JP2013217820A - Cesium removal method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination method of radioactive contaminants, capable of removing the contaminant itself such as cesium 137 basically.SOLUTION: By adding filamentous bacteria, basidiomycetes, and nutrition assisting polysaccharide to a cesium-containing radioactive contaminant X, adding moisture, agitating it and cultivating the bacteria, the cesium is removed from the contaminant. It is preferable that the bacteria are cultivated at temperature 35-70°C, and moisture 60-80%. The contaminant X includes fallen leaves of trees, rice straws, wooden chips, weeds, and vegetable residue.

Description

  The present invention relates to a method for decontaminating radioactive pollutants that removes cesium from fallen leaves, straw, weeds, plant residues, wood chips, and the like, to which radioactive pollutants have been attached due to a nuclear accident.

  According to the reports, the Fukushima nuclear accident has scattered a lot of radioactive pollutants and people are suffering. Among them, contamination by cesium 137 is serious, and the half-life is as long as about 30 years, and there is a problem that radiation is continuously emitted during that period.

  Decontamination of radioactive pollutants is also under consideration. For example, the surface of contaminated soil is peeled off, packed in a bag and transferred to another location, and the radioactive material itself such as cesium 137 is fundamentally used. It is not intended to be removed.

  The present invention has been made based on the above-described circumstances, and an object thereof is to provide a method for decontaminating radioactive pollutants that can fundamentally remove radioactive substances such as cesium 137 itself.

  The method for decontaminating radioactive pollutants of the present invention includes adding fungi, basidiomycetes and nutritional supplement polysaccharides to radioactive pollutants containing cesium, adding water, stirring, and culturing the bacteria. The cesium is removed from the contaminant.

  According to the present invention, filamentous fungi and basidiomycetes act on radioactive pollutants and have the property of decomposing / separating cesium. Therefore, by culturing the fungus using the pollutants as a medium, cesium is removed from the pollutants. It can be removed.

It is explanatory drawing of the apparatus used for experiment.

  FIG. 1 shows the apparatus used by the inventor for experiments on decontamination of radioactive contaminants. A transparent Erlenmeyer flask 11 is filled with radioactive contaminant X such as fallen leaves. Contaminant X has been collected from Minamisoma City, Fukushima Prefecture, etc., and is considered to contain cesium that has been detected due to radioactivity and scattered in the nuclear accident. And the flask 11 is arrange | positioned inside the constant temperature and humidity tank 12, and it adjusts so that the contaminant X may become the temperature 35-70 degreeC suitable for a culture medium, and humidity 60-80%. That is, filamentous fungi and basidiomycetes grow most actively in this temperature and humidity range.

  Further, air is injected from the compressor 13 into the pollutant X through the air supply pipe 14. And the exhaust pipe 15 and the filter 16 connected to this are provided, and it exhausts, filtering the air inside the flask 11. The filter 16 is made of carbon and zeolite. Furthermore, the inside of the contaminant X can be stirred. Therefore, the pollutant X is agitated and constantly supplied with fresh air at a temperature of 35 to 70 ° C. and a humidity of 60 to 80%.

  Under this environment, using a pollutant X such as fallen leaves as a culture medium, filamentous fungi, basidiomycetes, and nutritional supplement polysaccharides such as glucose, fructose, and oligosaccharide are added. In this experiment, filamentous fungi and basidiomycetes use the same fungus as that used for the production of Narihira enzyme SBN-11 (trade name: Patent No. 4129470). Then, filamentous fungi and basidiomycetes are cultured, and the propagation of the fungi progresses while decomposing the pollutant X. In the experiment, the culture was continued for 40 days. As a result, about one-fourth of the contaminant X was visually decomposed to become sandy, and bacterial growth was observed.

 At that time, the culture was stopped, the temperature of the medium was raised to 90-100 ° C., sterilization was performed, and the radioactivity of the pollutant X was measured. Table 1 shows the measurement results of radioactivity before and after the culture. Radioactivity was measured by a specialist and was performed by gamma-ray spectrometry using a germanium semiconductor detector.

  Prior to culture, cesium 134 was 3840 Bq / kg and cesium 137 was 4880 Bq / kg. Barium was present at 27 mg / kg. In contrast, after 40 days of culture, cesium 134 decreased 28% to 2770 Bq / kg and cesium 137 decreased 22% to 3810 Bq / kg. Barium was present at 31 mg / kg, an increase of 15%.

  From the above results, it is clear that cesium 134 and 137 are reduced by culturing filamentous fungi and basidiomycetes using contaminant X such as fallen leaves as a medium. And it is clear that barium is increasing. In addition, since no radioactivity is detected from the filter 16, it is unlikely that cesium 134, 137 has flowed out of the system.

  If the reason for the decrease in cesium 134,137 is estimated, the following can be considered. That is, enzymes and mucopolysaccharides (biopolymers) are secreted from the mycelial cells of filamentous fungi and basidiomycetes in culture. Then, hydrolysis of the enzyme and mucopolysaccharides generates acids and the like, and the rod collapses the cesium nucleus, emits beta rays, and cesium changes to barium. As a result, cesium decreased and barium increased.

  In addition, since filamentous fungi and basidiomycetes have the property of absorbing cesium from radioactive pollutants, by culturing the fungus using radioactive pollutants such as fallen leaves as a medium, the pollutants are decomposed and become sandy, It is considered that the bacterium absorbed cesium and the cesium was removed from the contaminant.

  In the first place, the phenomenon of bioconcentration is known for cesium 137. For example, cesium 137 diffused in the ocean is first accumulated in plankton. In the ocean, cesium 137 may exist as various compounds, but because the plankton, which is a microorganism, has high bioaccumulative properties, microorganisms and basidiomycetes found by the present inventors have been It can be confirmed that cesium 137 can be absorbed from the medium by the above action.

  Next, an example of how to use the present invention will be described. First, it is effective for decontamination of rice straw. In the rice field, do not cut the rice straw with a cutter, lay the rice straw as it is, and leave the rice straw. Then, the contaminated rice straw adsorbed with cesium is collected and used as a culture medium for filamentous fungi and basidiomycetes. Then, filamentous fungi, basidiomycetes and nutraceutical polysaccharides are added, water is added, stirred, and the fungus is cultured, so that the fungi and basidiomycetes grow on the rice straw and decompose the rice straw into sand. At the same time, filamentous fungi and basidiomycetes can decompose / absorb cesium and remove cesium from contaminated rice straw.

  It is also effective for decontamination of radioactive fallen leaves, dead branches and dead trees. These are collected and used as a medium. Filamentous fungi, basidiomycetes, and nutritional supplementary polysaccharides are added, water is added, stirred, and the fungi are cultured to decompose them into sand, and these fungi are cesium. It is possible to decompose / absorb and remove cesium from pollutants.

  Similarly, it can be applied to decontamination of radioactive wood chips, weeds, plant residues, soil, and the like.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

  The present invention is useful for decontamination of radioactive pollutants such as fallen leaves and straw caused by a nuclear accident.

Claims (3)

  Addition of filamentous fungi, basidiomycetes and nutritional supplement polysaccharides to radioactive pollutants containing cesium, adding water, stirring, culturing the fungus, removing the cesium from the pollutants Decontamination method for radioactive pollutants.   The decontamination method according to claim 1, wherein the culture of the fungus is performed at a temperature of 35 to 70 ° C and a humidity of 60 to 80%.   2. The decontamination method according to claim 1, wherein the pollutant includes fallen leaves of trees, rice straw, wood chips, weeds, and vegetable residues.

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