Method of producing fertilizer

Abstract

To provide a method of producing fertilizer, i.e., a simple and low-cost method of quickly producing fertilizer that can easily be scattered.SOLUTION: The method of producing fertilizer according to the present invention comprises a water content adjusting step of adjusting a water content in a range of more than 8% and less than 65%, by mixing organic sludge generated in the process of sewage treatment or wastewater treatment and biomass combustion ash, i.e., combustion ash of biomass, at a mixing ratio of higher than 1 and lower than 9 in terms of a weight ratio of the organic sludge provided that total weight of the organic sludge and the biomass combustion ash is 10. It is more preferable to adjust the water content between 22 and 43% by blending the organic sludge at a blend ratio of 3 to 6 on the weight basis.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing fertilizer from organic sludge generated in the process of sewage or wastewater treatment. [Background technology]

[0002] It has been known that organic sludge generated during sewage or wastewater treatment processes is rich in fertilizer components such as nitrogen, phosphorus, and potassium. For this reason, in order to reuse organic sludge, treatments such as artificial fermentation and composting have been carried out. For example, Japanese Patent Application Laid-Open No. 2013-72051 discloses a method of composting organic sludge by fermenting it with hyperthermophilic bacteria (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-72051 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional composting treatments of organic sludge, including the invention described in Patent Document 1, require a long period of time for fermentation. This necessitates the need for facilities to store the organic sludge during fermentation, and management is time-consuming, resulting in increased facility and management costs. On the other hand, organic sludge that has not been composted has an extremely high moisture content and is difficult to handle, meaning that it cannot be spread as fertilizer as is.

[0005] The present invention has been made to solve such problems, and an object of the present invention is to provide a method for producing a fertilizer that is simple, inexpensive, and capable of quickly producing a fertilizer that is easy to spread. [Means for solving the problem]

[0006] As a result of intensive research into achieving the above-mentioned object, the inventors have found that the above-mentioned object can be achieved by mixing organic sludge generated in the process of sewage treatment or wastewater treatment with biomass combustion ash, which is ash from the combustion of biomass, in a predetermined blending ratio and adjusting the mixture to a predetermined moisture content, which has led to the completion of the following inventions.

[0007] To solve the problem of quickly producing a fertilizer that is easy to spread while being simple and low-cost, the method for producing a fertilizer of the present invention includes a moisture content adjustment step of adjusting the moisture content to more than 8% and less than 65% by mixing organic sludge generated in the process of sewage treatment or wastewater treatment with biomass combustion ash, which is ash from biomass combustion, in a blending ratio of more than 1 and less than 9 by weight, where the total weight of the organic sludge and biomass combustion ash is 10.

[0008] In addition, as one aspect of the present invention, in order to solve the problem of further improving ease of handling as a fertilizer, in the moisture content adjustment step, the moisture content may be adjusted to 22 to 43% by mixing the organic sludge in a weight ratio of 3 to 6, where the total weight of the organic sludge and the biomass combustion ash is 10.

[0009] Furthermore, as one aspect of the present invention, in order to solve the problem of improving the moisture content reducing effect of biomass combustion ash, the biomass combustion ash may be fly ash having an average particle size of 44 μm or less as measured by a laser diffraction / scattering method.

[0010] In addition, as one aspect of the present invention, in order to solve the problem of promoting the effect of reducing the moisture content, the biomass combustion ash may be substituted with calcium oxide within a range of less than 80 wt %.

[0011] Furthermore, in one embodiment of the present invention, in order to solve the problem of suppressing the generation of ammonia and leaving more nitrogen components in the fertilizer, a pH adjustment step may be included in which 12 to 29 wt % of sulfuric acid is added to the biomass combustion ash to adjust the hydrogen ion exponent (pH).

[0012] Furthermore, in one aspect of the present invention, in order to solve the problem of suppressing the generation of ammonia and allowing a larger amount of nitrogen components to remain in the fertilizer, an ammonia generation suppression step may be provided in which magnesium chloride and phosphoric acid are added to the organic sludge to suppress the generation of ammonia. [Effects of the Invention]

[0013] According to the present invention, a fertilizer that is easy to spread can be produced quickly, simply, and at low cost. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an embodiment of a method for producing a fertilizer according to the present invention. FIG. [Figure 2] 1 is a flowchart showing a method for producing a fertilizer according to the present embodiment. [Figure 3] 1 is a table showing the experimental results of Example 1. [Figure 4] 10 is a table showing the experimental results of Example 2. [Figure 5] 10 is a table showing the experimental results of Example 3. [Figure 6] 10 is a table showing the experimental results of Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of a method for producing a fertilizer according to the present invention will be described below with reference to the drawings. The method for producing a fertilizer according to this embodiment is for producing a fertilizer from organic sludge generated in the process of sewage treatment or wastewater treatment, and as shown in Figures 1 and 2, includes a moisture content adjustment step (step S3), and a pre-treatment step of suppressing ammonia generation (step S1) and a pH adjustment step (step S2). Each step will be described in detail below.

[0016] The moisture content adjusting step is a step of adjusting the moisture content of the fertilizer. In this embodiment, as shown in Fig. 1, the moisture content adjusting step adjusts the fertilizer to a predetermined moisture content by mixing organic sludge generated in the process of sewage treatment or wastewater treatment and biomass combustion ash, which is combustion ash of biomass, at a predetermined blending ratio.

[0017] Organic sludge is organic muddy material removed by settling, filtration, or the like during sewage or wastewater treatment processes. Biomass combustion ash is ash obtained by burning biomass, which is an organic resource derived from living organisms. In this embodiment, fly ash obtained by burning plant-derived raw materials such as wood chips and palm kernel shells (PKS) at a biomass power plant is used as the biomass combustion ash.

[0018] In this embodiment, based on the results of Example 1 described below, when the total weight of the organic sludge and biomass combustion ash is 10, the weight ratio of the organic sludge is mixed at a blending ratio of more than 1 and less than 9. As a result, the biomass combustion ash absorbs the moisture in the organic sludge, making it possible to simply and inexpensively produce a fertilizer with an adjusted moisture content of more than 8% and less than 65%.

[0019] If the moisture content is more than 8% but less than 65%, the organic sludge and biomass combustion ash can be easily mixed uniformly, improving the quality of the fertilizer. Furthermore, excessive drying can cause the fertilizer to turn into powder, but if the moisture content is over 8%, this does not happen, making it less likely to become airborne and maintaining a state suitable for mass spreading. Furthermore, if the moisture content is less than 65%, the fertilizer is adequately dehydrated, making it easier to handle, transport, and spread.

[0020] Furthermore, in this embodiment, in the moisture content adjusting step, it is more preferable to mix the organic sludge with the biomass combustion ash at a weight ratio of 3 to 6, assuming that the total weight of the organic sludge and biomass combustion ash is 10. This adjusts the moisture content to 22 to 43%, further improving ease of handling as fertilizer.

[0021] Furthermore, in this embodiment, based on the results of Example 2 described below, it is more preferable that the biomass combustion ash be fly ash with an average particle size of 44 μm or less as measured by laser diffraction / scattering. This increases the specific surface area of ​​the biomass combustion ash, allowing it to absorb more water from the organic sludge, thereby improving the effect of reducing the moisture content.

[0022] Furthermore, in this embodiment, based on the results of Example 3 described later, it is more preferable that the biomass combustion ash is replaced by calcium oxide (CaO) such as quicklime within a range of less than 80 wt%. This causes the calcium oxide to react vigorously with the moisture in the sludge, absorb it, generate heat, and promote drying, thereby improving the effect of reducing the moisture content.

[0023] The biomass combustion ash contains at least silicon dioxide (SiO2), calcium oxide (CaO), and aluminum oxide (Al2O3). The organic sludge and the biomass combustion ash are mixed using a stirring device (not shown).

[0024] According to the moisture content adjustment process described above, all that is required is to mix organic sludge and biomass combustion ash in a predetermined ratio and adjust the moisture content to a predetermined level, making it possible to quickly produce a fertilizer that is easy to spread, while being simple and low-cost.

[0025] However, because biomass combustion ash is alkaline, when it is mixed with neutral organic sludge, the hydrogen ion exponent (pH) increases, making it more likely to generate ammonia (NH3). This reduces the nitrogen component, one of the three essential elements of fertilizer, and also generates a foul odor. For this reason, this embodiment has a pH adjustment process and an ammonia generation suppression process as optional processes for suppressing ammonia generation, as shown in Figure 1.

[0026] The pH adjustment step is a step of adjusting the hydrogen ion exponent of the biomass combustion ash. Specifically, as shown in FIG. 1, in the pH adjustment step, sulfuric acid, which exhibits strong acidity, is added to the biomass combustion ash before it is mixed with organic sludge, thereby adjusting the hydrogen ion exponent. In this embodiment, based on the results of Example 4 described below, 12 to 29 wt % of sulfuric acid is added to the biomass combustion ash. This brings the hydrogen ion exponent of the biomass combustion ash to a neutral range of 8.5 or less, thereby suppressing the generation of ammonia even when it is mixed with organic sludge, and allowing more nitrogen components to remain in the fertilizer.

[0027] The ammonia generation suppression step is a step of suppressing the generation of ammonia from organic sludge. In this embodiment, in the ammonia generation suppression step, magnesium chloride and phosphoric acid are added to the organic sludge before it is mixed with the biomass combustion ash. As a result, ammonium ions in the organic sludge react with the magnesium ions and phosphate ions and are immobilized as magnesium ammonium phosphate (MAP). In this way, if the organic sludge has ammonium ions immobilized, the generation of ammonia is suppressed even when it is mixed with biomass combustion ash whose pH has not been adjusted, and more nitrogen components remain in the fertilizer.

[0028] Furthermore, if the pH adjustment process is used to adjust the hydrogen ion exponent of the biomass combustion ash to a neutral pH (pH 7) or below, the generation of ammonia can be completely suppressed. However, since the raw material cost of sulfuric acid is high, the cost of retaining more nitrogen components in the fertilizer can be reduced by reducing the amount of sulfuric acid added and using this process in combination with the ammonia generation suppression process.

[0029] The method for producing a fertilizer according to the present embodiment as described above provides the following effects. 1. It is possible to quickly produce fertilizer that is easy to spread, at low cost, and simple. 2. By adjusting the blending ratio and moisture content to the optimum, it is possible to further improve the ease of handling as a fertilizer. 3. By using fly ash as biomass combustion ash, the effect of reducing the moisture content of biomass combustion ash can be improved. 4. By replacing part of the biomass combustion ash with calcium oxide, the moisture content can be reduced. 5. By adjusting the pH of biomass combustion ash to below the neutral range, the generation of ammonia can be suppressed and more nitrogen can be retained in the fertilizer. 6. By immobilizing ammonium ions in organic sludge, the generation of ammonia can be suppressed and more nitrogen components can remain in the fertilizer.

[0030] Next, specific examples of the method for producing a fertilizer according to the present invention will be described. Note that the technical scope of the present invention is not limited to the examples shown below. [Example]

[0031] In this Example 1, an experiment was conducted to identify a suitable blending ratio of organic sludge and biomass combustion ash. Specifically, dewatered sludge from an organic sludge treatment facility was used as the organic sludge. Furthermore, fly ash from wood chips and palm kernel shells (PKS) combusted in a stoker boiler at a biomass power plant was used as the biomass combustion ash.

[0032] The organic sludge and biomass combustion ash described above were mixed at weight ratios ranging from 1:9 to 9:1, and after mixing for 2.5 minutes, the moisture content was measured. The results are shown in Figure 3. As shown in Figure 3, when the weight ratio of organic sludge to biomass combustion ash was 1:9, the moisture content was too low at 8%, making it difficult to achieve uniform mixing. Furthermore, when the weight ratio of organic sludge to biomass combustion ash was 9:1, the moisture content was too high at 65%, making it difficult to achieve uniform mixing.

[0033] On the other hand, when organic sludge and biomass combustion ash were mixed at a weight ratio of 2:8 to 8:2, the moisture content was adjusted to an appropriate level of 18 to 62%, confirming that the fertilizer was easy to handle, as shown in Figure 3. Furthermore, when organic sludge and biomass combustion ash were mixed at a weight ratio of 3:7 to 6:4, the moisture content was adjusted to 22 to 43%, confirming that the fertilizer was even easier to handle.

[0034] The results of this Example 1 as described above show that, when the total weight of organic sludge and biomass combustion ash is 10, it is preferable to adjust the moisture content to more than 8% and less than 65% by mixing the organic sludge at a weight ratio of more than 1 and less than 9. In this case, the weight ratio of biomass combustion ash is also more than 1 and less than 9. It is also shown that it is more preferable to adjust the moisture content to 22 to 43% by mixing the organic sludge at a weight ratio of 3 to 6. [Example]

[0035] In this Example 2, an experiment was conducted to identify an average particle size suitable for biomass combustion ash. Specifically, as shown in Figure 4, fly ash collected at three different biomass power plants A to C was used as the biomass combustion ash. The fuel used at biomass power plant A was palm kernel shells (PKS), the fuel used at biomass power plant B was palm kernel shells (PKS) and wood pellets, and the fuel used at biomass power plant C was palm kernel shells (PKS), bark, thinned wood, etc.

[0036] Each of the above biomass combustion ash samples was dispersed in methanol by stirring, and then the average particle size was measured by laser diffraction / scattering using a laser diffraction / scattering particle size distribution analyzer (HORIBA, Ltd.: LA-950). The results are shown in Figure 4. As shown in Figure 4, the average particle size of all fly ashes was found to be 44 μm or less.

[0037] The results of Example 2 above show that fly ash with a large specific surface area, which can absorb more water from organic sludge and thereby improve the effect of reducing the moisture content, preferably has an average particle size of 44 μm or less as measured by the laser diffraction / scattering method. [Example]

[0038] In this Example 3, an experiment was conducted to identify the optimum ratio for replacing biomass combustion ash with calcium oxide. Specifically, a reference sample was prepared by mixing the organic sludge and biomass combustion ash used in Example 1 described above at a weight ratio of 5:5. In addition, the reference samples were prepared by replacing the biomass combustion ash with calcium oxide (quicklime) at weight ratios ranging from 4:1 to 0:5.

[0039] Each sample was then analyzed for moisture, nitrogen, phosphate, potassium, carbon-nitrogen ratio (C / N ratio), copper, zinc, and lime content (%) using the test methods specified in the Fertilizer Testing Methods. The results are shown in Figure 5. As shown in Figure 5, there was no significant change in the nitrogen content, the three elements of fertilizer, regardless of the calcium oxide substitution rate, whether the results were on a per-unit or per-dry unit basis.

[0040] Furthermore, it was confirmed that the other two elements, phosphorus (P2O5) and potassium (K2O), were contained to a certain extent when the calcium oxide substitution ratio was up to 2:3 (60 wt%), and that these elements were desirable for use as fertilizer. On the other hand, it was confirmed that when the calcium oxide substitution ratio was 1:4 (80 wt%), the phosphorus and potassium levels decreased significantly.

[0041] The results of Example 3 above show that by replacing biomass combustion ash with calcium oxide (CaO) such as quicklime within a range of less than 80 wt%, it is possible to improve the effect of reducing the moisture content while maintaining the three essential elements of fertilizer. [Example]

[0042] In this Example 4, an experiment was conducted to determine the amount of sulfuric acid to be added when adjusting the pH of biomass combustion ash. Specifically, various sulfuric acid addition rates were added to the biomass combustion ash used in Example 1 above. The resulting product was then added to 10 times the amount of water, and the pH of the liquid was measured after mixing with a stirrer for 5 minutes. The results are shown in Figure 6.

[0043] As shown in Figure 6, when the addition rate of sulfuric acid to biomass combustion ash was 11 wt% or less, the pH exceeded 9, confirming that the biomass combustion ash remained alkaline. On the other hand, when the addition rate of sulfuric acid to biomass combustion ash was 12 wt% or more, the pH was 8.5 or less, confirming that the biomass combustion ash had been neutralized to the neutral range.

[0044] However, as mentioned above, adding too much sulfuric acid increases raw material costs. In this regard, when the sulfuric acid addition rate to biomass combustion ash is 29 wt%, the pH becomes nearly neutral at 7.0. Therefore, it can be said that the ammonia generation suppression effect remains almost unchanged even if sulfuric acid is added at a rate exceeding 29 wt%.

[0045] The results of Example 4 above show that when adjusting the hydrogen ion exponent of biomass combustion ash, adding 12 to 29 wt% of sulfuric acid can reduce the pH to the desired neutral range.

[0046] The method for producing a fertilizer according to the present invention is not limited to the above-described embodiment, and can be modified as appropriate.

[0047] For example, in the above-described embodiment, the ammonia generation suppression step (step S1) and the pH adjustment step (step S2) are performed as pre-treatments for suppressing ammonia generation. However, if a predetermined nitrogen component is contained in the fertilizer produced only by the moisture content adjustment step (step S3), the ammonia generation suppression step (step S1) and the pH adjustment step (step S2) do not need to be performed.

Claims

1. A method for producing a fertilizer, comprising a moisture content adjustment step of adjusting the moisture content to more than 8% and less than 65% by mixing organic sludge generated in the process of sewage treatment or wastewater treatment and biomass combustion ash, which is ash from biomass combustion, in a mixing ratio of more than 1 and less than 9 by weight, where the total weight of the organic sludge and biomass combustion ash is 10.

2. 2. The method for producing a fertilizer according to claim 1, wherein in the moisture content adjusting step, the moisture content is adjusted to 22 to 43% by mixing the organic sludge in a blending ratio of 3 to 6 by weight, where the total weight of the organic sludge and the biomass combustion ash is 10.

3. 2. The method for producing a fertilizer according to claim 1, wherein the biomass combustion ash is fly ash having an average particle size of 44 μm or less as measured by a laser diffraction / scattering method.

4. 2. The method for producing a fertilizer according to claim 1, wherein the biomass combustion ash is substituted with calcium oxide in a range of less than 80 wt %.

5. 2. The method for producing a fertilizer according to claim 1, further comprising a pH adjustment step of adding 12 to 29 wt % of sulfuric acid to the biomass combustion ash to adjust the hydrogen ion exponent (pH).

6. 2. The method for producing a fertilizer according to claim 1, further comprising an ammonia generation suppression step of adding magnesium chloride and phosphoric acid to the organic sludge to suppress the generation of ammonia.

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