Method for producing solution-carrying pellets

Abstract

The present invention provides a method for producing solution-carrying pellets that comprises: a solution permeation step for immersing pellets that have been produced using sewage sludge, food residue, mushroom bed waste, animal excrement, or the like in a solution under a low vacuum environment, which has a gauge pressure of at least -0.06 MPa but lower than atmospheric pressure, to allow the solution to permeate into the pellets; and a solution fixing step for separating, from the solution which has been used for the immersion, the pellets into which the solution has penetrated and placing the pellets under a high vacuum environment, which has a gauge pressure of -0.08 MPa or less, to allow the pellets to carry the solution therein.

Description

Method for producing solution-carrying pellets

[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.

[0002] In recent years, efforts have been made to recycle sewage sludge residue generated from 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 (Innovative Sewerage Technology Demonstration Project), which is putting effort into solving these problems.

[0003] The characteristics of sewage sludge residue as a biomass resource include (1) a certain amount is always generated in accordance with human living environments, (2) its composition and state are consistent, and (3) it can be used for fuel, fertilizer, cement raw materials, etc. Taking advantage of these characteristics, practical research aimed at the practical application of 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 in 2012, was conducted at the Nagasaki City Eastern Sewage Treatment Plant. This system, called Metasaurus, is a new sludge reduction technology that combines hydrothermal reaction technology and high-rate methane fermentation technology (see Patent Documents 1 and 2). This system successfully reduced the amount of sludge discharged to one-fifth of that of existing systems, enabling significant savings in disposal costs. However, despite the significant reduction in the amount of dewatered sludge generated, it is primarily disposed of as waste.

[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. Also, 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, Bacillus bacteria and lactic acid bacteria, which have different temperature activity ranges, 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 producing useful fermented pellets that are free of the above-mentioned problems.

[0007] JP 2012-200691 A JP 2012-200692 A International Publication No. 2018 / 034135

[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.

[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 method for producing solution-supported pellets (solution-containing pellets), comprising: 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 with a gauge pressure of −0.06 MPa or more and lower than atmospheric pressure, to allow the solution to penetrate into the pellets; and a solution fixing step of separating the solution-impregnated pellets 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.

[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 degassed from the pellets.

[0015] [5] The method for producing solution-supported pellets according to any one of [1] to [4], 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 MMPa or less after the solution penetration step and before the solution fixing step.

[0016] [6] The method for producing solution-supported pellets according to [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 more and lower than atmospheric pressure are alternately repeated.

[0017] [7] The method for producing solution-carrying pellets according to [5] or [6], wherein the solution penetration adjusting 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] The method for producing solution-carrying pellets according to any one of [1] to [9], further comprising a moisturizing coating step of coating the surfaces 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 improvement material, compost, water quality improver, or filter material.

[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.

[0023] 1 is a flow diagram of one embodiment of a method for producing solution-carrying pellets of the present invention. FIG. 1A is an optical microscope photograph of a cross section of a solution-carrying pellet after a solution penetration step in the method for producing solution-carrying pellets of the present invention, and FIG. 1B is an optical microscope photograph of a cross section of a solution-carrying pellet after a solution fixing step in the method for producing solution-carrying pellets. The photographs show the effect of solution-carrying pellets on plants.

[0024] The method for producing solution-loaded pellets according to the present invention is characterized by comprising: a solution impregnation 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) having a gauge pressure of −0.06 MPa or more and lower than atmospheric pressure, thereby allowing the solution to penetrate into the pellets; and a solution fixation step of separating the solution-impregnated pellets from the solution and placing them in a high vacuum environment (high vacuum atmosphere) having a gauge pressure of −0.08 Pa or less, thereby allowing the solution to be loaded into the pellets.

[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, a moisture-retaining coating step carried out after the solution fixing step, etc. 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 operation to load bacteria onto pellets, enabling stable loading of bacteria onto pellets in a short period of time. For example, by placing the pellets under a low vacuum, unnecessary ammonia is removed from the pellets, quickly converting immature compost or fertilizer pellets into safe pellets equivalent to fully mature pellets. 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, depending on the physical properties of pellets produced from sewage sludge, food waste, waste mushroom beds, animal waste, etc., resulting from various production methods and compositions, as well as the physical, chemical, and biological conditions of the soil to which they are input, appropriate fertilizers, soil conditioners, compost, water quality modifiers, or filter materials can be produced and supplied in a short period of time, contributing to the appropriate reuse and recycling of waste, harmony with nature and the global environment, and sustainable social development.

[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 undergone general sewage treatment, as well as pelletized sewage sludge residue that has undergone a low-molecular-weight 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 treatment. Examples of such low-molecular-weight 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 treatments using hydrothermal treatment include the methods utilizing hydrothermal reactions described in JP 2012-200691 A and JP 2012-200692 A.

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

[0032] Each step of the present invention will be described below with reference to the drawings. As shown in Figure 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, the gauge pressure is a pressure with atmospheric pressure (0.1 MPa) as the reference (zero), so that -0.1 MPa is an absolute vacuum (complete vacuum).

[0033] Each step will be specifically described below.

[0034] (Solution Penetration Step) The solution penetration step is a step of penetrating the solution into the pellets. First, the pellets and the solution are placed in a container, and the pellets are immersed in the solution. The solution can be changed depending on the application of the pellets. For example, when the pellets are used as a fertilizer, soil conditioner, compost, water quality improver, or filter material, the solution can be a bacterial culture solution in which soil-improving bacteria have been cultured, or a solution containing a chemical or natural organic fertilizer component.

[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. The method for obtaining Bacillus bacteria is not particularly limited, 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. The method for obtaining lactic acid bacteria is not particularly limited, 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 belongs to the genus Aspergillus (Koji mold), and examples thereof include yellow aspergillus, white aspergillus, and black aspergillus. Examples of yellow aspergillus include Aspergillus oryzae, Aspergillus sojae, and Aspergillus tamari. Examples of white aspergillus include Aspergillus Kawachii. Examples of black aspergillus include Aspergillus luchuensis. These aspergillus oryzae can be used alone 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, lower than atmospheric pressure. This decompression operation is an operation to naturally degas the pellets, specifically, an operation to expel air present in the countless pores within the pellets to the outside and to allow the solution to penetrate these pores. Note that, because the pores within the pellets are irregularly connected, this operation causes the solution that has penetrated the surface layer 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), and the pressure is 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, the pellets are degassed, and degassing gradually ceases over time. However, it is preferable to continue the decompression operation until degassing ceases. If the pellets immersed in the solution are placed in a low vacuum environment for a long period of time, some of the air in the solution will begin to degas, 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 in order 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 the 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 Step) In the manufacturing method of the present invention, it is preferable to include 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 described above, 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 reducing the physical load on the pellets, the mode of reducing the pressure from the former 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, it is possible to reduce or even prevent physical collapse inside the pellets 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 in the high vacuum environment described above, the pellets are degassed, and degassing gradually ceases over time. However, it is preferable to continue the decompression operation at least until degassing ceases. Furthermore, even after degassing from the pellets ceases, the decompression operation may be continued as needed. If the pellets immersed in the solution are placed 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, pellet collapse, the solution that has penetrated the pellets scattering to the outside, or damage to vacuum equipment due to boiling of the solution. Therefore, the time for maintaining the high vacuum environment is, for example, preferably 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, etc., 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 above-mentioned 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 process is a process performed following the solution penetration process or the solution penetration adjustment process described above. First, the storage container is removed from the vacuum chamber, and the penetration solution is then discharged from the storage container. The pellets are then removed and separated from the solution in which they were immersed. The surface of the pellets is wet (sticky) due to the influence of the solution that has penetrated them.

[0050] After the solution has been completely drained, the pellet is returned to the storage container and 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, causing the pellet itself 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, as an absolute vacuum may also be used, but in reality it is about −0.099 MPa.

[0052] By placing the pellets impregnated with the solution in the high vacuum environment described above, the pellets are degassed, and degassing gradually ceases over time. However, it is preferable to continue the decompression operation at least until degassing ceases. Furthermore, even after degassing from the pellets ceases, the decompression operation may be continued as needed. If the pellets impregnated with the solution are placed 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, pellet collapse, the solution that has penetrated the pellets being scattered and discharged to the outside, or damage to the vacuum equipment due to the boiling of the solution. Therefore, the time for which the pellets are held in the high vacuum environment is, for example, preferably 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] In the solution fixing step, it is preferable to alternately repeat the high vacuum environment and the atmospheric pressure environment two or more times, depending on the type of pellets, etc. This allows the treatment to be completed in a short time and reduces the risk of the pellets collapsing, the solution that has penetrated the pellets scattering to the outside, and damage to the vacuum equipment due to the solution boiling.

[0054] After the above-mentioned 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] These solution-loaded pellets may be dried, as needed, by natural drying, hot air drying, or other drying processes to dry their surface. Even after such drying processes, the openings in the pellet surface are blocked, preventing the interior from drying out and maintaining the presence of the solution. The moisture content of the pellets varies somewhat depending on the size of the pellets after loading, but drying conditions are typically 10 to 20 hours using hot air at 50 to 70°C. Natural drying may then be performed as needed. When loading a bacterial culture solution, natural drying is preferred. Rapid drying at high temperatures may cause the swollen pellets to collapse and lose their shape, but the loaded fertilizer components remain intact, allowing for processing into a powder-like product. Furthermore, the ammonia concentration of the loaded pellets that have been dried has an ammonia concentration of 10 ppm or less, ensuring sufficient 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 moist 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.

[0057] [Verification of Solution Retention Performance of Solution-Loaded Pellets] Here, the solution was loaded onto the pellets by performing a decompression operation under various conditions shown in Table 1, and then the pellets were naturally dried for two weeks. The weights of the solution-loaded pellets were measured to calculate the moisture content, and the results were compared. The pellets were produced using sewage sludge residue generated from sewage treatment plants, etc. Water was used as the solution.

[0058]

[0059] All of the solution-supported pellets of Examples 1 to 3 had a high moisture content. This allows bacteria to grow when a bacterial culture solution is supported on the pellets. In particular, Example 2 was the result of producing solution-supported 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 addition, Example 3 was the result of producing solution-supported pellets by performing a solution penetration adjustment step between the solution penetration step and the solution fixing step, and the moisture content was even higher than that of Example 2.

[0060] On the other hand, Comparative Example 1 is the result of immersing pellets in a solution and treating them only in a low vacuum environment of -0.04 MPa. However, because treatment (the solution fixing step) was not performed in a high vacuum environment, a large amount of solution remained on the surface of the pellets, making the solution prone to drying, and therefore the moisture content was lower than that of Example 1. Comparative Example 2 is the result of Example 2 in which vacuum treatment was not performed in the solution penetration step. However, penetration of the solution into the pellets was insufficient, and therefore the moisture content was lower than that of Example 1. Comparative Example 3 is the result of Example 1 in which the gauge pressure in the solution fixing step 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, preventing closure of the pores in the surface layer, and the solution that had penetrated into the pellets dried, resulting in a moisture content lower than that of Example 1.

[0061] [Production of Solution-Supported Pellets] Using the decompression operation of the method of the present invention, commercially available sludge fermented fertilizer pellets produced at a sewage treatment facility were loaded with (A) a soil-improving bacterial cell solution, (B) a solution containing an organic fertilizer component, and (C) a polyphenol solution to produce solution-supported pellets (A) to (C) according to the present invention.

[0062] [Confirmation Test for Ammonia Gas Generated from Pellets Elution Solution] The pellets used were 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 approximately 30 minutes. After that, 100 mL of gas from the top of the container was aspirated for 45 seconds using a gas detector tube, and the ammonia gas concentration was measured based on the change in the detector tube reading. The ammonia concentration was 10 ppm for the untreated pellets, while the treated pellets (A) to (C) according to the Examples were 5 ppm or less, resulting in a concentration difference of more than two-fold. Thus, it was confirmed that the manufacturing method of the present invention can remove unnecessary ammonia from the pellets compared to the untreated case.

[0063] [Confirmation test of ammonia gas generated from pellets] The ammonia gas concentration inside a container containing the treated pellets (C) according to the example and a container containing untreated pellets was measured. The ammonia concentration was approximately 20 ppm in the container containing the untreated pellets, while it was approximately 6.5 ppm in the container containing the treated pellets (C) according to the example, which was reduced to less than one-third. The ammonia concentration inside an unopened bag containing the above-mentioned commercially available pellets (untreated pellets) purchased within one month was approximately 50 ppm. Thus, it was confirmed that the manufacturing method of the present invention can remove unnecessary ammonia from the pellets compared to the untreated case.

[0064] [Evaluation of Solution-Supported Pellets as Fertilizer] A germination test was conducted using seeds. The test method involved placing 25 seeds on cotton in a glass container and observing them at room temperature. The cotton was impregnated with purified water, a liquid (liquid fertilizer) containing the treated pellets (C) of the Example, and a liquid (liquid fertilizer) containing the untreated pellets. As shown in FIG. 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. When the liquid (C) containing the treated pellets (C) of 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 as follows. The moisture content of the untreated organic pellets used was approximately 27.4%. The ammonia concentration was 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%). Five minutes after immersing the pellets in the solution, the moisture content was 33.8%.

[0067] First, a solution infiltration process was carried out. The mixture of pellets and solution was transferred to a storage container, placed in a vacuum chamber, and treated 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 carried out in a low vacuum environment. During this process, the gauge pressure in the vacuum chamber was maintained at -0.049 MPa, and degassing was carried out from 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, and processing was carried out in a high vacuum environment. Specifically, the pressure in the chamber was reduced from -0.049 MPa to -0.099 MPa as a gauge pressure, and gas-liquid exchange was carried out in a high vacuum environment. At this time, after the gauge pressure in the vacuum chamber reached -0.099 MPa, this state was maintained until degassing from the pellets ceased.

[0069] If normal degassing due to gas-liquid exchange was confirmed, the pressure inside the chamber was returned to atmospheric pressure while monitoring the gauge pressure for approximately one minute. The container containing the pellets was then removed from the vacuum chamber, and the solution inside the container was recovered, leaving the pellets in place. The moisture content of the pellets immediately after loading was 39.4%, and the amount of solution recovered was approximately 300 mL for the 600 mL of solution into which the pellets were added. In other words, it is estimated that the pellets contained 300 mL of solution containing fertilizer-effective ingredients at this point. The ammonia concentration of the recovered solution was also below 5 ppm, making it fully usable as liquid fertilizer.

[0070] Furthermore, a solution fixing process was carried out. The container containing the pellets was placed in a vacuum chamber and treated 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 fix deep into the pellets by gas-liquid exchange in a high vacuum environment. At this time, after the gauge pressure in the vacuum chamber reached -0.099 MPa, this state was maintained until degassing from the pellets ceased.

[0071] If normal 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 one minute. The container containing the pellets was then removed from the vacuum chamber, and the solution was recovered, leaving the pellets in place. The recovered solution had an ammonia concentration of 5 ppm or less, making it suitable for use as liquid fertilizer.

[0072] Next, 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, and then naturally dried for about 8 hours.

[0073] From various tests, including the one above, we learned the following: - By loading pellets with a solution in a vacuum environment, the amount of fertilizer components can be freely adjusted. - When loading pellets with a solution containing a large amount of 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. However, because the dissolved water-soluble fertilizer components also penetrate deep inside the pellets, only the water evaporates during the subsequent drying process, leaving the fertilizer components contained in the solution completely fixed in the deep layers of the pellets. - The higher the moisture content of the pellets, the more likely it is that the fertilizer components from the solution will be transferred to the pellets, increasing fertilizer effectiveness.

[0074] - It is possible to reduce the ammonia concentration of the pellets to below 10 ppm. - The recovered solution has an ammonia concentration as low as 5 ppm, making it possible to use it as liquid fertilizer. - Pellets dried after being loaded in a vacuum environment can maintain their fertilizing effect even if they lose their shape and become granular. - By adjusting the organic solution to be loaded, it is possible to increase the growth of fungi. - Pellets made from sludge showed no natural growth of bacteria even when left in their original state for more than a month, but pellets loaded with a solution in a vacuum environment showed growth of bacteria three to four days after loading.

[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 method for producing solution-loaded pellets, comprising: 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 with a gauge pressure of -0.06 MPa or more and lower than atmospheric pressure, to allow the solution to penetrate into the pellets; and a solution fixation step of separating the solution-loaded pellets 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 allow the solution to be loaded into the pellets.

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

3. 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. The method for producing solution-carrying pellets according to claim 1, characterized in that the solution penetration step and / or the solution fixing step are carried out until no more bubbles are released from the pellets.

5. A method for producing solution-carrying pellets according to claim 1, 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.

6. The method for producing solution-loaded pellets according to claim 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 higher and lower than atmospheric pressure are alternately repeated.

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

8. The method for producing solution-carrying pellets according to claim 1, wherein the solution is a bacterial culture solution in which bacteria are cultured.

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

10. 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 conditioner, compost, water quality improver, or filter material.

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