Solid starting material production method

Abstract

[Problem] The present invention provides a solid starting material production method with which it is possible to efficiently use waste liquid after a used paper diaper has been broken down and treated and recyclable resources have been recovered, and to easily generate a solid starting material from the waste liquid. [Solution] This solid starting material production method comprises: a separation step 1 in which a used paper diaper is agitated together with a treatment liquid by a separator, and then broken down into materials constituting the paper diaper and treated; a sorting step 2 in which pulp 8 and plastic in a solid component separated in the separation step 1 are sorted by a sorter 10; a first pulp recovery step 4 in which pulp 8 is recovered from a first waste liquid 3 which is a liquid component separated in the separation step 1; a dehydration step 6 in which a solid component and a liquid component of a second waste liquid 5 after the pulp 8 has been recovered in the first pulp recovery step 4 are separated; and a drying step 7 in which the solid component separated from the second waste liquid 5 in the dehydration step 6 is dried.

Description

Method for producing solid raw materials

[0001] The present invention relates to a method for producing a solid raw material for producing a raw material for solid fertilizer or solid fuel from solid components contained in a wastewater after decomposition treatment of used disposable diapers.

[0002] In October 2022, the government announced a policy to promote domestic production of chemical fertilizers by getting serious about using sludge produced during sewage treatment as fertilizer, aiming to avoid the financial pressure on farmers and rising food prices caused by the soaring cost of chemical raw materials.The government has also compiled a policy for using sewage sludge as fertilizer for agriculture, and has announced a policy to encourage the national and local governments to use sewage sludge as fertilizer, thereby reducing dependence on imported chemical fertilizer raw materials.

[0003] Furthermore, in July 2022, the Green Transformation (GX) Executive Council, chaired by the Prime Minister, was held to consider the necessary measures to transition the fossil fuel-centered economy, society, and industrial structure that has existed since the Industrial Revolution to one centered on clean energy, thereby transforming the entire economic and social system, in other words, GX (Green Transformation).

[0004] The conference outlined the roles and direction of efforts of the relevant parties in expanding the use of sewage sludge as fertilizer, and indicated that with the aim of domestically producing fertilizer, ensuring a stable supply, and building a resource-circulating society, the Ministry of Agriculture, Forestry and Fisheries, the Ministry of Land, Infrastructure, Transport and Tourism, the agricultural sector, and the sewerage sector will work together to ensure safety and quality, while also promoting understanding, including among consumers, and that all parties involved will take the initiative in making a concerted effort to significantly expand the use of sewage sludge as fertilizer.

[0005] Meanwhile, Patent Document 1 proposes decomposing used disposable diapers, which have become widely used in recent years, and recovering the materials that make up the disposable diapers as recyclable resources (pulp, plastic, etc.). In addition to the materials that make up the disposable diapers, used disposable diapers also contain feces and urine excreted from the human body, and the discharged liquid after decomposing the used disposable diapers with a treatment liquid contains the feces and urine.

[0006] Used disposable diapers are decomposed using a treatment solution, and the wastewater after recovering the recyclable resources is treated and then ultimately discharged into the sewer system. After being treated at a sewage treatment plant, the wastewater is released into the natural environment, such as rivers and the ocean.

[0007] The wastewater discharged after decomposing used disposable diapers and recovering recyclable resources contains feces and urine excreted from the human body, which contains nutrients beneficial to the soil (nitrogen, phosphate, potassium). Furthermore, the solid component (scum) extracted from the wastewater can be compressed and molded to become a raw material for solid fuel.

[0008] Therefore, Patent Document 2 discloses that used disposable diapers are finely crushed in a crusher, then mixed with water in a water mixing tank, and the suspended matter (solid matter) that is suspended in a settling tank is used as a soil conditioner, fertilizer, etc. The aqueous liquid from which the suspended matter has been removed is then subjected to sewage treatment and discharged into a sewer system.

[0009] JP 2021-121699 A JP 2004-25574 A

[0010] However, in Patent Documents 1 and 2, although the wastewater after the decomposition process of used paper diapers (the wastewater after the recycled resources are recovered) contains nutrients that are beneficial to the soil, this wastewater is treated and then wasted and released into the sewer system, and is not effectively utilized, which is an issue.

[0011] Furthermore, the effluent discharged into the sewer system and then released to a sewage treatment plant is mixed with other sewage sludge to become sewage sludge, and when this sewage sludge is used as fertilizer, it needs to be disinfected and sterilized to remove bacteria, etc., because it contains substances other than feces and urine excreted from the human body. Therefore, when using sewage sludge as fertilizer, processes such as disinfection and sterilization are required, which poses the problem that it cannot be easily produced as fertilizer.

[0012] Therefore, the present invention aims to provide a method for producing solid raw materials that can effectively utilize the wastewater after decomposing used paper diapers and recovering recyclable resources, and that can easily produce solid raw materials from the wastewater.

[0013] In order to solve the above-mentioned problems and achieve the object, a first aspect of the present invention includes a separation step (1) in which used disposable diapers are agitated with a treatment liquid in a separator (9) without being crushed, and decomposed and treated into components constituting the disposable diaper; a sorting step (2) in which pulp (8) and plastic (28), which are solid components separated in the separation step (1), are sorted in a sorter (10); a pulp recovery step (4) in which pulp (8) is recovered from a first effluent (3), which is a liquid component separated in the separation step (1); a dewatering step (6) in which solid components and liquid components are separated from a second effluent (5) after the pulp (8) is recovered in the pulp recovery step (4); a drying step (7) in which the solid components separated from the second effluent (5) in the dewatering step (6) are dried; and a process for producing a solid raw material (20) from the solid components dried in the drying step (7). and a liquid fertilizer production step (13) for producing a liquid fertilizer (14) from the liquid component separated from the second effluent (5) in the dewatering step (6) and mixing the water separated from the solid sludge component in the drying step (7) with the liquid component separated from the second effluent (5) to produce the liquid fertilizer (14).

[0014] A second aspect of the present invention is characterized in that the solid raw material production step (16) produces one of powder fertilizer (17), granular fertilizer (19), and solid fuel raw material (26).

[0015] In a third aspect of the present invention, the drying step (7) is characterized in that the solid component is dried by any one of vacuum drying, freeze drying, and vacuum freeze drying to produce the solid raw material (20).

[0016] According to the present invention, used paper diapers are decomposed and processed in a separation process, the solid components pulp and plastic separated in the separation process are sorted in a sorting process, the pulp is recovered from the effluent, which is the liquid component separated in the separation process, in a pulp recovery process, the solid components and liquid components in the effluent after the pulp has been recovered in the pulp recovery process are separated in a dehydration process, and the solid components separated from the effluent in the dehydration process are dried in a drying process, thereby producing solid raw materials.Therefore, it is possible to effectively utilize the effluent after decomposing and processing used paper diapers and recovering recyclable resources, and to easily produce solid raw materials from the effluent.

[0017] It is a block diagram showing the steps of a method for producing a solid raw material according to an embodiment of the present invention, and it is a block diagram showing devices used in each step of the method for producing a solid raw material according to an embodiment of the present invention.

[0018] A method for producing a solid raw material according to an embodiment of the present invention will be described below with reference to the drawings. A used disposable diaper according to this embodiment is recyclable and includes a liquid-permeable top sheet, a liquid-impermeable back sheet, an absorbent core disposed between the top sheet and the back sheet, and multiple elastic members that provide stretchability. The multiple elastic members, i.e., the rubber that provides stretchability to the gathered portion, include multiple short elastic members, each having a length of 10 mm to 200 mm in an unstretched state. These elastic members are solid components separated in the separation step 1 described below, and are recovered together with solid components such as pulp and plastic to form a solid raw material. The hot melt adhesive used in the used disposable diaper according to this embodiment includes a softening point hot melt adhesive having a softening point of 60°C to 90°C. Furthermore, the absorbent core used in the used disposable diaper according to this embodiment includes a biodegradable superabsorbent polymer.

[0019] As shown in Figures 1 and 2, the method for producing solid raw materials in this embodiment includes a separation process 1 in which used disposable diapers are agitated with a processing liquid in a separator 9 to decompose and process them into components that make up the disposable diapers; a sorting process 2 in which the solid components separated in the separation process 1 are sorted into pulp and plastic in a sorter 10; a first pulp recovery process 4 in which pulp 8 is recovered from waste liquid 3, which is the liquid component separated in the separation process 1; a dewatering process 6 in which solid components and liquid components are separated from the waste liquid 5 after the pulp 8 has been recovered in the first pulp recovery process 4; and a drying process 7 in which the solid components separated from the waste liquid 5 in the dewatering process 6 are dried.

[0020] The separator 9 used in the separation process 1 is composed of an outer body separating tank fixed to a housing, and an inner body separating tank with a large number of small holes formed on its outer peripheral surface and rotatably supported within the outer body separating tank. Used disposable diapers and treatment liquid are placed into the inner body separating tank, and the rotation of the inner body separating tank agitates the used disposable diapers together with the treatment liquid, causing them to be decomposed and processed into the materials that make up the disposable diapers. The used disposable diapers are decomposed and processed into pulp, plastic, and other components in the inner body separating tank, with most of the pulp being mixed in the treatment liquid.

[0021] When the treatment liquid is discharged from the inner body separation tank, what remains in the tank are plastic 28 as solid matter, plastic 24 with a small amount of pulp attached, and other materials. The treatment liquid discharged from the inner body separation tank (hereinafter referred to as "first waste liquid 3") has pulp 8 recovered by the first pulp recovery device 11.

[0022] Furthermore, the first waste liquid 3 discharged from the inner body separation tank is used as a methane fermentation raw material by a methane fermentation raw material recovery device 30 in a methane fermentation raw material recovery step 29, in addition to being used as a methane fermentation raw material by a first pulp recovery device 11. The first waste liquid 3 discharged from the inner body separation tank can be returned to the inner body separation tank and used again as part of the treatment liquid for used disposable diapers. In this case, by repeatedly using the first waste liquid 3 discharged from the inner body separation tank as part of the treatment liquid, the concentration of sludge components contained in the first waste liquid 3 increases, making it possible to use it as a good methane fermentation raw material.

[0023] The effluent remaining after the pulp 8 has been collected from the first effluent 3 (hereinafter referred to as "second effluent 5") contains sludge components. This second effluent 5 is dehydrated by a dehydrator 12 in a dehydration step 6, and separated into a solid sludge component (scum) and a liquid portion. The liquid component separated from the second effluent 5 by the dehydrator 12 becomes liquid fertilizer 14 in a liquid fertilizer production step 13, and the solid sludge component is dried by a dryer 15 in a drying step 7. In this case, even after dehydration by the dehydrator 12, the solid sludge component still contains some moisture, and the moisture content is reduced as much as possible by the dryer 15.

[0024] The drying device 15 may be vacuum drying, vacuum freeze drying, freeze drying, or heat drying using a heater. The solid sludge component (scum) dried by the drying device 15 is used to produce solid raw material 20 in the solid raw material production process 16. This solid raw material 20 is then crushed into powder by a solid fertilizer production device 18 to produce powdered fertilizer 17, or crushed into granules to produce granular fertilizer 19. These powdered fertilizers 17 and granular fertilizers 19 are sludge recovered from used disposable diapers. These sludge are organic matter excreted from the human body and contain nutrients such as nitrogen, phosphate, and potassium that are beneficial to soil. Furthermore, harmful bacteria are killed by sterilization and disinfection during the decomposition process of used disposable diapers.

[0025] The solid raw material 20 produced by the drying device 15 is mixed with pulp recovered by the first pulp recovery device 11 and the like in a solid fuel production device 25, and compressed and molded to produce a solid fuel raw material 26. The water separated from the solid sludge components by the drying device 15 is mixed with the water dehydrated by the dehydration device 12 to become a raw material for liquid fertilizer 14.

[0026] The solid matter remaining in the inner body separation tank of separator 9, namely plastic 28, plastic pulp 24 with a small amount of pulp attached, and the rest are sent to sorter 10 in sorting process 2. Sorter 10 is made up of an outer body sorting tank fixed to a housing, and an inner body sorting tank with many small holes formed on its outer periphery and rotatably supported within the outer body sorting tank. Pulp, plastic, plastic with a small amount of pulp attached, and the rest, which are the solid components remaining in the inner body separation tank, are fed into the inner body sorting tank.

[0027] Dry air is supplied into the outer body sorting tank, and is blown onto the pulp 8, plastic 28, plastic pulp 24 with a small amount of pulp attached, and other materials in the inner body sorting tank rotating inside the outer body sorting tank, sorting them into pulp 8, plastic 28, plastic pulp 24, and other materials. The dry air supplied to the outer body sorting tank and used to dry the pulp 8, plastic 28, plastic pulp 24, and other materials still contains pulp 8, and this dry air is collected by a second pulp recovery device 22 in a second pulp recovery process 21, where the pulp 8 is captured using a filter or the like. The plastic pulp 24 in the inner body sorter is collected in a plastic pulp recovery process 23. The plastic 28 remaining in the outer body sorting tank is collected in a plastic recovery process 27.

[0028] Next, the analysis results of the powder fertilizer 17 and the granular fertilizer 19 produced from the solid raw material by the method for producing a solid raw material according to this embodiment will be described. (Table 1) As shown in Table 1, the powder fertilizer 17 and granular fertilizer 19 produced from the solid raw material of this embodiment contain lime, zinc, and copper in addition to nitrogen, phosphoric acid, and potassium. The lime is contained in the treatment liquid used to treat used disposable diapers.

[0029] Furthermore, the levels of harmful substances such as arsenic, cadmium, nickel, chromium, mercury, lead, and mercury are below the levels set by the Fertilizer Control Act, and there are no problems with spreading them on fields as fertilizer and releasing them into the natural environment.

[0030] Powdered and granular fertilizers made from solid raw materials contain lime, which makes them highly alkaline, but this can be neutralized by mixing in a neutralizing agent.Furthermore, powdered and granular fertilizers made from solid raw materials contain lime, so they can also be used as soil conditioners to neutralize acidic soil.

[0031] As described above, according to the method for producing a solid raw material of this embodiment, the second waste liquid 5 obtained after decomposing and processing used disposable diapers and recovering recyclable resources is not discharged into sewage or the like, so that the second waste liquid 5 can be effectively utilized and the solid raw material 20 can be easily produced from waste liquid that would have been discarded in the past. On the other hand, lime is strongly alkaline, so it can be neutralized by mixing it with a neutralizing agent before use.

[0032] The solid raw material 20 produced by the solid raw material manufacturing method according to this embodiment is sterilized and disinfected when used paper diapers are decomposed, and therefore does not contain any bacteria harmful to the human body, making it possible to produce raw materials in a highly hygienic condition.

[0033] Furthermore, the solid raw material 20 according to this embodiment is sludge adhering to used disposable diapers and excreted from the human body, and therefore does not contain any other sludge (livestock manure or other substances). As a result, the powdered fertilizer, granular fertilizer, and solid fuel produced from this solid raw material 20 are hygienic and do not pose any harm to the human body or the environment. Furthermore, burning the solid fuel does not adversely affect the environment.

[0034] Furthermore, according to the method for manufacturing solid raw materials in this embodiment, in addition to decomposing used paper diapers and recovering the recyclable resources pulp 8, plastic 28, and plastic 24, the second waste liquid 5 obtained by processing the used paper diapers is also separated into solid and liquid components, and the liquid components are used as liquid fertilizer 14, and the solid components are used as solid raw materials 20 to produce powder fertilizer 17, granular fertilizer 19, and solid fuel raw material 26, making it possible to almost completely recycle used paper diapers.

[0035] As a result, no used disposable diapers are released into the environment after being processed, so there is no adverse impact on the natural environment. In particular, in the method for producing solid raw materials of this embodiment, used disposable diapers are not crushed, so small pieces of plastic (microplastics) are not generated and microplastics are not released into the ocean.

[0036] Furthermore, according to this embodiment, the first effluent 3 can be returned to the inner body separation tank and used again as part of the treatment liquid for treating used disposable diapers, thereby making it a good methane fermentation raw material. In this case, by repeatedly using the first effluent 3 as the treatment liquid for treating used disposable diapers, the amount of pulp contained in the first effluent 3 also increases, so that a larger amount of pulp can be recovered by the first pulp recovery device 11 in the first pulp recovery device process 4.

[0037] Furthermore, according to this embodiment, the used paper diapers to be processed by the separator 9 are made of a short elastic member (rubber) used in the gathered portion having a length of 10 mm or more and 200 mm or less, a hot melt adhesive having a softening point of 60°C or more and 90°C or less, and the absorbent material is a biodegradable highly absorbent polymer, which makes the decomposition process easier and enables material recycling.

[0038] As described above, while an embodiment of the present invention has been disclosed, it will be apparent that modifications may be made by those skilled in the art without departing from the scope of the present invention. All such modifications and equivalents are intended to be included in the claims.

[0039] The method for producing solid raw materials according to the present invention is not limited to a method for producing solid raw materials from used disposable diapers, but can also be used to decompose and process urine absorption pads and other sanitary products and produce solid raw materials from these urine absorption pads and other sanitary products.

[0040] 1 Separation process 2 Screening process 3 First effluent 4 First pulp recovery process 5 Second effluent 6 Dewatering process 7 Drying process 8 Pulp 9 Separator

Claims

1. A separation process (1) in which used disposable diapers are agitated with a processing liquid in a separator (9) without being crushed, and decomposed and processed into components constituting disposable diapers; a sorting process (2) in which the solid components pulp (8) and plastic (28) separated in the separation process (1) are sorted in a sorting machine (10); a pulp recovery process (4) in which the pulp (8) is recovered from the first effluent (3), which is the liquid component separated in the separation process (1); a dewatering process (6) in which the solid components and liquid components in the second effluent (5) after the pulp (8) is recovered in the pulp recovery process (4) are separated; a drying process (7) in which the solid components separated from the second effluent (5) in the dewatering process (6) are dried; and a solid raw material production process (16) in which a solid raw material (20) is produced from the solid components dried in the drying process (7). a liquid fertilizer production step (13) for producing liquid fertilizer (14) from the liquid component separated from the second effluent (5) in the dehydration step (6), and for producing liquid fertilizer (14) by mixing the water separated from the solid sludge component in the drying step (7) with the liquid component separated from the second effluent (5).

2. The method for producing a solid raw material according to claim 1, characterized in that the solid raw material production process (16) produces one of powder fertilizer (17), granular fertilizer (19), and solid fuel raw material (26).

3. A method for producing a raw material as described in claim 1 or 2, characterized in that in the drying step (7), the solid component is dried by one of vacuum drying, freeze drying, and vacuum freeze drying to produce the solid raw material (20).

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