JP6460323B2 - Method for treating plant biomass containing radioactive cesium - Google Patents

Description

  The present invention relates to a method for treating plant biomass containing radioactive cesium.

  A large amount of plant biomass contaminated with radioactive materials has been generated by the accident at the Fukushima Daiichi Nuclear Power Station. Plant biomass contaminated with radioactive materials is stored at disposal sites as unusable waste. However, the amount of plant biomass is enormous, and it is required to reduce the volume significantly before storage.

  A common method for reducing plant biomass is incineration. However, if plant biomass contaminated with radioactive material is incinerated, the radioactive material may be scattered. In particular, since cesium has a relatively low boiling point of 641 ° C., it may be vaporized by incineration. For this reason, direct incineration of biomass contaminated with radioactive substances causes the radioactive substances to be scattered again and cannot be employed.

  On the other hand, as a method for effectively using plant biomass, a wet milling method in which an enzyme is added has been studied (see, for example, Patent Document 1). In addition, production of biogas by methane fermentation of plant biomass has also been studied (see, for example, Patent Document 2). A combination of these two techniques to effectively use plant biomass and to significantly reduce the final residue volume has also been studied (see, for example, Non-Patent Document 1). These treatments may significantly reduce the volume of plant biomass contaminated with radioactive materials.

JP 2011-92151 A JP 2006-205017 A

“Biotechnology”, 2014, Vol. 92, No. 6, p.287-290

  However, until now, such treatment has not actually been performed on plant biomass contaminated with radioactive materials, and it is not clear how the radioactive materials affect such treatment. Unless we consider various points such as which fraction the radioactive material is transferred to by the treatment, and whether it is possible to produce biogas even if it contains the radioactive material, the biomass contaminated with the radioactive material will be removed. It cannot be processed. If the radioactive substance is transferred to the obtained biogas, the radioactive substance may be scattered. Further, depending on the behavior of the radioactive substance, the volume of the substance contaminated with the radioactive substance may increase on the contrary.

  An object of the present invention is to make it possible to reduce the volume of plant biomass containing radioactive cesium contaminated with radioactive materials while effectively utilizing it, and to make it possible to easily remove the radioactive cesium.

  One aspect of the method for treating plant biomass containing radioactive cesium is a decomposition step of obtaining a liquid phase part containing carbohydrate and 50% or more of the radioactive cesium transferred from the plant biomass containing radioactive cesium, and a solid phase part. Fermenting the liquid phase part containing radioactive cesium, obtaining the liquid phase part waste liquid containing radioactive cesium and the first gas phase part not containing radioactive cesium, and fermenting the solid phase part A solid phase portion fermentation step for obtaining a solid phase portion residue, a solid phase portion waste liquid, and a second gas phase portion that does not contain radioactive cesium, and the decomposition step is a wet process in which a saccharifying enzyme is added to plant biomass and pulverized Includes milling.

  In one embodiment of the method for treating plant biomass containing radioactive cesium, a removal step of removing radioactive cesium from at least one of the liquid phase part waste liquid and the solid phase part waste liquid may be further provided.

  In one aspect of the method for treating plant biomass containing radioactive cesium, the liquid phase part fermentation step may include a wet methane fermentation treatment using an upflow anaerobic sludge bed.

  In one aspect of the method for treating plant biomass containing radioactive cesium, the solid phase fermentation step may include a dry methane fermentation treatment.

  In one embodiment of the method for treating plant biomass containing radioactive cesium, the decomposition step may include a re-saccharification treatment in which a saccharification enzyme is added to the solid content obtained by the wet milling treatment.

  In this case, the reglycation treatment may be performed a plurality of times.

  In one aspect of the method for treating plant biomass containing radioactive cesium, in the decomposition step, radioactive cesium contained in the solid residue may be set below the detection limit.

  In one aspect of the method for treating plant biomass containing radioactive cesium, the solid phase part may contain radioactive cesium, and the solid phase residue and the solid phase waste liquid may contain radioactive cesium.

  In one embodiment of the method for treating plant biomass containing radioactive cesium, 50% or more of the radioactive cesium may be transferred to the liquid phase waste liquid and the solid phase waste liquid.

  According to the method for treating plant biomass containing radioactive cesium of the present invention, the plant biomass containing radioactive cesium contaminated with radioactive materials can be reduced in volume while being effectively utilized, and the radioactive cesium can be easily removed. It can be shaped like this. Thereby, it becomes possible to preserve | save the plant biomass contaminated with radioactive cesium, or to remove the radioactive cesium easily. As a result, according to the present invention, it is possible to treat plant biomass contaminated with a large amount of radioactive substances, which has become a social problem.

FIG. 1 is a flowchart showing an example of a process for treating plant biomass containing radioactive cesium. FIG. 2 is a flowchart showing an example of the disassembling process. FIG. 3 is a perspective view showing an example of a methane fermentation tank.

  As shown in FIG. 1, the processing method of the plant biomass containing radioactive cesium according to the present embodiment firstly decomposes a liquid phase part that is a saccharified liquid and a solid phase part that is a solid residue from the plant biomass containing radioactive cesium. Perform the process. In the decomposition step, 50% or more of the radioactive cesium is transferred to the liquid phase side.

  The liquid phase part which is a saccharified liquid containing radioactive cesium can be fermented in a liquid phase part fermentation step to obtain a gas phase part and a liquid phase part waste liquid. The liquid phase fermentation process can be, for example, a wet methane fermentation process. The gas phase part is a biogas containing methane. Since radioactive cesium transferred to the gas phase part is below the detection limit, the gas phase part can be used as an energy source or the like as in the case of normal biogas. All of the radioactive cesium contained in the liquid phase part can be transferred to the liquid phase part waste liquid. Since most of the organic matter is consumed in the liquid phase waste liquid, it is hard to rot and there is almost no possibility of generating explosive gas even if stored for a long time. Moreover, if radioactive cesium is removed by a physicochemical technique or a biochemical technique, it can be disposed of in accordance with a normal wastewater treatment procedure.

  The solid phase part can be fermented in a solid phase part fermentation step to obtain a gas phase part and a residue. The residue can be further separated into a solid phase waste liquid and a solid phase residue. The solid phase fermentation process can be, for example, a dry methane fermentation process. The gas phase part is a biogas containing methane. Like the biogas obtained from the liquid phase part, radioactive cesium is below the detection limit and can be used as an energy source or the like. All radioactive cesium contained in the solid phase can be transferred to the solid phase waste liquid and solid phase residue. Although depending on the conditions of the solid phase fermentation process, the migration ratio of radioactive cesium between the solid phase waste liquid and the solid phase residue is about 20:80 to 5:95. The solid phase waste liquid can be discarded according to a normal waste water treatment procedure if the radioactive cesium is removed in the same manner as the liquid phase part waste liquid. The solid phase residue is hardly perished because it contains almost no organic matter that is a nutrient for microorganisms, and there is almost no possibility of generating explosive gas even if it is stored in a storage facility for a long time.

  In the decomposition process, if the radioactive cesium contained in the plant biomass is almost completely transferred to the liquid phase part and the radioactive cesium contained in the solid phase part is set to a predetermined value or less, the solid phase part does not contain radioactive cesium. Can be processed as In this case, the solid phase waste liquid and the solid phase residue can be treated as normal waste containing no radioactive cesium.

  Plant biomass is plant-derived biomass containing cellulose, hemicellulose, and lignin, and includes woody biomass (hard biomass) mainly generated from trees and the like, herbaceous biomass (soft biomass) mainly generated from agricultural products and the like. Specific examples of the woody biomass include those derived from conifers such as cedar and birch, and those derived from broad-leaved trees such as poplar and birch. Specific examples of herbaceous biomass include those derived from rice, wheat and corn. The plant biomass also includes building waste and agricultural waste.

  The radioactive cesium contained in the plant biomass may be cesium 137, cesium 134, or both.

  The decomposition process for obtaining a saccharified solution and a solid residue from plant biomass can be performed by a wet milling process to which a saccharifying enzyme is added, as shown in FIG. In the wet milling process, plant biomass is pulverized as a slurry state suspended in a medium. The volume of the slurry varies depending on various factors such as the type of biomass and the configuration of the processing apparatus, but is about 200% to 300% of the volume of the original plant biomass as an example. For example, a ball mill or a bead mill can be used as the processing apparatus. In order to pulverize efficiently, the plant biomass is preferably coarsely pulverized to about 5 mm or less before being introduced into the treatment apparatus.

  The saccharifying enzyme added in the wet milling treatment is an enzyme that saccharifies cellulose, hemicellulose and the like contained in the cell wall of plant biomass, and examples thereof include cellulase, hemicellulase, and pectinase. Cellulase is an enzyme that hydrolyzes the glucoside bond of β-1,4-glucan. Cellulases include endoglucanase that cleaves from the inside of cellulose molecules, exoglucanase that breaks down from the reducing or non-reducing end of cellulose and releases cellobiose, and β-glucosidase that cleaves the glucoside bond of cellobiose and converts it to glucose. included. Hemicellulase is an enzyme that degrades polysaccharides other than cellulose and pectin among the polysaccharides constituting the cell wall of the plant body. Pectinase is an enzyme having a catalytic function for degrading pectin, and includes polygalacturonase, pectin lyase, pectin esterase, pectin methyl esterase, and the like. These enzymes may be used alone or in combination.

  The amount of saccharifying enzyme added may be appropriately determined according to the type and amount of plant biomass to be treated, the type of saccharifying enzyme, the structure of the apparatus, and the like. For example, in the case of rice straw, it can be about 200 U to 20000 U per 1 g of plant biomass.

  The medium used for the wet milling process may be a liquid that can hold the object to be ground in a slurry state without deactivating the enzyme to be added. Examples thereof include water (which may contain an additive such as a salt), an organic solvent, and an ionic liquid. A buffer may be used to keep the pH constant.

  What is necessary is just to select the implementation conditions of a wet milling process suitably with a grinding | pulverization target object. For example, when using a bead mill, the pH of the medium is 2.0 to 11.0, the weight ratio of the medium and the object to be pulverized is 1: 1 to 100: 1, the bead diameter of the pulverizer is 0.1 mm to 20 mm, the bead circumference is The speed may be appropriately selected within a range of 0.3 m / sec to 50 m / sec and the slurry flow rate within a range of 0.1 L / min to 10 L / min. The temperature of the wet milling process may be a temperature suitable for the enzyme reaction, preferably 10 ° C or higher, more preferably 20 ° C or higher, and further preferably 30 ° C or higher. And 100 degrees C or less is preferable, 80 degrees C or less is more preferable, and 60 degrees C or less is further more preferable.

  The time of the wet milling process may be terminated when the particle size and slurry viscosity of the pulverized product are measured over time and an arbitrary numerical value (an average particle size of 1 μm or less is desirable). From the viewpoint of increasing the saccharification rate, the treatment time is preferably 10 minutes or more, more preferably 30 minutes or more, still more preferably 60 minutes or more, and even more preferably 100 minutes or more. From the viewpoint of efficiency, it is preferably 300 minutes or less, more preferably 240 minutes or less, and even more preferably 180 minutes or less.

  After the pulverization, the liquid saccharified solution and the solid residue are separated by solid-liquid separation means. Centrifugation or the like can be used as the solid-liquid separation means. The solid residue may be washed. The residue washing liquid produced by washing can be sent to the next liquid phase part fermentation step as a liquid phase part together with the saccharified liquid. The washing operation may be performed a plurality of times.

  The solid residue obtained by the wet milling process can be directly sent to the solid phase fermentation process as a solid phase part, but can also be re-saccharified. The re-saccharification treatment may be performed by further adding a saccharifying enzyme to the solid residue. The saccharifying enzyme added during the re-saccharification treatment may be the same as or different from that during the wet milling treatment. The amount of saccharifying enzyme added is not particularly limited, but can be about 200 U to 20000 U per gram of the original plant biomass. The treatment temperature may be a temperature suitable for the enzyme reaction, preferably 10 ° C or higher, more preferably 20 ° C or higher, and further preferably 30 ° C or higher. And 100 degrees C or less is preferable, 80 degrees C or less is more preferable, and 60 degrees C or less is further more preferable. The treatment time may be selected according to the required saccharification rate, but from the viewpoint of increasing the saccharification rate, it is preferably 1 hour or longer, more preferably 10 hours or longer, and even more preferably 20 hours or longer. And from a viewpoint of efficiency, 50 hours or less are preferred, 40 hours or less are more preferred, and 30 hours or less are still more preferred.

  After the re-saccharification treatment, the re-saccharification solution and the solid residue are separated by solid-liquid separation means. Centrifugation or the like can be used as the solid-liquid separation means. The re-saccharified liquid can be sent to the next liquid phase part fermentation step as a liquid phase part together with the saccharified liquid obtained by the wet milling process. In order to further reduce the amount of radioactive cesium contained in the solid residue, the solid residue after the re-saccharification treatment may be washed. The residue washing liquid produced by washing can be sent to the next liquid phase part fermentation step as a liquid phase part together with the saccharified liquid. The washing operation may be performed a plurality of times. The solid residue subjected to the re-saccharification treatment can be sent to the next solid phase part fermentation step as a solid phase part.

  The re-saccharification treatment may be performed as necessary, and may not be performed as long as the separation of the saccharide and the reduction of the amount of radioactive cesium remaining on the solid residue side can be sufficiently performed in the wet milling treatment. Moreover, the reglycation treatment may be performed once or may be performed twice or more.

  The radioactive cesium contained in the plant biomass is one in which radioactive cesium contained mainly in the soil is taken into the plant tissue during the growth of the plant. Therefore, it is associated with the plant tissue and cannot be removed from the plant biomass simply by crushing or washing. In the present embodiment, plant biomass is pulverized with saccharifying enzymes added, and plant tissues are decomposed and saccharified by enzymes. For this reason, radioactive cesium in plant tissue can be moved to the liquid phase side. Considering the removal process of radioactive cesium, it is easier to be contained in the liquid content than in the solid content. Therefore, it is preferable to transfer radioactive cesium as much as possible to the liquid phase part side, preferably 50% or more of the radioactive cesium is transferred to the liquid phase part side, more preferably 70% or more, more preferably 75% or more. More preferably. Most preferably, the radioactive cesium contained on the solid phase side is below the detection limit.

  Although the volume of the liquid phase part obtained by a decomposition | disassembly process is fluctuate | varied by various factors, such as a kind of biomass and a structure of a processing apparatus, it becomes about 160%-260% of the volume of the original biomass as an example. In the liquid phase part for fermenting the liquid phase part containing radioactive cesium, organic substances such as carbohydrates contained in the liquid phase part are decomposed by microorganisms, and the gas phase part containing methane and the liquid phase part waste liquid in which the sugar is consumed Occurs. The liquid phase fermentation step may be any method, but a wet methane fermentation method is preferable, and can be performed using, for example, an upflow anaerobic sludge bed (UASB). Specifically, as shown in FIG. 3, a large amount of highly active cells are retained in the reaction tank as granules (a granular sludge having a diameter of 2 mm to 3 mm) by utilizing the aggregating action of anaerobic microorganisms, and the reaction is performed. What is necessary is just to inject | pour the liquid phase part containing radioactive cesium from the lower part of a tank, and to decompose | disassemble the organic substance in a liquid phase part in an anaerobic state. What is necessary is just to adjust suitably the supply amount of a liquid phase part, and the density | concentration of the organic substance in a liquid phase part according to the processing capacity of an apparatus.

  The liquid phase portion injected into the reaction vessel is uniformly diffused into the granule layer precipitated at the bottom. The organic matter in the liquid phase part is decomposed to produce biogas containing methane gas and carbon dioxide and the liquid phase part waste liquid. Granules with biogas adhering to the surface float with the treated water due to the air lift effect, so that the biogas can be collected by a settler provided at the top. By separating the liquid phase waste liquid and the granule, the liquid phase waste liquid containing almost no organic matter can be recovered. Although the volume of the liquid phase waste liquid varies depending on various factors such as the configuration of the processing apparatus, it is about 150% to 250% of the original plant biomass as an example. The radioactive cesium contained in the liquid phase part is almost directly transferred to the liquid phase part waste liquid. Since the liquid phase waste liquid containing almost no organic matter is not easily spoiled, it can be stored for a long time before the predetermined treatment.

  The radioactive cesium contained in the liquid phase part hardly affects methane fermentation by anaerobic microorganisms, and even if it contains radioactive cesium, it can be fermented in the same manner as when it does not contain radioactive cesium. Methane fermentation can be performed at a temperature of about 30 ° C to 60 ° C. For this reason, there is almost no possibility that the radioactive cesium contained in the liquid phase part is vaporized, and the radioactive cesium contained in the generated biogas is below the detection limit. Therefore, the obtained biogas can be used as a fuel or the like, similar to the biogas obtained by a normal process.

  The volume of the solid phase part obtained by the decomposition step varies depending on various factors such as the type of plant biomass and the configuration of the processing apparatus, but is 30% to 70% of the original plant biomass as an example. The solid phase part after separating the liquid phase part, which is a saccharified solution, still contains a large amount of organic components. For this reason, biogas can be generated in the solid phase fermentation process which is the next process. The solid phase fermentation process can be, for example, a dry methane fermentation process. The dry methane fermentation treatment can be performed under the condition that the water content is 80% or less. For example, the solid phase part after separating the liquid phase part can be mixed with high-temperature anaerobic digested sludge and subjected to methane fermentation under anaerobic conditions. The fermentation temperature can be about 45 ° C to 60 ° C. What is necessary is just to adjust suitably the supply amount of a solid-phase part, fermentation time, etc. according to the structure of a device, processing capacity, etc. For example, the solid phase portion and the sludge can be mixed at a ratio of about 1:10 to 1: 3. The fermentation time can be about 20 to 50 days.

  In the solid phase fermentation process, as in the liquid phase fermentation process, the radioactive cesium contained in the generated biogas is below the detection limit. For this reason, it can be used as a fuel or the like in the same manner as ordinary biogas.

  The residue generated in the solid phase fermentation process can be separated into a solid phase residue that is a solid content and a solid phase waste liquid by solid-liquid separation. About 5% to 20% of the radioactive cesium contained in the solid phase part moves to the solid phase waste liquid, and almost all of the rest moves to the solid phase residue. Since the solid phase waste liquid contains almost no organic matter, it can be stored for a long time without being easily spoiled. Moreover, since the solid phase residue is mainly composed of lignin or the like which is not easily spoiled, it can be stored for a long time. When storing the solid phase residue, it is preferable to dry it until the water content is about 10% or less. The volume of the solid phase waste liquid and the final dried solid phase residue varies depending on various factors such as the type of the original biomass and the configuration of the processing apparatus. 20% to 50%, and solid phase residue is about 3% to 10% of the original plant biomass in a dry state.

  The radioactive cesium contained in the liquid phase waste liquid and the solid phase waste liquid can be removed by a physicochemical technique or a biochemical technique. For example, it can be removed using an adsorbent. Examples of the radioactive cesium adsorbent include zeolite, Prussian blue, and ion exchange resin. Since organic substances in the liquid phase waste liquid are greatly reduced by methane fermentation, the radioactive cesium can be efficiently removed by the adsorbent. Moreover, radioactive cesium can also be removed using photosynthetic bacteria or the like that adsorb heavy metals. In this case, the organic component remaining in the liquid phase part waste liquid can be used as a nutrient source such as photosynthetic bacteria. The liquid phase waste liquid after removing radioactive cesium below the detection limit or below the specified value can be discarded as a normal waste liquid by performing a predetermined treatment.

  The liquid phase waste liquid and the solid phase waste liquid can be mixed to remove radioactive cesium. Moreover, radioactive cesium can also be removed separately. Moreover, at least a part of the liquid phase part waste liquid and the solid phase part waste liquid can be fed back to the decomposition process, the liquid phase part fermentation process or the solid phase part fermentation process for recycling.

  The processing method of the plant biomass containing the radioactive substance of this indication is explained more concretely using an example below. The following examples are illustrative and do not limit the present invention.

<Plant biomass containing radioactive substances>
Rice straw and cedar wood chips were used as plant biomass containing radioactive substances. The amount of radioactive cesium contained in the rice straw was 7000 Bq / kg, and the amount of radioactive cesium contained in the cedar chips was 500 Bq / Kg.

<Disassembly process>
50 g of coarsely pulverized plant biomass, 445 mL of distilled water, and 5 mL of pH 5.5 phosphate buffer were mixed to form a slurry. To this, 5 mL (59225 U) of OPTIMASH BG (GENENCOR), which is a cellulase, and 5 mL (35650 U) of OPTIMASH XL (GENENCOR), a hemicellulase, were added as saccharifying enzymes. The slurry to which the saccharifying enzyme was added was wet milled for a predetermined time using a bead mill. The bead mill was made of ceramic having a capacity of 0.15 L (Ashizawa Finetech, Lab Ministar LM2015), and zirconia beads having a diameter of 0.5 mm were used. The processing temperature for wet milling was 50 ° C., and the peripheral speed of the mill was 14 m / s.

  After the wet milling treatment, the recovered slurry was subjected to solid-liquid separation to recover a primary saccharified solution and a solid residue. While adding 200 mL to 400 mL of distilled water and 5 mL (59225U) of OPTIMASH BG (GENENCOR) and 5 mL (35650U) of OPTIMASH XL (GENENCOR) as an enzyme solution to the solid residue and keeping the temperature at 50 ° C. A secondary saccharification treatment was performed by stirring slowly and continuing the saccharification reaction for 24 hours. After the secondary saccharification treatment, the solid-liquid separation was performed again, and the secondary saccharified solution was recovered. The solid residue was resuspended by adding distilled water, and recovered again after the solid-liquid separation. The supernatant was collected as residue washing water. Radiation contained in rice saccharified liquid, secondary saccharified liquid, washing water, solid residue total 4 samples, and cedar chips included primary saccharified liquid, secondary saccharified liquid, solid residue total 3 samples The ability of radioactive cesium by wet milling was investigated. The radioactivity was measured by filling a sample in a 100 mL container and using a germanium semiconductor detector.

  When rice straw was used as plant biomass, 51% of the radioactive cesium was transferred to the primary saccharified solution by the wet milling treatment for 120 minutes. By further secondary saccharification of the solid residue obtained by the wet milling treatment for 120 minutes, 18% of the radioactive cesium was transferred to the secondary saccharified solution. 4% of the radioactive cesium was transferred to the residue washing water that washed the solid residue after the secondary saccharification, and the radioactive cesium contained in the final solid residue was 27% of the original rice straw.

  When cedar chips were used as plant biomass, 75% of the radioactive cesium was transferred to the primary saccharified solution by the wet milling treatment for 120 minutes. By further subjecting the solid residue obtained by the wet milling treatment for 120 minutes to secondary saccharification, 25% of the radioactive cesium was transferred to the secondary saccharified solution. Radiocesium contained in the solid residue after secondary saccharification was below the detection limit.

<Liquid phase fermentation process>
A liquid phase portion prepared from rice straw containing radioactive cesium was subjected to methane fermentation using an upward flow anaerobic sludge bed (UASB) reaction tank as shown in FIG. The liquid phase part was a mixture of a saccharified solution obtained by wet milling treatment, a secondary saccharified solution obtained by secondary saccharification treatment, and washing water. The anaerobic sludge bed had a granule of 700 mL to 800 mL. The liquid phase part was diluted to have a chemical oxygen demand (COD) of 1200 mg / L and supplied to the anaerobic sludge bed. The operation was performed at a temperature of 35 ° C. and a residence time of 6.0 hours.

  First, the saccharified liquid which does not contain radioactive cesium was supplied to the UASB reaction tank, and it confirmed that methane fermentation produced normally. The amount of biogas produced in this case was about 1400 mL / L / day to 1500 mL / L / day. After operating for about 20 days with a saccharified solution containing no radioactive cesium, supply of the saccharified solution containing radioactive cesium was started. Even after the start of the supply of the saccharified solution containing radioactive cesium (56Bq / L), no significant change was observed in the amount of biogas produced. About 24 hours after the start of the supply of the saccharified solution containing radioactive cesium, the radioactivity of the supplied solution from the UASB reaction tank and the wastewater became almost the same. The amount of radioactive cesium contained in the biogas was below the detection limit even after 24 hours or more had passed since the supply of the saccharified liquid containing radioactive cesium was started. The COD of the waste water was 131 mg / L.

<Solid phase fermentation process>
The solid phase prepared from rice straw containing radioactive cesium was stabilized and reduced in volume by dry methane fermentation. The solid phase part was made into the solid residue after the wet milling process which has not performed the secondary saccharification process. For the dry fermentation treatment, a mixed stirring type stirring tank having a sludge stirring function and an actual capacity of about 10 L was used. For the sludge, high temperature anaerobic digested sludge of surplus activated sludge tested from a water treatment center in Hiroshima Prefecture was used. The moisture content of the sludge was 78.5%, and the loss on ignition (volatile solids; VS) was 0.857 g / g-DW. The fermentation temperature was 55 ° C., and the sludge residence time was about 30 days. The solid residue obtained from 100 g of rice straw powder was made up to 1 L and charged into a fermenter. The input sample had a water content of 90% to 95%, a density of 1050 kg / m ³ , and a viscosity of 100,000 mPa · s. The fermentation process was continued for 85 days while the sample was loaded and withdrawn every 3 days.

  The sample extracted after the fermentation treatment was separated by centrifugation into a solid phase waste liquid as a supernatant and a solid phase residue as a solid content. The mass of the solid phase waste liquid was 600 g, and the mass of the solid phase residue in the wet state was 390 g. The amount of radioactivity was measured for the solid phase waste liquid and the solid phase residue. The radioactivity was measured by filling a sample in a 100 mL container and using a germanium semiconductor detector.

  The amount of biogas produced was measured with a wet gas meter. The wet gas meter has a measuring chamber divided into 3 to 4 chambers from the upper part of the liquid level and a spiral drum, and the accumulated flow rate value was measured by integrating the rotational movement of the drum shaft by the gas entering from the entrance with a mechanical counter. .

  The amount of biogas produced per gram of rice straw during the treatment period was 217 mL / g, of which the amount of methane produced was 114 mL / g. The amount of radioactive cesium in the biogas was evaluated by measuring the amount of radioactivity in the water in the wet gas flow meter, but it was below the detection limit.

  The volume of 100 g of rice straw was about 800 mL. In the decomposition step, a liquid phase part of about 1700 mL and a solid phase part of about 360 mL were obtained. By subjecting the solid phase part to solid phase fermentation, about 160 mL of solid phase part waste liquid and about 205 mL of solid phase part residue were generated. When the solid phase residue was dried until the water content was about 10%, it was about 48 mL (about 36 g).

  The amount of radioactivity of 100 g of the original rice straw was 700 Bq, the amount of radioactivity of the final solid phase residue (36 g) was 311 Bq, and the amount of radioactivity of the solid phase waste liquid was 27 Bq. Therefore, about 44% (311Bq / 700Bq) of radioactive cesium contained in the original rice straw was transferred to the solid phase residue. Although the secondary saccharification treatment is not performed in this example, the proportion of radioactive cesium that migrates to the solid phase residue can be further reduced by performing the secondary saccharification treatment.

The volume reduction rate (%) of plant biomass can be expressed by the following formula.
Volume reduction rate (%) = (biomass volume-solid waste volume) / biomass volume ...

  In this embodiment, the solid waste volume is the volume of the solid phase residue. Strictly speaking, when radioactive cesium is removed from liquid phase waste liquid and solid phase waste liquid, waste containing radioactive cesium is generated, but since the amount is small compared to the solid phase residue, if the batch is small Can be ignored. Therefore, in this embodiment, the volume of solid waste is 48 mL, and the volume reduction rate is 94%.

  Based on this result, when the balance of a plant that processes one batch of 600 kg of biomass is simulated, the volume of plant biomass is about 4800 L, and a solid phase residue of about 290 L (220 kg, moisture content 10%) is generated. The volume of the liquid phase waste liquid and the solid phase waste liquid is about 12000 L, and the ratio of solid waste generated when removing radioactive cesium is about 60 L when the ratio of solid waste is 0.5%. Therefore, the solid waste volume is 290L + 60L = 350L, and the volume reduction rate is 93%.

  The method for treating plant biomass containing radioactive cesium according to the present disclosure can be reduced in volume while being effectively utilized, and can be configured to easily remove the radioactive cesium, and the method for treating plant biomass containing radioactive cesium Useful as such.

Claims (6)

From plant biomass containing radioactive cesium, and decomposition step to obtain a including liquid phase carbohydrate and a solid phase portion,
A liquid phase part fermentation step of fermenting the liquid phase part containing radioactive cesium to obtain a liquid phase waste liquid containing radioactive cesium and a first gas phase part not containing radioactive cesium;
A solid phase portion fermentation step for fermenting the solid phase portion to obtain a solid phase residue, a solid phase waste solution, and a second gas phase portion not containing radioactive cesium,
The plant biomass is a woody biomass,
The decomposition step includes a wet milling process in which saccharification enzyme is added to the plant biomass and pulverized, and a re-saccharification process in which a saccharification enzyme is added to the solid content obtained by the wet milling process, The processing method of the plant biomass containing radioactive cesium which makes radioactive cesium contained in a part below a detection limit . Further comprising a removing step of removing the liquid phase waste liquid or al the radioactive cesium, processing method of plant biomass containing radioactive cesium according to claim 1.   The said liquid phase part fermentation process is a processing method of the plant biomass containing the radioactive cesium of Claim 1 or 2 including the wet methane fermentation process using an upward flow type anaerobic sludge bed.   The said solid-phase part fermentation process is a processing method of the plant biomass containing the radioactive cesium of any one of Claims 1-3 containing a dry-type methane fermentation process. The processing method of the plant biomass containing the radioactive cesium of any one of Claims 1-4 which performs the said re-saccharification process in multiple times. The said woody biomass is a cedar chip, The processing method of the plant biomass containing the radioactive cesium of any one of Claims 1-5.

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