Manufacturing method for solution carrying pellet

Abstract

To provide a method capable of allowing a pellet to carry various components such as bacteria and fertilizing components in a short time and stably.SOLUTION: A method includes: a solution permeation step of immersing pellets in a solution under a low vacuum environment with a gauge pressure of -0.06 MPa or higher, which is lower than atmospheric pressure, the pellets being produced using sewage sludge, food residue, used mushroom bed, stock excrement, etc., and allowing the solution to permeate the pellets; and a solution settlement step of separating the solution permeated pellets from the immersion solution, leaving the pellets to stand under a high vacuum environment with a gauge pressure of -0.08 MPa or lower, and allowing pellets to carry the solution.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing solution-carrying pellets using pellets produced from sewage sludge, food waste, waste mushroom beds, animal excrement, etc. [Background technology]

[0002] In recent years, efforts have been made to recycle sewage sludge residue generated at sewage treatment plants, etc., and dehydrated sewage sludge residue is being used as a biomass resource for fertilizer, fuel, etc. As an example, the Ministry of Land, Infrastructure, Transport and Tourism is implementing the B-DASH Project (Sewerage Innovative Technology Demonstration Project) and is focusing on solving these problems.

[0003] The characteristics of sewage sludge residue as a biomass resource include (1) the generation of a certain amount in line with human living environments, (2) its composition and state are consistent, and (3) its potential for use as fuel, fertilizer, cement raw material, and other uses. Taking advantage of these characteristics, a practical study aimed at commercializing a sewage sludge treatment system developed by Mitsubishi Nagasaki Machinery Works, Ltd., part of the Ministry of Land, Infrastructure, Transport and Tourism's B-DASH project, was conducted at the Nagasaki City Eastern Sewage Treatment Plant in 2012. This system, known as Metasaurus, combines hydrothermal reaction technology and high-rate methane fermentation technology to reduce sludge volume (see Patent Documents 1 and 2). This system successfully reduced the volume of sludge discharged to one-fifth of that of existing systems, enabling significant savings in disposal costs. However, despite the significant reduction in dewatered sludge generation, most of the sludge is still disposed of.

[0004] Therefore, from the perspective of achieving zero emissions in the area including the sewage treatment plant, effective ways of utilizing sewage sludge residue that has been treated to reduce its molecular weight were investigated. Because the sewage sludge residue generated by this system contains nitrogen, phosphorus, and potassium, which are elements necessary for plant growth, attempts were made to use this sewage sludge residue as fertilizer or soil conditioner, and this sewage sludge residue was registered as a fertilizer by the Minister of Agriculture, Forestry and Fisheries as "Higashi-Nagasaki Demonstration No. 1."

[0005] However, this fertilizer had problems such as a high moisture content, the presence of various bacteria, and a strong ammonia odor. Furthermore, because it was not fully matured compost, there were concerns that applying it to soil as is could cause problems such as impaired crop growth.

[0006] Therefore, the present inventors improved the above-mentioned "Higashinagasaki Demonstration No. 1" and proposed a functional compost with extremely high fertilizer efficiency (see Patent Document 3). Specifically, during research into improving the above-mentioned fertilizer, they supported two types of bacteria with different temperature activity ranges, Bacillus bacteria and lactic acid bacteria, respectively, inside and on the surface of sewage sludge residue pellets, and then subjected the bacteria-supported sewage sludge residue pellets to self-cyclic fermentation, thereby successfully producing useful fermented pellets that are free of the above-mentioned problems. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-200691 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-200692 [Patent Document 3] International Publication No. 2018 / 034135 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, the fermented pellets proposed by the present inventors achieve the desired effects, but because they use natural fermentation and require a long processing time, there has been a need to develop a method that can stably load bacteria, etc. onto pellets in a shorter time, and a new pellet manufacturing process that can load bacteria other than Bacillus bacteria and lactic acid bacteria or other components according to the purpose, thereby further improving fertilizer efficacy and expanding applications.

[0009] An object of the present invention is to provide a method by which various components such as bacteria can be stably supported on pellets in a short period of time. [Means for solving the problem]

[0010] As a result of investigations to achieve the above object, the present inventors focused on the idea of ​​stably confining a solution containing bacteria, etc., within a pellet, and discovered that by performing a specified decompression operation, it is possible to reduce the physical collapse of the internal structure of the pellet due to sudden degassing and the peeling that occurs from the surface of the pellet due to the effect of density changes caused by swelling, and thereby make it possible to stably load various components such as bacteria onto the pellet in a short period of time, thereby completing the present invention.

[0011] That is, the present invention is as follows. [1] A solution penetration step in which pellets made from one or more of sewage sludge, food waste, waste mushroom beds, and animal excrement are immersed in a solution in a low vacuum environment with a gauge pressure of -0.06 MPa or more, which is lower than atmospheric pressure, and the solution is penetrated into the pellets; a solution fixing step of separating the pellets impregnated with the solution from the solution in which they were immersed and placing them in a high vacuum environment with a gauge pressure of −0.08 MMPa or less to support (confine) the solution within the pellets; A method for producing solution-carrying pellets (solution-containing pellets), comprising:

[0012] [2] The method for producing solution-supported pellets according to [1], wherein the solution penetration step alternates between the low vacuum environment and the atmospheric pressure environment.

[0013] [3] The method for producing solution-carrying pellets according to [1] or [2], wherein in the solution fixing step, the high vacuum environment and the atmospheric pressure environment are alternately repeated.

[0014] [4] The method for producing solution-carrying pellets according to any one of [1] to [3], wherein the solution penetration step and / or the solution fixing step are performed until no more bubbles are removed from the pellets.

[0015] [5] The method for producing solution-supported pellets according to any one of [1] to [4], characterized in that after the solution penetration step and before the solution fixing step, a solution penetration adjustment step is performed in which the pellets immersed in the solution are placed in a high vacuum environment with a gauge pressure of -0.08 MPa or less.

[0016] [6] The method for producing solution-supported pellets according to [5], characterized in that in the solution penetration adjustment step, the high vacuum environment and a low vacuum environment in which the gauge pressure is -0.06 MPa or more and lower than atmospheric pressure are alternately repeated.

[0017] [7] The method for producing solution-loaded pellets according to [5] or [6], wherein the solution penetration adjustment step is performed until no more bubbles are released from the pellets.

[0018] [8] The method for producing solution-supported pellets according to any one of [1] to [7], wherein the solution is a bacterial culture solution in which a bacterium is cultured.

[0019] [9] The method for producing solution-supported pellets according to any one of [1] to [8], wherein the solution contains a fertilizer component.

[0020]

[10] A method for producing solution-supported pellets according to any one of [1] to [9], characterized by comprising a moisturizing coating step of coating the surface of the pellets produced in the solution fixing step with moist rice bran.

[0021]

[11] Use of solution-carrying pellets, characterized in that the solution-carrying pellets produced by the method for producing solution-carrying pellets according to any one of [1] to

[10] are used as fertilizer, soil conditioner, compost, water quality improver, or filter material. [Effects of the Invention]

[0022] According to the method for producing solution-carrying pellets of the present invention, a solution containing various components such as bacteria can be stably carried in pellets produced from sewage sludge or the like in a short period of time. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a flow diagram of one embodiment of a method for producing solution-carrying pellets of the present invention. [Figure 2] A is an optical microscope photograph of the cross section of a solution-loaded pellet after the solution penetration step in the manufacturing method of the solution-loaded pellet, and B is an optical microscope photograph of the cross section of a solution-loaded pellet after the solution fixing step in the manufacturing method of the solution-loaded pellet. [Figure 3] Photographs showing the effect of solution-carrying pellets on plants. DETAILED DESCRIPTION OF THE INVENTION

[0024] The method for producing solution-supported pellets according to the present invention includes a solution penetration step of immersing pellets produced using one or more of sewage sludge, food waste, waste mushroom beds, and animal excrement in a solution in a low vacuum environment (low vacuum atmosphere) where the gauge pressure is −0.06 MPa or more and lower than atmospheric pressure, thereby allowing the solution to penetrate into the pellets; a solution fixing step in which the pellets impregnated with the solution are separated from the solution and placed in a high vacuum environment (high vacuum atmosphere) with a gauge pressure of -0.08 Pa or less to retain the solution within the pellets; The present invention is characterized by having the following.

[0025] The method for producing solution-carrying pellets of the present invention may include steps carried out before or after the solution penetration step and the solution fixing step, such as a solution penetration adjustment step carried out after the solution penetration step and before the solution fixing step, or a moisture-retaining coating step carried out after the solution fixing step. For example, the solution penetration adjustment step is preferably carried out by placing the pellets immersed in the solution in a high vacuum environment (high vacuum atmosphere, the same applies hereinafter) with a gauge pressure of −0.08 Pa or less.

[0026] The solution-supported pellets produced by the method for producing solution-supported pellets of the present invention are preferably used as fertilizer, soil conditioner, or compost by carrying soil-improving bacteria or fertilizer components, but can also be used for other purposes, such as water quality improvement materials or filter materials for the sea, lakes, ponds, etc. Furthermore, the solution-supported pellets of the present invention can be suitably used, for example, as filter materials for biofilter devices described in Japanese Patent No. 7144027 and Japanese Patent No. 6925032.

[0027] The method for producing solution-loaded pellets of the present invention is a novel technique that utilizes a special decompression process to load bacteria and other microorganisms onto pellets, enabling stable loading of bacteria and other microorganisms onto pellets in a short period of time. For example, by placing the pellets under a low vacuum, unnecessary ammonia in the pellets is removed, making immature compost or fertilizer pellets as safe as fully matured pellets in a short period of time. Furthermore, adding the produced solution-loaded pellets to soil promotes an increase in the diversity and density of symbiotic microorganisms, such as rhizosphere microorganisms, thereby improving the health of soil microorganisms. Furthermore, it is possible to quickly produce and supply appropriate fertilizers, soil conditioners, compost, water quality improvers, or filter materials depending on the differences in physical properties resulting from the various manufacturing methods and compositions of pellets made from sewage sludge, food waste, waste mushroom beds, animal waste, etc., and the physical, chemical, and biological conditions of the soil to which they are input, thereby contributing to the appropriate reuse and recycling of waste, harmony with nature and the global environment, and the sustainable development of society.

[0028] The pellets that can be used in the production method of the present invention are not particularly limited as long as they are produced using one or more of sewage sludge, food residues, waste mushroom beds, and animal excrement, and may contain other components such as wood flour, binder components, etc. That is, the pellets of the present invention are mainly composed of one or more of sewage sludge, food residues, waste mushroom beds, and animal excrement, and preferably contain 70% by mass or more of sewage sludge, food residues, waste mushroom beds, and animal excrement, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and most preferably consist solely of sewage sludge, food residues, waste mushroom beds, and animal excrement (100%).

[0029] The pellets may be, for example, rectangular or cylindrical pellets with a base side or diameter of 5 mm to 15 mm and a length of about 10 mm to 50 mm, and considering transportation, storage, etc., pellets with a length of about three times the base side or diameter are preferred. Also, pellets with a moisture content of 35% or less are preferred.

[0030] Examples of pellets made from sewage sludge include sewage sludge residue that has been subjected to general sewage treatment, as well as pellets made from sewage sludge residue that has been subjected to a low-molecular-weight reduction treatment to reduce the molecular weight of persistent polymers such as lignin and cellulose. Various organic resources, such as food waste, may be added during the low-molecular-weight reduction treatment. Examples of such low-molecular-weight reduction treatments include hydrothermal treatment, ozone treatment, biological activated carbon treatment, and ultrasonic treatment (e.g., JP 2003-144097 A), and various treatments may be combined. Specific examples of low-molecular-weight reduction treatments using hydrothermal treatment include the methods utilizing hydrothermal reactions described in JP 2012-200691 A and JP 2012-200692 A.

[0031] Food waste is food-related waste generated by food-related businesses, and includes, for example, food waste from restaurants, leftovers from customers, unsold food, and expired food. Waste mushroom beds are mushroom beds (culture media) discarded after artificial cultivation of mushrooms such as shiitake, oyster mushroom, maitake, king oyster mushroom, and shimeji mushroom. Animal waste is so-called livestock waste (livestock manure), and examples thereof include the excrement of cows, pigs, chickens, and the like.

[0032] Each step of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the method for producing solution-supported pellets of the present invention includes, for example, a solution penetration step (S1), a solution penetration adjustment step (S2), and a solution fixing step (S3). In the present invention, gauge pressure is used as the pressure. Here, gauge pressure is pressure with atmospheric pressure (0.1 MPa) as the reference (zero), so −0.1 MPa is an absolute vacuum (complete vacuum).

[0033] Each step will be specifically described below.

[0034] (Solution penetration process) The solution impregnation step is a step of impregnating the pellets with a solution. First, pellets and a solution are placed in a container, and the pellets are immersed in the solution. The solution can be varied depending on the use of the pellets. For example, when the pellets are used as fertilizer, soil conditioner, compost, water quality modifier, or filter material, the solution can be a bacterial culture solution containing soil-improving bacteria or a solution containing synthetic or natural organic fertilizer components.

[0035] When the pellets are used as fertilizer, soil conditioner, compost, water quality modifier, or filter material, the bacteria supported on the pellets are preferably a complex of bacteria containing lactic acid bacteria and Bacillus bacteria, and more preferably contain koji mold and yeast.

[0036] Examples of Bacillus bacteria include Bacillus subtilis, Bacillus tequilensis, Bacillus vallismortis, Bacillus mojavensis, Bacillus amyloliquefaciens, Bacillus subtilis subsp. subtilis, Bacillus subtilis subsp. spizizenii, Bacillus subtilis subsp. inaquosorum, and Bacillus subtilis var. natto. Among these, Bacillus subtilis var. natto (natto bacteria) is preferred. These Bacillus bacteria can be used alone or in combination of two or more. There are no particular limitations on how Bacillus bacteria can be obtained, and commercially available products can be used. Alternatively, for example, foods containing Bacillus bacteria, such as natto, or Bacillus bacteria isolated therefrom may be used.

[0037] Examples of lactic acid bacteria include lactic acid bacteria of the genera Lactobacillus, Bifidobacterium, Lactococcus, Enterococcus, Streptococcus, Pediococcus, and Leuconostoc. These lactic acid bacteria can be used alone or in combination of two or more. There are no particular limitations on how the lactic acid bacteria can be obtained, and commercially available products can be used. In addition, for example, foods containing lactic acid bacteria, such as yogurt, or lactic acid bacteria isolated therefrom may also be used.

[0038] Aspergillus oryzae (Koji mold) is a microorganism involved in koji fermentation. Aspergillus oryzae belong to the genus Aspergillus (Koji mold), and examples thereof include yellow aspergillus, white aspergillus, and black aspergillus. Examples of yellow koji molds include Aspergillus oryzae, Aspergillus sojae, and Aspergillus tamari, examples of white koji molds include Aspergillus Kawachii, and examples of black koji molds include Aspergillus luchuensis. These koji molds can be used singly or in combination of two or more.

[0039] As the yeast, yeasts of the genus Saccharomyces, Schizosaccharomyces, Candida, etc. can be used. These yeasts can be used alone or in combination of two or more. There is no particular limitation on the method for obtaining the yeast, and commercially available products can be used.

[0040] Examples of fertilizer components include chemical components such as nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, zinc, copper, molybdenum, boron, chlorine, nickel, silicon, and sodium, as well as organic substances such as slag, oil cake, rice bran, converter lime, and used tea leaves. These fertilizer components can be used alone or in combination of two or more. There are no particular limitations on how the fertilizer components can be obtained, and commercially available products can be used.

[0041] Next, the container containing the pellets and solution is placed in a vacuum chamber, and the chamber is isolated from the atmosphere and placed in a low vacuum environment with a gauge pressure of -0.06 MPa or higher, which is lower than atmospheric pressure. This decompression operation is an operation to naturally degas the pellets, specifically, to expel the air present in the countless pores inside the pellets and to allow the solution to penetrate into these pores. Note that, because the pores inside the pellets are irregularly interconnected, this operation allows the solution that has penetrated into the surface of the pellets to gradually penetrate from the periphery to the interior, as shown in Figure 2A.

[0042] As described above, in the present invention, in order to allow the solution to penetrate into the pellets, the low vacuum environment is an environment in which the gauge pressure is −0.06 MPa or more and lower than atmospheric pressure (gauge pressure less than 0 MPa), preferably −0.06 MPa or more and −0.025 MPa or less, more preferably −0.06 MPa or more and −0.03 MPa or less, and even more preferably −0.055 MPa or more and −0.035 MPa or less.

[0043] By placing the pellets immersed in the solution in the low vacuum environment described above, bubbles are removed from the pellets, and as time passes, bubbles gradually stop being removed. It is preferable to continue the reduced pressure operation until bubbles stop being removed. If pellets immersed in a solution are left in a low vacuum environment for a long time, the air in the solution will begin to degas to a certain extent, which may result in the death of the bacteria in the case of a bacterial culture solution. Therefore, even when placed in a low vacuum environment, the holding time is preferably, for example, 30 minutes or less, more preferably 20 minutes or less, and even more preferably 15 minutes or less. The lower limit can be determined based on the degassing status of the pellets, but the shorter the time, the better to increase the survival rate of the microorganisms. For example, it is about 5 minutes.

[0044] Furthermore, in the solution penetration step, it is preferable to alternately repeat the above-mentioned low vacuum environment and atmospheric pressure environment two or more times, depending on the type of pellet, etc. This promotes degassing from the pellet and penetration of the solution into the pellet while keeping the pores in the pellet unblocked, allowing the solution to fully penetrate deeper into the pellet. Furthermore, the processing time for the solution penetration step can be further shortened. Note that an atmospheric pressure environment refers to, for example, an environment with a gauge pressure of 0 MPa, but also includes an environment with a gauge pressure of -0.01 MPa or higher (the same applies hereinafter).

[0045] (Solution penetration adjustment process) The manufacturing method of the present invention preferably includes a solution penetration adjustment step after the solution penetration step and before the solution fixing step. The solution penetration adjustment step is a step performed following the solution penetration step, in which the pellets, while immersed in the solution, are placed in a high vacuum environment with a gauge pressure of -0.08 MPa or less. The high vacuum environment may be achieved by further reducing the pressure after the low vacuum environment described above, or by reducing the pressure from an atmospheric pressure environment to a high vacuum environment. However, from the viewpoint of suppressing physical loads on the pellets, the mode of reducing the pressure from the low vacuum environment to a high vacuum environment is preferred. This reduces the effects of reduced pressure in a high vacuum environment in the subsequent solution fixing step, specifically, suppressing or even preventing physical collapse of the pellet interior due to a sudden reduction in pressure.

[0046] As described above, in order to reduce the influence of reduced pressure in the solution fixing step described below, the high vacuum environment is an environment with a gauge pressure of -0.08 MPa or less, preferably -0.085 MPa or less, more preferably -0.09 MPa or less, and even more preferably -0.095 MPa or less. The lower limit is not particularly limited because an absolute vacuum may also be used, but in reality it is about -0.099 MPa.

[0047] By placing the pellets immersed in the solution under the high vacuum environment, bubbles are degassed from the pellets, and the degassing gradually stops over time. However, it is preferable to continue the degassing operation at least until the degassing stops. Furthermore, the degassing operation may be continued as needed even after the degassing from the pellets has stopped. If the pellets immersed in the solution are left in a high vacuum environment for a long period of time in the solution penetration adjustment step, the pellets may shrink, which may result in, for example, the collapse of the pellets, the scattering of the solution that has penetrated the pellets to the outside, or damage to the vacuum equipment due to the boiling of the solution. Therefore, the time for maintaining the pellets in a high vacuum environment is preferably, for example, 5 minutes or less, more preferably 3 minutes or less, and even more preferably 1 minute or less. The lower limit is not particularly limited, as it may be even for a moment, but is, for example, preferably about 5 seconds, more preferably about 10 seconds.

[0048] Furthermore, in the solution penetration adjustment step, although depending on the type of pellets, it is preferable to alternately repeat two or more times the above-mentioned high vacuum environment and the same low vacuum environment as in the solution penetration step, where the gauge pressure is -0.06 MPa or more and lower than atmospheric pressure. This allows processing to be completed in a short time and reduces the risk of pellet collapse, scattering of the solution that has penetrated the pellets to the outside, damage to vacuum equipment due to boiling of the solution, etc.

[0049] (Solution fixing process) The solution fixing step is a step carried out following the solution penetration step or the solution penetration adjustment step described above. First, the storage container is removed from the vacuum chamber, and then the penetrating solution is drained from the storage container, after which the pellets are removed and separated from the solution they were immersed in. The surface of the pellets is wet (sticky) due to the influence of the penetrating solution.

[0050] After the solution has been completely drained, the pellet is placed back into the storage container and returned to the vacuum chamber, where it is placed in a high-vacuum environment with a gauge pressure of -0.08 MPa or less. This decompression operation further expels the residual expanded air bubbles inside the pellet's pores, which have been returned to atmospheric pressure. This reaction forces the solution inside the pores deeper into the pellet, resulting in a gas-liquid exchange. As a result, the pores on the outer surface, which dry quickly, shrink, and the pellet itself tends to shrink. As a result, the solution and bacteria that have penetrated the interior become stably supported within the pellet, as shown in Figure 2B. The solution (culture medium) present within the pellet allows the bacteria to survive for a long period of time.

[0051] As described above, in order to fix the solution in the pellets, the high vacuum environment is an environment with a gauge pressure of -0.08 MPa or less, preferably -0.085 MPa or less, more preferably -0.09 MPa or less, and even more preferably -0.095 MPa or less. The lower limit is not particularly limited because an absolute vacuum may also be used, but in reality it is about -0.099 MPa.

[0052] The pellets soaked in the solution are placed in the high vacuum environment, whereby the pellets are degassed and gradually stop degassing over time. However, it is preferable to continue the degassing operation at least until the pellets stop degassing. Furthermore, the degassing operation may be continued as needed even after the pellets have stopped degassing. If the pellets permeated with the solution are left in a high vacuum environment for a long period of time in the solution fixing step, the pellets may shrink, which may result in, for example, the pellets collapsing, the solution that has permeated the pellets scattering to the outside, or damage to the vacuum equipment due to the solution boiling. Therefore, the time for holding in the high vacuum environment is preferably, for example, 5 minutes or less, more preferably 3 minutes or less, and even more preferably 1 minute or less. The lower limit is not particularly limited, as it may be even for a moment, but is, for example, preferably about 5 seconds, more preferably about 10 seconds.

[0053] Furthermore, in the solution fixing step, it is preferable to alternately repeat the above-mentioned high vacuum environment and atmospheric pressure environment two or more times, although this depends on the type of pellets, etc. This allows processing to be completed in a short time and reduces the risk of pellet collapse, scattering of the solution that has penetrated the pellets to the outside, damage to vacuum equipment due to boiling of the solution, etc.

[0054] After the solution fixing step is completed, the pellets containing the solution, i.e., the solution-carrying pellets, are removed from the vacuum chamber and used. The process from the solution immersion step to the solution fixing step, including the solution penetration adjustment step, can be completed in about 30 minutes.

[0055] The solution-supported pellets may be subjected to a drying treatment such as natural drying or hot air drying as needed to dry the surface layer. Even if such a drying treatment is performed, the openings in the surface layer of the pellets are closed, so the interior does not dry out and the solution remains present. As for the drying conditions, the moisture content varies somewhat depending on the size of the pellets after the solution is supported, but drying is performed, for example, with hot air at 50 to 70°C for about 10 to 20 hours. Thereafter, natural drying may be performed as needed. When a bacterial culture solution is supported, natural drying is preferred. Furthermore, when dried at high temperatures and high speed, the swollen pellets may collapse and lose their shape, but the fertilizer ingredients that have been loaded remain unchanged, so they can be processed into a powder-like product. Furthermore, the ammonia concentration of the loaded and dried pellets is 10 ppm or less, ensuring their safety in soil.

[0056] Furthermore, in the manufacturing method of the present invention, the surface of the pellets containing the solution can be coated with wet rice bran (moisture-retaining coating step). This prevents the solution-carrying pellets from drying out over a long period of time, thereby preventing, for example, the death of the carried bacteria. It also prevents the growth of unwanted bacteria. [Example]

[0057] [Verification of solution retention performance of solution-loaded pellets] Here, the solution was impregnated into the pellets by reducing the pressure under various conditions shown in Table 1, followed by natural drying for two weeks. The weight of the solution-impregnated pellets was measured, and the moisture content was calculated and compared. The pellets were produced using sewage sludge residue generated from sewage treatment plants, etc. Water was used as the solution.

[0058] [Table 1]

[0059] The solution-supported pellets of Examples 1 to 3 all had a high water content, which allows bacteria to grow when a bacterial culture solution is supported on the pellets. In particular, Example 2 was the result of producing solution-carrying pellets under more favorable conditions for the gauge pressure in the solution penetration step and the solution fixing step, and the moisture content was higher than that of Example 1. In Example 3, a solution penetration adjustment step was carried out between the solution penetration step and the solution fixing step to produce solution-supported pellets, and the moisture content was even higher than that of Example 2.

[0060] On the other hand, in Comparative Example 1, the pellets were immersed in the solution and treated only in a low vacuum environment of -0.04 MPa. However, since the treatment (solution fixing process) was not performed in a high vacuum environment, a large amount of solution remained on the surface of the pellets and the solution was prone to drying, resulting in a lower moisture content compared to Example 1. Comparative Example 2 is the result of Example 2 in which vacuum treatment was not performed in the solution penetration step. Since the solution did not penetrate the pellets sufficiently, the moisture content was lower than that of Example 1. In Comparative Example 3, the gauge pressure during the solution fixing process in Example 1 was set to a low vacuum of -0.07 MPa, which is higher than the upper limit of the appropriate range of the present invention. However, the volumetric shrinkage of the pellets was insufficient, the pores in the surface layer were not blocked, the solution that had penetrated into the pellets dried, and the moisture content was lower than in Example 1.

[0061] [Production of solution-loaded pellets] Commercially available sludge fermented fertilizer pellets produced at sewage treatment facilities were loaded with (A) a soil-improving bacterial cell solution, (B) a solution containing organic fertilizer components, and (C) a polyphenol solution using the decompression operation of the method of the present invention, to produce solution-loaded pellets (A) to (C) according to the present invention.

[0062] [Confirmation test for ammonia gas generated from pellet eluate] The pellets used were the solution-supported pellets (A) to (C) according to the examples, and pellets produced without using a vacuum operation (hereinafter referred to as untreated pellets). 1.5 g of the crushed pellets was added to a container containing 30 mL of pure water and shaken for about 30 minutes. After that, 100 mL of gas from the top of the container was sucked in using a gas detector tube for 45 seconds, and the concentration of ammonia gas was measured based on the change in the detector tube. The ammonia concentration was 10 ppm for the untreated pellets, whereas the treated pellets (A) to (C) according to the examples had an ammonia concentration of 5 ppm or less, resulting in a concentration difference of more than two times. In this way, it was confirmed that by using the production method of the present invention, unnecessary ammonia in the pellets can be removed more effectively than in the untreated case.

[0063] [Confirmation test for ammonia gas generated from pellets] The concentration of ammonia gas inside the container containing the treated pellets (C) according to the example and the container containing untreated pellets was measured. The ammonia concentration in the container containing untreated pellets was about 20 ppm, while that in the container containing the treated pellets (C) according to the example was about 6.5 ppm, a reduction of less than one-third. Note that the ammonia concentration in an unopened bag containing the above-mentioned commercially available pellets (untreated pellets) purchased within one month was about 50 ppm. In this way, it was confirmed that by using the production method of the present invention, unnecessary ammonia in the pellets can be removed more effectively than in the untreated case.

[0064] [Evaluation of solution-loaded pellets as fertilizer] A germination test was carried out using seeds. The test method was to place 25 seeds on cotton in a glass container and observe them at room temperature. The cotton was soaked in purified water, a liquid (liquid fertilizer) of the treated pellets (C) according to the example, and a liquid (liquid fertilizer) of the untreated pellets. As shown in Figure 3, when purified water was used, radicles emerged from five seeds after one day (20 seeds remained unchanged), and all seeds germinated after five days. Furthermore, when the solution of the treated pellets (C) according to the example was used, radicles emerged from 12 seeds after one day (13 seeds remained unchanged), and all seeds germinated after five days. The growth conditions were better than when purified water was used, and were very good after seven days. On the other hand, when the liquid from untreated pellets was used, no radicles emerged from the seeds even after one day, but after six days, radicles emerged from two seeds and shoots sprouted from 23 seeds, but after seven days, it was determined that growth had been impaired.

[0065] From the above, it was confirmed that the use of solution-carrying pellets produced by the method for producing solution-carrying pellets of the present invention can promote seed growth.

[0066] [Production of solution-loaded pellets] The test was carried out in the following manner. The organic untreated pellets used had a moisture content of approximately 27.4% and an ammonia concentration of 50 ppm. 600 mL of solution was added to 1,000 g of these pellets. This solution was a 100-fold dilution of a stock solution of organic fertilizer components (N (nitrogen), P (phosphorus), K (potassium) = 5%, 5%, 5%). The moisture content of the pellets was 33.8% after 5 minutes of immersion in the solution.

[0067] First, a solution infiltration step was carried out. The mixture of pellets and solution was transferred to a storage container, placed in a vacuum chamber, and processed in a low vacuum environment. Specifically, the pressure in the chamber was reduced from atmospheric pressure to a gauge pressure of -0.049 MPa, and gas-liquid exchange was performed in a low vacuum environment. During this process, the gauge pressure in the vacuum chamber was maintained at -0.049 MPa, and degassing was performed on the surface layer of the pellets for approximately 2 minutes.

[0068] Next, a solution penetration adjustment step was carried out. The pressure was further reduced from the low vacuum environment described above to a high vacuum environment. Specifically, the pressure in the chamber was reduced from -0.049 MPa to -0.099 MPa (gauge pressure), and gas-liquid exchange was performed in a high vacuum environment. After the gauge pressure in the vacuum chamber reached -0.099 MPa, this state was maintained until degassing from the pellets ceased.

[0069] If degassing due to gas-liquid exchange was confirmed, the pressure in the chamber was returned to atmospheric pressure while monitoring the gauge pressure for about 1 minute. The container containing the pellets was then removed from the vacuum chamber, and the solution was recovered, leaving the pellets in the container. The water content of the pellets immediately after the solution was added was 39.4%, and the amount of solution recovered was approximately 300 mL for the 600 mL of solution the pellets were added to. In other words, it is estimated that the pellets contained 300 mL of solution containing fertilizer-effective ingredients at this point. The recovered solution has an ammonia concentration of 5 ppm or less, and can be used as a liquid fertilizer.

[0070] Further, a solution fixing step was carried out. The container containing the pellets was placed in a vacuum chamber and processed in a high-vacuum environment. Specifically, the pressure in the chamber was reduced from atmospheric pressure to a gauge pressure of -0.099 MPa, and the solution was allowed to penetrate and settle deep into the pellets through gas-liquid exchange in a high-vacuum environment. After the gauge pressure in the vacuum chamber reached -0.099 MPa, this state was maintained until degassing from the pellets ceased.

[0071] If degassing due to gas-liquid exchange was confirmed, the pressure in the chamber was returned to atmospheric pressure while monitoring the gauge pressure for about 1 minute. The container containing the pellets was then removed from the vacuum chamber, and the solution was recovered, leaving the pellets in the container. The recovered solution has an ammonia concentration of 5 ppm or less, and can be used as a liquid fertilizer.

[0072] Subsequently, a drying step was carried out. The pellets were transferred from the storage container to a drying tray and dried with hot air at 65°C for about 16 hours, followed by natural drying for about 8 hours.

[0073] From various tests including the above test, the following was found. By applying a solution to the pellets in a vacuum environment, the amount of fertilizer components can be adjusted freely. When pellets are loaded with a solution containing many fertilizer components in a vacuum environment, the moisture content of the pellets themselves increases due to the effect of gas-liquid exchange that occurs inside the pellets. At the same time, however, the dissolved water-soluble fertilizer components penetrate deep inside the pellets, so only the water evaporates during the subsequent drying process, and the fertilizer components contained in the solution are left behind in the deep layers of the pellets, becoming completely fixed. The higher the moisture content of the pellets, the more effective fertilizer components in the solution can be transferred to the pellets, increasing the fertilizer effectiveness.

[0074] -It is possible to reduce the ammonia concentration in the pellets to below 10 ppm. The recovered solution has a low ammonia concentration of 5 ppm, making it possible to use it as liquid fertilizer. - Pellets that have been dried after being loaded in a vacuum environment can maintain their fertilizer effectiveness even if they lose their shape and become granular. By adjusting the organic solution to be supported, it is possible to enhance the growth of fungi. - When pellets made from sludge were left in their original state for over a month, no natural growth of bacteria was observed. However, when pellets were loaded with a solution in a vacuum environment, bacterial growth was observed within 3 to 4 days after loading. [Industrial Applicability]

[0075] The present invention is industrially useful because it can stably support various components such as bacteria in a short period of time on pellets produced from sewage sludge, food waste, waste mushroom beds, animal excrement, etc.

Claims

1. a solution permeation step in which pellets produced using one or more of sewage sludge, food waste, waste mushroom beds, and animal excrement are immersed in a solution in a low vacuum environment with a gauge pressure of −0.06 MPa or more, which is lower than atmospheric pressure, to permeate the solution into the pellets; a solution fixing step of separating the pellets impregnated with the solution from the solution in which they were immersed and placing them in a high vacuum environment with a gauge pressure of −0.08 MPa or less to cause the solution to be carried within the pellets; A method for producing solution-carrying pellets, comprising:

2. 2. The method for producing solution-supported pellets according to claim 1, wherein the solution penetration step alternates between the low vacuum environment and the atmospheric pressure environment.

3. 2. The method for producing solution-carrying pellets according to claim 1, wherein the solution fixing step alternates between the high vacuum environment and the atmospheric pressure environment.

4. 2. The method for producing solution-carrying pellets according to claim 1, wherein the solution permeation step and / or the solution fixing step are performed until no more bubbles are removed from the pellets.

5. 2. The method for producing solution-supported pellets according to claim 1, further comprising a solution penetration adjustment step of placing the pellets immersed in the solution in a high vacuum environment with a gauge pressure of −0.08 MPa or less after the solution penetration step and before the solution fixing step.

6. 6. The method for producing solution-loaded pellets according to claim 5, wherein in the solution penetration adjusting step, the high vacuum environment and a low vacuum environment having a gauge pressure of −0.06 MPa or higher and lower than atmospheric pressure are alternately repeated.

7. 6. The method for producing solution-carrying pellets according to claim 5, wherein the solution penetration adjusting step is performed until no more bubbles are released from the pellets.

8. 2. The method for producing solution-supported pellets according to claim 1, wherein the solution is a bacterial culture solution in which a bacterium is cultured.

9. 2. The method for producing solution-loaded pellets according to claim 1, wherein the solution contains a fertilizer component.

10. 2. The method for producing solution-carrying pellets according to claim 1, further comprising a moisturizing coating step of coating the surfaces of the pellets produced in the solution fixing step with moist rice bran.

11. Use of solution-carrying pellets, characterized in that the solution-carrying pellets produced by the method for producing solution-carrying pellets according to any one of claims 8 to 10 are used as fertilizer, soil improvement material, compost, water quality improvement material, or filter material.

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