Manufacturing method for bacterial cell phosphate fertilizer using wood chip and sewage sludge

Abstract

To provide a manufacturing method for bacterial cell phosphate fertilizer that can ensure a content ratio of phosphate being a fertilizer component.SOLUTION: A manufacturing method includes: a first fermentation step 1 of kneading wood chips 12 set to have a predetermined crushed diameter and a predetermined volume into sewage sludge 11 set to have a 65-85% water content and a predetermined weight, putting in the obtained kneaded material into a fermentation tank, and performing aeration and turning back for 12 to 16 days while keeping at 60 to 80°C to obtain a first fermented fertilizer 13 whose water content is adjusted to 50-65%; a second fermentation step 2 of mounding the first fermented fertilizer 13 in a fermentation tank in a compost depot and performing standing and turning back for 12-16 days while keeping at 50-70°C to obtain a second fermented fertilizer 21 whose water content is adjusted to 30-35%; a screening step 3 of screening the second fermented fertilizer 21 to obtain a third fermented fertilizer 31 that has been adjusted to a predetermined size; and an aging step 4 of storing the third fermented fertilizer 31 in an air permeable flexible container bag and performing standing for one to two months to obtain a phosphate fertilizer 41 whose water content is adjusted to 10-15%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing bacterial phosphate fertilizer using wood chips and sewage sludge. [Background technology]

[0002] The applicant has developed a sludge-derived vegetation base material for use in slope greening work (Patent Document 1), which is characterized by the following: sewage sludge is mixed with wood chips made from crushed root-removed felled wood or unused wood, and crushed bark; the mixture is then put into a fermentation tank and aerobic fermentation is carried out by aeration and turning over; the moisture content is adjusted to 40-45% using the heat of the fermentation reaction to obtain fermented fertilizer; this fermented fertilizer is then sieved to a size of 20 mm or less, placed in a breathable flexible container bag and left to stand; and the fermented fertilizer is obtained after a maturation period of 4-6 months in which the heat of the fermentation reaction has subsided (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6426311 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to continue stable agricultural production, it is important to expand the use of sewage sludge resources. However, conventional sludge-derived fertilizers generally have a large variation in fertilizer components, making it impossible to guarantee their content, and mixing with other fertilizers is not permitted. For this reason, in order to further expand the use of sewage sludge resources, the Ministry of Agriculture, Forestry and Fisheries established the official standard "microbial phosphate fertilizer" in 2023, which is subject to strict quality control and can guarantee the content of the fertilizer component, phosphoric acid.

[0005] The official specifications for bacterial phosphate fertilizer are as follows: 1. It must be produced in accordance with a quality control plan; 2. The total amount of phosphate must be guaranteed to be 1.0% or more; 3. The heavy metal content must not exceed the standard value, and no harm must be found in plant damage tests; and 4. The raw material must be sludge resources managed in accordance with a quality control plan.

[0006] However, the above-mentioned conventional greening base material for slope greening work does not meet the official standards for bacterial phosphate fertilizer, particularly the guaranteed phosphate content (1% or more) in 2. above, so there is room for further improvement.

[0007] The problem to be solved by the present invention is to provide a method for producing a bacterial phosphate fertilizer that can guarantee the content of phosphoric acid, which is a fertilizer component. [Means for solving the problem]

[0008] The present invention provides a primary fermentation process in which sewage sludge having a moisture content of 65 to 85% and a predetermined weight is mixed with wood chips having a predetermined crushing size and a predetermined volume, and the resulting mixture is placed in a fermentation tank, where it is aerated and turned over for 12 to 16 days while maintaining the temperature at 60 to 80°C, thereby obtaining a primary fermented fertilizer with a moisture content adjusted to 50 to 65%; A secondary fermentation process in which the primary fermented fertilizer is piled up in a fermentation tank in a compost shed, and left to stand and turned over for 12 to 16 days while maintaining the temperature at 50 to 70°C, thereby obtaining a secondary fermented fertilizer with a moisture content adjusted to 30 to 35%; a sieving step of sieving the secondary fermented fertilizer to obtain a tertiary fermented fertilizer adjusted to a predetermined size; a maturation step of storing the tertiary fermented fertilizer in a breathable flexible container bag and leaving it to stand for 1 to 2 months to obtain a phosphate fertilizer with a moisture content adjusted to 10 to 15%; The above problems are solved by a method for producing a bacterial phosphate fertilizer having the above structure.

[0009] In one embodiment of the present invention, the primary fermentation step is carried out by subjecting sewage sludge with a moisture content of 75% and a weight of 9.5 tons to crushing using a crusher with a diameter of 20 mm and a capacity of 10 m 3Mix the wood chips set at .

[0010] In one embodiment of the present invention, the primary fermentation step involves charging the mixture of sewage sludge and wood chips into a fermenter equipped with a rotary fermenter, and repeating the aeration and the turning over.

[0011] In one embodiment of the present invention, the sieving step uses a sieving device having a screen with a mesh size of 8 mm to adjust the secondary fermented fertilizer into the tertiary fermented fertilizer having a size of 8 mm or less. [Effects of the Invention]

[0012] According to the present invention, a bacterial phosphate fertilizer can be obtained that can guarantee the content of phosphoric acid, which is a fertilizer component. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a production process diagram showing one embodiment of a method for producing a bacterial phosphate fertilizer according to the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a production process diagram showing one embodiment of a method for producing a bacterial phosphate fertilizer according to the present invention. As shown in the figure, the method for producing a bacterial phosphate fertilizer of this embodiment comprises a primary fermentation step 1, a secondary fermentation step 2, a sieving step 3, and an aging step 4. Each of steps 1 to 4 will be described below.

[0015] In the primary fermentation step 1 of this embodiment, sewage sludge 11, which has been adjusted to a predetermined moisture content and weight, is mixed with wood chips 12, which have been adjusted to a predetermined crushed size and volume, and the resulting mixture is placed in a fermentation tank where aerobic fermentation is carried out for 12 to 16 days with aeration and turning over, thereby producing a primary fermented fertilizer 13, which has been adjusted to a moisture content of 50 to 65%.

[0016] In this case, the mixing ratio of the sewage sludge 11 and the wood chips 12 is not particularly limited, but it is preferable to mix them at a ratio of 50% sewage sludge to 50% wood chips. For example, the sewage sludge 11 is set to a moisture content of 75% and a weight of 9.5 tons, and a crusher with a crushing diameter of 20 mm and a capacity of 10 m 3 The weight of the sewage sludge 11 was set to 9.5 tons because this is generally equivalent to the load of one sludge collection and transportation vehicle. The wood chips 12 are obtained by crushing felled timber, root removal, bamboo, and other wood waste generated during forest and bamboo forest maintenance in a primary crusher, passing them through a sieving device screen with a mesh size of 38 mm to obtain primary wood chips with a crushed diameter of 38 mm or less, which are then further crushed in a secondary crusher and passed through a sieving device screen with a mesh size of 20 mm to obtain wood chips 13 with a crushed diameter of 20 mm or less.

[0017] Wastewater from households and other sources flows through main sewerage pipes from the basin-related public sewerage system and into designated water purification centers. This inflowing wastewater is passed through a sand trap to remove large debris and sand, then through a primary sedimentation tank where solids that settle easily are removed (primary sludge), then through a reaction tank where microorganisms break down the dirt and turn it into a mass of microorganisms that settle easily (activated sludge), then through a final sedimentation tank where it is separated into sludge and supernatant water, then through a disinfection facility where it is disinfected with chlorine, and then through a discharge facility into the river. The sludge generated in the primary and final sedimentation tanks is sent to a sludge treatment facility where it is reduced in volume using a dehydrator or other device, and activated sediment (sewage) is produced for wastewater treatment. The sewage sludge 11 of this embodiment is obtained by concentrating and dewatering sludge generated from the treatment facilities of the above-mentioned specified water purification center, and polyacrylic acid ester polymers and polymethacrylic acid ester polymers are used as polymer flocculants in an amount of 0.006% and 0.24% or less, respectively, per sludge weight.

[0018] The moisture content of sewage sludge 11 varies depending on the sewage treatment plant, but the moisture content of sewage sludge discharged from general sewage is 65 to 85%. When sewage sludge discharged from a specific sewage treatment plant is used, the phosphate and moisture contents vary little and are stable. Therefore, although not particularly limited, it is more preferable to identify a specific sewage treatment plant and use sewage sludge discharged from there as sewage sludge 11 in this embodiment.

[0019] In the primary fermentation step 1, return material 32 may be added to the mixture of sewage sludge 11 and wood chips 12. The return material 32 refers to the oversized secondary fermented fertilizer obtained in the secondary fermentation step 2 after sieving in the sieving step 3. For example, it is the oversized material obtained when sieving through an 8 mm mesh screen. This type of return material 32 has the function of promoting aerobic fermentation because it contains a large amount of soil bacteria that are useful for decomposing organic matter.

[0020] Next, in the primary fermentation step 1 of this embodiment, a mixture of sewage sludge 11 and wood chips 12, or a mixture of this and returning material 32, is placed in a fermenter equipped with a rotary fermenter, and aeration and turning are repeated in the rotary fermenter for about two weeks (12 to 16 days) while maintaining the temperature at 60 to 80°C. Here, the mixture is turned once every 12 hours. By turning the mixture once every 12 hours, oxygen can be supplied while maintaining an appropriate amount of fermentation heat. If the mixture is turned too frequently, the heat accumulated inside the mixture will dissipate, suppressing fermentation, while if the mixture is not turned over, oxygen will not be supplied to the mixture, preventing the growth of aerobic microorganisms.

[0021] This aeration and turning causes aerobic fermentation, and at the same time, excess water evaporates, resulting in primary fermented fertilizer 13 with a moisture content reduced to 50 to 65%, which is then removed from the fermentation tank.

[0022] The moisture content is measured in accordance with Section 3.1 Moisture or Moisture Content of the "Testing Methods for Fertilizers, etc. (2020)" published by the Agriculture, Forestry and Fisheries Agricultural Materials Inspection Technology Center. For actual process control, moisture content can be measured using a measuring instrument such as a halogen moisture meter, or the degree of moisture can be observed by touch.

[0023] In the secondary fermentation step 2 of this embodiment, the primary fermented fertilizer 13 is piled (piled) in a fermentation tank in a compost house, and while the temperature of the piled primary fermented fertilizer 13 is maintained at 50 to 70°C, the fermentation is repeated for about two weeks (12 to 16 days). The primary fermented fertilizer 13 piled in the fermentation tank in the compost house is turned over using a shovel loader or the like, but the frequency of turning is not particularly limited. As long as the temperature of the piled primary fermented fertilizer 13 is maintained at 50 to 70°C, it is preferable to turn it over as frequently as possible, for example, about once every three days. This standing and turning promotes fermentation, and at the same time, excess water evaporates, resulting in secondary fermented fertilizer 21 with a moisture content reduced to 30 to 35%.

[0024] In the sieving step 3 of this embodiment, the secondary fermented fertilizer 21 obtained in the secondary fermentation step 2 is sieved using a sieving device to obtain a tertiary fermented fertilizer 31 adjusted to a predetermined size. The sieving size is not particularly limited, but it is preferable to sieve the tertiary fermented fertilizer 31 using a trommel screen with a mesh size of 8 mm, for example, to adjust the size of the tertiary fermented fertilizer 31 to 8 mm or less. As described above, the returned material 32 that becomes oversized in this sieving step 3 is supplied to the primary fermentation step 1 and reused.

[0025] In the aging step 4 of this embodiment, the tertiary fermented fertilizer 31 is stored in a breathable flexible container bag and left to stand for 1 to 2 months to obtain a bacterial phosphate fertilizer 41 with a moisture content adjusted to 10 to 15%. The breathable flexible container bag is a flexible packaging bag made of chemical fibers such as polypropylene or polyethylene. The size of the flexible container bag is not particularly limited, but an example is a round bag with a diameter of 1 m and a height of 1 m. In this aging step 4, the tertiary fertilizer 31 is left to stand, thereby allowing additional heat to be added, and the moisture content can be reduced to 10 to 15% by storing it in the breathable flexible container bag. The obtained phosphate fertilizer is a bacterial phosphate fertilizer 41 that satisfies the specifications of a phosphorus content of 2.5% or more, a nitrogen content of 2.5% or more, and a moisture content of approximately 15%.

[0026] As described above, the method for producing a bacterial phosphate fertilizer of this embodiment includes a secondary fermentation process 2 in addition to a primary fermentation process 1, and fermentation and moisture content adjustment are performed in these two processes. This allows the moisture content of the tertiary fermented fertilizer 31 transported to the aging process 4 to be accurately adjusted to 30 to 35%. The moisture content varies greatly depending on the degree of additional heating and drying in the flexible container bag in the aging process 4. Large fluctuations in moisture content also result in large fluctuations in the volume, which in turn results in large fluctuations in the component ratios of the fertilizer after full ripening. In this regard, the method for producing a bacterial phosphate fertilizer of this embodiment accurately adjusts the moisture content of the tertiary fermented fertilizer 31 to 30 to 35%, which minimizes fluctuations in moisture content and volume change during the aging process, thereby minimizing fluctuations in the component ratios of the resulting fertilizer.

[0027] In the method for producing a greening base material for slope greening work described in Patent Document 1 listed in the Background Art section, fermented fertilizer with a moisture content adjusted to 40% to 45% is matured in a flexible container bag, which causes large fluctuations in moisture content and volume change during the maturation process. Consequently, the component ratios contained in the resulting greening base material also vary greatly. In contrast, the method for producing a bacterial phosphate fertilizer of this embodiment can suppress these fluctuations.

[0028] Furthermore, the method for producing bacterial phosphate fertilizer of this embodiment makes it easier to control the moisture content, volume, and components of the fertilizer, including the intermediate product, compared to the conventional method for producing a greening base material for slope greening work.

[0029] Furthermore, according to the method for producing bacterial phosphate fertilizer of this embodiment, secondary fermentation step 2 is provided to ferment and adjust the moisture content to 30-35%, thereby shortening the period for full maturation in ripening step 4. For example, while the conventional method for producing a greening base material for slope greening work requires 4-6 months for full maturation, this embodiment shortens the period to 1-2 months. Moreover, even including the additional 12-16 days of the secondary fermentation step, the overall production period is significantly shortened. [Explanation of symbols]

[0030] 1...Primary fermentation process 11...Sewage sludge 12...Wood chips 13...Primary fermented fertilizer 2...Second fermentation process 21...Secondary fermented fertilizer 3...Sieving process 31...Tertiary fermented fertilizer 32...Return material 4…Aging process 41...Fungal phosphate fertilizer

Claims

1. a primary fermentation step in which sewage sludge having a moisture content of 65 to 85% and a predetermined weight is mixed with wood chips having a predetermined crushed diameter and a predetermined volume, and the resulting mixture is placed in a fermentation tank, where it is aerated and turned over for 12 to 16 days while maintaining the temperature at 60 to 80°C, thereby obtaining a primary fermented fertilizer with a moisture content adjusted to 50 to 65%; A secondary fermentation step in which the primary fermented fertilizer is piled up in a fermentation tank in a compost shed, and left to stand and turned over for 12 to 16 days while maintaining the temperature at 50 to 70°C, thereby obtaining a secondary fermented fertilizer with a moisture content adjusted to 30 to 35%; a sieving step of sieving the secondary fermented fertilizer to obtain a tertiary fermented fertilizer adjusted to a predetermined size; an aging step of storing the tertiary fermented fertilizer in a breathable flexible container bag and leaving it to stand for 1 to 2 months to obtain a phosphate fertilizer with a moisture content adjusted to 10 to 15%; A method for producing a bacterial phosphate fertilizer comprising the steps of:

2. The primary fermentation process was carried out by crushing sewage sludge with a water content of 75% and a weight of 9.5 tons into a crusher with a diameter of 20 mm and a capacity of 10 m ３ 2. The method for producing a bacterial phosphate fertilizer according to claim 1, wherein wood chips set at a temperature of 100° C. or more are kneaded together.

3. 3. The method for producing a bacterial phosphate fertilizer according to claim 2, wherein the primary fermentation step involves feeding the mixture of the sewage sludge and the wood chips into a fermentation tank equipped with a rotary fermentation device, and repeating the aeration and the turning over.

4. 4. The method for producing a bacterial cell phosphate fertilizer according to claim 3, wherein the sieving step uses a sieving device having a screen with a mesh size of 8 mm to adjust the secondary fermented fertilizer into the tertiary fermented fertilizer having a size of 8 mm or less.

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