uptake ability-inducing bacteria were cultured in a solution containing Sr, the time required for Sr absorption and whether the absorbed Sr would be released by longer culture were confirmed. Specifically, the Sr uptake ability-inducing bacteria #101235 were cultured with shaking in an aqueous Sr solution, and the Sr concentration in the culture supernatant was measured in the same manner as in Example 2 to determine the Sr concentration absorbed by the bacteria.

[0025] Three 1000-mL Erlenmeyer flasks containing 300 mL of Sr absorption induction medium were inoculated with 3 mL of the pre-cultured bacteria solution, and Sr absorption induction culture was performed at 30°C and 110 rpm for 24 hours. After 24 hours, the three cultures were mixed and homogenized to prepare 900 mL of Sr absorption induction bacteria solution. 30 mL of this bacteria solution was dispensed into 50-mL tubes and centrifuged at 1500 rpm for 10 minutes. The resulting precipitate was suspended in 10 mL of water and centrifuged again to obtain a precipitate. This precipitate is the Sr absorption induction bacteria (washed bacteria pellet) for 30 mL of Sr absorption induction bacteria solution. 30 mL of 20 mg / L Sr aqueous solution was added to this and suspended, and the suspension was transferred to a 300-mL baffled Erlenmeyer flask and cultured at 30°C and 110 rpm for a specified time. The cultured bacteria solution was centrifuged, and the Sr concentration in the supernatant was measured. For #101235, measurements were taken at seven points over a long period of time, ranging from 3 to 60 hours.

[0026] The results are shown in Figure 3. The absorption rate increased almost linearly up to 12 hours after the start of cultivation in the Sr aqueous solution, then the increase in the absorption rate became gradual, and almost no change was observed from 23 hours to 60 hours of continued analysis. This data allowed us to know the Sr absorption cultivation time that showed the highest absorption ability and the time period when the amount of absorption decreased, and we were able to set a highly effective Sr absorption cultivation time. Since about 85% of Sr was absorbed 12 hours after the start of cultivation, it is possible to concentrate and remove Sr by culturing bacteria with Sr-inducing ability for more than 12 hours and recovering the bacteria. Although the data is not shown here, when the bacteria were collected and washed twice with pure water, about 10% of Sr was eluted, but the remainder remained in the bacterial pellet, indicating that it was stably retained by the bacteria.

[0027] In addition, the dry weight of the solid portion contained in one washed bacterial pellet was 31 mg. If 90% of the 20 mg / L of Sr is absorbed, the amount of Sr absorbed in 30 mL is 0.54 mg, which is processed by 31 mg of solids. In other words, the processing amount per weight is very high.

[0028] [Example 4] Examination of methods for preserving bacterial cells Since it was shown that Sr was efficiently absorbed by the bacteria, we investigated whether long-term storage was possible while maintaining Sr absorption ability. The bacteria were cultured using the washed bacteria pellet (Sr absorption-induced bacteria) prepared by the method described in Example 3, Sr absorption ability was induced, the bacteria were collected by centrifugation, washed with pure water, and then centrifuged again to collect the bacteria (washed bacteria pellet). The washed bacteria pellet was stored at 25°C, 4°C, and -80°C, and then Sr absorption ability was measured to analyze whether Sr absorption ability was maintained. In addition, Sr absorption ability was measured by suspending the bacteria in an Sr aqueous solution, culturing for 24 hours, measuring the Sr concentration in the supernatant, and calculating the absorption rate. The results are shown in Table 2.

[0029] [Table 2]

[0030] Immediately after induction of Sr absorption, the Sr absorption rate was 72.2%, but when stored at 4°C and -80°C, the Sr absorption rate was maintained at 60% or more even after 34 days. Compared to storage at -80°C, storage at 4°C showed a tendency for the Sr absorption rate to be slightly lower, but the difference was not so large. When stored at 25°C, spoilage was observed on the 17th day, so measurements were not performed thereafter. Even when stored at 4°C, there is a possibility of spoilage if stored for a longer period, so if stored for one month or more, it is preferable to store it frozen, for example, at -20°C to -80°C or lower. It is thought that it is possible to store it while maintaining the Sr absorption rate by freezing it in liquid nitrogen (-196°C), storing it at 0°C or lower, and maintaining the frozen state, as in the case of general storage methods for bacteria. Considering that the Sr absorption capacity varies between 70 and 90% for each culture lot, Sr can be absorbed and removed more efficiently by measuring Sr absorption capacity, storing lots with high absorption capacity at low temperatures, and using them in a controlled area.

[0031] [Example 5] Microscopic observation of spore-forming ability of spore-forming bacteria with different storage periods and temperatures The washed bacterial pellets were stored under different temperature and time conditions in the same manner as in Example 4, and then suspended in an aqueous Sr solution and Sr absorption culture was performed for 24 hours. The bacterial suspension immediately after the Sr absorption culture was completed (before centrifugation) and the bacterial suspension at the end of the main culture were used for spore staining and microscopic observation to confirm spore formation (Figure 4). Spore staining was performed using the Meller staining method. Although the spores are stained red in the color, the spores shown in the white triangles in the figure are light in color and spherical in shape. Spore formation was observed at the end of the main culture, and it was also confirmed from morphological observation that a large number of spores were formed after Sr absorption culture at any storage temperature.

[0032] [Water treatment equipment using bacteria with Sr absorption capacity] A water treatment device that uses bacteria with Sr absorption ability to treat contaminated water will be described. As shown in Figure 5, the contaminated water is first adjusted in the contaminated water adjustment tank to conditions such as pH and ion concentration that allow the bacteria to survive. If the pH of the contaminated water is biased toward acidic or alkaline, a pH regulator is added to adjust the pH to a suitable level for spore formation. In addition, the concentration of ions that play an important role in spore formation, such as calcium ions, is estimated by measuring the electrical conductivity to confirm that there is no problem with spore formation. In addition, in order to continue spore formation in the absorption tank, it is monitored to see if there is a condition that does not hinder spore formation, that is, whether the water is in a poor nutritional state. In the case of contaminated water treatment at the Fukushima Daiichi Nuclear Power Plant, the water quality is relatively constant and is not in a situation where organic matter or calcium is contained in high concentrations, but if it exceeds a certain value, water can be added to adjust it. Organic matter can be measured by measuring COD (chemical oxygen demand), BOD (biochemical oxygen demand), and TOC (total organic carbon), or the amount of glucose contained in the contaminated water can be measured using a glucose sensor. In the contaminated water adjustment tank, the water in the tank may be sampled as appropriate to measure pH, ion concentration, organic matter, etc., but in order to reduce the risk of exposure, it is preferable to install an automatic pH sensor, conductivity measuring device, and COD, BOD, and TOD measuring device in the contaminated water adjustment tank to monitor and automatically adjust the temperature. It is also preferable to measure the water temperature and adjust it to a temperature suitable for the habitat of microorganisms (approximately 25°C). The contaminated water adjustment tank is equipped with an agitator to stir the water when a pH adjuster or the like is added, and to maintain a constant water quality.

[0033] The contaminated water, which has been adjusted to a certain water quality in the contaminated water adjustment tank, is sent to the absorption tank. In the absorption tank, the contaminated water is mixed with bacteria in the spore-forming process that have been cultivated and stored outside the radiation control area. The Sr is absorbed in the absorption tank while being aerated for more than 24 hours. The absorption tank is equipped with an aeration device for aeration, a heating and cooling device to keep the temperature constant, and an agitator to cultivate the bacteria and efficiently expose them to Sr. The spores that have formed and absorbed sufficient Sr are transferred to the solid-liquid separation tank. Since it is thought that there are bacteria that have not completely formed spores within 24 hours, a heating and cooling device and an aeration device are installed so that spore formation can continue in the solid-liquid separation tank. Here, a separation membrane is used to perform solid-liquid separation to separate Sr-purified water and spore-forming bacteria that have absorbed Sr, but any separation method may be used. For example, spore-forming bacteria may be precipitated and separated into a supernatant and a sediment, and the sediment may be further centrifuged, compressed, or the like to remove water, thereby separating the Sr-purified water from the Sr-containing bacteria.

[0034] The water treatment device of this embodiment, compared to the conventional water treatment device shown in Fig. 6, does not only not require a culture tank for culturing vegetative cells, but also only requires an absorption tank and a solid-liquid separation tank in addition to a wastewater adjustment tank, making it a very compact water treatment device. In addition, since bacteria in the spore formation process can be directly added, it is possible to absorb Sr in about 24 hours, and the time required for Sr purification can also be shortened. As shown above, water treatment according to this embodiment not only minimizes the risk of exposure during work, but also significantly reduces time and costs. [Industrial Applicability]

[0035] Since the work in the radiation controlled area is short, the risk of exposure during work can be minimized. In addition, since the bacteria are preserved in a spore-forming state, the state of the bacteria is easy to control, bacteria with high spore-forming ability can be stably supplied, and high contamination treatment efficiency can be maintained. As with the conventional method, metal ions are concentrated using microorganisms, so compared to removal methods using adsorbents, contaminated water can be treated quickly and at low cost, and the amount of industrial waste generated is very small, while the same advantages can be maintained, and contaminated water can be treated safely and efficiently.

Claims

1. A method for treating radioactive contaminated water, comprising the steps of: adjusting the contaminated water to an environment in which spore-forming bacteria can survive; an absorption process in which bacteria in the spore-forming process in which spore formation has been previously induced are introduced into the conditioned contaminated water to absorb strontium; A contaminated water treatment method comprising a solid-liquid separation step of separating strontium-purified water from a solid containing strontium.

2. The bacteria undergoing the sporulation process are cultured outside of a radiation controlled area to induce sporulation ability, The bacteria are washed and concentrated while still capable of forming spores.

2. The method for treating contaminated water according to claim 1, further comprising storing the contaminated water.

3. 3. The method for treating contaminated water according to claim 2, wherein the bacteria in the spore-forming process are stored at a temperature of 4° C. or lower.

4. 4. The method for treating contaminated water according to claim 3, wherein the bacteria in the spore-forming process are stored at freezing temperatures.

5. A water treatment device using spore-forming bacteria, a contaminated water adjustment tank for adjusting the contaminated water to an environment in which spore-forming bacteria can survive; An absorption tank where bacteria in the spore-forming process are introduced to absorb strontium; A water treatment device comprising a solid-liquid separation tank for separating strontium-purified water from a solid in which strontium is concentrated.

6. The contaminated water adjustment tank is a tank that adjusts the water quality so that microorganisms can grow. Equipped with a pH adjusting device and / or a diluting device, 6. The water treatment device according to claim 5, wherein the absorption tank is provided with at least one of an aeration device, a heating / cooling device, and an agitator to efficiently carry out sporulation by bacteria in the sporulation process.

7. 7. The water treatment device according to claim 5, wherein the solid-liquid separation tank is provided with a separation membrane for performing solid-liquid separation.

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