Anaerobic bioreactor

Abstract

To provide an anaerobic bioreactor capable of easily repairing and regenerating a fixed bed even partially.SOLUTION: An anaerobic bioreactor includes an anaerobic fermenter 3 in which an organic slurry E is taken and retained, a slurry circulation channel 22 in which the organic slurry E (fermentation liquid S) in the anaerobic fermenter 3 is extracted from one end and circulated back to the other end, and a wire net microorganism carrier 10 arranged on multiple surfaces in the fermenter 3 along the slurry circulation flow generated in the fermenter 3 by circulation of the organic slurry E. Preferably, the wire net microorganism carrier 10 is made of a plurality of wires woven together so as to be stretchable in at least one direction. Preferably, the wire net microorganism carrier 10 is placed over both sides of the inner surface of the anaerobic fermenter 3. Even more preferably, the net size of the wire net microorganism carrier 10 should be 50 mm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an anaerobic bioreactor, and more particularly to an anaerobic bioreactor for decomposing organic waste such as food waste using microorganisms. [Background technology]

[0002] A wet methane fermentation process has been developed in which organic waste such as food waste and sludge, or a fluid made by pulverizing biomass (hereinafter referred to as organic slurry) is fed into an anaerobic bioreactor equipped with a fixed bed, and the fluid is fermented while being brought into contact with microorganisms attached to the fixed bed, and decomposed into biogas (methane gas, etc.) and a fermentation liquid (see Non-Patent Document 1). The fixed bed of the bioreactor is required to satisfy the following conditions: it can attach microorganisms at a high concentration, it can contact the charged organic slurry over a wide area, and it is difficult to cause deformation or clogging that reduces the contact efficiency with the organic slurry. As an example of a fixed bed that satisfies these conditions, a fixed bed using a microbial carrier 40 using a pair of acid-resistant resin rectangular cloths 41, 42 and multiple hollow cylindrical frames 44, as shown in Figs. 5 and 6, has been developed (see Patent Document 1).

[0003] The microorganism carrier 40 shown in Fig. 5 is composed of a pair of acid-resistant resin rectangular cloths 41, 42 (see Fig. 5(A)), a plurality of (seven in the illustrated example) hollow cylindrical frames 44 (see Fig. 5(C)) arranged in parallel at a predetermined interval G1 between the pair of rectangular cloths 41, 42, and a connecting member 48 (see Fig. 5(D)) that connects them. An example of the rectangular cloths 41, 42 is a nonwoven fabric made of polyester fiber whose strength does not deteriorate even when immersed in acidic conditions for a long period of time, and an example of the hollow cylindrical frame 44 is an axial member 44a and a circumferential member 44b made of polyester assembled into a hollow cylinder.

[0004] As shown in Fig. 5(B), a pair of overlapping rectangular cloths 41, 42 are sewn together with a polyester fiber joint member 47 along seam lines J1 to J6 at a predetermined interval G0, and a hollow cylindrical frame 44 is fitted into each of the cylindrical gaps 43 surrounded by the adjacent seam lines J and the rectangular cloths 41, 42, to integrate the rectangular cloths 41, 42 and the hollow cylindrical frame 44. Then, the rectangular cloths 41, 42 and the hollow cylindrical frame 44 are bundled together with a binding member 48 as shown in Fig. 5(D) to assemble the microorganism carrier 40 so that they do not fall apart even when immersed for a long period of time in the organic matter slurry E (hereinafter sometimes referred to as fermentation liquid S) being fermented and decomposed in the bioreactor. An example of the binding member 48 is an acid-resistant resin band made of the same material (polyester fiber) as the rectangular cloths 41, 42.

[0005] FIG. 6 shows a side view and a cross-sectional view of a fixed bed of a bioreactor 50 using the microbial carrier 40 of FIG. 5. The bioreactor 50 shown in the figure has an anaerobic fermentation tank 30, a raw material supply path (supply line) 21 for introducing an organic matter slurry E into the fermentation tank 30, a circulation path (circulation line) 22 with a circulation pump 22a for extracting the fermentation liquid S in the fermentation tank 30 from the bottom and returning it to the top for circulation, and a gas discharge path (gas line) 24 for discharging biogas generated during the fermentation and decomposition of the fermentation liquid S from the fermentation tank 30. Inside the fermentation tank 30, a perforated support 6 for placing the fixed bed thereon and a perforated presser lid 7 for preventing the placed fixed bed from floating up are provided. In addition, the circulation path 22 is provided with a heat exchanger 23 for maintaining the fermentation liquid S in the bioreactor at a temperature suitable for biological treatment (methane fermentation treatment).

[0006] As described above with reference to Fig. 5, for example, rectangular cloths 41, 42 and a hollow cylindrical frame 44 with a length L0 of about 10 m manufactured in a factory or the like are carried to the installation site of the bioreactor 50, and a microbial carrier 40 with a length L0 of about 10 m is assembled according to the procedures shown in Fig. 5 (B) to (D). The assembled microbial carrier 40 is carried into the inside of the bioreactor 50 through the manhole 5, and as shown in Fig. 6, a fixed bed with a height L0 of about 10 m can be created in the bioreactor 50 by filling the inside of the bioreactor 50 while aligning the circulation direction of the fermentation liquid S and the length direction of the microbial carrier 40 and adhering them to each other.

[0007] 6, the fixed bed of the bioreactor 50 can attach microorganisms at a high concentration to the rectangular cloths 41, 42 of the numerous microbial carriers 40 packed in close contact with each other, and can circulate the fermentation liquid S inside the hollow cylindrical frame 44 aligned in the circulation direction of the fermentation liquid S, so that a high concentration of microorganisms can come into contact with the fermentation liquid S over a wide area. Moreover, by using the rectangular cloths 41, 42 and hollow cylindrical frame 44 made of acid-resistant resin to form the microbial carrier 40, it is possible to form a fixed bed that is resistant to deformation and clogging even when immersed for a long period of time in the fermentation liquid S that is easily acidified by organic acids. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] "Biomass Technology Handbook: Know-how for Introduction and Commercialization, Chapter 3: Methane Fermentation," edited by the New Energy Foundation, Ohmsha Co., Ltd., October 25, 2008, pp. 206-447 [Non-Patent Document 2] Satoshi Okabe, "Understanding and Controlling Biofilms, and Coexistence," Journal of the Society of Sea Water Science, Vol. 66, No. 4, August 2012 [Patent documents]

[0009] [Patent Document 1] JP 2018-143902 A [Patent Document 2] JP 2021-175562 A Summary of the Invention [Problem to be solved by the invention]

[0010] However, the fixed bed of the conventional bioreactor 50 as shown in FIG. 6 has a problem that the assembly work of the microbial carriers 40 is very laborious and costly. The fixed bed of the bioreactor 50 needs to be inspected and repaired / regenerated at regular intervals of use. In order to repair / regenerate the fixed bed filled with a large number of microbial carriers 40, it is necessary to secure a space near the site for carrying in the rectangular cloths 41, 42 and the hollow cylindrical frame 44, and then to manually assemble a large number of microbial carriers 40 by connecting the carried-in rectangular cloths 41, 42 and the hollow cylindrical frame 44. This requires a huge amount of labor and cost for the assembly work of the microbial carriers 40, including securing the carrying-in space. From the viewpoint of keeping the running costs of the wet methane fermentation treatment low, it is desired to develop a fixed bed of a bioreactor that can be repaired / regenerated economically without labor.

[0011] In addition, as shown in Fig. 6, a fixed bed packed with many microbial carriers 40 may inevitably undergo partial deformation or clogging, but even if deformation or clogging occurs only partially, it is difficult to repair or regenerate only that part, and there is a problem that the entire fixed bed must be removed from the bioreactor 50 and refilled. Furthermore, if the fermentation liquid S is completely removed from the bioreactor 50 in order to repair or regenerate the fixed bed, the weight of the attached microorganisms may cause the fixed bed packed with many microbial carriers 40 to be unable to stand on its own and to collapse. From this perspective, there is a need for the development of a fixed bed for a bioreactor that allows easy partial repair and regeneration.

[0012] Therefore, an object of the present invention is to provide an anaerobic bioreactor in which the fixed bed can be easily repaired and regenerated even partially. [Means for solving the problem]

[0013] The inventors focused on using wire mesh as the microbial carrier for the fixed bed of a bioreactor, instead of fabric materials such as conventional nonwoven fabrics (rectangular fabrics 41 and 42 in Fig. 5). By using wire mesh as the microbial carrier instead of fabric materials, repair and regeneration are expected to be simplified, since the conventional work of assembling the microbial carrier by joining the fabric material to a frame is no longer necessary. In addition, it is expected that the fixed bed can be made such that even if partial deformation occurs, only that part can be repaired and regenerated.

[0014] However, it is expected that a wire mesh alone will not be able to attach microorganisms at a high concentration, and that the wide contact area between the organic slurry and the microorganisms required for a fixed bed will not be secured, but the inventor has found through preliminary experiments that a biofilm (microbial aggregate) is formed by extracellular polymers produced by the microorganisms on the surface of the wire mesh immersed in a circulating flow of organic slurry, and gradually grows and proliferates, and that the proliferated and grown biofilm covers the wide surface area of ​​the wire mesh, making it possible to contact the microorganisms over an area as wide as that of a carrier using a conventional nonwoven fabric. The present invention was completed as a result of research and development based on this finding.

[0015] Referring to the embodiment in Fig. 1, the anaerobic bioreactor of the present invention comprises an anaerobic fermentation tank 3 that takes in and retains an organic slurry E, a slurry circulation path 22 that draws out the organic slurry E (fermentation liquid S) from the fermentation tank 3 from one end and returns it to the other end for circulation, and microbial carriers 10 made of wire mesh 11 that are arranged on multiple surfaces in the fermentation tank 3 along the slurry circulation flow generated in the fermentation tank 3 by the circulation of the organic slurry E (fermentation liquid S). In a preferred embodiment, as shown in Fig. 2(A), the microbial carriers 10 made of wire mesh 11 are woven together so as to be stretchable in at least one direction.

[0016] In a preferred embodiment, as shown in Fig. 2, microbial carriers 10 made of wire mesh 11 are arranged across both sides of the inner surface of the anaerobic fermenter 3. In a more preferred embodiment, the mesh size of the microbial carriers 10 made of wire mesh 11 is set to 50 mm or less. Effect of the Invention

[0017] The anaerobic bioreactor of the present invention has microbial carriers 10 made of wire mesh 11 arranged on multiple surfaces along the slurry circulating flow generated in the anaerobic fermenter 3 to form a fixed bed, which makes it easier to repair and regenerate the fixed bed, even if only partially, compared to when conventional microbial carriers made of nonwoven fabric are used as the fixed bed. [Brief description of the drawings]

[0018] Hereinafter, modes and embodiments for carrying out the present invention will be described with reference to the accompanying drawings. [Figure 1] FIG. 1 is an explanatory diagram of one embodiment of an anaerobic bioreactor according to the present invention. [Diagram 2] FIG. 2 is an explanatory diagram of a wire mesh microbial carrier placed in the anaerobic bioreactor of FIG. 1. [Diagram 3] FIG. 2 is an explanatory diagram of an experimental apparatus for confirming the performance of the anaerobic bioreactor of FIG. [Figure 4] FIG. 2 is an explanatory diagram of the experimental results confirming the performance of the anaerobic bioreactor of FIG. [Diagram 5] FIG. 1 is an explanatory diagram of an example of a conventional microbial carrier. [Figure 6] FIG. 6 is an explanatory diagram of an example of a conventional anaerobic bioreactor in which the microbial carrier of FIG. 5 is arranged. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Fig. 1 shows an embodiment of an anaerobic bioreactor 1 according to the present invention. The bioreactor 1 in the illustrated example has a cylindrical anaerobic fermenter 3 for retaining an organic slurry E, and a raw material supply path (supply line) 21 for sending the organic slurry E to a supply port provided in a top plate 3a of the fermenter 3, as in the conventional bioreactor in Fig. 6. However, the fermenter 3 of the anaerobic bioreactor 1 of the present invention is not limited to a cylindrical shape. Note that the anaerobic fermenter 3 generally maintains anaerobic conditions suitable for methane fermentation treatment by sealing the inside with a top plate 3a, a bottom plate 3b, and a surrounding wall, but in the illustrated example, for the purpose of explanation, the surrounding wall is shown as transparent so that the inside of the fermenter 3 can be observed.

[0020] The bioreactor 1 in the illustrated example also has a circulation path (circulation line) 22 with a circulation pump 22a that draws out the fermentation liquid S from one end of the fermentation tank 3 and returns it to the other end for circulation, a gas exhaust path (gas line) 24 that discharges the biogas generated during fermentation and decomposition from the fermentation tank 3, and an outflow path (overflow line) 26 that allows the treated fermentation liquid S that has been retained in the fermentation tank 3 for a certain period of time to naturally flow out of the tank. The circulation path 22 is provided with a heat exchanger 23 that maintains the fermentation liquid S in the bioreactor 1 at a temperature suitable for methane fermentation treatment (mesophilic fermentation treatment or high-temperature fermentation treatment) (approximately 35°C for mesophilic fermentation treatment, approximately 55°C for high-temperature fermentation treatment).

[0021] The circulation path 22 with the circulation pump 22a can form a slurry circulation flow (circulation flow of the fermentation liquid S) in a fixed direction inside the fermentation tank 3. In the illustrated example, the fermentation liquid S extracted from the lower end of the bottom plate 3b is merged with the raw material supply path 21 and returned to the supply port of the top plate 3a, thereby generating a downward circulation flow from the top plate 3a to the bottom plate 3b inside the fermentation tank 3. By forming a circulation flow inside the fermentation tank 3, the contact efficiency between the microorganisms attached to the fixed bed in the fermentation tank 3 and the fermentation liquid S can be increased, and the fermentation reaction can be promoted. However, the direction of the circulation flow is not limited to the illustrated example.

[0022] Furthermore, the bioreactor 1 in the illustrated example is provided with a fixed bed consisting of a plurality of microbial carriers 10 made of wire mesh 11 arranged on each of a plurality of surfaces along the circulating flow of the fermentation liquid S generated in the fermenter 3. In the illustrated example, since a circulating flow from the top plate 3a to the bottom plate 3b occurs inside the fermenter 3, a plane perpendicular to the top plate 3a and bottom plate 3b of the fermenter 3 is assumed, and flat wire mesh 11 is arranged on each of a plurality of planes parallel to the perpendicular plane (planes parallel to the circulating flow) to form the microbial carriers 10.

[0023] FIG. 2(A) shows an enlarged perspective view of the fixed bed in FIG. 1, which is made of a microorganism carrier 10 using a wire mesh 11. The illustrated example of the microorganism carrier 10 uses a wire mesh 11 woven from multiple wires so that it can be stretched and contracted in at least one direction. The stretchable wire mesh 11 has the advantage that it can be easily transported by contracting, and can be expanded and expanded in the bioreactor 1 to form a microorganism carrier 10 with a large area. One example of such a wire mesh 11 is a diamond-shaped wire mesh in which multiple wires (wires) bent into a mountain shape at a specified pitch are arranged in parallel at specified intervals, and adjacent wires are entangled with each other to form a diamond-shaped mesh. The diamond-shaped wire mesh is a flexible, flat wire mesh that is stretchable in the direction perpendicular to the multiple wires arranged in parallel, and can be easily transported by rolling it up or contracting it. In addition, the diamond-shaped wire mesh can have a larger area when stretched and expanded by increasing the number of wires and connecting them endlessly.

[0024] However, since the wire mesh 11, which is stretchable in one direction, easily curves and deforms when stretched or unfolded when used alone, it is desirable to increase rigidity by attaching a metal frame 12 to the edge or periphery that suppresses stretching. For example, the metal frame 12 can be made by wrapping rod-shaped steel material (flat steel, round steel, etc.) around the edge or periphery of the diamond-shaped wire mesh 11. Diamond-shaped wire mesh has the advantage of being economical to manufacture and obtain, but the wire mesh used in the present invention is not limited to diamond-shaped wire mesh, and other types of wire mesh (for example, tortoise-shell wire mesh, crimped wire mesh, etc.) can also be used as necessary.

[0025] Fig. 2(B) shows a top view of the fixed bed in Fig. 1 as seen from the top plate 3a side. In the illustrated example, the fermentation tank 3 has an upper annular frame 15 as a metal beam attached to the inner peripheral surface near the top plate 3a in parallel with the top plate 3a, and a lower annular frame 16 as a metal beam attached to the inner peripheral surface near the bottom plate 3b in parallel with the bottom plate 3b. The metal frames 12 at the edge or periphery of each diamond-shaped wire mesh 11 are engaged with the upper annular frame 15 and the lower annular frame 16, respectively, thereby fixing each diamond-shaped wire mesh 11 on a plane parallel to the circulating flow of the fermentation liquid S. The annular frames 15 and 16 in the fermentation tank 3 can be formed, for example, by welding multiple channel steel members with mounting plates 17 at both ends along the inner peripheral surface of the fermentation tank 3. In addition, the metal frame 12 at the edge or periphery of the wire mesh 11 may be provided with protrusions 14 for engaging with and bolting to the upper and lower annular frames 15 and 16, respectively.

[0026] As shown in FIG. 2(A), the microbial carrier 10 with fixed upper and lower ends can be formed by bolting the overhanging portion 14 of the metal frame 12 of the wire mesh 11 to the upper annular frame 15 and the lower annular frame 16, respectively. However, the microbial carrier 10 using the wire mesh 11 does not necessarily need to have both upper and lower ends fixed. For example, it can be hung in the fermentation liquid S with only the upper end fixed and the lower end as a free end. Even if the lower end of the wire mesh 11 is made a free end, the wire mesh itself has weight, so excessive shaking in the circulating flow of the fermentation liquid S is suppressed, and it can function as a microbial carrier 10. That is, the microbial carrier 10 using the wire mesh 11 can be fixed at both upper and lower ends, or only the upper end can be fixed and the lower end as a free end. In addition, the attachment of the metal frame 12 to the free end of the wire mesh 11 that is not fixed can be omitted.

[0027] As can be seen from Fig. 2(B), it is desirable to arrange each of the microbial carriers 10 on both sides of the inner surface of the circulating slurry flow generated in the fermenter 3 so that the microbial carriers 10 come into contact with the circulating slurry flow over as wide an area as possible, that is, by arranging the microbial carriers 10 over the entire length of a chord with both ends on the circumference of the horizontal circular cross section of the cylindrical fermenter 3, thereby widening the area of ​​the microbial carriers 10 that come into contact with the circulating slurry flow. It is also desirable to arrange as many microbial carriers 10 as possible in the fermenter 3 so that the contact area of ​​the entire fixed bed with the circulating slurry flow is as wide as possible. In the illustrated example, a plurality of wire meshes 11 are stretched inside the fermenter 3 at a predetermined interval W so as to be parallel to each other, and each wire mesh 11 is arranged over the entire length of a chord with both ends on the circumference of the circular cross section, thereby ensuring a wide area of ​​contact with the circulating slurry flow.

[0028] As shown in Fig. 2, multiple planes perpendicular to the top plate 3a and bottom plate 3b and spaced at a predetermined distance W from each other are assumed inside the cylindrical fermenter 3, and a fixed bed is formed on each plane by arranging microbial carriers 10 made of flat wire mesh 11 along the entire length of a chord with both ends on the circumference of the circular cross section of the fermenter 3. In the anaerobic bioreactor 1 in Fig. 1 in which such a fixed bed is formed, for example, organic matter slurry E prepared by adding water to food waste is fed in constant amounts from the raw material supply line 21, and the fermentation liquid S inside the fermenter 3 is circulated while being kept at a predetermined fermentation temperature through the circulation line 22, forming a circulation flow inside the fermenter 3 in a direction parallel to the flat wire mesh 11 of each microbial carrier 10, and a microbial reaction in which organic matter is decomposed proceeds on the surface of the wire mesh 11.

[0029] However, the wire mesh 11 is made by weaving together a number of wires to form meshes of a specified size, and there is a limit to the concentration of microorganisms that can adhere to the surface of the wires alone. For example, calcium Ca + When the organic matter slurry E having a high concentration of calcium ions is treated, calcium ions react with metal ions in the fermentation tank 3 under reducing conditions, and calcium phosphate (Ca 10It is expected that the adhesion area of ​​microorganisms will gradually increase as scale such as calcium carbonate (CaCO3) and calcium (OH)2 (PO4)6 precipitates (see Patent Document 2 for details on the adhesion of scale). + When the organic matter slurry E with a low concentration of microbial adhesion is also considered, an increase in the adhesion area of ​​microorganisms due to the precipitation of scale cannot be expected.

[0030] In response to this, the present inventors have developed calcium + It was experimentally found that even when organic matter slurry E with a low concentration of fermentation liquid S was used as the target, a biofilm gradually formed and grew on the surface of the wire mesh 11 immersed on the surface along the circulating flow of the fermentation liquid S. A biofilm is a collection of microorganisms that attach to and grow on the surface of a material in contact with a solution such as organic matter slurry E by extracellular polymers produced by microorganisms (see Non-Patent Document 2). According to the inventor's experiments, when the wire mesh 11 is immersed in the circulating flow of the fermentation liquid S in an appropriate direction, a biofilm is formed on the surface of the wire material, and the biofilm gradually grows and grows in the gaps in the mesh to cover the wide surface of the wire mesh. On the surface of the wire mesh 11 covered with a biofilm in this way, a microbial reaction can proceed to the same extent as a microbial carrier using a conventional nonwoven fabric.

[0031] [Experimental Example 1] In order to confirm the effectiveness of the anaerobic bioreactor 1 of the present invention, an experiment was carried out using two experimental devices shown in Fig. 3. As with the bioreactor 1 in Fig. 1, the experimental device in Fig. 3 has a cylindrical anaerobic fermenter 3 for retaining an organic slurry E, a supply line 21 for supplying the raw material (organic slurry) E from a raw material tank 20 to the fermenter 3 by a raw material pump 21a, a circulation line 22 with a circulation pump 22a for extracting the fermentation liquid S from the fermenter 3 from one end and returning it to the other end for circulation, a gas line 24 for discharging biogas from the fermenter 3, and an overflow line 26 for discharging the treated fermentation liquid S from the fermenter 3 to a recovery device (waste liquid pot) 26a. A heat exchanger 23 is provided in the circulation line 22, and a water seal device (seal pot) 24a and a gas meter 25 are provided in the gas line 24.

[0032] In the fermenter 3 of one experimental device, a fixed bed was installed in which microbial carriers 10 made of flat diamond-shaped wire mesh 11 were placed on multiple surfaces parallel to the circulating flow of the fermentation liquid S, as shown in Figure 2. In the fermenter 3 of the other experimental device, a fixed bed was installed by filling a large number of microbial carriers 40 made of nonwoven fabric, as shown in Figure 6. Organic slurry E, which was prepared by adding water to food waste, was stored in the raw material tank 20 of each experimental device, and the organic slurry E was fed into the fermenter 3 by the raw material pump 21a, while the fermentation liquid S inside the fermenter 3 was circulated through the circulation line 22, generating a circulating flow inside the fermenter 3 in a direction parallel to the flat wire mesh 11 (parallel to the hollow axis of the microbial carriers 40). In both experimental devices, the fermentation liquid S in the fermenter 3 was controlled to about 55°C, which is suitable for high-temperature fermentation treatment.

[0033] In each experimental device, the amount of organic slurry E fed to the fermentation tank 3 (T-CODcr volume load) was gradually increased while measuring and monitoring the volatile fatty acid (VFA) concentration and alkalinity (TAK) of the fermentation liquid S in the fermentation tank 3, and after the measured values ​​of the volatile fatty acid (VFA) concentration and alkalinity (TAK) stabilized and the start-up of methane fermentation in the fermentation tank 3 was confirmed, the amount of organic slurry E fed (T-CODcr volume load) was kept constant, and the amount of biogas generated and the organic decomposition rate (CODcr decomposition rate) in each experimental device were continuously measured and monitored for the next 20 days. Figure 4(A) shows the experimental results of the biogas generation amount in each experimental device, and Figure 4(B) shows the experimental results of the organic decomposition rate in each experimental device.

[0034] From Fig. 4(A), it can be seen that the experimental apparatus with the diamond-shaped wire mesh fixed bed (graph indicated by squares in the figure) continuously generates the same amount of biogas as the experimental apparatus with the nonwoven fabric fixed bed (graph indicated by diamonds in the figure). Also, from Fig. 4(B), it can be seen that the experimental apparatus with the diamond-shaped wire mesh fixed bed (graph indicated by squares in the figure) has the same organic matter decomposition rate (CODcr decomposition rate) as the experimental apparatus with the nonwoven fabric fixed bed (graph indicated by diamonds in the figure). These experimental results show that the microbial reaction proceeds to the same extent in the wire mesh fixed bed of the present invention as in the conventional nonwoven fabric fixed bed.

[0035] In addition, the changes over time in the volatile fatty acid (VFA) concentration and alkalinity (TAK) of the fermentation liquid S in each experimental device were also measured over the 20-day experimental period. Figure 4(C) shows the changes over time in the experimental device equipped with a diamond-shaped wire mesh fixed bed, and Figure 4(D) shows the changes over time in the experimental device equipped with a nonwoven fabric fixed bed. Figures 4(C) and 4(D) show that smooth methane fermentation was observed over a 20-day period in both experimental devices, and it was confirmed that the microbial reaction proceeded to the same extent in the wire mesh fixed bed of the present invention as in the conventional nonwoven fabric fixed bed.

[0036] Furthermore, after the completion of the 20-day experiment, the fermenter 3 of the experimental apparatus equipped with a diamond-shaped wire mesh fixed bed was opened and the diamond-shaped wire mesh 11 of the fixed bed was inspected, and it was observed that the surface of the wires was covered with a biofilm, and that the biofilm had also proliferated and grown in the gaps in the mesh between the wires, and that many, but not all, of the mesh gaps were covered and blocked by the biofilm. From these observation results, it can be seen that the reason that the wire mesh fixed bed of the present invention achieved the same level of microbial reaction as the conventional nonwoven fabric fixed bed is the biofilm that covers a wide area of ​​the surface of the wire mesh.

[0037] Although the details of the principle by which the surface of a wire mesh immersed in a circulating flow of organic slurry becomes covered with a biofilm are unclear, one possible reason is that when the wire mesh 11 is immersed on a surface along the circulating flow of fermentation liquid S, the proliferation and growth of the biofilm attached to the surface of the wire is promoted by the circulating flow, and the biofilm proliferates and grows so as to cover the gaps in the mesh between the wires. It is also possible to adjust the circulation speed of the circulating flow of fermentation liquid S so as to promote the proliferation and growth of the biofilm.

[0038] In order to shorten the period during which the surface of the wire mesh is covered with a biofilm, it is also effective to adjust the mesh size of the wire mesh 11 used as the microorganism carrier 10 so that the biofilm can easily grow. For example, by making the mesh size of the wire mesh 11 used as the microorganism carrier 10 50 mm or less at its maximum part, and preferably 10 mm or less at its maximum part, it is possible to shorten the period during which the surface of the wire mesh is covered with a biofilm and to shorten the fermentation start-up period of the anaerobic bioreactor 1 of the present invention. By making the mesh size of the wire mesh 11 2 mm or more at its maximum part, it is possible to enable it to function as the microorganism carrier 10.

[0039] The bioreactor 1 of the present invention uses a wire mesh microbial carrier 10 as the fixed bed instead of a fabric material such as nonwoven fabric, and therefore does not require the work of assembling a nonwoven fabric and a frame, as compared to the case where a nonwoven fabric microbial carrier is used as the fixed bed, and the fixed bed can be easily repaired and regenerated in a short construction period. For example, when a wire mesh microbial carrier 10 with a metal frame 12 attached to its periphery to increase its rigidity is used as shown in Fig. 2(A), the fixed bed can be repaired and regenerated simply by fixing the wire mesh microbial carrier 10 to the fermenter 3, and even if partial deformation or blockage occurs, the fixed bed can be easily repaired and regenerated simply by removing only that part of the wire mesh microbial carrier 10 and replacing it with a new wire mesh.

[0040] However, the metal frame 12 attached to the periphery of the wire mesh microbial carrier 10 is not essential to the present invention, and it is also possible for only the wire mesh 11 without the metal frame 12 to serve as the microbial carrier 10. The wire mesh microbial carrier 10 can be transported in a rolled up and compact state, and installation in the fermenter 3 can be completed simply by bringing it into the fermenter 3 in a rolled or contracted state and fixing the upper end, and then unfolding it and fixing the lower end, making it possible to construct a fixed bed with a minimum of work.

[0041] In addition, in the fixed bed using a conventional nonwoven fabric shown in Fig. 6, the microbial reaction mainly proceeds inside (one side of the nonwoven fabric) the hollow cylindrical frame 44 through which the fermentation liquid S is circulated, whereas the fixed bed using the wire mesh 11 of the present invention shown in Fig. 1 and Fig. 2 has the advantage that the fermentation liquid S is circulated in the intervals W between the wire mesh 11, allowing the microbial reaction to proceed on both sides of the wire mesh 11. Moreover, the bioreactor 1 of the present invention, which uses the wire mesh microbial carriers 10 as a fixed bed, also makes it possible to adjust the concentration of attached microorganisms by adjusting the intervals W at which the multiple wire mesh microbial carriers 10 are arranged.

[0042] In this way, the object of the present invention can be achieved by providing an anaerobic bioreactor in which the fixed bed can be easily repaired and regenerated even partially.

[0043] In the embodiment of Fig. 1 and Fig. 2, a flat wire mesh 11 is used as the microbial carrier 10, but the wire mesh 11 used in the present invention is not limited to a flat one. For example, a cylindrical wire mesh 11 with its central axis aligned with the direction of the circulating flow of the fermentation liquid S can be arranged in the fermenter 3 to serve as the microbial carrier 10. By arranging the peripheral surface of the cylindrical wire mesh 11 parallel to the circulating flow of the fermentation liquid S, a wide area of ​​the surface of the cylindrical wire mesh 11 can be covered with a biofilm, as with the above-mentioned flat wire mesh 11, to allow the microorganisms to grow at a high concentration. In addition, a plurality of cylindrical wire meshes 11 can be arranged concentrically so that the central axis direction of each coincides with the direction of the circulating flow to form a fixed bed. [Explanation of symbols]

[0044] 1...Anaerobic bioreactor 3...Anaerobic fermenter 3a...Top plate (notebook surface) member 3b...Bottom plate (bottom surface) member 5...Manhole 6...Perforated pedestal 7...Perforated presser cover 10... Wire mesh microorganism carrier 11... Wire mesh (plate-shaped wire mesh) 12...Metal frame 14...Overhanging part 15...(Upper) Metal ring frame 16...(Lower) Metal ring frame 17...Mounting plate 18...Retaining plate 20...raw material tank 21...supply line 21a...supply pump 22...circulation line 22a... Circulation pump 23... Heat exchanger 24...Gas line 24a...Seal pot (water seal device) 25...Gas meter 26...Outflow line (overflow line) 26a... Waste liquid pot (recovery device) 28... Temperature controller (TIC) 30...Anaerobic fermentation tank 40...Microorganism carrier 41, 42...Rectangular cloth 43...Cylindrical cavity 44...Hollow cylindrical frame 44a...Axial member 44b...Annular member 47 ... Joining member 48 ... Binding member 50…Anaerobic bioreactor A: Biogas d: Gap E: Organic treatment liquid G: Predetermined interval H...heating medium J...joining line L: Length S: Fermentation liquid W: Arrangement interval φ: Diameter of hollow cylindrical frame

Claims

1. An anaerobic bioreactor comprising: an anaerobic fermentation tank for taking in and retaining an organic slurry; a slurry circulation path for extracting the organic slurry from one end of the fermentation tank and returning it to the other end for circulating; and wire mesh microbial carriers arranged on each of a plurality of surfaces within the fermentation tank along a slurry circulation flow generated within the fermentation tank by the circulation of the organic slurry.

2. 2. The anaerobic bioreactor according to claim 1, wherein the wire mesh microorganism carrier is made by weaving together a plurality of wires so as to be stretchable in at least one direction.

3. 3. The anaerobic bioreactor according to claim 1 or 2, wherein the wire mesh microbial carriers are disposed across both sides of the inner surface of the fermentation tank.

4. 3. The anaerobic bioreactor according to claim 1 or 2, wherein the mesh size of the wire mesh microbial carrier is 50 mm or less.

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